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delete some dead ones. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@32694 91177308-0d34-0410-b5e6-96231b3b80d8
921 lines
36 KiB
C++
921 lines
36 KiB
C++
//===- LoopSimplify.cpp - Loop Canonicalization Pass ----------------------===//
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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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// This pass performs several transformations to transform natural loops into a
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// simpler form, which makes subsequent analyses and transformations simpler and
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// more effective.
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//
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// Loop pre-header insertion guarantees that there is a single, non-critical
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// entry edge from outside of the loop to the loop header. This simplifies a
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// number of analyses and transformations, such as LICM.
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//
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// Loop exit-block insertion guarantees that all exit blocks from the loop
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// (blocks which are outside of the loop that have predecessors inside of the
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// loop) only have predecessors from inside of the loop (and are thus dominated
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// by the loop header). This simplifies transformations such as store-sinking
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// that are built into LICM.
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//
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// This pass also guarantees that loops will have exactly one backedge.
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//
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// Note that the simplifycfg pass will clean up blocks which are split out but
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// end up being unnecessary, so usage of this pass should not pessimize
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// generated code.
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//
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// This pass obviously modifies the CFG, but updates loop information and
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// dominator information.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "loopsimplify"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/Constant.h"
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#include "llvm/Instructions.h"
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#include "llvm/Function.h"
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#include "llvm/Type.h"
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/Analysis/Dominators.h"
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#include "llvm/Analysis/LoopInfo.h"
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#include "llvm/Support/CFG.h"
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#include "llvm/Support/Compiler.h"
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#include "llvm/ADT/SetOperations.h"
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#include "llvm/ADT/SetVector.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/ADT/DepthFirstIterator.h"
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using namespace llvm;
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STATISTIC(NumInserted, "Number of pre-header or exit blocks inserted");
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STATISTIC(NumNested , "Number of nested loops split out");
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namespace {
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struct VISIBILITY_HIDDEN LoopSimplify : public FunctionPass {
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// AA - If we have an alias analysis object to update, this is it, otherwise
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// this is null.
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AliasAnalysis *AA;
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LoopInfo *LI;
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virtual bool runOnFunction(Function &F);
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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// We need loop information to identify the loops...
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AU.addRequired<LoopInfo>();
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AU.addRequired<DominatorSet>();
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AU.addRequired<DominatorTree>();
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AU.addPreserved<LoopInfo>();
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AU.addPreserved<DominatorSet>();
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AU.addPreserved<ImmediateDominators>();
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AU.addPreserved<ETForest>();
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AU.addPreserved<DominatorTree>();
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AU.addPreserved<DominanceFrontier>();
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AU.addPreservedID(BreakCriticalEdgesID); // No critical edges added.
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}
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private:
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bool ProcessLoop(Loop *L);
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BasicBlock *SplitBlockPredecessors(BasicBlock *BB, const char *Suffix,
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const std::vector<BasicBlock*> &Preds);
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BasicBlock *RewriteLoopExitBlock(Loop *L, BasicBlock *Exit);
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void InsertPreheaderForLoop(Loop *L);
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Loop *SeparateNestedLoop(Loop *L);
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void InsertUniqueBackedgeBlock(Loop *L);
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void PlaceSplitBlockCarefully(BasicBlock *NewBB,
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std::vector<BasicBlock*> &SplitPreds,
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Loop *L);
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void UpdateDomInfoForRevectoredPreds(BasicBlock *NewBB,
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std::vector<BasicBlock*> &PredBlocks);
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};
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RegisterPass<LoopSimplify>
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X("loopsimplify", "Canonicalize natural loops", true);
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}
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// Publically exposed interface to pass...
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const PassInfo *llvm::LoopSimplifyID = X.getPassInfo();
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FunctionPass *llvm::createLoopSimplifyPass() { return new LoopSimplify(); }
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/// runOnFunction - Run down all loops in the CFG (recursively, but we could do
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/// it in any convenient order) inserting preheaders...
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///
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bool LoopSimplify::runOnFunction(Function &F) {
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bool Changed = false;
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LI = &getAnalysis<LoopInfo>();
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AA = getAnalysisToUpdate<AliasAnalysis>();
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// Check to see that no blocks (other than the header) in loops have
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// predecessors that are not in loops. This is not valid for natural loops,
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// but can occur if the blocks are unreachable. Since they are unreachable we
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// can just shamelessly destroy their terminators to make them not branch into
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// the loop!
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for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
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// This case can only occur for unreachable blocks. Blocks that are
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// unreachable can't be in loops, so filter those blocks out.
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if (LI->getLoopFor(BB)) continue;
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bool BlockUnreachable = false;
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TerminatorInst *TI = BB->getTerminator();
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// Check to see if any successors of this block are non-loop-header loops
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// that are not the header.
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for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
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// If this successor is not in a loop, BB is clearly ok.
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Loop *L = LI->getLoopFor(TI->getSuccessor(i));
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if (!L) continue;
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// If the succ is the loop header, and if L is a top-level loop, then this
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// is an entrance into a loop through the header, which is also ok.
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if (L->getHeader() == TI->getSuccessor(i) && L->getParentLoop() == 0)
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continue;
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// Otherwise, this is an entrance into a loop from some place invalid.
