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52eec54820
indexing an empty std::vector. Updates to all clients. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@40660 91177308-0d34-0410-b5e6-96231b3b80d8
1906 lines
80 KiB
C++
1906 lines
80 KiB
C++
//===- SimplifyCFG.cpp - Code to perform CFG simplification ---------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file was developed by the LLVM research group and is distributed under
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// the University of Illinois Open Source License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// Peephole optimize the CFG.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "simplifycfg"
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#include "llvm/Transforms/Utils/Local.h"
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#include "llvm/Constants.h"
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#include "llvm/Instructions.h"
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#include "llvm/Type.h"
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#include "llvm/DerivedTypes.h"
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#include "llvm/Support/CFG.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Analysis/ConstantFolding.h"
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#include "llvm/Transforms/Utils/BasicBlockUtils.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include <algorithm>
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#include <functional>
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#include <set>
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#include <map>
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using namespace llvm;
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/// SafeToMergeTerminators - Return true if it is safe to merge these two
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/// terminator instructions together.
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///
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static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) {
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if (SI1 == SI2) return false; // Can't merge with self!
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// It is not safe to merge these two switch instructions if they have a common
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// successor, and if that successor has a PHI node, and if *that* PHI node has
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// conflicting incoming values from the two switch blocks.
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BasicBlock *SI1BB = SI1->getParent();
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BasicBlock *SI2BB = SI2->getParent();
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SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
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for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
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if (SI1Succs.count(*I))
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for (BasicBlock::iterator BBI = (*I)->begin();
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isa<PHINode>(BBI); ++BBI) {
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PHINode *PN = cast<PHINode>(BBI);
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if (PN->getIncomingValueForBlock(SI1BB) !=
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PN->getIncomingValueForBlock(SI2BB))
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return false;
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}
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return true;
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}
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/// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will
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/// now be entries in it from the 'NewPred' block. The values that will be
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/// flowing into the PHI nodes will be the same as those coming in from
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/// ExistPred, an existing predecessor of Succ.
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static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
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BasicBlock *ExistPred) {
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assert(std::find(succ_begin(ExistPred), succ_end(ExistPred), Succ) !=
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succ_end(ExistPred) && "ExistPred is not a predecessor of Succ!");
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if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
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for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
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PHINode *PN = cast<PHINode>(I);
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Value *V = PN->getIncomingValueForBlock(ExistPred);
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PN->addIncoming(V, NewPred);
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}
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}
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// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an
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// almost-empty BB ending in an unconditional branch to Succ, into succ.
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//
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// Assumption: Succ is the single successor for BB.
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//
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static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
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assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
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// Check to see if one of the predecessors of BB is already a predecessor of
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// Succ. If so, we cannot do the transformation if there are any PHI nodes
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// with incompatible values coming in from the two edges!
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//
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if (isa<PHINode>(Succ->front())) {
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SmallPtrSet<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
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for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ);
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PI != PE; ++PI)
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if (BBPreds.count(*PI)) {
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// Loop over all of the PHI nodes checking to see if there are
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// incompatible values coming in.
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for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
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PHINode *PN = cast<PHINode>(I);
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// Loop up the entries in the PHI node for BB and for *PI if the
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// values coming in are non-equal, we cannot merge these two blocks
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// (instead we should insert a conditional move or something, then
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// merge the blocks).
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if (PN->getIncomingValueForBlock(BB) !=
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PN->getIncomingValueForBlock(*PI))
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return false; // Values are not equal...
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}
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}
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}
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// Finally, if BB has PHI nodes that are used by things other than the PHIs in
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// Succ and Succ has predecessors that are not Succ and not Pred, we cannot
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// fold these blocks, as we don't know whether BB dominates Succ or not to
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// update the PHI nodes correctly.
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if (!isa<PHINode>(BB->begin()) || Succ->getSinglePredecessor()) return true;
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// If the predecessors of Succ are only BB and Succ itself, handle it.
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bool IsSafe = true;
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for (pred_iterator PI = pred_begin(Succ), E = pred_end(Succ); PI != E; ++PI)
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if (*PI != Succ && *PI != BB) {
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IsSafe = false;
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break;
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}
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if (IsSafe) return true;
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// If the PHI nodes in BB are only used by instructions in Succ, we are ok if
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// BB and Succ have no common predecessors.
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for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++I) {
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PHINode *PN = cast<PHINode>(I);
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for (Value::use_iterator UI = PN->use_begin(), E = PN->use_end(); UI != E;
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++UI)
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if (cast<Instruction>(*UI)->getParent() != Succ)
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return false;
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}
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// Scan the predecessor sets of BB and Succ, making sure there are no common
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// predecessors. Common predecessors would cause us to build a phi node with
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// differing incoming values, which is not legal.
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SmallPtrSet<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
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for (pred_iterator PI = pred_begin(Succ), E = pred_end(Succ); PI != E; ++PI)
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if (BBPreds.count(*PI))
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return false;
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return true;
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}
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/// TryToSimplifyUncondBranchFromEmptyBlock - BB contains an unconditional
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/// branch to Succ, and contains no instructions other than PHI nodes and the
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/// branch. If possible, eliminate BB.
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static bool TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB,
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BasicBlock *Succ) {
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// If our successor has PHI nodes, then we need to update them to include
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// entries for BB's predecessors, not for BB itself. Be careful though,
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// if this transformation fails (returns true) then we cannot do this
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// transformation!
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//
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if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false;
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DOUT << "Killing Trivial BB: \n" << *BB;
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if (isa<PHINode>(Succ->begin())) {
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// If there is more than one pred of succ, and there are PHI nodes in
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// the successor, then we need to add incoming edges for the PHI nodes
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//
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const std::vector<BasicBlock*> BBPreds(pred_begin(BB), pred_end(BB));
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// Loop over all of the PHI nodes in the successor of BB.
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for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
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PHINode *PN = cast<PHINode>(I);
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Value *OldVal = PN->removeIncomingValue(BB, false);
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assert(OldVal && "No entry in PHI for Pred BB!");
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// If this incoming value is one of the PHI nodes in BB, the new entries
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// in the PHI node are the entries from the old PHI.
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if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
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PHINode *OldValPN = cast<PHINode>(OldVal);
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for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i)
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PN->addIncoming(OldValPN->getIncomingValue(i),
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OldValPN->getIncomingBlock(i));
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} else {
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for (std::vector<BasicBlock*>::const_iterator PredI = BBPreds.begin(),
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End = BBPreds.end(); PredI != End; ++PredI) {
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// Add an incoming value for each of the new incoming values...
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PN->addIncoming(OldVal, *PredI);
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}
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}
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}
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}
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if (isa<PHINode>(&BB->front())) {
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std::vector<BasicBlock*>
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OldSuccPreds(pred_begin(Succ), pred_end(Succ));
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// Move all PHI nodes in BB to Succ if they are alive, otherwise
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// delete them.
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while (PHINode *PN = dyn_cast<PHINode>(&BB->front()))
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if (PN->use_empty()) {
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// Just remove the dead phi. This happens if Succ's PHIs were the only
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// users of the PHI nodes.
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PN->eraseFromParent();
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} else {
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// The instruction is alive, so this means that Succ must have
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// *ONLY* had BB as a predecessor, and the PHI node is still valid
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// now. Simply move it into Succ, because we know that BB
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// strictly dominated Succ.
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Succ->getInstList().splice(Succ->begin(),
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BB->getInstList(), BB->begin());
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// We need to add new entries for the PHI node to account for
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// predecessors of Succ that the PHI node does not take into
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// account. At this point, since we know that BB dominated succ,
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// this means that we should any newly added incoming edges should
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// use the PHI node as the value for these edges, because they are
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// loop back edges.
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for (unsigned i = 0, e = OldSuccPreds.size(); i != e; ++i)
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if (OldSuccPreds[i] != BB)
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PN->addIncoming(PN, OldSuccPreds[i]);
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}
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}
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// Everything that jumped to BB now goes to Succ.
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BB->replaceAllUsesWith(Succ);
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if (!Succ->hasName()) Succ->takeName(BB);
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BB->eraseFromParent(); // Delete the old basic block.
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return true;
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}
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/// GetIfCondition - Given a basic block (BB) with two predecessors (and
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/// presumably PHI nodes in it), check to see if the merge at this block is due
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/// to an "if condition". If so, return the boolean condition that determines
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/// which entry into BB will be taken. Also, return by references the block
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/// that will be entered from if the condition is true, and the block that will
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/// be entered if the condition is false.
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///
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///
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static Value *GetIfCondition(BasicBlock *BB,
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BasicBlock *&IfTrue, BasicBlock *&IfFalse) {
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assert(std::distance(pred_begin(BB), pred_end(BB)) == 2 &&
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"Function can only handle blocks with 2 predecessors!");
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BasicBlock *Pred1 = *pred_begin(BB);
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BasicBlock *Pred2 = *++pred_begin(BB);
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// We can only handle branches. Other control flow will be lowered to
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// branches if possible anyway.
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if (!isa<BranchInst>(Pred1->getTerminator()) ||
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!isa<BranchInst>(Pred2->getTerminator()))
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return 0;
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BranchInst *Pred1Br = cast<BranchInst>(Pred1->getTerminator());
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BranchInst *Pred2Br = cast<BranchInst>(Pred2->getTerminator());
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// Eliminate code duplication by ensuring that Pred1Br is conditional if
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// either are.
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if (Pred2Br->isConditional()) {
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// If both branches are conditional, we don't have an "if statement". In
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// reality, we could transform this case, but since the condition will be
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// required anyway, we stand no chance of eliminating it, so the xform is
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// probably not profitable.
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if (Pred1Br->isConditional())
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return 0;
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std::swap(Pred1, Pred2);
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std::swap(Pred1Br, Pred2Br);
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}
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if (Pred1Br->isConditional()) {
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// If we found a conditional branch predecessor, make sure that it branches
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// to BB and Pred2Br. If it doesn't, this isn't an "if statement".
