mirror of
https://github.com/c64scene-ar/llvm-6502.git
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@26114 91177308-0d34-0410-b5e6-96231b3b80d8
654 lines
26 KiB
C++
654 lines
26 KiB
C++
//===-- LoopUnswitch.cpp - Hoist loop-invariant conditionals in loop ------===//
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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 transforms loops that contain branches on loop-invariant conditions
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// to have multiple loops. For example, it turns the left into the right code:
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//
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// for (...) if (lic)
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// A for (...)
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// if (lic) A; B; C
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// B else
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// C for (...)
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// A; C
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//
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// This can increase the size of the code exponentially (doubling it every time
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// a loop is unswitched) so we only unswitch if the resultant code will be
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// smaller than a threshold.
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//
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// This pass expects LICM to be run before it to hoist invariant conditions out
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// of the loop, to make the unswitching opportunity obvious.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "loop-unswitch"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/Constants.h"
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#include "llvm/Function.h"
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#include "llvm/Instructions.h"
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#include "llvm/Analysis/LoopInfo.h"
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#include "llvm/Transforms/Utils/Cloning.h"
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#include "llvm/Transforms/Utils/Local.h"
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#include "llvm/Transforms/Utils/BasicBlockUtils.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/CommandLine.h"
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#include <algorithm>
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#include <iostream>
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#include <set>
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using namespace llvm;
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namespace {
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Statistic<> NumUnswitched("loop-unswitch", "Number of loops unswitched");
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cl::opt<unsigned>
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Threshold("loop-unswitch-threshold", cl::desc("Max loop size to unswitch"),
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cl::init(10), cl::Hidden);
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class LoopUnswitch : public FunctionPass {
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LoopInfo *LI; // Loop information
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public:
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virtual bool runOnFunction(Function &F);
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bool visitLoop(Loop *L);
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/// This transformation requires natural loop information & requires that
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/// loop preheaders be inserted into the CFG...
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///
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequiredID(LoopSimplifyID);
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AU.addPreservedID(LoopSimplifyID);
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AU.addRequired<LoopInfo>();
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AU.addPreserved<LoopInfo>();
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}
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private:
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bool UnswitchIfProfitable(Value *LoopCond, Constant *Val,Loop *L);
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unsigned getLoopUnswitchCost(Loop *L, Value *LIC);
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void VersionLoop(Value *LIC, Constant *OnVal,
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Loop *L, Loop *&Out1, Loop *&Out2);
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BasicBlock *SplitEdge(BasicBlock *From, BasicBlock *To);
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void RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,Constant *Val,
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bool isEqual);
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void UnswitchTrivialCondition(Loop *L, Value *Cond, bool EntersLoopOnCond,
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BasicBlock *ExitBlock);
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};
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RegisterOpt<LoopUnswitch> X("loop-unswitch", "Unswitch loops");
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}
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FunctionPass *llvm::createLoopUnswitchPass() { return new LoopUnswitch(); }
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bool LoopUnswitch::runOnFunction(Function &F) {
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bool Changed = false;
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LI = &getAnalysis<LoopInfo>();
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// Transform all the top-level loops. Copy the loop list so that the child
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// can update the loop tree if it needs to delete the loop.
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std::vector<Loop*> SubLoops(LI->begin(), LI->end());
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for (unsigned i = 0, e = SubLoops.size(); i != e; ++i)
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Changed |= visitLoop(SubLoops[i]);
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return Changed;
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}
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/// LoopValuesUsedOutsideLoop - Return true if there are any values defined in
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/// the loop that are used by instructions outside of it.
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static bool LoopValuesUsedOutsideLoop(Loop *L) {
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// We will be doing lots of "loop contains block" queries. Loop::contains is
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// linear time, use a set to speed this up.
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std::set<BasicBlock*> LoopBlocks;
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for (Loop::block_iterator BB = L->block_begin(), E = L->block_end();
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BB != E; ++BB)
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LoopBlocks.insert(*BB);
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for (Loop::block_iterator BB = L->block_begin(), E = L->block_end();
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BB != E; ++BB) {
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for (BasicBlock::iterator I = (*BB)->begin(), E = (*BB)->end(); I != E; ++I)
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for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;
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++UI) {
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BasicBlock *UserBB = cast<Instruction>(*UI)->getParent();
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if (!LoopBlocks.count(UserBB))
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return true;
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}
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}
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return false;
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}
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/// FindTrivialLoopExitBlock - We know that we have a branch from the loop
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/// header to the specified latch block. See if one of the successors of the
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/// latch block is an exit, and if so what block it is.