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// Either the loop structure is invalid and this is not a natural loop (in
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// which case the compiler is buggy somewhere else) or BB is unreachable.
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BlockUnreachable = true;
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break;
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}
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// If this block is ok, check the next one.
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if (!BlockUnreachable) continue;
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// Otherwise, this block is dead. To clean up the CFG and to allow later
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// loop transformations to ignore this case, we delete the edges into the
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// loop by replacing the terminator.
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// Remove PHI entries from the successors.
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for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
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TI->getSuccessor(i)->removePredecessor(BB);
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// Add a new unreachable instruction.
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new UnreachableInst(TI);
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// Delete the dead terminator.
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if (AA) AA->deleteValue(&BB->back());
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BB->getInstList().pop_back();
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Changed |= true;
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}
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for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I)
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Changed |= ProcessLoop(*I);
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return Changed;
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}
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/// ProcessLoop - Walk the loop structure in depth first order, ensuring that
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/// all loops have preheaders.
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///
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bool LoopSimplify::ProcessLoop(Loop *L) {
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bool Changed = false;
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ReprocessLoop:
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// Canonicalize inner loops before outer loops. Inner loop canonicalization
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// can provide work for the outer loop to canonicalize.
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for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I)
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Changed |= ProcessLoop(*I);
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assert(L->getBlocks()[0] == L->getHeader() &&
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"Header isn't first block in loop?");
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// Does the loop already have a preheader? If so, don't insert one.
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if (L->getLoopPreheader() == 0) {
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InsertPreheaderForLoop(L);
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NumInserted++;
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Changed = true;
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}
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// Next, check to make sure that all exit nodes of the loop only have
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// predecessors that are inside of the loop. This check guarantees that the
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// loop preheader/header will dominate the exit blocks. If the exit block has
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// predecessors from outside of the loop, split the edge now.
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std::vector<BasicBlock*> ExitBlocks;
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L->getExitBlocks(ExitBlocks);
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SetVector<BasicBlock*> ExitBlockSet(ExitBlocks.begin(), ExitBlocks.end());
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for (SetVector<BasicBlock*>::iterator I = ExitBlockSet.begin(),
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E = ExitBlockSet.end(); I != E; ++I) {
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BasicBlock *ExitBlock = *I;
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for (pred_iterator PI = pred_begin(ExitBlock), PE = pred_end(ExitBlock);
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PI != PE; ++PI)
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// Must be exactly this loop: no subloops, parent loops, or non-loop preds
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// allowed.
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if (!L->contains(*PI)) {
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RewriteLoopExitBlock(L, ExitBlock);
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NumInserted++;
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Changed = true;
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break;
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}
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}
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// If the header has more than two predecessors at this point (from the
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// preheader and from multiple backedges), we must adjust the loop.
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unsigned NumBackedges = L->getNumBackEdges();
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if (NumBackedges != 1) {
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// If this is really a nested loop, rip it out into a child loop. Don't do
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// this for loops with a giant number of backedges, just factor them into a
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// common backedge instead.
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if (NumBackedges < 8) {
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if (Loop *NL = SeparateNestedLoop(L)) {
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++NumNested;
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// This is a big restructuring change, reprocess the whole loop.
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ProcessLoop(NL);
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Changed = true;
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// GCC doesn't tail recursion eliminate this.
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goto ReprocessLoop;
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}
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}
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// If we either couldn't, or didn't want to, identify nesting of the loops,
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// insert a new block that all backedges target, then make it jump to the
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// loop header.
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InsertUniqueBackedgeBlock(L);
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NumInserted++;
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Changed = true;
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}
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// Scan over the PHI nodes in the loop header. Since they now have only two
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// incoming values (the loop is canonicalized), we may have simplified the PHI
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// down to 'X = phi [X, Y]', which should be replaced with 'Y'.
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PHINode *PN;
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for (BasicBlock::iterator I = L->getHeader()->begin();
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(PN = dyn_cast<PHINode>(I++)); )
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if (Value *V = PN->hasConstantValue()) {
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PN->replaceAllUsesWith(V);
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PN->eraseFromParent();
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}
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return Changed;
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}
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/// SplitBlockPredecessors - Split the specified block into two blocks. We want
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/// to move the predecessors specified in the Preds list to point to the new
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/// block, leaving the remaining predecessors pointing to BB. This method
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/// updates the SSA PHINode's, but no other analyses.
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///
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BasicBlock *LoopSimplify::SplitBlockPredecessors(BasicBlock *BB,
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const char *Suffix,
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const std::vector<BasicBlock*> &Preds) {
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// Create new basic block, insert right before the original block...
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BasicBlock *NewBB = new BasicBlock(BB->getName()+Suffix, BB->getParent(), BB);
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// The preheader first gets an unconditional branch to the loop header...
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BranchInst *BI = new BranchInst(BB, NewBB);
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// For every PHI node in the block, insert a PHI node into NewBB where the
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// incoming values from the out of loop edges are moved to NewBB. We have two
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// possible cases here. If the loop is dead, we just insert dummy entries
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// into the PHI nodes for the new edge. If the loop is not dead, we move the
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// incoming edges in BB into new PHI nodes in NewBB.