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if (Pred1Br->getSuccessor(0) == BB &&
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Pred1Br->getSuccessor(1) == Pred2) {
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IfTrue = Pred1;
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IfFalse = Pred2;
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} else if (Pred1Br->getSuccessor(0) == Pred2 &&
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Pred1Br->getSuccessor(1) == BB) {
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IfTrue = Pred2;
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IfFalse = Pred1;
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} else {
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// We know that one arm of the conditional goes to BB, so the other must
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// go somewhere unrelated, and this must not be an "if statement".
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return 0;
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}
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// The only thing we have to watch out for here is to make sure that Pred2
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// doesn't have incoming edges from other blocks. If it does, the condition
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// doesn't dominate BB.
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if (++pred_begin(Pred2) != pred_end(Pred2))
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return 0;
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return Pred1Br->getCondition();
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}
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// Ok, if we got here, both predecessors end with an unconditional branch to
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// BB. Don't panic! If both blocks only have a single (identical)
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// predecessor, and THAT is a conditional branch, then we're all ok!
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if (pred_begin(Pred1) == pred_end(Pred1) ||
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++pred_begin(Pred1) != pred_end(Pred1) ||
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pred_begin(Pred2) == pred_end(Pred2) ||
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++pred_begin(Pred2) != pred_end(Pred2) ||
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*pred_begin(Pred1) != *pred_begin(Pred2))
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return 0;
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// Otherwise, if this is a conditional branch, then we can use it!
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BasicBlock *CommonPred = *pred_begin(Pred1);
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if (BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator())) {
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assert(BI->isConditional() && "Two successors but not conditional?");
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if (BI->getSuccessor(0) == Pred1) {
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IfTrue = Pred1;
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IfFalse = Pred2;
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} else {
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IfTrue = Pred2;
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IfFalse = Pred1;
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}
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return BI->getCondition();
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}
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return 0;
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}
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// If we have a merge point of an "if condition" as accepted above, return true
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// if the specified value dominates the block. We don't handle the true
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// generality of domination here, just a special case which works well enough
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// for us.
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//
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// If AggressiveInsts is non-null, and if V does not dominate BB, we check to
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// see if V (which must be an instruction) is cheap to compute and is
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// non-trapping. If both are true, the instruction is inserted into the set and
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// true is returned.
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static bool DominatesMergePoint(Value *V, BasicBlock *BB,
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std::set<Instruction*> *AggressiveInsts) {
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Instruction *I = dyn_cast<Instruction>(V);
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if (!I) {
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// Non-instructions all dominate instructions, but not all constantexprs
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// can be executed unconditionally.
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if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
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if (C->canTrap())
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return false;
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return true;
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}
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BasicBlock *PBB = I->getParent();
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// We don't want to allow weird loops that might have the "if condition" in
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// the bottom of this block.
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if (PBB == BB) return false;
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// If this instruction is defined in a block that contains an unconditional
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// branch to BB, then it must be in the 'conditional' part of the "if
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// statement".
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if (BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator()))
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if (BI->isUnconditional() && BI->getSuccessor(0) == BB) {
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if (!AggressiveInsts) return false;
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// Okay, it looks like the instruction IS in the "condition". Check to
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// see if its a cheap instruction to unconditionally compute, and if it
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// only uses stuff defined outside of the condition. If so, hoist it out.
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switch (I->getOpcode()) {
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default: return false; // Cannot hoist this out safely.
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case Instruction::Load:
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// We can hoist loads that are non-volatile and obviously cannot trap.
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if (cast<LoadInst>(I)->isVolatile())
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return false;
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if (!isa<AllocaInst>(I->getOperand(0)) &&
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!isa<Constant>(I->getOperand(0)))
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return false;
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// Finally, we have to check to make sure there are no instructions
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// before the load in its basic block, as we are going to hoist the loop
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// out to its predecessor.
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if (PBB->begin() != BasicBlock::iterator(I))
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return false;
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break;
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case Instruction::Add:
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case Instruction::Sub:
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case Instruction::And:
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case Instruction::Or:
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case Instruction::Xor:
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case Instruction::Shl:
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case Instruction::LShr:
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case Instruction::AShr:
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case Instruction::ICmp:
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case Instruction::FCmp:
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break; // These are all cheap and non-trapping instructions.
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}
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// Okay, we can only really hoist these out if their operands are not
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// defined in the conditional region.
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for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
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if (!DominatesMergePoint(I->getOperand(i), BB, 0))
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return false;
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// Okay, it's safe to do this! Remember this instruction.
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AggressiveInsts->insert(I);
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}
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return true;
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}
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// GatherConstantSetEQs - Given a potentially 'or'd together collection of
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// icmp_eq instructions that compare a value against a constant, return the
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// value being compared, and stick the constant into the Values vector.
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static Value *GatherConstantSetEQs(Value *V, std::vector<ConstantInt*> &Values){
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if (Instruction *Inst = dyn_cast<Instruction>(V))
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if (Inst->getOpcode() == Instruction::ICmp &&
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cast<ICmpInst>(Inst)->getPredicate() == ICmpInst::ICMP_EQ) {
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if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) {
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Values.push_back(C);
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return Inst->getOperand(0);
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} else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) {
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Values.push_back(C);
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return Inst->getOperand(1);
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}
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} else if (Inst->getOpcode() == Instruction::Or) {
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if (Value *LHS = GatherConstantSetEQs(Inst->getOperand(0), Values))
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if (Value *RHS = GatherConstantSetEQs(Inst->getOperand(1), Values))
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if (LHS == RHS)
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return LHS;
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}
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return 0;
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}
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// GatherConstantSetNEs - Given a potentially 'and'd together collection of
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// setne instructions that compare a value against a constant, return the value
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// being compared, and stick the constant into the Values vector.
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static Value *GatherConstantSetNEs(Value *V, std::vector<ConstantInt*> &Values){
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if (Instruction *Inst = dyn_cast<Instruction>(V))
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if (Inst->getOpcode() == Instruction::ICmp &&
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cast<ICmpInst>(Inst)->getPredicate() == ICmpInst::ICMP_NE) {
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if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) {
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Values.push_back(C);
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return Inst->getOperand(0);
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} else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) {
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Values.push_back(C);
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return Inst->getOperand(1);
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}
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} else if (Inst->getOpcode() == Instruction::And) {
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if (Value *LHS = GatherConstantSetNEs(Inst->getOperand(0), Values))
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if (Value *RHS = GatherConstantSetNEs(Inst->getOperand(1), Values))
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if (LHS == RHS)
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return LHS;
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
|
|
|
|
/// GatherValueComparisons - If the specified Cond is an 'and' or 'or' of a
|
|
/// bunch of comparisons of one value against constants, return the value and
|
|
/// the constants being compared.
|
|
static bool GatherValueComparisons(Instruction *Cond, Value *&CompVal,
|
|
std::vector<ConstantInt*> &Values) {
|
|
if (Cond->getOpcode() == Instruction::Or) {
|
|
CompVal = GatherConstantSetEQs(Cond, Values);
|
|
|
|
// Return true to indicate that the condition is true if the CompVal is
|
|
// equal to one of the constants.
|
|
return true;
|
|
} else if (Cond->getOpcode() == Instruction::And) {
|
|
CompVal = GatherConstantSetNEs(Cond, Values);
|
|
|
|
// Return false to indicate that the condition is false if the CompVal is
|
|
// equal to one of the constants.
|
|
return false;
|
|
}
|
|
return false;
|
|
}
|
|
|
|
/// ErasePossiblyDeadInstructionTree - If the specified instruction is dead and
|
|
/// has no side effects, nuke it. If it uses any instructions that become dead
|
|
/// because the instruction is now gone, nuke them too.
|
|
static void ErasePossiblyDeadInstructionTree(Instruction *I) {
|
|
if (!isInstructionTriviallyDead(I)) return;
|
|
|
|
std::vector<Instruction*> InstrsToInspect;
|
|
InstrsToInspect.push_back(I);
|
|
|
|
while (!InstrsToInspect.empty()) {
|
|
I = InstrsToInspect.back();
|
|
InstrsToInspect.pop_back();
|
|
|
|
if (!isInstructionTriviallyDead(I)) continue;
|
|
|
|
// If I is in the work list multiple times, remove previous instances.
|
|
for (unsigned i = 0, e = InstrsToInspect.size(); i != e; ++i)
|
|
if (InstrsToInspect[i] == I) {
|
|
InstrsToInspect.erase(InstrsToInspect.begin()+i);
|
|
--i, --e;
|
|
}
|
|
|
|
// Add operands of dead instruction to worklist.
|
|
for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
|
|
if (Instruction *OpI = dyn_cast<Instruction>(I->getOperand(i)))
|
|
InstrsToInspect.push_back(OpI);
|
|
|
|
// Remove dead instruction.
|
|
I->eraseFromParent();
|
|
}
|
|
}
|
|
|
|
// isValueEqualityComparison - Return true if the specified terminator checks to
|
|
// see if a value is equal to constant integer value.
|
|
static Value *isValueEqualityComparison(TerminatorInst *TI) {
|
|
if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
|
|
// Do not permit merging of large switch instructions into their
|
|
// predecessors unless there is only one predecessor.
|
|
if (SI->getNumSuccessors() * std::distance(pred_begin(SI->getParent()),
|
|
pred_end(SI->getParent())) > 128)
|
|
return 0;
|
|
|
|
return SI->getCondition();
|
|
}
|
|
if (BranchInst *BI = dyn_cast<BranchInst>(TI))
|
|
if (BI->isConditional() && BI->getCondition()->hasOneUse())
|
|
if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
|
|
if ((ICI->getPredicate() == ICmpInst::ICMP_EQ ||
|
|
ICI->getPredicate() == ICmpInst::ICMP_NE) &&
|
|
isa<ConstantInt>(ICI->getOperand(1)))
|
|
return ICI->getOperand(0);
|
|
return 0;
|
|
}
|
|
|
|
// Given a value comparison instruction, decode all of the 'cases' that it
|
|
// represents and return the 'default' block.
