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6f65d79750
constants out of loops. These aren't covered by the regular LICM pass, because in LLVM IR constants don't require separate instructions. They're not always covered by the MachineLICM pass either, because it doesn't know how to unfold folded constant-pool loads. This is somewhat experimental at this point, and off by default. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@82076 91177308-0d34-0410-b5e6-96231b3b80d8
118 lines
4.0 KiB
C++
118 lines
4.0 KiB
C++
//===- CodeGenLICM.cpp - LICM a function for code generation --------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This function performs late LICM, hoisting constants out of loops that
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// are not valid immediates. It should not be followed by instcombine,
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// because instcombine would quickly stuff the constants back into the loop.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "codegen-licm"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/Constants.h"
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#include "llvm/DerivedTypes.h"
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#include "llvm/Instructions.h"
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#include "llvm/IntrinsicInst.h"
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#include "llvm/LLVMContext.h"
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#include "llvm/Analysis/LoopPass.h"
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/Analysis/ScalarEvolution.h"
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#include "llvm/Analysis/IVUsers.h"
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#include "llvm/ADT/DenseMap.h"
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using namespace llvm;
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namespace {
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class CodeGenLICM : public LoopPass {
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virtual bool runOnLoop(Loop *L, LPPassManager &LPM);
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virtual void getAnalysisUsage(AnalysisUsage &AU) const;
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public:
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static char ID; // Pass identification, replacement for typeid
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explicit CodeGenLICM() : LoopPass(&ID) {}
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};
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}
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char CodeGenLICM::ID = 0;
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static RegisterPass<CodeGenLICM> X("codegen-licm",
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"hoist constants out of loops");
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Pass *llvm::createCodeGenLICMPass() {
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return new CodeGenLICM();
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}
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bool CodeGenLICM::runOnLoop(Loop *L, LPPassManager &) {
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bool Changed = false;
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// Only visit outermost loops.
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if (L->getParentLoop()) return Changed;
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Instruction *PreheaderTerm = L->getLoopPreheader()->getTerminator();
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DenseMap<Constant *, BitCastInst *> HoistedConstants;
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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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for (BasicBlock::iterator BBI = BB->begin(), BBE = BB->end();
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BBI != BBE; ++BBI) {
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Instruction *I = BBI;
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// Don't bother hoisting constants out of loop-header phi nodes.
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if (BB == L->getHeader() && isa<PHINode>(I))
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continue;
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// TODO: For now, skip all intrinsic instructions, because some of them
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// can require their operands to be constants, and we don't want to
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// break that.
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if (isa<IntrinsicInst>(I))
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continue;
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// LLVM represents fneg as -0.0-x; don't hoist the -0.0 out.
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if (BinaryOperator::isFNeg(I) ||
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BinaryOperator::isNeg(I) ||
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BinaryOperator::isNot(I))
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continue;
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for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
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// Don't hoist out switch case constants.
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if (isa<SwitchInst>(I) && i == 1)
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break;
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// Don't hoist out shuffle masks.
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if (isa<ShuffleVectorInst>(I) && i == 2)
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break;
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Value *Op = I->getOperand(i);
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Constant *C = dyn_cast<Constant>(Op);
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if (!C) continue;
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// TODO: Ask the target which constants are legal. This would allow
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// us to add support for hoisting ConstantInts and GlobalValues too.
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if (isa<ConstantFP>(C) ||
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isa<ConstantVector>(C) ||
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isa<ConstantAggregateZero>(C)) {
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BitCastInst *&BC = HoistedConstants[C];
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if (!BC)
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BC = new BitCastInst(C, C->getType(), "hoist", PreheaderTerm);
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I->setOperand(i, BC);
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Changed = true;
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}
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}
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}
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}
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return Changed;
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}
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void CodeGenLICM::getAnalysisUsage(AnalysisUsage &AU) const {
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// This pass preserves just about everything. List some popular things here.
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AU.setPreservesCFG();
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AU.addPreservedID(LoopSimplifyID);
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AU.addPreserved<LoopInfo>();
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AU.addPreserved<AliasAnalysis>();
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AU.addPreserved<DominanceFrontier>();
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AU.addPreserved<DominatorTree>();
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AU.addPreserved<ScalarEvolution>();
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AU.addPreserved<IVUsers>();
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// Hoisting requires a loop preheader.
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AU.addRequiredID(LoopSimplifyID);
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}
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