forked from OSchip/llvm-project
[IndVars] Eliminate op.with.overflow when possible
Summary: If we can prove that an op.with.overflow intrinsic does not overflow, we can get rid of the intrinsic, and replace it with non-wrapping arithmetic. Reviewers: atrick, regehr Subscribers: sanjoy, mcrosier, llvm-commits Differential Revision: http://reviews.llvm.org/D18685 llvm-svn: 265913
This commit is contained in:
Sanjoy Das
parent
3c529a40ca
commit
a07ad647ee
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@ -71,6 +71,7 @@ namespace {
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bool eliminateIdentitySCEV(Instruction *UseInst, Instruction *IVOperand);
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bool eliminateOverflowIntrinsic(CallInst *CI);
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bool eliminateIVUser(Instruction *UseInst, Instruction *IVOperand);
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void eliminateIVComparison(ICmpInst *ICmp, Value *IVOperand);
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void eliminateIVRemainder(BinaryOperator *Rem, Value *IVOperand,
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@ -318,6 +319,108 @@ void SimplifyIndvar::eliminateIVRemainder(BinaryOperator *Rem,
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DeadInsts.emplace_back(Rem);
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}
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bool SimplifyIndvar::eliminateOverflowIntrinsic(CallInst *CI) {
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auto *F = CI->getCalledFunction();
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if (!F)
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return false;
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typedef const SCEV *(ScalarEvolution::*OperationFunctionTy)(
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const SCEV *, const SCEV *, SCEV::NoWrapFlags);
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typedef const SCEV *(ScalarEvolution::*ExtensionFunctionTy)(
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const SCEV *, Type *);
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OperationFunctionTy Operation;
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ExtensionFunctionTy Extension;
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Instruction::BinaryOps RawOp;
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// We always have exactly one of nsw or nuw. If NoSignedOverflow is false, we
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// have nuw.
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bool NoSignedOverflow;
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switch (F->getIntrinsicID()) {
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default:
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return false;
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case Intrinsic::sadd_with_overflow:
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Operation = &ScalarEvolution::getAddExpr;
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Extension = &ScalarEvolution::getSignExtendExpr;
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RawOp = Instruction::Add;
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NoSignedOverflow = true;
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break;
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case Intrinsic::uadd_with_overflow:
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Operation = &ScalarEvolution::getAddExpr;
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Extension = &ScalarEvolution::getZeroExtendExpr;
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RawOp = Instruction::Add;
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NoSignedOverflow = false;
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break;
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case Intrinsic::ssub_with_overflow:
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Operation = &ScalarEvolution::getMinusSCEV;
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Extension = &ScalarEvolution::getSignExtendExpr;
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RawOp = Instruction::Sub;
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NoSignedOverflow = true;
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break;
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case Intrinsic::usub_with_overflow:
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Operation = &ScalarEvolution::getMinusSCEV;
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Extension = &ScalarEvolution::getZeroExtendExpr;
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RawOp = Instruction::Sub;
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NoSignedOverflow = false;
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break;
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}
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const SCEV *LHS = SE->getSCEV(CI->getArgOperand(0));
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const SCEV *RHS = SE->getSCEV(CI->getArgOperand(1));
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auto *NarrowTy = cast<IntegerType>(LHS->getType());
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auto *WideTy =
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IntegerType::get(NarrowTy->getContext(), NarrowTy->getBitWidth() * 2);
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const SCEV *A =
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(SE->*Extension)((SE->*Operation)(LHS, RHS, SCEV::FlagAnyWrap), WideTy);
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const SCEV *B =
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(SE->*Operation)((SE->*Extension)(LHS, WideTy),
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(SE->*Extension)(RHS, WideTy), SCEV::FlagAnyWrap);
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if (A != B)
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return false;
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// Proved no overflow, nuke the overflow check and, if possible, the overflow
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// intrinsic as well.