|
|
static BasicBlock *
|
|
GetValueEqualityComparisonCases(TerminatorInst *TI,
|
|
std::vector<std::pair<ConstantInt*,
|
|
BasicBlock*> > &Cases) {
|
|
if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
|
|
Cases.reserve(SI->getNumCases());
|
|
for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
|
|
Cases.push_back(std::make_pair(SI->getCaseValue(i), SI->getSuccessor(i)));
|
|
return SI->getDefaultDest();
|
|
}
|
|
|
|
BranchInst *BI = cast<BranchInst>(TI);
|
|
ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
|
|
Cases.push_back(std::make_pair(cast<ConstantInt>(ICI->getOperand(1)),
|
|
BI->getSuccessor(ICI->getPredicate() ==
|
|
ICmpInst::ICMP_NE)));
|
|
return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
|
|
}
|
|
|
|
|
|
// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
|
|
// in the list that match the specified block.
|
|
static void EliminateBlockCases(BasicBlock *BB,
|
|
std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases) {
|
|
for (unsigned i = 0, e = Cases.size(); i != e; ++i)
|
|
if (Cases[i].second == BB) {
|
|
Cases.erase(Cases.begin()+i);
|
|
--i; --e;
|
|
}
|
|
}
|
|
|
|
// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
|
|
// well.
|
|
static bool
|
|
ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1,
|
|
std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) {
|
|
std::vector<std::pair<ConstantInt*, BasicBlock*> > *V1 = &C1, *V2 = &C2;
|
|
|
|
// Make V1 be smaller than V2.
|
|
if (V1->size() > V2->size())
|
|
std::swap(V1, V2);
|
|
|
|
if (V1->size() == 0) return false;
|
|
if (V1->size() == 1) {
|
|
// Just scan V2.
|
|
ConstantInt *TheVal = (*V1)[0].first;
|
|
for (unsigned i = 0, e = V2->size(); i != e; ++i)
|
|
if (TheVal == (*V2)[i].first)
|
|
return true;
|
|
}
|
|
|
|
// Otherwise, just sort both lists and compare element by element.
|
|
std::sort(V1->begin(), V1->end());
|
|
std::sort(V2->begin(), V2->end());
|
|
unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
|
|
while (i1 != e1 && i2 != e2) {
|
|
if ((*V1)[i1].first == (*V2)[i2].first)
|
|
return true;
|
|
if ((*V1)[i1].first < (*V2)[i2].first)
|
|
++i1;
|
|
else
|
|
++i2;
|
|
}
|
|
return false;
|
|
}
|
|
|
|
// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
|
|
// terminator instruction and its block is known to only have a single
|
|
// predecessor block, check to see if that predecessor is also a value
|
|
// comparison with the same value, and if that comparison determines the outcome
|
|
// of this comparison. If so, simplify TI. This does a very limited form of
|
|
// jump threading.
|
|
static bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
|
|
BasicBlock *Pred) {
|
|
Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
|
|
if (!PredVal) return false; // Not a value comparison in predecessor.
|
|
|
|
Value *ThisVal = isValueEqualityComparison(TI);
|
|
assert(ThisVal && "This isn't a value comparison!!");
|
|
if (ThisVal != PredVal) return false; // Different predicates.
|
|
|
|
// Find out information about when control will move from Pred to TI's block.
|
|
std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
|
|
BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
|
|
PredCases);
|
|
EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
|
|
|
|
// Find information about how control leaves this block.
|
|
std::vector<std::pair<ConstantInt*, BasicBlock*> > ThisCases;
|
|
BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
|
|
EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
|
|
|
|
// If TI's block is the default block from Pred's comparison, potentially
|
|
// simplify TI based on this knowledge.
|
|
if (PredDef == TI->getParent()) {
|
|
// If we are here, we know that the value is none of those cases listed in
|
|
// PredCases. If there are any cases in ThisCases that are in PredCases, we
|
|
// can simplify TI.
|
|
if (ValuesOverlap(PredCases, ThisCases)) {
|
|
if (BranchInst *BTI = dyn_cast<BranchInst>(TI)) {
|
|
// Okay, one of the successors of this condbr is dead. Convert it to a
|
|
// uncond br.
|
|
assert(ThisCases.size() == 1 && "Branch can only have one case!");
|
|
Value *Cond = BTI->getCondition();
|
|
// Insert the new branch.
|
|
Instruction *NI = new BranchInst(ThisDef, TI);
|
|
|
|
// Remove PHI node entries for the dead edge.
|
|
ThisCases[0].second->removePredecessor(TI->getParent());
|
|
|
|
DOUT << "Threading pred instr: " << *Pred->getTerminator()
|
|
<< "Through successor TI: " << *TI << "Leaving: " << *NI << "\n";
|
|
|
|
TI->eraseFromParent(); // Nuke the old one.
|
|
// If condition is now dead, nuke it.
|
|
if (Instruction *CondI = dyn_cast<Instruction>(Cond))
|
|
ErasePossiblyDeadInstructionTree(CondI);
|
|
return true;
|
|
|
|
} else {
|
|
SwitchInst *SI = cast<SwitchInst>(TI);
|
|
// Okay, TI has cases that are statically dead, prune them away.
|
|
SmallPtrSet<Constant*, 16> DeadCases;
|
|
for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
|
|
DeadCases.insert(PredCases[i].first);
|
|
|
|
DOUT << "Threading pred instr: " << *Pred->getTerminator()
|
|
<< "Through successor TI: " << *TI;
|
|
|
|
for (unsigned i = SI->getNumCases()-1; i != 0; --i)
|
|
if (DeadCases.count(SI->getCaseValue(i))) {
|
|
SI->getSuccessor(i)->removePredecessor(TI->getParent());
|
|
SI->removeCase(i);
|
|
}
|
|
|
|
DOUT << "Leaving: " << *TI << "\n";
|
|
return true;
|
|
}
|
|
}
|
|
|
|
} else {
|
|
// Otherwise, TI's block must correspond to some matched value. Find out
|
|
// which value (or set of values) this is.
|
|
ConstantInt *TIV = 0;
|
|
BasicBlock *TIBB = TI->getParent();
|
|
for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
|
|
if (PredCases[i].second == TIBB)
|
|
if (TIV == 0)
|
|
TIV = PredCases[i].first;
|
|
else
|
|
return false; // Cannot handle multiple values coming to this block.
|
|
assert(TIV && "No edge from pred to succ?");
|
|
|
|
// Okay, we found the one constant that our value can be if we get into TI's
|
|
// BB. Find out which successor will unconditionally be branched to.
|
|
BasicBlock *TheRealDest = 0;
|
|
for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
|
|
if (ThisCases[i].first == TIV) {
|
|
TheRealDest = ThisCases[i].second;
|
|
break;
|
|
}
|
|
|
|
// If not handled by any explicit cases, it is handled by the default case.
|
|
if (TheRealDest == 0) TheRealDest = ThisDef;
|
|
|
|
// Remove PHI node entries for dead edges.
|
|
BasicBlock *CheckEdge = TheRealDest;
|
|
for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
|
|
if (*SI != CheckEdge)
|
|
(*SI)->removePredecessor(TIBB);
|
|
else
|
|
CheckEdge = 0;
|
|
|
|
// Insert the new branch.
|
|
Instruction *NI = new BranchInst(TheRealDest, TI);
|
|
|
|
DOUT << "Threading pred instr: " << *Pred->getTerminator()
|
|
<< "Through successor TI: " << *TI << "Leaving: " << *NI << "\n";
|
|
Instruction *Cond = 0;
|
|
if (BranchInst *BI = dyn_cast<BranchInst>(TI))
|
|
Cond = dyn_cast<Instruction>(BI->getCondition());
|
|
TI->eraseFromParent(); // Nuke the old one.
|
|
|
|
if (Cond) ErasePossiblyDeadInstructionTree(Cond);
|
|
return true;
|
|
}
|
|
return false;
|
|
}
|
|
|
|
// FoldValueComparisonIntoPredecessors - The specified terminator is a value
|
|
// equality comparison instruction (either a switch or a branch on "X == c").
|
|
// See if any of the predecessors of the terminator block are value comparisons
|
|
// on the same value. If so, and if safe to do so, fold them together.
|
|
static bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI) {
|
|
BasicBlock *BB = TI->getParent();
|
|
Value *CV = isValueEqualityComparison(TI); // CondVal
|
|
assert(CV && "Not a comparison?");
|
|
bool Changed = false;
|
|
|
|
std::vector<BasicBlock*> Preds(pred_begin(BB), pred_end(BB));
|
|
while (!Preds.empty()) {
|
|
BasicBlock *Pred = Preds.back();
|
|
Preds.pop_back();
|
|
|
|
// See if the predecessor is a comparison with the same value.
|
|
TerminatorInst *PTI = Pred->getTerminator();
|
|
Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
|
|
|
|
if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
|
|
// Figure out which 'cases' to copy from SI to PSI.
|
|
std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases;
|
|
BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
|
|
|
|
std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
|
|
BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
|
|
|
|
// Based on whether the default edge from PTI goes to BB or not, fill in
|
|
// PredCases and PredDefault with the new switch cases we would like to
|
|
// build.
|
|
std::vector<BasicBlock*> NewSuccessors;
|
|
|
|
if (PredDefault == BB) {
|
|
// If this is the default destination from PTI, only the edges in TI
|
|
// that don't occur in PTI, or that branch to BB will be activated.
|
|
std::set<ConstantInt*> PTIHandled;
|
|
for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
|
|
if (PredCases[i].second != BB)
|
|
PTIHandled.insert(PredCases[i].first);
|
|
else {
|
|
// The default destination is BB, we don't need explicit targets.
|
|
std::swap(PredCases[i], PredCases.back());
|
|
PredCases.pop_back();
|
|
--i; --e;
|
|
}
|
|
|
|
// Reconstruct the new switch statement we will be building.
|
|
if (PredDefault != BBDefault) {
|
|
PredDefault->removePredecessor(Pred);
|
|
PredDefault = BBDefault;
|
|
NewSuccessors.push_back(BBDefault);
|
|
}
|
|
for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
|
|
if (!PTIHandled.count(BBCases[i].first) &&
|
|
BBCases[i].second != BBDefault) {
|
|
PredCases.push_back(BBCases[i]);
|
|
NewSuccessors.push_back(BBCases[i].second);
|
|
}
|
|
|
|
} else {
|
|
// If this is not the default destination from PSI, only the edges
|
|
// in SI that occur in PSI with a destination of BB will be
|
|
// activated.
