From 6f65d79750154c92c3e184c8cf3233a66c411c87 Mon Sep 17 00:00:00 2001 From: Dan Gohman Date: Wed, 16 Sep 2009 20:25:11 +0000 Subject: [PATCH] Add a new pass for doing late hoisting of floating-point and vector 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 --- include/llvm/LinkAllPasses.h | 1 + include/llvm/Transforms/Scalar.h | 5 ++ lib/CodeGen/LLVMTargetMachine.cpp | 7 +- lib/Transforms/Scalar/CodeGenLICM.cpp | 117 ++++++++++++++++++++++++++ 4 files changed, 129 insertions(+), 1 deletion(-) create mode 100644 lib/Transforms/Scalar/CodeGenLICM.cpp diff --git a/include/llvm/LinkAllPasses.h b/include/llvm/LinkAllPasses.h index 20801060247..f5017116de0 100644 --- a/include/llvm/LinkAllPasses.h +++ b/include/llvm/LinkAllPasses.h @@ -120,6 +120,7 @@ namespace { (void) llvm::createIndMemRemPass(); (void) llvm::createInstCountPass(); (void) llvm::createPredicateSimplifierPass(); + (void) llvm::createCodeGenLICMPass(); (void) llvm::createCodeGenPreparePass(); (void) llvm::createGVNPass(); (void) llvm::createMemCpyOptPass(); diff --git a/include/llvm/Transforms/Scalar.h b/include/llvm/Transforms/Scalar.h index f193b8d9dd5..093da644fae 100644 --- a/include/llvm/Transforms/Scalar.h +++ b/include/llvm/Transforms/Scalar.h @@ -329,6 +329,11 @@ FunctionPass *createSimplifyHalfPowrLibCallsPass(); // FunctionPass *createCodeGenPreparePass(const TargetLowering *TLI = 0); +//===----------------------------------------------------------------------===// +// +// CodeGenLICM - This pass performs late LICM; hoisting constants out of loops. +// +Pass *createCodeGenLICMPass(); //===----------------------------------------------------------------------===// // diff --git a/lib/CodeGen/LLVMTargetMachine.cpp b/lib/CodeGen/LLVMTargetMachine.cpp index 5b6cfdc989f..94c6fa6b833 100644 --- a/lib/CodeGen/LLVMTargetMachine.cpp +++ b/lib/CodeGen/LLVMTargetMachine.cpp @@ -39,6 +39,8 @@ static cl::opt PrintEmittedAsm("print-emitted-asm", cl::Hidden, cl::desc("Dump emitter generated instructions as assembly")); static cl::opt PrintGCInfo("print-gc", cl::Hidden, cl::desc("Dump garbage collector data")); +static cl::opt HoistConstants("hoist-constants", cl::Hidden, + cl::desc("Hoist constants out of loops")); static cl::opt VerifyMachineCode("verify-machineinstrs", cl::Hidden, cl::desc("Verify generated machine code"), cl::init(getenv("LLVM_VERIFY_MACHINEINSTRS")!=NULL)); @@ -259,8 +261,11 @@ bool LLVMTargetMachine::addCommonCodeGenPasses(PassManagerBase &PM, // Make sure that no unreachable blocks are instruction selected. PM.add(createUnreachableBlockEliminationPass()); - if (OptLevel != CodeGenOpt::None) + if (OptLevel != CodeGenOpt::None) { + if (HoistConstants) + PM.add(createCodeGenLICMPass()); PM.add(createCodeGenPreparePass(getTargetLowering())); + } PM.add(createStackProtectorPass(getTargetLowering())); diff --git a/lib/Transforms/Scalar/CodeGenLICM.cpp b/lib/Transforms/Scalar/CodeGenLICM.cpp new file mode 100644 index 00000000000..ef9f81e266d --- /dev/null +++ b/lib/Transforms/Scalar/CodeGenLICM.cpp @@ -0,0 +1,117 @@ +//===- CodeGenLICM.cpp - LICM a function for code generation --------------===// +// +// The LLVM Compiler Infrastructure +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +// +// This function