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static BasicBlock *FindTrivialLoopExitBlock(Loop *L, BasicBlock *Latch) {
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BasicBlock *Header = L->getHeader();
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BranchInst *LatchBranch = dyn_cast<BranchInst>(Latch->getTerminator());
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if (!LatchBranch || !LatchBranch->isConditional()) return 0;
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// Simple case, the latch block is a conditional branch. The target that
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// doesn't go to the loop header is our block if it is not in the loop.
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if (LatchBranch->getSuccessor(0) == Header) {
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if (L->contains(LatchBranch->getSuccessor(1))) return false;
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return LatchBranch->getSuccessor(1);
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} else {
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assert(LatchBranch->getSuccessor(1) == Header);
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if (L->contains(LatchBranch->getSuccessor(0))) return false;
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return LatchBranch->getSuccessor(0);
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}
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}
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/// IsTrivialUnswitchCondition - Check to see if this unswitch condition is
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/// trivial: that is, that the condition controls whether or not the loop does
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/// anything at all. If this is a trivial condition, unswitching produces no
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/// code duplications (equivalently, it produces a simpler loop and a new empty
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/// loop, which gets deleted).
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///
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/// If this is a trivial condition, return ConstantBool::True if the loop body
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/// runs when the condition is true, False if the loop body executes when the
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/// condition is false. Otherwise, return null to indicate a complex condition.
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static bool IsTrivialUnswitchCondition(Loop *L, Value *Cond,
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bool *CondEntersLoop = 0,
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BasicBlock **LoopExit = 0) {
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BasicBlock *Header = L->getHeader();
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BranchInst *HeaderTerm = dyn_cast<BranchInst>(Header->getTerminator());
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// If the header block doesn't end with a conditional branch on Cond, we can't
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// handle it.
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if (!HeaderTerm || !HeaderTerm->isConditional() ||
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HeaderTerm->getCondition() != Cond)
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return false;
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// Check to see if the conditional branch goes to the latch block. If not,
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// it's not trivial. This also determines the value of Cond that will execute
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// the loop.
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BasicBlock *Latch = L->getLoopLatch();
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if (HeaderTerm->getSuccessor(1) == Latch) {
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if (CondEntersLoop) *CondEntersLoop = true;
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} else if (HeaderTerm->getSuccessor(0) == Latch)
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if (CondEntersLoop) *CondEntersLoop = false;
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else
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return false; // Doesn't branch to latch block.
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// The latch block must end with a conditional branch where one edge goes to
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// the header (this much we know) and one edge goes OUT of the loop.
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BasicBlock *LoopExitBlock = FindTrivialLoopExitBlock(L, Latch);
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if (!LoopExitBlock) return 0;
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if (LoopExit) *LoopExit = LoopExitBlock;
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// We already know that nothing uses any scalar values defined inside of this
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// loop. As such, we just have to check to see if this loop will execute any
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// side-effecting instructions (e.g. stores, calls, volatile loads) in the
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// part of the loop that the code *would* execute.
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for (BasicBlock::iterator I = Header->begin(), E = Header->end(); I != E; ++I)
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if (I->mayWriteToMemory())
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return false;
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for (BasicBlock::iterator I = Latch->begin(), E = Latch->end(); I != E; ++I)
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if (I->mayWriteToMemory())
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return false;
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return true;
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}
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/// getLoopUnswitchCost - Return the cost (code size growth) that will happen if
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/// we choose to unswitch the specified loop on the specified value.
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///
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unsigned LoopUnswitch::getLoopUnswitchCost(Loop *L, Value *LIC) {
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// If the condition is trivial, always unswitch. There is no code growth for
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// this case.
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if (IsTrivialUnswitchCondition(L, LIC))
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return 0;
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unsigned Cost = 0;
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// FIXME: this is brain dead. It should take into consideration code
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// shrinkage.