|
|
std::set<ConstantInt*> PTIHandled;
|
|
for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
|
|
if (PredCases[i].second == BB) {
|
|
PTIHandled.insert(PredCases[i].first);
|
|
std::swap(PredCases[i], PredCases.back());
|
|
PredCases.pop_back();
|
|
--i; --e;
|
|
}
|
|
|
|
// Okay, now we know which constants were sent to BB from the
|
|
// predecessor. Figure out where they will all go now.
|
|
for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
|
|
if (PTIHandled.count(BBCases[i].first)) {
|
|
// If this is one we are capable of getting...
|
|
PredCases.push_back(BBCases[i]);
|
|
NewSuccessors.push_back(BBCases[i].second);
|
|
PTIHandled.erase(BBCases[i].first);// This constant is taken care of
|
|
}
|
|
|
|
// If there are any constants vectored to BB that TI doesn't handle,
|
|
// they must go to the default destination of TI.
|
|
for (std::set<ConstantInt*>::iterator I = PTIHandled.begin(),
|
|
E = PTIHandled.end(); I != E; ++I) {
|
|
PredCases.push_back(std::make_pair(*I, BBDefault));
|
|
NewSuccessors.push_back(BBDefault);
|
|
}
|
|
}
|
|
|
|
// Okay, at this point, we know which new successor Pred will get. Make
|
|
// sure we update the number of entries in the PHI nodes for these
|
|
// successors.
|
|
for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
|
|
AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
|
|
|
|
// Now that the successors are updated, create the new Switch instruction.
|
|
SwitchInst *NewSI = new SwitchInst(CV, PredDefault, PredCases.size(),PTI);
|
|
for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
|
|
NewSI->addCase(PredCases[i].first, PredCases[i].second);
|
|
|
|
Instruction *DeadCond = 0;
|
|
if (BranchInst *BI = dyn_cast<BranchInst>(PTI))
|
|
// If PTI is a branch, remember the condition.
|
|
DeadCond = dyn_cast<Instruction>(BI->getCondition());
|
|
Pred->getInstList().erase(PTI);
|
|
|
|
// If the condition is dead now, remove the instruction tree.
|
|
if (DeadCond) ErasePossiblyDeadInstructionTree(DeadCond);
|
|
|
|
// Okay, last check. If BB is still a successor of PSI, then we must
|
|
// have an infinite loop case. If so, add an infinitely looping block
|
|
// to handle the case to preserve the behavior of the code.
|
|
BasicBlock *InfLoopBlock = 0;
|
|
for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
|
|
if (NewSI->getSuccessor(i) == BB) {
|
|
if (InfLoopBlock == 0) {
|
|
// Insert it at the end of the loop, because it's either code,
|
|
// or it won't matter if it's hot. :)
|
|
InfLoopBlock = new BasicBlock("infloop", BB->getParent());
|
|
new BranchInst(InfLoopBlock, InfLoopBlock);
|
|
}
|
|
NewSI->setSuccessor(i, InfLoopBlock);
|
|
}
|
|
|
|
Changed = true;
|
|
}
|
|
}
|
|
return Changed;
|
|
}
|
|
|
|
/// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
|
|
/// BB2, hoist any common code in the two blocks up into the branch block. The
|
|
/// caller of this function guarantees that BI's block dominates BB1 and BB2.
|
|
static bool HoistThenElseCodeToIf(BranchInst *BI) {
|
|
// This does very trivial matching, with limited scanning, to find identical
|
|
// instructions in the two blocks. In particular, we don't want to get into
|
|
// O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
|
|
// such, we currently just scan for obviously identical instructions in an
|
|
// identical order.
|
|
BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
|
|
BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
|
|
|
|
Instruction *I1 = BB1->begin(), *I2 = BB2->begin();
|
|
if (I1->getOpcode() != I2->getOpcode() || isa<PHINode>(I1) ||
|
|
isa<InvokeInst>(I1) || !I1->isIdenticalTo(I2))
|
|
return false;
|
|
|
|
// If we get here, we can hoist at least one instruction.
|
|
BasicBlock *BIParent = BI->getParent();
|
|
|
|
do {
|
|
// If we are hoisting the terminator instruction, don't move one (making a
|
|
// broken BB), instead clone it, and remove BI.
|
|
if (isa<TerminatorInst>(I1))
|
|
goto HoistTerminator;
|
|
|
|
// For a normal instruction, we just move one to right before the branch,
|
|
// then replace all uses of the other with the first. Finally, we remove
|
|
// the now redundant second instruction.
|
|
BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
|
|
if (!I2->use_empty())
|
|
I2->replaceAllUsesWith(I1);
|
|
BB2->getInstList().erase(I2);
|
|
|
|
I1 = BB1->begin();
|
|
I2 = BB2->begin();
|
|
} while (I1->getOpcode() == I2->getOpcode() && I1->isIdenticalTo(I2));
|
|
|
|
return true;
|
|
|
|
HoistTerminator:
|
|
// Okay, it is safe to hoist the terminator.
|
|
Instruction *NT = I1->clone();
|
|
BIParent->getInstList().insert(BI, NT);
|
|
if (NT->getType() != Type::VoidTy) {
|
|
I1->replaceAllUsesWith(NT);
|
|
I2->replaceAllUsesWith(NT);
|
|
NT->takeName(I1);
|
|
}
|
|
|
|
// Hoisting one of the terminators from our successor is a great thing.
|
|
// Unfortunately, the successors of the if/else blocks may have PHI nodes in
|
|
// them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
|
|
// nodes, so we insert select instruction to compute the final result.
|
|
std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
|
|
for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
|
|
PHINode *PN;
|
|
for (BasicBlock::iterator BBI = SI->begin();
|
|
(PN = dyn_cast<PHINode>(BBI)); ++BBI) {
|
|
Value *BB1V = PN->getIncomingValueForBlock(BB1);
|
|
Value *BB2V = PN->getIncomingValueForBlock(BB2);
|
|
if (BB1V != BB2V) {
|
|
// These values do not agree. Insert a select instruction before NT
|
|
// that determines the right value.
|
|
SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
|
|
if (SI == 0)
|
|
SI = new SelectInst(BI->getCondition(), BB1V, BB2V,
|
|
BB1V->getName()+"."+BB2V->getName(), NT);
|
|
// Make the PHI node use the select for all incoming values for BB1/BB2
|
|
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
|
|
if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
|
|
PN->setIncomingValue(i, SI);
|
|
}
|
|
}
|
|
}
|
|
|
|
// Update any PHI nodes in our new successors.
|
|
for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
|
|
AddPredecessorToBlock(*SI, BIParent, BB1);
|
|
|
|
BI->eraseFromParent();
|
|
return true;
|
|
}
|
|
|
|
/// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
|
|
/// across this block.
|
|
static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
|
|
BranchInst *BI = cast<BranchInst>(BB->getTerminator());
|
|
unsigned Size = 0;
|
|
|
|
// If this basic block contains anything other than a PHI (which controls the
|
|
// branch) and branch itself, bail out. FIXME: improve this in the future.
|
|
for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI, ++Size) {
|
|
if (Size > 10) return false; // Don't clone large BB's.
|
|
|
|
// We can only support instructions that are do not define values that are
|
|
// live outside of the current basic block.
|
|
for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
|
|
UI != E; ++UI) {
|
|
Instruction *U = cast<Instruction>(*UI);
|
|
if (U->getParent() != BB || isa<PHINode>(U)) return false;
|
|
}
|
|
|
|
// Looks ok, continue checking.
|
|
}
|
|
|
|
return true;
|
|
}
|
|
|
|
/// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
|
|
/// that is defined in the same block as the branch and if any PHI entries are
|
|
/// constants, thread edges corresponding to that entry to be branches to their
|
|
/// ultimate destination.
|
|
static bool FoldCondBranchOnPHI(BranchInst *BI) {
|
|
BasicBlock *BB = BI->getParent();
|
|
PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
|
|
// NOTE: we currently cannot transform this case if the PHI node is used
|
|
// outside of the block.
|
|
if (!PN || PN->getParent() != BB || !PN->hasOneUse())
|
|
return false;
|
|
|
|
// Degenerate case of a single entry PHI.
|
|
if (PN->getNumIncomingValues() == 1) {
|
|
if (PN->getIncomingValue(0) != PN)
|
|
PN->replaceAllUsesWith(PN->getIncomingValue(0));
|
|
else
|
|
PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
|
|
PN->eraseFromParent();
|
|
return true;
|
|
}
|
|
|
|
// Now we know that this block has multiple preds and two succs.
|
|
if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
|
|
|
|
// Okay, this is a simple enough basic block. See if any phi values are
|
|
// constants.
|
|
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
|
|
ConstantInt *CB;
|
|
if ((CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i))) &&
|
|
CB->getType() == Type::Int1Ty) {
|
|
// Okay, we now know that all edges from PredBB should be revectored to
|
|
// branch to RealDest.
|
|
BasicBlock *PredBB = PN->getIncomingBlock(i);
|
|
BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
|
|
|
|
if (RealDest == BB) continue; // Skip self loops.
|
|
|
|
// The dest block might have PHI nodes, other predecessors and other
|
|
// difficult cases. Instead of being smart about this, just insert a new
|
|
// block that jumps to the destination block, effectively splitting
|
|
// the edge we are about to create.
|
|
BasicBlock *EdgeBB = new BasicBlock(RealDest->getName()+".critedge",
|
|
RealDest->getParent(), RealDest);
|
|
new BranchInst(RealDest, EdgeBB);
|
|
PHINode *PN;
|
|
for (BasicBlock::iterator BBI = RealDest->begin();
|
|
(PN = dyn_cast<PHINode>(BBI)); ++BBI) {
|
|
Value *V = PN->getIncomingValueForBlock(BB);
|
|
PN->addIncoming(V, EdgeBB);
|
|
}
|
|
|
|
// BB may have instructions that are being threaded over. Clone these
|
|
// instructions into EdgeBB. We know that there will be no uses of the
|
|
// cloned instructions outside of EdgeBB.
|
|
BasicBlock::iterator InsertPt = EdgeBB->begin();
|
|
std::map<Value*, Value*> TranslateMap; // Track translated values.
|
|
for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
|
|
if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
|
|
TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
|
|
} else {
|
|
// Clone the instruction.