performs late LICM, hoisting constants out of loops that +// are not valid immediates. It should not be followed by instcombine, +// because instcombine would quickly stuff the constants back into the loop. +// +//===----------------------------------------------------------------------===// + +#define DEBUG_TYPE "codegen-licm" +#include "llvm/Transforms/Scalar.h" +#include "llvm/Constants.h" +#include "llvm/DerivedTypes.h" +#include "llvm/Instructions.h" +#include "llvm/IntrinsicInst.h" +#include "llvm/LLVMContext.h" +#include "llvm/Analysis/LoopPass.h" +#include "llvm/Analysis/AliasAnalysis.h" +#include "llvm/Analysis/ScalarEvolution.h" +#include "llvm/Analysis/IVUsers.h" +#include "llvm/ADT/DenseMap.h" +using namespace llvm; + +namespace { + class CodeGenLICM : public LoopPass { + virtual bool runOnLoop(Loop *L, LPPassManager &LPM); + virtual void getAnalysisUsage(AnalysisUsage &AU) const; + public: + static char ID; // Pass identification, replacement for typeid + explicit CodeGenLICM() : LoopPass(&ID) {} + }; +} + +char CodeGenLICM::ID = 0; +static RegisterPass X("codegen-licm", + "hoist constants out of loops"); + +Pass *llvm::createCodeGenLICMPass() { + return new CodeGenLICM(); +} + +bool CodeGenLICM::runOnLoop(Loop *L, LPPassManager &) { + bool Changed = false; + + // Only visit outermost loops. + if (L->getParentLoop()) return Changed; + + Instruction *PreheaderTerm = L->getLoopPreheader()->getTerminator(); + DenseMap HoistedConstants; + + for (Loop::block_iterator I = L->block_begin(), E = L->block_end(); + I != E; ++I) { + BasicBlock *BB = *I; + for (BasicBlock::iterator BBI = BB->begin(), BBE = BB->end(); + BBI != BBE; ++BBI) { + Instruction *I = BBI; + // Don't bother hoisting constants out of loop-header phi nodes. + if (BB == L->getHeader() && isa(I)) + continue; + // TODO: For now, skip all intrinsic instructions, because some of them + // can require their operands to be constants, and we don't want to + // break that. + if (isa(I)) + continue; + // LLVM represents fneg as -0.0-x; don't hoist the -0.0 out. + if (BinaryOperator::isFNeg(I) || + BinaryOperator::isNeg(I) || + BinaryOperator::isNot(I)) + continue; + for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) { + // Don't hoist out switch case constants. + if (isa(I) && i == 1) + break; + // Don't hoist out shuffle masks. + if (isa(I) && i == 2) + break; + Value *Op = I->getOperand(i); + Constant *C = dyn_cast(Op); + if (!C) continue; + // TODO: Ask the target which constants are legal. This would allow + // us to add support for hoisting ConstantInts and GlobalValues too. + if (isa(C) || + isa(C) || + isa(C)) { + BitCastInst *&BC = HoistedConstants[C]; + if (!BC) + BC = new BitCastInst(C, C->getType(), "hoist", PreheaderTerm); + I->setOperand(i, BC); + Changed = true; + } + } + } + } + + return Changed; +} + +void CodeGenLICM::getAnalysisUsage(AnalysisUsage &AU) const { + // This pass preserves just about everything. List some popular things here. + AU.setPreservesCFG(); + AU.addPreservedID(LoopSimplifyID); + AU.addPreserved(); + AU.addPreserved(); + AU.addPreserved(); + AU.addPreserved(); + AU.addPreserved(); + AU.addPreserved(); + + // Hoisting requires a loop preheader. + AU.addRequiredID(LoopSimplifyID); +} -- 2.34.1