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//
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if (!Preds.empty()) { // Is the loop not obviously dead?
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// Check to see if the values being merged into the new block need PHI
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// nodes. If so, insert them.
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for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ) {
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PHINode *PN = cast<PHINode>(I);
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++I;
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// Check to see if all of the values coming in are the same. If so, we
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// don't need to create a new PHI node.
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Value *InVal = PN->getIncomingValueForBlock(Preds[0]);
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for (unsigned i = 1, e = Preds.size(); i != e; ++i)
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if (InVal != PN->getIncomingValueForBlock(Preds[i])) {
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InVal = 0;
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break;
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}
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// If the values coming into the block are not the same, we need a PHI.
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if (InVal == 0) {
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// Create the new PHI node, insert it into NewBB at the end of the block
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PHINode *NewPHI = new PHINode(PN->getType(), PN->getName()+".ph", BI);
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if (AA) AA->copyValue(PN, NewPHI);
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// Move all of the edges from blocks outside the loop to the new PHI
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for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
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Value *V = PN->removeIncomingValue(Preds[i], false);
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NewPHI->addIncoming(V, Preds[i]);
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}
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InVal = NewPHI;
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} else {
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// Remove all of the edges coming into the PHI nodes from outside of the
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// block.
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for (unsigned i = 0, e = Preds.size(); i != e; ++i)
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PN->removeIncomingValue(Preds[i], false);
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}
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// Add an incoming value to the PHI node in the loop for the preheader
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// edge.
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PN->addIncoming(InVal, NewBB);
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// Can we eliminate this phi node now?
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if (Value *V = PN->hasConstantValue(true)) {
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if (!isa<Instruction>(V) ||
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getAnalysis<DominatorSet>().dominates(cast<Instruction>(V), PN)) {
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PN->replaceAllUsesWith(V);
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if (AA) AA->deleteValue(PN);
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BB->getInstList().erase(PN);
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}
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}
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}
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// Now that the PHI nodes are updated, actually move the edges from
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// Preds to point to NewBB instead of BB.
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//
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for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
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TerminatorInst *TI = Preds[i]->getTerminator();
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for (unsigned s = 0, e = TI->getNumSuccessors(); s != e; ++s)
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if (TI->getSuccessor(s) == BB)
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TI->setSuccessor(s, NewBB);
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}
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} else { // Otherwise the loop is dead...
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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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// Insert dummy values as the incoming value...
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PN->addIncoming(Constant::getNullValue(PN->getType()), NewBB);
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}
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}
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return NewBB;
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}
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/// InsertPreheaderForLoop - Once we discover that a loop doesn't have a
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/// preheader, this method is called to insert one. This method has two phases:
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/// preheader insertion and analysis updating.
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///
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void LoopSimplify::InsertPreheaderForLoop(Loop *L) {
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BasicBlock *Header = L->getHeader();
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// Compute the set of predecessors of the loop that are not in the loop.
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std::vector<BasicBlock*> OutsideBlocks;
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for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
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PI != PE; ++PI)
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if (!L->contains(*PI)) // Coming in from outside the loop?
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OutsideBlocks.push_back(*PI); // Keep track of it...
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// Split out the loop pre-header.
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BasicBlock *NewBB =
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SplitBlockPredecessors(Header, ".preheader", OutsideBlocks);
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//===--------------------------------------------------------------------===//
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// Update analysis results now that we have performed the transformation
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//
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// We know that we have loop information to update... update it now.
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if (Loop *Parent = L->getParentLoop())
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Parent->addBasicBlockToLoop(NewBB, *LI);
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UpdateDomInfoForRevectoredPreds(NewBB, OutsideBlocks);
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// Make sure that NewBB is put someplace intelligent, which doesn't mess up
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// code layout too horribly.
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PlaceSplitBlockCarefully(NewBB, OutsideBlocks, L);
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}
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/// RewriteLoopExitBlock - Ensure that the loop preheader dominates all exit
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/// blocks. This method is used to split exit blocks that have predecessors
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/// outside of the loop.
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BasicBlock *LoopSimplify::RewriteLoopExitBlock(Loop *L, BasicBlock *Exit) {
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std::vector<BasicBlock*> LoopBlocks;
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for (pred_iterator I = pred_begin(Exit), E = pred_end(Exit); I != E; ++I)
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if (L->contains(*I))
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LoopBlocks.push_back(*I);
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assert(!LoopBlocks.empty() && "No edges coming in from outside the loop?");
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BasicBlock *NewBB = SplitBlockPredecessors(Exit, ".loopexit", LoopBlocks);
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// Update Loop Information - we know that the new block will be in whichever
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// loop the Exit block is in. Note that it may not be in that immediate loop,
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// if the successor is some other loop header. In that case, we continue
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// walking up the loop tree to find a loop that contains both the successor
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// block and the predecessor block.
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Loop *SuccLoop = LI->getLoopFor(Exit);
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while (SuccLoop && !SuccLoop->contains(L->getHeader()))
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SuccLoop = SuccLoop->getParentLoop();
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if (SuccLoop)
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SuccLoop->addBasicBlockToLoop(NewBB, *LI);
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// Update dominator information (set, immdom, domtree, and domfrontier)
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UpdateDomInfoForRevectoredPreds(NewBB, LoopBlocks);
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return NewBB;
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}
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/// AddBlockAndPredsToSet - Add the specified block, and all of its
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/// predecessors, to the specified set, if it's not already in there. Stop
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/// predecessor traversal when we reach StopBlock.