|
|
Instruction *N = BBI->clone();
|
|
if (BBI->hasName()) N->setName(BBI->getName()+".c");
|
|
|
|
// Update operands due to translation.
|
|
for (unsigned i = 0, e = N->getNumOperands(); i != e; ++i) {
|
|
std::map<Value*, Value*>::iterator PI =
|
|
TranslateMap.find(N->getOperand(i));
|
|
if (PI != TranslateMap.end())
|
|
N->setOperand(i, PI->second);
|
|
}
|
|
|
|
// Check for trivial simplification.
|
|
if (Constant *C = ConstantFoldInstruction(N)) {
|
|
TranslateMap[BBI] = C;
|
|
delete N; // Constant folded away, don't need actual inst
|
|
} else {
|
|
// Insert the new instruction into its new home.
|
|
EdgeBB->getInstList().insert(InsertPt, N);
|
|
if (!BBI->use_empty())
|
|
TranslateMap[BBI] = N;
|
|
}
|
|
}
|
|
}
|
|
|
|
// Loop over all of the edges from PredBB to BB, changing them to branch
|
|
// to EdgeBB instead.
|
|
TerminatorInst *PredBBTI = PredBB->getTerminator();
|
|
for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
|
|
if (PredBBTI->getSuccessor(i) == BB) {
|
|
BB->removePredecessor(PredBB);
|
|
PredBBTI->setSuccessor(i, EdgeBB);
|
|
}
|
|
|
|
// Recurse, simplifying any other constants.
|
|
return FoldCondBranchOnPHI(BI) | true;
|
|
}
|
|
}
|
|
|
|
return false;
|
|
}
|
|
|
|
/// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
|
|
/// PHI node, see if we can eliminate it.
|
|
static bool FoldTwoEntryPHINode(PHINode *PN) {
|
|
// Ok, this is a two entry PHI node. Check to see if this is a simple "if
|
|
// statement", which has a very simple dominance structure. Basically, we
|
|
// are trying to find the condition that is being branched on, which
|
|
// subsequently causes this merge to happen. We really want control
|
|
// dependence information for this check, but simplifycfg can't keep it up
|
|
// to date, and this catches most of the cases we care about anyway.
|
|
//
|
|
BasicBlock *BB = PN->getParent();
|
|
BasicBlock *IfTrue, *IfFalse;
|
|
Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
|
|
if (!IfCond) return false;
|
|
|
|
// Okay, we found that we can merge this two-entry phi node into a select.
|
|
// Doing so would require us to fold *all* two entry phi nodes in this block.
|
|
// At some point this becomes non-profitable (particularly if the target
|
|
// doesn't support cmov's). Only do this transformation if there are two or
|
|
// fewer PHI nodes in this block.
|
|
unsigned NumPhis = 0;
|
|
for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
|
|
if (NumPhis > 2)
|
|
return false;
|
|
|
|
DOUT << "FOUND IF CONDITION! " << *IfCond << " T: "
|
|
<< IfTrue->getName() << " F: " << IfFalse->getName() << "\n";
|
|
|
|
// Loop over the PHI's seeing if we can promote them all to select
|
|
// instructions. While we are at it, keep track of the instructions
|
|
// that need to be moved to the dominating block.
|
|
std::set<Instruction*> AggressiveInsts;
|
|
|
|
BasicBlock::iterator AfterPHIIt = BB->begin();
|
|
while (isa<PHINode>(AfterPHIIt)) {
|
|
PHINode *PN = cast<PHINode>(AfterPHIIt++);
|
|
if (PN->getIncomingValue(0) == PN->getIncomingValue(1)) {
|
|
if (PN->getIncomingValue(0) != PN)
|
|
PN->replaceAllUsesWith(PN->getIncomingValue(0));
|
|
else
|
|
PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
|
|
} else if (!DominatesMergePoint(PN->getIncomingValue(0), BB,
|
|
&AggressiveInsts) ||
|
|
!DominatesMergePoint(PN->getIncomingValue(1), BB,
|
|
&AggressiveInsts)) {
|
|
return false;
|
|
}
|
|
}
|
|
|
|
// If we all PHI nodes are promotable, check to make sure that all
|
|
// instructions in the predecessor blocks can be promoted as well. If
|
|
// not, we won't be able to get rid of the control flow, so it's not
|
|
// worth promoting to select instructions.
|
|
BasicBlock *DomBlock = 0, *IfBlock1 = 0, *IfBlock2 = 0;
|
|
PN = cast<PHINode>(BB->begin());
|
|
BasicBlock *Pred = PN->getIncomingBlock(0);
|
|
if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
|
|
IfBlock1 = Pred;
|
|
DomBlock = *pred_begin(Pred);
|
|
for (BasicBlock::iterator I = Pred->begin();
|
|
!isa<TerminatorInst>(I); ++I)
|
|
if (!AggressiveInsts.count(I)) {
|
|
// This is not an aggressive instruction that we can promote.
|
|
// Because of this, we won't be able to get rid of the control
|
|
// flow, so the xform is not worth it.
|
|
return false;
|
|
}
|
|
}
|
|
|
|
Pred = PN->getIncomingBlock(1);
|
|
if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
|
|
IfBlock2 = Pred;
|
|
DomBlock = *pred_begin(Pred);
|
|
for (BasicBlock::iterator I = Pred->begin();
|
|
!isa<TerminatorInst>(I); ++I)
|
|
if (!AggressiveInsts.count(I)) {
|
|
// This is not an aggressive instruction that we can promote.
|
|
// Because of this, we won't be able to get rid of the control
|
|
// flow, so the xform is not worth it.
|
|
return false;
|
|
}
|
|
}
|
|
|
|
// If we can still promote the PHI nodes after this gauntlet of tests,
|
|
// do all of the PHI's now.
|
|
|
|
// Move all 'aggressive' instructions, which are defined in the
|
|
// conditional parts of the if's up to the dominating block.
|
|
if (IfBlock1) {
|
|
DomBlock->getInstList().splice(DomBlock->getTerminator(),
|
|
IfBlock1->getInstList(),
|
|
IfBlock1->begin(),
|
|
IfBlock1->getTerminator());
|
|
}
|
|
if (IfBlock2) {
|
|
DomBlock->getInstList().splice(DomBlock->getTerminator(),
|
|
IfBlock2->getInstList(),
|
|
IfBlock2->begin(),
|
|
IfBlock2->getTerminator());
|
|
}
|
|
|
|
while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
|
|
// Change the PHI node into a select instruction.
|
|
Value *TrueVal =
|
|
PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
|
|
Value *FalseVal =
|
|
PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
|
|
|
|
Value *NV = new SelectInst(IfCond, TrueVal, FalseVal, "", AfterPHIIt);
|
|
PN->replaceAllUsesWith(NV);
|
|
NV->takeName(PN);
|
|
|
|
BB->getInstList().erase(PN);
|
|
}
|
|
return true;
|
|
}
|
|
|
|
namespace {
|
|
/// ConstantIntOrdering - This class implements a stable ordering of constant
|
|
/// integers that does not depend on their address. This is important for
|
|
/// applications that sort ConstantInt's to ensure uniqueness.
|
|
struct ConstantIntOrdering {
|
|
bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
|
|
return LHS->getValue().ult(RHS->getValue());
|
|
}
|
|
};
|
|
}
|
|
|
|
// SimplifyCFG - This function is used to do simplification of a CFG. For
|
|
// example, it adjusts branches to branches to eliminate the extra hop, it
|
|
// eliminates unreachable basic blocks, and does other "peephole" optimization
|
|
// of the CFG. It returns true if a modification was made.
|
|
//
|
|
// WARNING: The entry node of a function may not be simplified.
|
|
//
|
|
bool llvm::SimplifyCFG(BasicBlock *BB) {
|
|
bool Changed = false;
|
|
Function *M = BB->getParent();
|
|
|
|
assert(BB && BB->getParent() && "Block not embedded in function!");
|
|
assert(BB->getTerminator() && "Degenerate basic block encountered!");
|
|
assert(&BB->getParent()->getEntryBlock() != BB &&
|
|
"Can't Simplify entry block!");
|
|
|
|
// Remove basic blocks that have no predecessors... which are unreachable.
|
|
if (pred_begin(BB) == pred_end(BB) ||
|
|
*pred_begin(BB) == BB && ++pred_begin(BB) == pred_end(BB)) {
|
|
DOUT << "Removing BB: \n" << *BB;
|
|
|
|
// Loop through all of our successors and make sure they know that one
|
|
// of their predecessors is going away.
|
|
for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI)
|
|
SI->removePredecessor(BB);
|
|
|
|
while (!BB->empty()) {
|
|
Instruction &I = BB->back();
|
|
// If this instruction is used, replace uses with an arbitrary
|
|
// value. Because control flow can't get here, we don't care
|
|
// what we replace the value with. Note that since this block is
|
|
// unreachable, and all values contained within it must dominate their
|
|
// uses, that all uses will eventually be removed.
|
|
if (!I.use_empty())
|
|
// Make all users of this instruction use undef instead
|
|
I.replaceAllUsesWith(UndefValue::get(I.getType()));
|
|
|
|
// Remove the instruction from the basic block
|
|
BB->getInstList().pop_back();
|
|
}
|
|
M->getBasicBlockList().erase(BB);
|
|
return true;
|
|
}
|
|
|
|
// Check to see if we can constant propagate this terminator instruction
|
|
// away...
|
|
Changed |= ConstantFoldTerminator(BB);
|
|
|
|
// If this is a returning block with only PHI nodes in it, fold the return
|
|
// instruction into any unconditional branch predecessors.
|
|
//
|
|
// If any predecessor is a conditional branch that just selects among
|
|
// different return values, fold the replace the branch/return with a select
|
|
// and return.
|
|
if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
|
|
BasicBlock::iterator BBI = BB->getTerminator();
|
|
if (BBI == BB->begin() || isa<PHINode>(--BBI)) {
|
|
// Find predecessors that end with branches.