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for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
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I != E; ++I) {
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BasicBlock *BB = *I;
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// Do not include empty blocks in the cost calculation. This happen due to
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// loop canonicalization and will be removed.
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if (BB->begin() == BasicBlock::iterator(BB->getTerminator()))
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continue;
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// Count basic blocks.
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++Cost;
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}
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return Cost;
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}
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/// FindLIVLoopCondition - Cond is a condition that occurs in L. If it is
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/// invariant in the loop, or has an invariant piece, return the invariant.
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/// Otherwise, return null.
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static Value *FindLIVLoopCondition(Value *Cond, Loop *L, bool &Changed) {
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// Constants should be folded, not unswitched on!
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if (isa<Constant>(Cond)) return false;
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// TODO: Handle: br (VARIANT|INVARIANT).
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// TODO: Hoist simple expressions out of loops.
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if (L->isLoopInvariant(Cond)) return Cond;
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if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Cond))
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if (BO->getOpcode() == Instruction::And ||
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BO->getOpcode() == Instruction::Or) {
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// If either the left or right side is invariant, we can unswitch on this,
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// which will cause the branch to go away in one loop and the condition to
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// simplify in the other one.
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if (Value *LHS = FindLIVLoopCondition(BO->getOperand(0), L, Changed))
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return LHS;
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if (Value *RHS = FindLIVLoopCondition(BO->getOperand(1), L, Changed))
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return RHS;
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}
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return 0;
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}
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bool LoopUnswitch::visitLoop(Loop *L) {
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bool Changed = false;
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// Recurse through all subloops before we process this loop. Copy the loop
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// list so that the child can update the loop tree if it needs to delete the
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// loop.
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std::vector<Loop*> SubLoops(L->begin(), L->end());
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for (unsigned i = 0, e = SubLoops.size(); i != e; ++i)
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Changed |= visitLoop(SubLoops[i]);
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// Loop over all of the basic blocks in the loop. If we find an interior
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// block that is branching on a loop-invariant condition, we can unswitch this
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// loop.
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for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
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I != E; ++I) {
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TerminatorInst *TI = (*I)->getTerminator();
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if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
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// If this isn't branching on an invariant condition, we can't unswitch
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// it.
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if (BI->isConditional()) {
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// See if this, or some part of it, is loop invariant. If so, we can
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// unswitch on it if we desire.
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Value *LoopCond = FindLIVLoopCondition(BI->getCondition(), L, Changed);
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if (LoopCond && UnswitchIfProfitable(LoopCond, ConstantBool::True, L))
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return true;
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}
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} else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
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Value *LoopCond = FindLIVLoopCondition(SI->getCondition(), L, Changed);
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if (LoopCond && SI->getNumCases() > 1) {
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// Find a value to unswitch on:
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// FIXME: this should chose the most expensive case!
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Constant *UnswitchVal = SI->getCaseValue(1);
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if (UnswitchIfProfitable(LoopCond, UnswitchVal, L))
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return true;
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}
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}
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// Scan the instructions to check for unswitchable values.
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for (BasicBlock::iterator BBI = (*I)->begin(), E = (*I)->end();
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BBI != E; ++BBI)
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if (SelectInst *SI = dyn_cast<SelectInst>(BBI)) {
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Value *LoopCond = FindLIVLoopCondition(SI->getCondition(), L, Changed);
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if (LoopCond && UnswitchIfProfitable(LoopCond, ConstantBool::True, L))
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return true;
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}
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}
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return Changed;
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}
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/// UnswitchIfProfitable - We have found that we can unswitch L when
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/// LoopCond == Val to simplify the loop. If we decide that this is profitable,
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/// unswitch the loop, reprocess the pieces, then return true.
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bool LoopUnswitch::UnswitchIfProfitable(Value *LoopCond, Constant *Val,Loop *L){
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// Check to see if it would be profitable to unswitch this loop.
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if (getLoopUnswitchCost(L, LoopCond) > Threshold) {
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// FIXME: this should estimate growth by the amount of code shared by the
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// resultant unswitched loops.