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static void AddBlockAndPredsToSet(BasicBlock *BB, BasicBlock *StopBlock,
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std::set<BasicBlock*> &Blocks) {
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if (!Blocks.insert(BB).second) return; // already processed.
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if (BB == StopBlock) return; // Stop here!
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for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I)
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AddBlockAndPredsToSet(*I, StopBlock, Blocks);
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}
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/// FindPHIToPartitionLoops - The first part of loop-nestification is to find a
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/// PHI node that tells us how to partition the loops.
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static PHINode *FindPHIToPartitionLoops(Loop *L, DominatorSet &DS,
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AliasAnalysis *AA) {
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for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ) {
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PHINode *PN = cast<PHINode>(I);
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++I;
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if (Value *V = PN->hasConstantValue())
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if (!isa<Instruction>(V) || DS.dominates(cast<Instruction>(V), PN)) {
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// This is a degenerate PHI already, don't modify it!
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PN->replaceAllUsesWith(V);
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if (AA) AA->deleteValue(PN);
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PN->eraseFromParent();
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continue;
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}
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// Scan this PHI node looking for a use of the PHI node by itself.
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for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
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if (PN->getIncomingValue(i) == PN &&
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L->contains(PN->getIncomingBlock(i)))
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// We found something tasty to remove.
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return PN;
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}
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return 0;
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}
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// PlaceSplitBlockCarefully - If the block isn't already, move the new block to
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// right after some 'outside block' block. This prevents the preheader from
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// being placed inside the loop body, e.g. when the loop hasn't been rotated.
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void LoopSimplify::PlaceSplitBlockCarefully(BasicBlock *NewBB,
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std::vector<BasicBlock*>&SplitPreds,
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Loop *L) {
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// Check to see if NewBB is already well placed.
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Function::iterator BBI = NewBB; --BBI;
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for (unsigned i = 0, e = SplitPreds.size(); i != e; ++i) {
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if (&*BBI == SplitPreds[i])
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return;
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}
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// If it isn't already after an outside block, move it after one. This is
|
|
// always good as it makes the uncond branch from the outside block into a
|
|
// fall-through.
|
|
|
|
// Figure out *which* outside block to put this after. Prefer an outside
|
|
// block that neighbors a BB actually in the loop.
|
|
BasicBlock *FoundBB = 0;
|
|
for (unsigned i = 0, e = SplitPreds.size(); i != e; ++i) {
|
|
Function::iterator BBI = SplitPreds[i];
|
|
if (++BBI != NewBB->getParent()->end() &&
|
|
L->contains(BBI)) {
|
|
FoundBB = SplitPreds[i];
|
|
break;
|
|
}
|
|
}
|
|
|
|
// If our heuristic for a *good* bb to place this after doesn't find
|
|
// anything, just pick something. It's likely better than leaving it within
|
|
// the loop.
|
|
if (!FoundBB)
|
|
FoundBB = SplitPreds[0];
|
|
NewBB->moveAfter(FoundBB);
|
|
}
|
|
|
|
|
|
/// SeparateNestedLoop - If this loop has multiple backedges, try to pull one of
|
|
/// them out into a nested loop. This is important for code that looks like
|
|
/// this:
|
|
///
|
|
/// Loop:
|
|
/// ...
|
|
/// br cond, Loop, Next
|
|
/// ...
|
|
/// br cond2, Loop, Out
|
|
///
|
|
/// To identify this common case, we look at the PHI nodes in the header of the
|
|
/// loop. PHI nodes with unchanging values on one backedge correspond to values
|
|
/// that change in the "outer" loop, but not in the "inner" loop.
|
|
///
|
|
/// If we are able to separate out a loop, return the new outer loop that was
|
|
/// created.
|
|
///
|
|
Loop *LoopSimplify::SeparateNestedLoop(Loop *L) {
|
|
PHINode *PN = FindPHIToPartitionLoops(L, getAnalysis<DominatorSet>(), AA);
|
|
if (PN == 0) return 0; // No known way to partition.
|
|
|
|
// Pull out all predecessors that have varying values in the loop. This
|
|
// handles the case when a PHI node has multiple instances of itself as
|
|
// arguments.
|
|
std::vector<BasicBlock*> OuterLoopPreds;
|
|
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
|
|
if (PN->getIncomingValue(i) != PN ||
|
|
!L->contains(PN->getIncomingBlock(i)))
|
|
OuterLoopPreds.push_back(PN->getIncomingBlock(i));
|
|
|
|
BasicBlock *Header = L->getHeader();
|
|
BasicBlock *NewBB = SplitBlockPredecessors(Header, ".outer", OuterLoopPreds);
|
|
|
|
// Update dominator information (set, immdom, domtree, and domfrontier)
|
|
UpdateDomInfoForRevectoredPreds(NewBB, OuterLoopPreds);
|
|
|
|
// Make sure that NewBB is put someplace intelligent, which doesn't mess up
|
|
// code layout too horribly.