|
|
std::vector<BasicBlock*> UncondBranchPreds;
|
|
std::vector<BranchInst*> CondBranchPreds;
|
|
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
|
|
TerminatorInst *PTI = (*PI)->getTerminator();
|
|
if (BranchInst *BI = dyn_cast<BranchInst>(PTI))
|
|
if (BI->isUnconditional())
|
|
UncondBranchPreds.push_back(*PI);
|
|
else
|
|
CondBranchPreds.push_back(BI);
|
|
}
|
|
|
|
// If we found some, do the transformation!
|
|
if (!UncondBranchPreds.empty()) {
|
|
while (!UncondBranchPreds.empty()) {
|
|
BasicBlock *Pred = UncondBranchPreds.back();
|
|
DOUT << "FOLDING: " << *BB
|
|
<< "INTO UNCOND BRANCH PRED: " << *Pred;
|
|
UncondBranchPreds.pop_back();
|
|
Instruction *UncondBranch = Pred->getTerminator();
|
|
// Clone the return and add it to the end of the predecessor.
|
|
Instruction *NewRet = RI->clone();
|
|
Pred->getInstList().push_back(NewRet);
|
|
|
|
// If the return instruction returns a value, and if the value was a
|
|
// PHI node in "BB", propagate the right value into the return.
|
|
if (NewRet->getNumOperands() == 1)
|
|
if (PHINode *PN = dyn_cast<PHINode>(NewRet->getOperand(0)))
|
|
if (PN->getParent() == BB)
|
|
NewRet->setOperand(0, PN->getIncomingValueForBlock(Pred));
|
|
// Update any PHI nodes in the returning block to realize that we no
|
|
// longer branch to them.
|
|
BB->removePredecessor(Pred);
|
|
Pred->getInstList().erase(UncondBranch);
|
|
}
|
|
|
|
// If we eliminated all predecessors of the block, delete the block now.
|
|
if (pred_begin(BB) == pred_end(BB))
|
|
// We know there are no successors, so just nuke the block.
|
|
M->getBasicBlockList().erase(BB);
|
|
|
|
return true;
|
|
}
|
|
|
|
// Check out all of the conditional branches going to this return
|
|
// instruction. If any of them just select between returns, change the
|
|
// branch itself into a select/return pair.
|
|
while (!CondBranchPreds.empty()) {
|
|
BranchInst *BI = CondBranchPreds.back();
|
|
CondBranchPreds.pop_back();
|
|
BasicBlock *TrueSucc = BI->getSuccessor(0);
|
|
BasicBlock *FalseSucc = BI->getSuccessor(1);
|
|
BasicBlock *OtherSucc = TrueSucc == BB ? FalseSucc : TrueSucc;
|
|
|
|
// Check to see if the non-BB successor is also a return block.
|
|
if (isa<ReturnInst>(OtherSucc->getTerminator())) {
|
|
// Check to see if there are only PHI instructions in this block.
|
|
BasicBlock::iterator OSI = OtherSucc->getTerminator();
|
|
if (OSI == OtherSucc->begin() || isa<PHINode>(--OSI)) {
|
|
// Okay, we found a branch that is going to two return nodes. If
|
|
// there is no return value for this function, just change the
|
|
// branch into a return.
|
|
if (RI->getNumOperands() == 0) {
|
|
TrueSucc->removePredecessor(BI->getParent());
|
|
FalseSucc->removePredecessor(BI->getParent());
|
|
new ReturnInst(0, BI);
|
|
BI->getParent()->getInstList().erase(BI);
|
|
return true;
|
|
}
|
|
|
|
// Otherwise, figure out what the true and false return values are
|
|
// so we can insert a new select instruction.
|
|
Value *TrueValue = TrueSucc->getTerminator()->getOperand(0);
|
|
Value *FalseValue = FalseSucc->getTerminator()->getOperand(0);
|
|
|
|
// Unwrap any PHI nodes in the return blocks.
|
|
if (PHINode *TVPN = dyn_cast<PHINode>(TrueValue))
|
|
if (TVPN->getParent() == TrueSucc)
|
|
TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
|
|
if (PHINode *FVPN = dyn_cast<PHINode>(FalseValue))
|
|
if (FVPN->getParent() == FalseSucc)
|
|
FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
|
|
|
|
// In order for this transformation to be safe, we must be able to
|
|
// unconditionally execute both operands to the return. This is
|
|
// normally the case, but we could have a potentially-trapping
|
|
// constant expression that prevents this transformation from being
|
|
// safe.
|
|
if ((!isa<ConstantExpr>(TrueValue) ||
|
|
!cast<ConstantExpr>(TrueValue)->canTrap()) &&
|
|
(!isa<ConstantExpr>(TrueValue) ||
|
|
!cast<ConstantExpr>(TrueValue)->canTrap())) {
|
|
TrueSucc->removePredecessor(BI->getParent());
|
|
FalseSucc->removePredecessor(BI->getParent());
|
|
|
|
// Insert a new select instruction.
|
|
Value *NewRetVal;
|
|
Value *BrCond = BI->getCondition();
|
|
if (TrueValue != FalseValue)
|
|
NewRetVal = new SelectInst(BrCond, TrueValue,
|
|
FalseValue, "retval", BI);
|
|
else
|
|
NewRetVal = TrueValue;
|
|
|
|
DOUT << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
|
|
<< "\n " << *BI << "Select = " << *NewRetVal
|
|
<< "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc;
|
|
|
|
new ReturnInst(NewRetVal, BI);
|
|
BI->eraseFromParent();
|
|
if (Instruction *BrCondI = dyn_cast<Instruction>(BrCond))
|
|
if (isInstructionTriviallyDead(BrCondI))
|
|
BrCondI->eraseFromParent();
|
|
return true;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
} else if (isa<UnwindInst>(BB->begin())) {
|
|
// Check to see if the first instruction in this block is just an unwind.
|
|
// If so, replace any invoke instructions which use this as an exception
|
|
// destination with call instructions, and any unconditional branch
|
|
// predecessor with an unwind.
|
|
//
|
|
std::vector<BasicBlock*> Preds(pred_begin(BB), pred_end(BB));
|
|
while (!Preds.empty()) {
|
|
BasicBlock *Pred = Preds.back();
|
|
if (BranchInst *BI = dyn_cast<BranchInst>(Pred->getTerminator())) {
|
|
if (BI->isUnconditional()) {
|
|
Pred->getInstList().pop_back(); // nuke uncond branch
|
|
new UnwindInst(Pred); // Use unwind.
|
|
Changed = true;
|
|
}
|
|
} else if (InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator()))
|
|
if (II->getUnwindDest() == BB) {
|
|
// Insert a new branch instruction before the invoke, because this
|
|
// is now a fall through...
|
|
BranchInst *BI = new BranchInst(II->getNormalDest(), II);
|
|
Pred->getInstList().remove(II); // Take out of symbol table
|
|
|
|
// Insert the call now...
|
|
SmallVector<Value*,8> Args(II->op_begin()+3, II->op_end());
|
|
CallInst *CI = new CallInst(II->getCalledValue(),
|
|
Args.begin(), Args.end(), II->getName(), BI);
|
|
CI->setCallingConv(II->getCallingConv());
|
|
// If the invoke produced a value, the Call now does instead
|
|
II->replaceAllUsesWith(CI);
|
|
delete II;
|
|
Changed = true;
|
|
}
|
|
|
|
Preds.pop_back();
|
|
}
|
|
|
|
// If this block is now dead, remove it.
|
|
if (pred_begin(BB) == pred_end(BB)) {
|
|
// We know there are no successors, so just nuke the block.
|
|
M->getBasicBlockList().erase(BB);
|
|
return true;
|
|
}
|
|
|
|
} else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
|
|
if (isValueEqualityComparison(SI)) {
|
|
// If we only have one predecessor, and if it is a branch on this value,
|
|
// see if that predecessor totally determines the outcome of this switch.
|
|
if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
|
|
if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred))
|
|
return SimplifyCFG(BB) || 1;
|
|
|
|
// If the block only contains the switch, see if we can fold the block
|
|
// away into any preds.
|
|
if (SI == &BB->front())
|
|
if (FoldValueComparisonIntoPredecessors(SI))
|
|
return SimplifyCFG(BB) || 1;
|
|
}
|
|
} else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
|
|
if (BI->isUnconditional()) {
|
|
BasicBlock::iterator BBI = BB->begin(); // Skip over phi nodes...
|
|
while (isa<PHINode>(*BBI)) ++BBI;
|
|
|
|
BasicBlock *Succ = BI->getSuccessor(0);
|
|
if (BBI->isTerminator() && // Terminator is the only non-phi instruction!
|
|
Succ != BB) // Don't hurt infinite loops!
|
|
if (TryToSimplifyUncondBranchFromEmptyBlock(BB, Succ))
|
|
return 1;
|
|
|
|
} else { // Conditional branch
|
|
if (isValueEqualityComparison(BI)) {
|
|
// If we only have one predecessor, and if it is a branch on this value,
|
|
// see if that predecessor totally determines the outcome of this
|
|
// switch.
|
|
if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
|
|
if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred))
|
|
return SimplifyCFG(BB) || 1;
|
|
|
|
// This block must be empty, except for the setcond inst, if it exists.
|
|
BasicBlock::iterator I = BB->begin();
|
|
if (&*I == BI ||
|
|
(&*I == cast<Instruction>(BI->getCondition()) &&
|
|
&*++I == BI))
|
|
if (FoldValueComparisonIntoPredecessors(BI))
|
|
return SimplifyCFG(BB) | true;
|
|
}
|
|
|
|
// If this is a branch on a phi node in the current block, thread control
|
|
// through this block if any PHI node entries are constants.
|
|
if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
|
|
if (PN->getParent() == BI->getParent())
|
|
if (FoldCondBranchOnPHI(BI))
|
|
return SimplifyCFG(BB) | true;
|
|
|
|
// If this basic block is ONLY a setcc and a branch, and if a predecessor
|
|
// branches to us and one of our successors, fold the setcc into the
|
|
// predecessor and use logical operations to pick the right destination.