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//
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DEBUG(std::cerr << "NOT unswitching loop %"
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<< L->getHeader()->getName() << ", cost too high: "
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<< L->getBlocks().size() << "\n");
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return false;
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}
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// If this loop has live-out values, we can't unswitch it. We need something
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// like loop-closed SSA form in order to know how to insert PHI nodes for
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// these values.
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if (LoopValuesUsedOutsideLoop(L)) {
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DEBUG(std::cerr << "NOT unswitching loop %" << L->getHeader()->getName()
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<< ", a loop value is used outside loop!\n");
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return false;
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}
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//std::cerr << "BEFORE:\n"; LI->dump();
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Loop *NewLoop1 = 0, *NewLoop2 = 0;
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// If this is a trivial condition to unswitch (which results in no code
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// duplication), do it now.
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bool EntersLoopOnCond;
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BasicBlock *ExitBlock;
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if (IsTrivialUnswitchCondition(L, LoopCond, &EntersLoopOnCond, &ExitBlock)){
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UnswitchTrivialCondition(L, LoopCond, EntersLoopOnCond, ExitBlock);
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NewLoop1 = L;
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} else {
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VersionLoop(LoopCond, Val, L, NewLoop1, NewLoop2);
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}
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++NumUnswitched;
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//std::cerr << "AFTER:\n"; LI->dump();
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// Try to unswitch each of our new loops now!
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if (NewLoop1) visitLoop(NewLoop1);
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if (NewLoop2) visitLoop(NewLoop2);
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return true;
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}
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BasicBlock *LoopUnswitch::SplitEdge(BasicBlock *BB, BasicBlock *Succ) {
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TerminatorInst *LatchTerm = BB->getTerminator();
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unsigned SuccNum = 0;
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for (unsigned i = 0, e = LatchTerm->getNumSuccessors(); ; ++i) {
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assert(i != e && "Didn't find edge?");
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if (LatchTerm->getSuccessor(i) == Succ) {
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SuccNum = i;
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break;
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}
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}
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// If this is a critical edge, let SplitCriticalEdge do it.
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if (SplitCriticalEdge(BB->getTerminator(), SuccNum, this))
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return LatchTerm->getSuccessor(SuccNum);
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// If the edge isn't critical, then BB has a single successor or Succ has a
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// single pred. Split the block.
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BasicBlock *BlockToSplit;
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BasicBlock::iterator SplitPoint;
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if (BasicBlock *SP = Succ->getSinglePredecessor()) {
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// If the successor only has a single pred, split the top of the successor
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// block.
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assert(SP == BB && "CFG broken");
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BlockToSplit = Succ;
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SplitPoint = Succ->begin();
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} else {
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// Otherwise, if BB has a single successor, split it at the bottom of the
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// block.
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assert(BB->getTerminator()->getNumSuccessors() == 1 &&
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"Should have a single succ!");
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BlockToSplit = BB;
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SplitPoint = BB->getTerminator();
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}
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BasicBlock *New =
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BlockToSplit->splitBasicBlock(SplitPoint,
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BlockToSplit->getName()+".tail");
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// New now lives in whichever loop that BB used to.
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if (Loop *L = LI->getLoopFor(BlockToSplit))
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L->addBasicBlockToLoop(New, *LI);
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return New;
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}
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// RemapInstruction - Convert the instruction operands from referencing the
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// current values into those specified by ValueMap.
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//
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static inline void RemapInstruction(Instruction *I,
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std::map<const Value *, Value*> &ValueMap) {
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for (unsigned op = 0, E = I->getNumOperands(); op != E; ++op) {
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Value *Op = I->getOperand(op);
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std::map<const Value *, Value*>::iterator It = ValueMap.find(Op);
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if (It != ValueMap.end()) Op = It->second;
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I->setOperand(op, Op);
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}
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}
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/// CloneLoop - Recursively clone the specified loop and all of its children,
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/// mapping the blocks with the specified map.
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static Loop *CloneLoop(Loop *L, Loop *PL, std::map<const Value*, Value*> &VM,
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LoopInfo *LI) {
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Loop *New = new Loop();
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if (PL)
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PL->addChildLoop(New);
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else
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LI->addTopLevelLoop(New);
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// Add all of the blocks in L to the new loop.
