From 69adc159ee69de7a2f36a6e69dba56f36d859b8b Mon Sep 17 00:00:00 2001 From: Jingyue Wu Date: Wed, 12 Nov 2014 06:58:45 +0000 Subject: [PATCH] Disable indvar widening if arithmetics on the wider type are more expensive Summary: IndVarSimplify should not widen an indvar if arithmetics on the wider indvar are more expensive than those on the narrower indvar. For instance, although NVPTX64 treats i64 as a legal type, an ADD on i64 is twice as expensive as that on i32, because the hardware needs to simulate a 64-bit integer using two 32-bit integers. Split from D6188, and based on D6195 which adds NVPTXTargetTransformInfo. Fixes PR21148. Test Plan: Added @indvar_32_bit that verifies we do not widen an indvar if the arithmetics on the wider type are more expensive. Reviewers: jholewinski, eliben, meheff, atrick Reviewed By: atrick Subscribers: jholewinski, llvm-commits Differential Revision: http://reviews.llvm.org/D6196 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221772 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Target/NVPTX/NVPTXTargetTransformInfo.cpp | 41 ++++++++++++++++++- lib/Transforms/Scalar/IndVarSimplify.cpp | 40 +++++++++++++----- .../IndVarSimplify/no-widen-expensive.ll | 37 +++++++++++++++++ 3 files changed, 106 insertions(+), 12 deletions(-) create mode 100644 test/Transforms/IndVarSimplify/no-widen-expensive.ll diff --git a/lib/Target/NVPTX/NVPTXTargetTransformInfo.cpp b/lib/Target/NVPTX/NVPTXTargetTransformInfo.cpp index bcac6392a67..5aea7021e42 100644 --- a/lib/Target/NVPTX/NVPTXTargetTransformInfo.cpp +++ b/lib/Target/NVPTX/NVPTXTargetTransformInfo.cpp @@ -36,12 +36,14 @@ void initializeNVPTXTTIPass(PassRegistry &); namespace { class NVPTXTTI final : public ImmutablePass, public TargetTransformInfo { + const NVPTXTargetLowering *TLI; public: - NVPTXTTI() : ImmutablePass(ID) { + NVPTXTTI() : ImmutablePass(ID), TLI(nullptr) { llvm_unreachable("This pass cannot be directly constructed"); } - NVPTXTTI(const NVPTXTargetMachine *TM) : ImmutablePass(ID) { + NVPTXTTI(const NVPTXTargetMachine *TM) + : ImmutablePass(ID), TLI(TM->getSubtargetImpl()->getTargetLowering()) { initializeNVPTXTTIPass(*PassRegistry::getPassRegistry()); } @@ -63,6 +65,12 @@ public: bool hasBranchDivergence() const override; + unsigned getArithmeticInstrCost( + unsigned Opcode, Type *Ty, OperandValueKind Opd1Info = OK_AnyValue, + OperandValueKind Opd2Info = OK_AnyValue, + OperandValueProperties Opd1PropInfo = OP_None, + OperandValueProperties Opd2PropInfo = OP_None) const override; + /// @} }; @@ -78,3 +86,32 @@ llvm::createNVPTXTargetTransformInfoPass(const NVPTXTargetMachine *TM) { } bool NVPTXTTI::hasBranchDivergence() const { return true; } + +unsigned NVPTXTTI::getArithmeticInstrCost( + unsigned Opcode, Type *Ty, OperandValueKind Opd1Info, + OperandValueKind Opd2Info, OperandValueProperties Opd1PropInfo, + OperandValueProperties Opd2PropInfo) const { + // Legalize the type. + std::pair LT = TLI->getTypeLegalizationCost(Ty); + + int ISD = TLI->InstructionOpcodeToISD(Opcode); + + switch (ISD) { + default: + return TargetTransformInfo::getArithmeticInstrCost( + Opcode, Ty, Opd1Info, Opd2Info, Opd1PropInfo, Opd2PropInfo); + case ISD::ADD: + case ISD::MUL: + case ISD::XOR: + case ISD::OR: + case ISD::AND: + // The machine code (SASS) simulates an i64 with two i32. Therefore, we + // estimate that arithmetic operations on i64 are twice as expensive as + // those on types that can fit into one machine register. + if (LT.second.SimpleTy == MVT::i64) + return 2 * LT.first; + // Delegate other cases to the basic TTI. + return TargetTransformInfo::getArithmeticInstrCost( + Opcode, Ty, Opd1Info, Opd2Info, Opd1PropInfo, Opd2PropInfo); + } +} diff --git a/lib/Transforms/Scalar/IndVarSimplify.cpp b/lib/Transforms/Scalar/IndVarSimplify.cpp index 03dffb66f35..bf90912ebd0 100644 --- a/lib/Transforms/Scalar/IndVarSimplify.cpp +++ b/lib/Transforms/Scalar/IndVarSimplify.cpp @@ -31,6 +31,7 @@ #include "llvm/Analysis/LoopInfo.h" #include "llvm/Analysis/LoopPass.h" #include "llvm/Analysis/ScalarEvolutionExpander.h" +#include "llvm/Analysis/TargetTransformInfo.h" #include "llvm/IR/BasicBlock.h" #include "llvm/IR/CFG.h" #include "llvm/IR/Constants.h" @@ -69,11 +70,12 @@ static cl::opt ReduceLiveIVs("liv-reduce", cl::Hidden, namespace { class IndVarSimplify : public LoopPass { - LoopInfo *LI; - ScalarEvolution *SE; - DominatorTree *DT; - const DataLayout *DL; - TargetLibraryInfo *TLI; + LoopInfo *LI; + ScalarEvolution *SE; + DominatorTree *DT; + const DataLayout *DL; + TargetLibraryInfo *TLI; + const TargetTransformInfo *TTI; SmallVector DeadInsts; bool Changed; @@ -661,7 +663,7 @@ namespace { /// extended by this sign or zero extend operation. This is used to determine /// the final width of the IV before actually widening it. static void visitIVCast(CastInst *Cast, WideIVInfo &WI, ScalarEvolution *SE, - const DataLayout *DL) { + const DataLayout *DL, const TargetTransformInfo *TTI) { bool IsSigned = Cast->getOpcode() == Instruction::SExt; if (!IsSigned && Cast->getOpcode() != Instruction::ZExt) return; @@ -671,6 +673,19 @@ static void visitIVCast(CastInst *Cast, WideIVInfo &WI, ScalarEvolution *SE, if (DL && !DL->isLegalInteger(Width)) return; + // Cast is either an sext or zext up to this point. + // We should not widen an indvar if arithmetics on the wider indvar are more + // expensive than those on the narrower indvar. We check only the cost of ADD + // because at least an ADD is required to increment the induction variable. We + // could compute more comprehensively the cost of all instructions on the + // induction variable when necessary. + if (TTI && + TTI->getArithmeticInstrCost(Instruction::Add, Ty) > + TTI->getArithmeticInstrCost(Instruction::Add, + Cast->getOperand(0)->getType())) { + return; + } + if (!WI.WidestNativeType) { WI.WidestNativeType = SE->getEffectiveSCEVType(Ty); WI.IsSigned = IsSigned; @@ -1187,14 +1202,16 @@ namespace { class IndVarSimplifyVisitor : public IVVisitor { ScalarEvolution *SE; const DataLayout *DL; + const TargetTransformInfo *TTI; PHINode *IVPhi; public: WideIVInfo WI; IndVarSimplifyVisitor(PHINode *IV, ScalarEvolution *SCEV, - const DataLayout *DL, const DominatorTree *DTree): - SE(SCEV), DL(DL), IVPhi(IV) { + const DataLayout *DL, const TargetTransformInfo *TTI, + const DominatorTree *DTree) + : SE(SCEV), DL(DL), TTI(TTI), IVPhi(IV) { DT = DTree; WI.NarrowIV = IVPhi; if (ReduceLiveIVs) @@ -1202,7 +1219,9 @@ namespace { } // Implement the interface used by simplifyUsersOfIV. - void visitCast(CastInst *Cast) override { visitIVCast(Cast, WI, SE, DL); } + void visitCast(CastInst *Cast) override { + visitIVCast(Cast, WI, SE, DL, TTI); + } }; } @@ -1236,7 +1255,7 @@ void IndVarSimplify::SimplifyAndExtend(Loop *L, PHINode *CurrIV = LoopPhis.pop_back_val(); // Information about sign/zero extensions of CurrIV. - IndVarSimplifyVisitor Visitor(CurrIV, SE, DL, DT); + IndVarSimplifyVisitor Visitor(CurrIV, SE, DL, TTI, DT); Changed |= simplifyUsersOfIV(CurrIV, SE, &LPM, DeadInsts, &Visitor); @@ -1895,6 +1914,7 @@ bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) { DataLayoutPass *DLP = getAnalysisIfAvailable(); DL = DLP ? &DLP->getDataLayout() : nullptr; TLI = getAnalysisIfAvailable(); + TTI = getAnalysisIfAvailable(); DeadInsts.clear(); Changed = false; diff --git a/test/Transforms/IndVarSimplify/no-widen-expensive.ll b/test/Transforms/IndVarSimplify/no-widen-expensive.ll new file mode 100644 index 00000000000..8744b19d5e2 --- /dev/null +++ b/test/Transforms/IndVarSimplify/no-widen-expensive.ll @@ -0,0 +1,37 @@ +; RUN: opt < %s -indvars -S | FileCheck %s + +target triple = "nvptx64-unknown-unknown" + +; For the nvptx64 architecture, the cost of an arithmetic instruction on a +; 64-bit integer is twice as expensive as that on a 32-bit integer, because the +; hardware needs to simulate a 64-bit integer using two 32-bit integers. +; Therefore, in this particular architecture, we should not widen induction +; variables to 64-bit integers even though i64 is a legal type in the 64-bit +; PTX ISA. + +define void @indvar_32_bit(i32 %n, i32* nocapture %output) { +; CHECK-LABEL: @indvar_32_bit +entry: + %cmp5 = icmp sgt i32 %n, 0 + br i1 %cmp5, label %for.body.preheader, label %for.end + +for.body.preheader: ; preds = %entry + br label %for.body + +for.body: ; preds = %for.body.preheader, %for.body + %i.06 = phi i32 [ 0, %for.body.preheader ], [ %add, %for.body ] +; CHECK: phi i32 + %mul = mul nsw i32 %i.06, %i.06 + %0 = sext i32 %i.06 to i64 + %arrayidx = getelementptr inbounds i32* %output, i64 %0 + store i32 %mul, i32* %arrayidx, align 4 + %add = add nsw i32 %i.06, 3 + %cmp = icmp slt i32 %add, %n + br i1 %cmp, label %for.body, label %for.end.loopexit + +for.end.loopexit: ; preds = %for.body + br label %for.end + +for.end: ; preds = %for.end.loopexit, %entry + ret void +}