|
|
BasicBlock *TrueDest = BI->getSuccessor(0);
|
|
BasicBlock *FalseDest = BI->getSuccessor(1);
|
|
if (Instruction *Cond = dyn_cast<Instruction>(BI->getCondition())) {
|
|
BasicBlock::iterator CondIt = Cond;
|
|
if ((isa<CmpInst>(Cond) || isa<BinaryOperator>(Cond)) &&
|
|
Cond->getParent() == BB && &BB->front() == Cond &&
|
|
&*++CondIt == BI && Cond->hasOneUse() &&
|
|
TrueDest != BB && FalseDest != BB)
|
|
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI!=E; ++PI)
|
|
if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
|
|
if (PBI->isConditional() && SafeToMergeTerminators(BI, PBI)) {
|
|
BasicBlock *PredBlock = *PI;
|
|
if (PBI->getSuccessor(0) == FalseDest ||
|
|
PBI->getSuccessor(1) == TrueDest) {
|
|
// Invert the predecessors condition test (xor it with true),
|
|
// which allows us to write this code once.
|
|
Value *NewCond =
|
|
BinaryOperator::createNot(PBI->getCondition(),
|
|
PBI->getCondition()->getName()+".not", PBI);
|
|
PBI->setCondition(NewCond);
|
|
BasicBlock *OldTrue = PBI->getSuccessor(0);
|
|
BasicBlock *OldFalse = PBI->getSuccessor(1);
|
|
PBI->setSuccessor(0, OldFalse);
|
|
PBI->setSuccessor(1, OldTrue);
|
|
}
|
|
|
|
if ((PBI->getSuccessor(0) == TrueDest && FalseDest != BB) ||
|
|
(PBI->getSuccessor(1) == FalseDest && TrueDest != BB)) {
|
|
// Clone Cond into the predecessor basic block, and or/and the
|
|
// two conditions together.
|
|
Instruction *New = Cond->clone();
|
|
PredBlock->getInstList().insert(PBI, New);
|
|
New->takeName(Cond);
|
|
Cond->setName(New->getName()+".old");
|
|
Instruction::BinaryOps Opcode =
|
|
PBI->getSuccessor(0) == TrueDest ?
|
|
Instruction::Or : Instruction::And;
|
|
Value *NewCond =
|
|
BinaryOperator::create(Opcode, PBI->getCondition(),
|
|
New, "bothcond", PBI);
|
|
PBI->setCondition(NewCond);
|
|
if (PBI->getSuccessor(0) == BB) {
|
|
AddPredecessorToBlock(TrueDest, PredBlock, BB);
|
|
PBI->setSuccessor(0, TrueDest);
|
|
}
|
|
if (PBI->getSuccessor(1) == BB) {
|
|
AddPredecessorToBlock(FalseDest, PredBlock, BB);
|
|
PBI->setSuccessor(1, FalseDest);
|
|
}
|
|
return SimplifyCFG(BB) | 1;
|
|
}
|
|
}
|
|
}
|
|
|
|
// Scan predessor blocks for conditional branches.
|
|
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
|
|
if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
|
|
if (PBI != BI && PBI->isConditional()) {
|
|
|
|
// If this block ends with a branch instruction, and if there is a
|
|
// predecessor that ends on a branch of the same condition, make
|
|
// this conditional branch redundant.
|
|
if (PBI->getCondition() == BI->getCondition() &&
|
|
PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
|
|
// Okay, the outcome of this conditional branch is statically
|
|
// knowable. If this block had a single pred, handle specially.
|
|
if (BB->getSinglePredecessor()) {
|
|
// Turn this into a branch on constant.
|
|
bool CondIsTrue = PBI->getSuccessor(0) == BB;
|
|
BI->setCondition(ConstantInt::get(Type::Int1Ty, CondIsTrue));
|
|
return SimplifyCFG(BB); // Nuke the branch on constant.
|
|
}
|
|
|
|
// Otherwise, if there are multiple predecessors, insert a PHI
|
|
// that merges in the constant and simplify the block result.
|
|
if (BlockIsSimpleEnoughToThreadThrough(BB)) {
|
|
PHINode *NewPN = new PHINode(Type::Int1Ty,
|
|
BI->getCondition()->getName()+".pr",
|
|
BB->begin());
|
|
for (PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
|
|
if ((PBI = dyn_cast<BranchInst>((*PI)->getTerminator())) &&
|
|
PBI != BI && PBI->isConditional() &&
|
|
PBI->getCondition() == BI->getCondition() &&
|
|
PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
|
|
bool CondIsTrue = PBI->getSuccessor(0) == BB;
|
|
NewPN->addIncoming(ConstantInt::get(Type::Int1Ty,
|
|
CondIsTrue), *PI);
|
|
} else {
|
|
NewPN->addIncoming(BI->getCondition(), *PI);
|
|
}
|
|
|
|
BI->setCondition(NewPN);
|
|
// This will thread the branch.
|
|
return SimplifyCFG(BB) | true;
|
|
}
|
|
}
|
|
|
|
// If this is a conditional branch in an empty block, and if any
|
|
// predecessors is a conditional branch to one of our destinations,
|
|
// fold the conditions into logical ops and one cond br.
|
|
if (&BB->front() == BI) {
|
|
int PBIOp, BIOp;
|
|
if (PBI->getSuccessor(0) == BI->getSuccessor(0)) {
|
|
PBIOp = BIOp = 0;
|
|
} else if (PBI->getSuccessor(0) == BI->getSuccessor(1)) {
|
|
PBIOp = 0; BIOp = 1;
|
|
} else if (PBI->getSuccessor(1) == BI->getSuccessor(0)) {
|
|
PBIOp = 1; BIOp = 0;
|
|
} else if (PBI->getSuccessor(1) == BI->getSuccessor(1)) {
|
|
PBIOp = BIOp = 1;
|
|
} else {
|
|
PBIOp = BIOp = -1;
|
|
}
|
|
|
|
// Check to make sure that the other destination of this branch
|
|
// isn't BB itself. If so, this is an infinite loop that will
|
|
// keep getting unwound.
|
|
if (PBIOp != -1 && PBI->getSuccessor(PBIOp) == BB)
|
|
PBIOp = BIOp = -1;
|
|
|
|
// Do not perform this transformation if it would require
|
|
// insertion of a large number of select instructions. For targets
|
|
// without predication/cmovs, this is a big pessimization.
|
|
if (PBIOp != -1) {
|
|
BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
|
|
|
|
unsigned NumPhis = 0;
|
|
for (BasicBlock::iterator II = CommonDest->begin();
|
|
isa<PHINode>(II); ++II, ++NumPhis) {
|
|
if (NumPhis > 2) {
|
|
// Disable this xform.
|
|
PBIOp = -1;
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
|
|
// Finally, if everything is ok, fold the branches to logical ops.
|
|
if (PBIOp != -1) {
|
|
BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
|
|
BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
|
|
|
|
// If OtherDest *is* BB, then this is a basic block with just
|
|
// a conditional branch in it, where one edge (OtherDesg) goes
|
|
// back to the block. We know that the program doesn't get
|
|
// stuck in the infinite loop, so the condition must be such
|
|
// that OtherDest isn't branched through. Forward to CommonDest,
|
|
// and avoid an infinite loop at optimizer time.
|
|
if (OtherDest == BB)
|
|
OtherDest = CommonDest;
|
|
|
|
DOUT << "FOLDING BRs:" << *PBI->getParent()
|
|
<< "AND: " << *BI->getParent();
|
|
|
|
// BI may have other predecessors. Because of this, we leave
|
|
// it alone, but modify PBI.
|
|
|
|
// Make sure we get to CommonDest on True&True directions.
|
|
Value *PBICond = PBI->getCondition();
|
|
if (PBIOp)
|
|
PBICond = BinaryOperator::createNot(PBICond,
|
|
PBICond->getName()+".not",
|
|
PBI);
|
|
Value *BICond = BI->getCondition();
|
|
if (BIOp)
|
|
BICond = BinaryOperator::createNot(BICond,
|
|
BICond->getName()+".not",
|
|
PBI);
|
|
// Merge the conditions.
|
|
Value *Cond =
|
|
BinaryOperator::createOr(PBICond, BICond, "brmerge", PBI);
|
|
|
|
// Modify PBI to branch on the new condition to the new dests.
|
|
PBI->setCondition(Cond);
|
|
PBI->setSuccessor(0, CommonDest);
|
|
PBI->setSuccessor(1, OtherDest);
|
|
|
|
// OtherDest may have phi nodes. If so, add an entry from PBI's
|
|
// block that are identical to the entries for BI's block.
|
|
PHINode *PN;
|
|
for (BasicBlock::iterator II = OtherDest->begin();
|
|
(PN = dyn_cast<PHINode>(II)); ++II) {
|
|
Value *V = PN->getIncomingValueForBlock(BB);
|
|
PN->addIncoming(V, PBI->getParent());
|
|
}
|
|
|
|
// We know that the CommonDest already had an edge from PBI to
|
|
// it. If it has PHIs though, the PHIs may have different
|
|
// entries for BB and PBI's BB. If so, insert a select to make
|
|
// them agree.
|
|
for (BasicBlock::iterator II = CommonDest->begin();
|
|
(PN = dyn_cast<PHINode>(II)); ++II) {
|
|
Value * BIV = PN->getIncomingValueForBlock(BB);
|
|
unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
|
|
Value *PBIV = PN->getIncomingValue(PBBIdx);
|
|
if (BIV != PBIV) {
|
|
// Insert a select in PBI to pick the right value.
|
|
Value *NV = new SelectInst(PBICond, PBIV, BIV,
|
|
PBIV->getName()+".mux", PBI);
|
|
PN->setIncomingValue(PBBIdx, NV);
|
|
}
|
|
}
|
|
|
|
DOUT << "INTO: " << *PBI->getParent();
|
|
|
|
// This basic block is probably dead. We know it has at least
|
|
// one fewer predecessor.
|
|
return SimplifyCFG(BB) | true;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
} else if (isa<UnreachableInst>(BB->getTerminator())) {
|
|
// If there are any instructions immediately before the unreachable that can
|
|
// be removed, do so.
|
|
Instruction *Unreachable = BB->getTerminator();
|
|
while (Unreachable != BB->begin()) {
|
|
BasicBlock::iterator BBI = Unreachable;
|
|
--BBI;
|
|
if (isa<CallInst>(BBI)) break;
|
|
// Delete this instruction
|
|
BB->getInstList().erase(BBI);
|
|
Changed = true;
|
|
}
|
|
|
|
// If the unreachable instruction is the first in the block, take a gander
|
|
// at all of the predecessors of this instruction, and simplify them.