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for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
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I != E; ++I)
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if (LI->getLoopFor(*I) == L)
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New->addBasicBlockToLoop(cast<BasicBlock>(VM[*I]), *LI);
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// Add all of the subloops to the new loop.
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for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I)
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CloneLoop(*I, New, VM, LI);
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return New;
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}
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/// UnswitchTrivialCondition - Given a loop that has a trivial unswitchable
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/// condition in it (a cond branch from its header block to its latch block,
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/// where the path through the loop that doesn't execute its body has no
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/// side-effects), unswitch it. This doesn't involve any code duplication, just
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/// moving the conditional branch outside of the loop and updating loop info.
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void LoopUnswitch::UnswitchTrivialCondition(Loop *L, Value *Cond,
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bool EnterOnCond,
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BasicBlock *ExitBlock) {
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DEBUG(std::cerr << "loop-unswitch: Trivial-Unswitch loop %"
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<< L->getHeader()->getName() << " [" << L->getBlocks().size()
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<< " blocks] in Function " << L->getHeader()->getParent()->getName()
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<< " on cond:" << *Cond << "\n");
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// First step, split the preheader, so that we know that there is a safe place
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// to insert the conditional branch. We will change 'OrigPH' to have a
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// conditional branch on Cond.
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BasicBlock *OrigPH = L->getLoopPreheader();
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BasicBlock *NewPH = SplitEdge(OrigPH, L->getHeader());
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// Now that we have a place to insert the conditional branch, create a place
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// to branch to: this is the exit block out of the loop that we should
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// short-circuit to.
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// Split this edge now, so that the loop maintains its exit block.
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assert(!L->contains(ExitBlock) && "Exit block is in the loop?");
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BasicBlock *NewExit = SplitEdge(L->getLoopLatch(), ExitBlock);
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assert(NewExit != ExitBlock && "Edge not split!");
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// Okay, now we have a position to branch from and a position to branch to,
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|
// insert the new conditional branch.
|
|
new BranchInst(EnterOnCond ? NewPH : NewExit, EnterOnCond ? NewExit : NewPH,
|
|
Cond, OrigPH->getTerminator());
|
|
OrigPH->getTerminator()->eraseFromParent();
|
|
|
|
// Now that we know that the loop is never entered when this condition is a
|
|
// particular value, rewrite the loop with this info. We know that this will
|
|
// at least eliminate the old branch.
|
|
RewriteLoopBodyWithConditionConstant(L, Cond, ConstantBool::get(EnterOnCond),
|
|
true);
|
|
}
|
|
|
|
|
|
/// VersionLoop - We determined that the loop is profitable to unswitch when LIC
|
|
/// equal Val. Split it into loop versions and test the condition outside of
|
|
/// either loop. Return the loops created as Out1/Out2.
|
|
void LoopUnswitch::VersionLoop(Value *LIC, Constant *Val, Loop *L,
|
|
Loop *&Out1, Loop *&Out2) {
|
|
Function *F = L->getHeader()->getParent();
|
|
|
|
DEBUG(std::cerr << "loop-unswitch: Unswitching loop %"
|
|
<< L->getHeader()->getName() << " [" << L->getBlocks().size()
|
|
<< " blocks] in Function " << F->getName()
|
|
<< " when '" << *Val << "' == " << *LIC << "\n");
|
|
|
|
// LoopBlocks contains all of the basic blocks of the loop, including the
|
|
// preheader of the loop, the body of the loop, and the exit blocks of the
|
|
// loop, in that order.
|
|
std::vector<BasicBlock*> LoopBlocks;
|
|
|
|
// First step, split the preheader and exit blocks, and add these blocks to
|
|
// the LoopBlocks list.
|
|
BasicBlock *OrigPreheader = L->getLoopPreheader();
|
|
LoopBlocks.push_back(SplitEdge(OrigPreheader, L->getHeader()));
|
|
|
|
// We want the loop to come after the preheader, but before the exit blocks.
|
|
LoopBlocks.insert(LoopBlocks.end(), L->block_begin(), L->block_end());
|
|
|
|
std::vector<BasicBlock*> ExitBlocks;
|
|
L->getExitBlocks(ExitBlocks);
|
|
std::sort(ExitBlocks.begin(), ExitBlocks.end());
|
|
ExitBlocks.erase(std::unique(ExitBlocks.begin(), ExitBlocks.end()),
|
|
ExitBlocks.end());
|
|
// Split all of the edges from inside the loop to their exit blocks. This
|
|
// unswitching trivial: no phi nodes to update.