|
|
PlaceSplitBlockCarefully(NewBB, OuterLoopPreds, L);
|
|
|
|
// Create the new outer loop.
|
|
Loop *NewOuter = new Loop();
|
|
|
|
// Change the parent loop to use the outer loop as its child now.
|
|
if (Loop *Parent = L->getParentLoop())
|
|
Parent->replaceChildLoopWith(L, NewOuter);
|
|
else
|
|
LI->changeTopLevelLoop(L, NewOuter);
|
|
|
|
// This block is going to be our new header block: add it to this loop and all
|
|
// parent loops.
|
|
NewOuter->addBasicBlockToLoop(NewBB, *LI);
|
|
|
|
// L is now a subloop of our outer loop.
|
|
NewOuter->addChildLoop(L);
|
|
|
|
for (unsigned i = 0, e = L->getBlocks().size(); i != e; ++i)
|
|
NewOuter->addBlockEntry(L->getBlocks()[i]);
|
|
|
|
// Determine which blocks should stay in L and which should be moved out to
|
|
// the Outer loop now.
|
|
DominatorSet &DS = getAnalysis<DominatorSet>();
|
|
std::set<BasicBlock*> BlocksInL;
|
|
for (pred_iterator PI = pred_begin(Header), E = pred_end(Header); PI!=E; ++PI)
|
|
if (DS.dominates(Header, *PI))
|
|
AddBlockAndPredsToSet(*PI, Header, BlocksInL);
|
|
|
|
|
|
// Scan all of the loop children of L, moving them to OuterLoop if they are
|
|
// not part of the inner loop.
|
|
for (Loop::iterator I = L->begin(); I != L->end(); )
|
|
if (BlocksInL.count((*I)->getHeader()))
|
|
++I; // Loop remains in L
|
|
else
|
|
NewOuter->addChildLoop(L->removeChildLoop(I));
|
|
|
|
// Now that we know which blocks are in L and which need to be moved to
|
|
// OuterLoop, move any blocks that need it.
|
|
for (unsigned i = 0; i != L->getBlocks().size(); ++i) {
|
|
BasicBlock *BB = L->getBlocks()[i];
|
|
if (!BlocksInL.count(BB)) {
|
|
// Move this block to the parent, updating the exit blocks sets
|
|
L->removeBlockFromLoop(BB);
|
|
if ((*LI)[BB] == L)
|
|
LI->changeLoopFor(BB, NewOuter);
|
|
--i;
|
|
}
|
|
}
|
|
|
|
return NewOuter;
|
|
}
|
|
|
|
|
|
|
|
/// InsertUniqueBackedgeBlock - This method is called when the specified loop
|
|
/// has more than one backedge in it. If this occurs, revector all of these
|
|
/// backedges to target a new basic block and have that block branch to the loop
|
|
/// header. This ensures that loops have exactly one backedge.
|
|
///
|
|
void LoopSimplify::InsertUniqueBackedgeBlock(Loop *L) {
|
|
assert(L->getNumBackEdges() > 1 && "Must have > 1 backedge!");
|
|
|
|
// Get information about the loop
|
|
BasicBlock *Preheader = L->getLoopPreheader();
|
|
BasicBlock *Header = L->getHeader();
|
|
Function *F = Header->getParent();
|
|
|
|
// Figure out which basic blocks contain back-edges to the loop header.
|
|
std::vector<BasicBlock*> BackedgeBlocks;
|
|
for (pred_iterator I = pred_begin(Header), E = pred_end(Header); I != E; ++I)
|
|
if (*I != Preheader) BackedgeBlocks.push_back(*I);
|
|
|
|
// Create and insert the new backedge block...
|
|
BasicBlock *BEBlock = new BasicBlock(Header->getName()+".backedge", F);
|
|
BranchInst *BETerminator = new BranchInst(Header, BEBlock);
|
|
|
|
// Move the new backedge block to right after the last backedge block.
|
|
Function::iterator InsertPos = BackedgeBlocks.back(); ++InsertPos;
|
|
F->getBasicBlockList().splice(InsertPos, F->getBasicBlockList(), BEBlock);
|
|
|
|
// Now that the block has been inserted into the function, create PHI nodes in
|
|
// the backedge block which correspond to any PHI nodes in the header block.
|
|
for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
|
|
PHINode *PN = cast<PHINode>(I);
|
|
PHINode *NewPN = new PHINode(PN->getType(), PN->getName()+".be",
|
|
BETerminator);
|
|
NewPN->reserveOperandSpace(BackedgeBlocks.size());
|
|
if (AA) AA->copyValue(PN, NewPN);
|
|
|
|
// Loop over the PHI node, moving all entries except the one for the
|
|
// preheader over to the new PHI node.