|
|
if (&BB->front() == Unreachable) {
|
|
std::vector<BasicBlock*> Preds(pred_begin(BB), pred_end(BB));
|
|
for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
|
|
TerminatorInst *TI = Preds[i]->getTerminator();
|
|
|
|
if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
|
|
if (BI->isUnconditional()) {
|
|
if (BI->getSuccessor(0) == BB) {
|
|
new UnreachableInst(TI);
|
|
TI->eraseFromParent();
|
|
Changed = true;
|
|
}
|
|
} else {
|
|
if (BI->getSuccessor(0) == BB) {
|
|
new BranchInst(BI->getSuccessor(1), BI);
|
|
BI->eraseFromParent();
|
|
} else if (BI->getSuccessor(1) == BB) {
|
|
new BranchInst(BI->getSuccessor(0), BI);
|
|
BI->eraseFromParent();
|
|
Changed = true;
|
|
}
|
|
}
|
|
} else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
|
|
for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
|
|
if (SI->getSuccessor(i) == BB) {
|
|
BB->removePredecessor(SI->getParent());
|
|
SI->removeCase(i);
|
|
--i; --e;
|
|
Changed = true;
|
|
}
|
|
// If the default value is unreachable, figure out the most popular
|
|
// destination and make it the default.
|
|
if (SI->getSuccessor(0) == BB) {
|
|
std::map<BasicBlock*, unsigned> Popularity;
|
|
for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
|
|
Popularity[SI->getSuccessor(i)]++;
|
|
|
|
// Find the most popular block.
|
|
unsigned MaxPop = 0;
|
|
BasicBlock *MaxBlock = 0;
|
|
for (std::map<BasicBlock*, unsigned>::iterator
|
|
I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
|
|
if (I->second > MaxPop) {
|
|
MaxPop = I->second;
|
|
MaxBlock = I->first;
|
|
}
|
|
}
|
|
if (MaxBlock) {
|
|
// Make this the new default, allowing us to delete any explicit
|
|
// edges to it.
|
|
SI->setSuccessor(0, MaxBlock);
|
|
Changed = true;
|
|
|
|
// If MaxBlock has phinodes in it, remove MaxPop-1 entries from
|
|
// it.
|
|
if (isa<PHINode>(MaxBlock->begin()))
|
|
for (unsigned i = 0; i != MaxPop-1; ++i)
|
|
MaxBlock->removePredecessor(SI->getParent());
|
|
|
|
for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
|
|
if (SI->getSuccessor(i) == MaxBlock) {
|
|
SI->removeCase(i);
|
|
--i; --e;
|
|
}
|
|
}
|
|
}
|
|
} else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
|
|
if (II->getUnwindDest() == BB) {
|
|
// Convert the invoke to a call instruction. This would be a good
|
|
// place to note that the call does not throw though.
|
|
BranchInst *BI = new BranchInst(II->getNormalDest(), II);
|
|
II->removeFromParent(); // Take out of symbol table
|
|
|
|
// Insert the call now...
|
|
SmallVector<Value*, 8> Args(II->op_begin()+3, II->op_end());
|
|
CallInst *CI = new CallInst(II->getCalledValue(),
|
|
Args.begin(), Args.end(),
|
|
II->getName(), BI);
|
|
CI->setCallingConv(II->getCallingConv());
|
|
// If the invoke produced a value, the Call does now instead.
|
|
II->replaceAllUsesWith(CI);
|
|
delete II;
|
|
Changed = true;
|
|
}
|
|
}
|
|
}
|
|
|
|
// If this block is now dead, remove it.
|
|
if (pred_begin(BB) == pred_end(BB)) {
|
|
// We know there are no successors, so just nuke the block.
|
|
M->getBasicBlockList().erase(BB);
|
|
return true;
|
|
}
|
|
}
|
|
}
|
|
|
|
// Merge basic blocks into their predecessor if there is only one distinct
|
|
// pred, and if there is only one distinct successor of the predecessor, and
|
|
// if there are no PHI nodes.
|
|
//
|
|
pred_iterator PI(pred_begin(BB)), PE(pred_end(BB));
|
|
BasicBlock *OnlyPred = *PI++;
|
|
for (; PI != PE; ++PI) // Search all predecessors, see if they are all same
|
|
if (*PI != OnlyPred) {
|
|
OnlyPred = 0; // There are multiple different predecessors...
|
|
break;
|
|
}
|
|
|
|
BasicBlock *OnlySucc = 0;
|
|
if (OnlyPred && OnlyPred != BB && // Don't break self loops
|
|
OnlyPred->getTerminator()->getOpcode() != Instruction::Invoke) {
|
|
// Check to see if there is only one distinct successor...
|
|
succ_iterator SI(succ_begin(OnlyPred)), SE(succ_end(OnlyPred));
|
|
OnlySucc = BB;
|
|
for (; SI != SE; ++SI)
|
|
if (*SI != OnlySucc) {
|
|
OnlySucc = 0; // There are multiple distinct successors!
|
|
break;
|
|
}
|
|
}
|
|
|
|
if (OnlySucc) {
|
|
DOUT << "Merging: " << *BB << "into: " << *OnlyPred;
|
|
|
|
// Resolve any PHI nodes at the start of the block. They are all
|
|
// guaranteed to have exactly one entry if they exist, unless there are
|
|
// multiple duplicate (but guaranteed to be equal) entries for the
|
|
// incoming edges. This occurs when there are multiple edges from
|
|
// OnlyPred to OnlySucc.
|
|
//
|
|
while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
|
|
PN->replaceAllUsesWith(PN->getIncomingValue(0));
|
|
BB->getInstList().pop_front(); // Delete the phi node.
|
|
}
|
|
|
|
// Delete the unconditional branch from the predecessor.
|
|
OnlyPred->getInstList().pop_back();
|
|
|
|
// Move all definitions in the successor to the predecessor.
|
|
OnlyPred->getInstList().splice(OnlyPred->end(), BB->getInstList());
|
|
|
|
// Make all PHI nodes that referred to BB now refer to Pred as their
|
|
// source.
|
|
BB->replaceAllUsesWith(OnlyPred);
|
|
|
|
// Inherit predecessors name if it exists.
|
|
if (!OnlyPred->hasName())
|
|
OnlyPred->takeName(BB);
|
|
|
|
// Erase basic block from the function.
|
|
M->getBasicBlockList().erase(BB);
|
|
|
|
return true;
|
|
}
|
|
|
|
// Otherwise, if this block only has a single predecessor, and if that block
|
|
// is a conditional branch, see if we can hoist any code from this block up
|
|
// into our predecessor.
|
|
if (OnlyPred)
|
|
if (BranchInst *BI = dyn_cast<BranchInst>(OnlyPred->getTerminator()))
|
|
if (BI->isConditional()) {
|
|
// Get the other block.
|
|
BasicBlock *OtherBB = BI->getSuccessor(BI->getSuccessor(0) == BB);
|
|
PI = pred_begin(OtherBB);
|
|
++PI;
|
|
if (PI == pred_end(OtherBB)) {
|
|
// We have a conditional branch to two blocks that are only reachable
|
|
// from the condbr. We know that the condbr dominates the two blocks,
|
|
// so see if there is any identical code in the "then" and "else"
|
|
// blocks. If so, we can hoist it up to the branching block.
|
|
Changed |= HoistThenElseCodeToIf(BI);
|
|
}
|
|
}
|
|
|
|
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
|
|
if (BranchInst *BI = dyn_cast<BranchInst>((*PI)->getTerminator()))
|
|
// Change br (X == 0 | X == 1), T, F into a switch instruction.
|
|
if (BI->isConditional() && isa<Instruction>(BI->getCondition())) {
|
|
Instruction *Cond = cast<Instruction>(BI->getCondition());
|
|
// If this is a bunch of seteq's or'd together, or if it's a bunch of
|
|
// 'setne's and'ed together, collect them.
|
|
Value *CompVal = 0;
|
|
std::vector<ConstantInt*> Values;
|
|
bool TrueWhenEqual = GatherValueComparisons(Cond, CompVal, Values);
|
|
if (CompVal && CompVal->getType()->isInteger()) {
|
|
// There might be duplicate constants in the list, which the switch
|
|
// instruction can't handle, remove them now.
|
|
std::sort(Values.begin(), Values.end(), ConstantIntOrdering());
|
|
Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
|
|
|
|
// Figure out which block is which destination.
|
|
BasicBlock *DefaultBB = BI->getSuccessor(1);
|
|
BasicBlock *EdgeBB = BI->getSuccessor(0);
|
|
if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
|
|
|
|
// Create the new switch instruction now.
|
|
SwitchInst *New = new SwitchInst(CompVal, DefaultBB,Values.size(),BI);
|
|
|
|
// Add all of the 'cases' to the switch instruction.
|
|
for (unsigned i = 0, e = Values.size(); i != e; ++i)
|
|
New->addCase(Values[i], EdgeBB);
|
|
|
|
// We added edges from PI to the EdgeBB. As such, if there were any
|
|
// PHI nodes in EdgeBB, they need entries to be added corresponding to
|
|
// the number of edges added.
|
|
for (BasicBlock::iterator BBI = EdgeBB->begin();
|
|
isa<PHINode>(BBI); ++BBI) {
|
|
PHINode *PN = cast<PHINode>(BBI);
|
|
Value *InVal = PN->getIncomingValueForBlock(*PI);
|
|
for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
|
|
PN->addIncoming(InVal, *PI);
|
|
}
|
|
|
|
// Erase the old branch instruction.
|
|
(*PI)->getInstList().erase(BI);
|
|
|
|
// Erase the potentially condition tree that was used to computed the
|
|
// branch condition.
|
|
ErasePossiblyDeadInstructionTree(Cond);
|
|
return true;
|
|
}
|
|
}
|
|
|
|
// If there is a trivial two-entry PHI node in this basic block, and we can
|
|
// eliminate it, do so now.
|
|
if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
|
|
if (PN->getNumIncomingValues() == 2)
|
|
Changed |= FoldTwoEntryPHINode(PN);
|
|
|
|
return Changed;
|
|
}
|