|
|
for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
|
|
BasicBlock *ExitBlock = ExitBlocks[i];
|
|
std::vector<BasicBlock*> Preds(pred_begin(ExitBlock), pred_end(ExitBlock));
|
|
|
|
for (unsigned j = 0, e = Preds.size(); j != e; ++j) {
|
|
assert(L->contains(Preds[j]) &&
|
|
"All preds of loop exit blocks must be the same loop!");
|
|
SplitEdge(Preds[j], ExitBlock);
|
|
}
|
|
}
|
|
|
|
// The exit blocks may have been changed due to edge splitting, recompute.
|
|
ExitBlocks.clear();
|
|
L->getExitBlocks(ExitBlocks);
|
|
std::sort(ExitBlocks.begin(), ExitBlocks.end());
|
|
ExitBlocks.erase(std::unique(ExitBlocks.begin(), ExitBlocks.end()),
|
|
ExitBlocks.end());
|
|
|
|
// Add exit blocks to the loop blocks.
|
|
LoopBlocks.insert(LoopBlocks.end(), ExitBlocks.begin(), ExitBlocks.end());
|
|
|
|
// Next step, clone all of the basic blocks that make up the loop (including
|
|
// the loop preheader and exit blocks), keeping track of the mapping between
|
|
// the instructions and blocks.
|
|
std::vector<BasicBlock*> NewBlocks;
|
|
NewBlocks.reserve(LoopBlocks.size());
|
|
std::map<const Value*, Value*> ValueMap;
|
|
for (unsigned i = 0, e = LoopBlocks.size(); i != e; ++i) {
|
|
NewBlocks.push_back(CloneBasicBlock(LoopBlocks[i], ValueMap, ".us", F));
|
|
ValueMap[LoopBlocks[i]] = NewBlocks.back(); // Keep the BB mapping.
|
|
}
|
|
|
|
// Splice the newly inserted blocks into the function right before the
|
|
// original preheader.
|
|
F->getBasicBlockList().splice(LoopBlocks[0], F->getBasicBlockList(),
|
|
NewBlocks[0], F->end());
|
|
|
|
// Now we create the new Loop object for the versioned loop.
|
|
Loop *NewLoop = CloneLoop(L, L->getParentLoop(), ValueMap, LI);
|
|
Loop *ParentLoop = L->getParentLoop();
|
|
if (ParentLoop) {
|
|
// Make sure to add the cloned preheader and exit blocks to the parent loop
|
|
// as well.
|
|
ParentLoop->addBasicBlockToLoop(NewBlocks[0], *LI);
|
|
}
|
|
|
|
for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
|
|
BasicBlock *NewExit = cast<BasicBlock>(ValueMap[ExitBlocks[i]]);
|
|
if (ParentLoop)
|
|
ParentLoop->addBasicBlockToLoop(cast<BasicBlock>(NewExit), *LI);
|
|
|
|
assert(NewExit->getTerminator()->getNumSuccessors() == 1 &&
|
|
"Exit block should have been split to have one successor!");
|
|
BasicBlock *ExitSucc = NewExit->getTerminator()->getSuccessor(0);
|
|
|
|
// If the successor of the exit block had PHI nodes, add an entry for
|
|
// NewExit.
|
|
PHINode *PN;
|
|
for (BasicBlock::iterator I = ExitSucc->begin();
|
|
(PN = dyn_cast<PHINode>(I)); ++I) {
|
|
Value *V = PN->getIncomingValueForBlock(ExitBlocks[i]);
|
|
std::map<const Value *, Value*>::iterator It = ValueMap.find(V);
|
|
if (It != ValueMap.end()) V = It->second;
|
|
PN->addIncoming(V, NewExit);
|
|
}
|
|
}
|
|
|
|
// Rewrite the code to refer to itself.