|
|
unsigned PreheaderIdx = ~0U;
|
|
bool HasUniqueIncomingValue = true;
|
|
Value *UniqueValue = 0;
|
|
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
|
|
BasicBlock *IBB = PN->getIncomingBlock(i);
|
|
Value *IV = PN->getIncomingValue(i);
|
|
if (IBB == Preheader) {
|
|
PreheaderIdx = i;
|
|
} else {
|
|
NewPN->addIncoming(IV, IBB);
|
|
if (HasUniqueIncomingValue) {
|
|
if (UniqueValue == 0)
|
|
UniqueValue = IV;
|
|
else if (UniqueValue != IV)
|
|
HasUniqueIncomingValue = false;
|
|
}
|
|
}
|
|
}
|
|
|
|
// Delete all of the incoming values from the old PN except the preheader's
|
|
assert(PreheaderIdx != ~0U && "PHI has no preheader entry??");
|
|
if (PreheaderIdx != 0) {
|
|
PN->setIncomingValue(0, PN->getIncomingValue(PreheaderIdx));
|
|
PN->setIncomingBlock(0, PN->getIncomingBlock(PreheaderIdx));
|
|
}
|
|
// Nuke all entries except the zero'th.
|
|
for (unsigned i = 0, e = PN->getNumIncomingValues()-1; i != e; ++i)
|
|
PN->removeIncomingValue(e-i, false);
|
|
|
|
// Finally, add the newly constructed PHI node as the entry for the BEBlock.
|
|
PN->addIncoming(NewPN, BEBlock);
|
|
|
|
// As an optimization, if all incoming values in the new PhiNode (which is a
|
|
// subset of the incoming values of the old PHI node) have the same value,
|
|
// eliminate the PHI Node.
|
|
if (HasUniqueIncomingValue) {
|
|
NewPN->replaceAllUsesWith(UniqueValue);
|
|
if (AA) AA->deleteValue(NewPN);
|
|
BEBlock->getInstList().erase(NewPN);
|
|
}
|
|
}
|
|
|
|
// Now that all of the PHI nodes have been inserted and adjusted, modify the
|
|
// backedge blocks to just to the BEBlock instead of the header.
|
|
for (unsigned i = 0, e = BackedgeBlocks.size(); i != e; ++i) {
|
|
TerminatorInst *TI = BackedgeBlocks[i]->getTerminator();
|
|
for (unsigned Op = 0, e = TI->getNumSuccessors(); Op != e; ++Op)
|
|
if (TI->getSuccessor(Op) == Header)
|
|
TI->setSuccessor(Op, BEBlock);
|
|
}
|
|
|
|
//===--- Update all analyses which we must preserve now -----------------===//
|
|
|
|
// Update Loop Information - we know that this block is now in the current
|
|
// loop and all parent loops.
|
|
L->addBasicBlockToLoop(BEBlock, *LI);
|
|
|
|
// Update dominator information (set, immdom, domtree, and domfrontier)
|
|
UpdateDomInfoForRevectoredPreds(BEBlock, BackedgeBlocks);
|
|
}
|
|
|
|
/// UpdateDomInfoForRevectoredPreds - This method is used to update the four
|
|
/// different kinds of dominator information (dominator sets, immediate
|
|
/// dominators, dominator trees, and dominance frontiers) after a new block has
|
|
/// been added to the CFG.
|
|
///
|
|
/// This only supports the case when an existing block (known as "NewBBSucc"),
|
|
/// had some of its predecessors factored into a new basic block. This
|
|
/// transformation inserts a new basic block ("NewBB"), with a single
|
|
/// unconditional branch to NewBBSucc, and moves some predecessors of
|
|
/// "NewBBSucc" to now branch to NewBB. These predecessors are listed in
|
|
/// PredBlocks, even though they are the same as
|
|
/// pred_begin(NewBB)/pred_end(NewBB).
|
|
///
|
|
void LoopSimplify::UpdateDomInfoForRevectoredPreds(BasicBlock *NewBB,
|
|
std::vector<BasicBlock*> &PredBlocks) {
|
|
assert(!PredBlocks.empty() && "No predblocks??");
|
|
assert(succ_begin(NewBB) != succ_end(NewBB) &&
|
|
++succ_begin(NewBB) == succ_end(NewBB) &&
|
|
"NewBB should have a single successor!");
|
|
BasicBlock *NewBBSucc = *succ_begin(NewBB);
|
|
DominatorSet &DS = getAnalysis<DominatorSet>();
|
|
|
|
// Update dominator information... The blocks that dominate NewBB are the
|
|
// intersection of the dominators of predecessors, plus the block itself.
|
|
//
|
|
DominatorSet::DomSetType NewBBDomSet = DS.getDominators(PredBlocks[0]);
|
|
{
|
|
unsigned i, e = PredBlocks.size();
|
|
// It is possible for some preds to not be reachable, and thus have empty
|
|
// dominator sets (all blocks must dom themselves, so no domset would
|
|
// otherwise be empty). If we see any of these, don't intersect with them,
|
|
// as that would certainly leave the resultant set empty.
|
|
for (i = 1; NewBBDomSet.empty(); ++i) {
|
|
assert(i != e && "Didn't find reachable pred?");
|
|
NewBBDomSet = DS.getDominators(PredBlocks[i]);
|
|
}
|
|
|
|
// Intersect the rest of the non-empty sets.
|
|
for (; i != e; ++i) {
|
|
const DominatorSet::DomSetType &PredDS = DS.getDominators(PredBlocks[i]);
|
|
if (!PredDS.empty())
|
|
set_intersect(NewBBDomSet, PredDS);
|
|
}
|
|
NewBBDomSet.insert(NewBB); // All blocks dominate themselves.
|
|
DS.addBasicBlock(NewBB, NewBBDomSet);
|
|
}
|
|
|
|
// The newly inserted basic block will dominate existing basic blocks iff the
|
|
// PredBlocks dominate all of the non-pred blocks. If all predblocks dominate
|
|
// the non-pred blocks, then they all must be the same block!
|
|
//
|
|
bool NewBBDominatesNewBBSucc = true;
|
|
{
|
|
BasicBlock *OnePred = PredBlocks[0];
|
|
unsigned i, e = PredBlocks.size();
|
|
for (i = 1; !DS.isReachable(OnePred); ++i) {
|
|
assert(i != e && "Didn't find reachable pred?");
|
|
OnePred = PredBlocks[i];
|
|
}
|
|
|
|
for (; i != e; ++i)
|
|
if (PredBlocks[i] != OnePred && DS.isReachable(PredBlocks[i])) {
|
|
NewBBDominatesNewBBSucc = false;
|
|
break;
|
|
}
|
|
|
|
if (NewBBDominatesNewBBSucc)
|
|
for (pred_iterator PI = pred_begin(NewBBSucc), E = pred_end(NewBBSucc);
|
|
PI != E; ++PI)
|
|
if (*PI != NewBB && !DS.dominates(NewBBSucc, *PI)) {
|
|
NewBBDominatesNewBBSucc = false;
|
|
break;
|
|
}
|
|
}
|
|
|
|
// The other scenario where the new block can dominate its successors are when
|
|
// all predecessors of NewBBSucc that are not NewBB are dominated by NewBBSucc
|
|
// already.
|
|
if (!NewBBDominatesNewBBSucc) {
|
|
NewBBDominatesNewBBSucc = true;
|
|
for (pred_iterator PI = pred_begin(NewBBSucc), E = pred_end(NewBBSucc);
|
|
PI != E; ++PI)
|
|
if (*PI != NewBB && !DS.dominates(NewBBSucc, *PI)) {
|
|
NewBBDominatesNewBBSucc = false;
|
|
break;
|
|
}
|
|
}
|
|
|
|
// If NewBB dominates some blocks, then it will dominate all blocks that
|
|
// NewBBSucc does.
|
|
if (NewBBDominatesNewBBSucc) {
|
|
Function *F = NewBB->getParent();
|
|
for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I)
|
|
if (DS.dominates(NewBBSucc, I))
|
|
DS.addDominator(I, NewBB);
|
|
}
|
|
|
|
// Update immediate dominator information if we have it.
|
|
BasicBlock *NewBBIDom = 0;
|
|
if (ImmediateDominators *ID = getAnalysisToUpdate<ImmediateDominators>()) {
|
|
// To find the immediate dominator of the new exit node, we trace up the
|
|
// immediate dominators of a predecessor until we find a basic block that
|
|
// dominates the exit block.
|
|
//
|
|
BasicBlock *Dom = PredBlocks[0]; // Some random predecessor.
|
|
|
|
// Find a reachable pred.
|
|
for (unsigned i = 1; !DS.isReachable(Dom); ++i) {
|
|
assert(i != PredBlocks.size() && "Didn't find reachable pred!");
|
|
Dom = PredBlocks[i];
|
|
}
|
|
|
|
while (!NewBBDomSet.count(Dom)) { // Loop until we find a dominator.
|
|
assert(Dom != 0 && "No shared dominator found???");
|
|
Dom = ID->get(Dom);
|
|
}
|
|
|
|
// Set the immediate dominator now...
|
|
ID->addNewBlock(NewBB, Dom);
|
|
NewBBIDom = Dom; // Reuse this if calculating DominatorTree info...
|
|
|
|
// If NewBB strictly dominates other blocks, we need to update their idom's
|
|
// now. The only block that need adjustment is the NewBBSucc block, whose
|
|
// idom should currently be set to PredBlocks[0].
|
|
if (NewBBDominatesNewBBSucc)
|
|
ID->setImmediateDominator(NewBBSucc, NewBB);
|
|
}
|
|
|
|
// Update DominatorTree information if it is active.
|
|
if (DominatorTree *DT = getAnalysisToUpdate<DominatorTree>()) {
|
|
// If we don't have ImmediateDominator info around, calculate the idom as
|
|
// above.
|
|
DominatorTree::Node *NewBBIDomNode;
|
|
if (NewBBIDom) {
|
|
NewBBIDomNode = DT->getNode(NewBBIDom);
|
|
} else {
|
|
// Scan all the pred blocks that were pulled out. Any individual one may
|
|
// actually be unreachable, which would mean it doesn't have dom info.
|
|
NewBBIDomNode = 0;
|
|
for (unsigned i = 0; !NewBBIDomNode; ++i) {
|
|
assert(i != PredBlocks.size() && "No reachable preds?");
|
|
NewBBIDomNode = DT->getNode(PredBlocks[i]);
|
|
}
|
|
|
|
while (!NewBBDomSet.count(NewBBIDomNode->getBlock())) {
|
|
NewBBIDomNode = NewBBIDomNode->getIDom();
|
|
assert(NewBBIDomNode && "No shared dominator found??");
|
|
}
|
|
NewBBIDom = NewBBIDomNode->getBlock();
|
|
}
|
|
|
|
// Create the new dominator tree node... and set the idom of NewBB.