|
|
for (unsigned i = 0, e = NewBlocks.size(); i != e; ++i)
|
|
for (BasicBlock::iterator I = NewBlocks[i]->begin(),
|
|
E = NewBlocks[i]->end(); I != E; ++I)
|
|
RemapInstruction(I, ValueMap);
|
|
|
|
// Rewrite the original preheader to select between versions of the loop.
|
|
assert(isa<BranchInst>(OrigPreheader->getTerminator()) &&
|
|
cast<BranchInst>(OrigPreheader->getTerminator())->isUnconditional() &&
|
|
OrigPreheader->getTerminator()->getSuccessor(0) == LoopBlocks[0] &&
|
|
"Preheader splitting did not work correctly!");
|
|
|
|
// Insert a conditional branch on LIC to the two preheaders. The original
|
|
// code is the true version and the new code is the false version.
|
|
Value *BranchVal = LIC;
|
|
if (!isa<ConstantBool>(BranchVal)) {
|
|
BranchVal = BinaryOperator::createSetEQ(LIC, Val, "tmp",
|
|
OrigPreheader->getTerminator());
|
|
} else if (Val != ConstantBool::True) {
|
|
// We want to enter the new loop when the condition is true.
|
|
BranchVal = BinaryOperator::createNot(BranchVal, "tmp",
|
|
OrigPreheader->getTerminator());
|
|
}
|
|
|
|
// Remove the unconditional branch to LoopBlocks[0] and insert the new branch.
|
|
OrigPreheader->getInstList().pop_back();
|
|
new BranchInst(NewBlocks[0], LoopBlocks[0], BranchVal, OrigPreheader);
|
|
|
|
// Now we rewrite the original code to know that the condition is true and the
|
|
// new code to know that the condition is false.
|
|
RewriteLoopBodyWithConditionConstant(L, LIC, Val, false);
|
|
RewriteLoopBodyWithConditionConstant(NewLoop, LIC, Val, true);
|
|
Out1 = L;
|
|
Out2 = NewLoop;
|
|
}
|
|
|
|
// RewriteLoopBodyWithConditionConstant - We know either that the value LIC has
|
|
// the value specified by Val in the specified loop, or we know it does NOT have
|
|
// that value. Rewrite any uses of LIC or of properties correlated to it.
|
|
void LoopUnswitch::RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
|
|
Constant *Val,
|
|
bool IsEqual) {
|
|
assert(!isa<Constant>(LIC) && "Why are we unswitching on a constant?");
|
|
|
|
// FIXME: Support correlated properties, like:
|
|
// for (...)
|
|
// if (li1 < li2)
|
|
// ...
|
|
// if (li1 > li2)
|
|
// ...
|
|
|
|
// NotVal - If Val is a bool, this contains its inverse.
|
|
Constant *NotVal = 0;
|
|
if (ConstantBool *CB = dyn_cast<ConstantBool>(Val))
|
|
NotVal = ConstantBool::get(!CB->getValue());
|
|
|
|
// FOLD boolean conditions (X|LIC), (X&LIC). Fold conditional branches,
|
|
// selects, switches.
|
|
std::vector<User*> Users(LIC->use_begin(), LIC->use_end());
|
|
|
|
// Haha, this loop could be unswitched. Get it? The unswitch pass could
|
|
// unswitch itself. Amazing.
|
|
for (unsigned i = 0, e = Users.size(); i != e; ++i)
|
|
if (Instruction *U = cast<Instruction>(Users[i]))
|
|
if (L->contains(U->getParent()))
|
|
if (IsEqual) {
|
|
U->replaceUsesOfWith(LIC, Val);
|
|
} else if (NotVal) {
|
|
U->replaceUsesOfWith(LIC, NotVal);
|
|
} else {
|
|
// If we know that LIC is not Val, use this info to simplify code.
|
|
if (SwitchInst *SI = dyn_cast<SwitchInst>(U)) {
|
|
for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) {
|
|
if (SI->getCaseValue(i) == Val) {
|
|
// Found a dead case value. Don't remove PHI nodes in the
|
|
// successor if they become single-entry, those PHI nodes may
|
|
// be in the Users list.
|
|
SI->getSuccessor(i)->removePredecessor(SI->getParent(), true);
|
|
SI->removeCase(i);
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
|
|
// TODO: We could simplify stuff like X == C.
|
|
}
|
|
}
|