|
|
DominatorTree::Node *NewBBNode = DT->createNewNode(NewBB, NewBBIDomNode);
|
|
|
|
// If NewBB strictly dominates other blocks, then it is now the immediate
|
|
// dominator of NewBBSucc. Update the dominator tree as appropriate.
|
|
if (NewBBDominatesNewBBSucc) {
|
|
DominatorTree::Node *NewBBSuccNode = DT->getNode(NewBBSucc);
|
|
DT->changeImmediateDominator(NewBBSuccNode, NewBBNode);
|
|
}
|
|
}
|
|
|
|
// Update ET-Forest information if it is active.
|
|
if (ETForest *EF = getAnalysisToUpdate<ETForest>()) {
|
|
EF->addNewBlock(NewBB, NewBBIDom);
|
|
if (NewBBDominatesNewBBSucc)
|
|
EF->setImmediateDominator(NewBBSucc, NewBB);
|
|
}
|
|
|
|
// Update dominance frontier information...
|
|
if (DominanceFrontier *DF = getAnalysisToUpdate<DominanceFrontier>()) {
|
|
// If NewBB dominates NewBBSucc, then DF(NewBB) is now going to be the
|
|
// DF(PredBlocks[0]) without the stuff that the new block does not dominate
|
|
// a predecessor of.
|
|
if (NewBBDominatesNewBBSucc) {
|
|
DominanceFrontier::iterator DFI = DF->find(PredBlocks[0]);
|
|
if (DFI != DF->end()) {
|
|
DominanceFrontier::DomSetType Set = DFI->second;
|
|
// Filter out stuff in Set that we do not dominate a predecessor of.
|
|
for (DominanceFrontier::DomSetType::iterator SetI = Set.begin(),
|
|
E = Set.end(); SetI != E;) {
|
|
bool DominatesPred = false;
|
|
for (pred_iterator PI = pred_begin(*SetI), E = pred_end(*SetI);
|
|
PI != E; ++PI)
|
|
if (DS.dominates(NewBB, *PI))
|
|
DominatesPred = true;
|
|
if (!DominatesPred)
|
|
Set.erase(SetI++);
|
|
else
|
|
++SetI;
|
|
}
|
|
|
|
DF->addBasicBlock(NewBB, Set);
|
|
}
|
|
|
|
} else {
|
|
// DF(NewBB) is {NewBBSucc} because NewBB does not strictly dominate
|
|
// NewBBSucc, but it does dominate itself (and there is an edge (NewBB ->
|
|
// NewBBSucc)). NewBBSucc is the single successor of NewBB.
|
|
DominanceFrontier::DomSetType NewDFSet;
|
|
NewDFSet.insert(NewBBSucc);
|
|
DF->addBasicBlock(NewBB, NewDFSet);
|
|
}
|
|
|
|
// Now we must loop over all of the dominance frontiers in the function,
|
|
// replacing occurrences of NewBBSucc with NewBB in some cases. All
|
|
// blocks that dominate a block in PredBlocks and contained NewBBSucc in
|
|
// their dominance frontier must be updated to contain NewBB instead.
|
|
//
|
|
for (unsigned i = 0, e = PredBlocks.size(); i != e; ++i) {
|
|
BasicBlock *Pred = PredBlocks[i];
|
|
// Get all of the dominators of the predecessor...
|
|
const DominatorSet::DomSetType &PredDoms = DS.getDominators(Pred);
|
|
for (DominatorSet::DomSetType::const_iterator PDI = PredDoms.begin(),
|
|
PDE = PredDoms.end(); PDI != PDE; ++PDI) {
|
|
BasicBlock *PredDom = *PDI;
|
|
|
|
// If the NewBBSucc node is in DF(PredDom), then PredDom didn't
|
|
// dominate NewBBSucc but did dominate a predecessor of it. Now we
|
|
// change this entry to include NewBB in the DF instead of NewBBSucc.
|
|
DominanceFrontier::iterator DFI = DF->find(PredDom);
|
|
assert(DFI != DF->end() && "No dominance frontier for node?");
|
|
if (DFI->second.count(NewBBSucc)) {
|
|
// If NewBBSucc should not stay in our dominator frontier, remove it.
|
|
// We remove it unless there is a predecessor of NewBBSucc that we
|
|
// dominate, but we don't strictly dominate NewBBSucc.
|
|
bool ShouldRemove = true;
|
|
if (PredDom == NewBBSucc || !DS.dominates(PredDom, NewBBSucc)) {
|
|
// Okay, we know that PredDom does not strictly dominate NewBBSucc.
|
|
// Check to see if it dominates any predecessors of NewBBSucc.
|
|
for (pred_iterator PI = pred_begin(NewBBSucc),
|
|
E = pred_end(NewBBSucc); PI != E; ++PI)
|
|
if (DS.dominates(PredDom, *PI)) {
|
|
ShouldRemove = false;
|
|
break;
|
|
}
|
|
}
|
|
|
|
if (ShouldRemove)
|
|
DF->removeFromFrontier(DFI, NewBBSucc);
|
|
DF->addToFrontier(DFI, NewBB);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|