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BinaryOperator *NewResult = BinaryOperator::Create(
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RawOp, CI->getArgOperand(0), CI->getArgOperand(1), "", CI);
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if (NoSignedOverflow)
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NewResult->setHasNoSignedWrap(true);
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else
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NewResult->setHasNoUnsignedWrap(true);
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SmallVector<ExtractValueInst *, 4> ToDelete;
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for (auto *U : CI->users()) {
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if (auto *EVI = dyn_cast<ExtractValueInst>(U)) {
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if (EVI->getIndices()[0] == 1)
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EVI->replaceAllUsesWith(ConstantInt::getFalse(CI->getContext()));
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else {
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assert(EVI->getIndices()[0] == 0 && "Only two possibilities!");
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EVI->replaceAllUsesWith(NewResult);
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}
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ToDelete.push_back(EVI);
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}
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}
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for (auto *EVI : ToDelete)
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EVI->eraseFromParent();
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if (CI->use_empty())
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CI->eraseFromParent();
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return true;
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}
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/// Eliminate an operation that consumes a simple IV and has no observable
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/// side-effect given the range of IV values. IVOperand is guaranteed SCEVable,
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/// but UseInst may not be.
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@ -335,6 +438,10 @@ bool SimplifyIndvar::eliminateIVUser(Instruction *UseInst,
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}
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}
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if (auto *CI = dyn_cast<CallInst>(UseInst))
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if (eliminateOverflowIntrinsic(CI))
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return true;
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if (eliminateIdentitySCEV(UseInst, IVOperand))
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return true;
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@ -0,0 +1,137 @@
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; RUN: opt -S -indvars < %s | FileCheck %s
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target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
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target triple = "x86_64-unknown-linux-gnu"
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define void @f_sadd(i8* %a) {
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; CHECK-LABEL: @f_sadd(
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entry:
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br label %for.body
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for.cond.cleanup: ; preds = %cont
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ret void
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for.body: ; preds = %entry, %cont
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%i.04 = phi i32 [ 0, %entry ], [ %2, %cont ]
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%idxprom = sext i32 %i.04 to i64
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%arrayidx = getelementptr inbounds i8, i8* %a, i64 %idxprom
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store i8 0, i8* %arrayidx, align 1
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%0 = tail call { i32, i1 } @llvm.sadd.with.overflow.i32(i32 %i.04, i32 1)
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%1 = extractvalue { i32, i1 } %0, 1
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; CHECK: for.body:
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; CHECK-NOT: @llvm.sadd.with.overflow
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; CHECK: br i1 false, label %trap, label %cont, !nosanitize !0
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br i1 %1, label %trap, label %cont, !nosanitize !{}
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trap: ; preds = %for.body
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tail call void @llvm.trap() #2, !nosanitize !{}
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unreachable, !nosanitize !{}
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cont: ; preds = %for.body
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%2 = extractvalue { i32, i1 } %0, 0
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%cmp = icmp slt i32 %2, 16
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br i1 %cmp, label %for.body, label %for.cond.cleanup
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}
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define void @f_uadd(i8* %a) {
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; CHECK-LABEL: @f_uadd(
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entry:
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br label %for.body
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for.cond.cleanup: ; preds = %cont
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ret void
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for.body: ; preds = %entry, %cont
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%i.04 = phi i32 [ 0, %entry ], [ %2, %cont ]
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%idxprom = sext i32 %i.04 to i64
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%arrayidx = getelementptr inbounds i8, i8* %a, i64 %idxprom
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store i8 0, i8* %arrayidx, align 1
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%0 = tail call { i32, i1 } @llvm.uadd.with.overflow.i32(i32 %i.04, i32 1)
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%1 = extractvalue { i32, i1 } %0, 1
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; CHECK: for.body:
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; CHECK-NOT: @llvm.uadd.with.overflow
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; CHECK: br i1 false, label %trap, label %cont, !nosanitize !0
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br i1 %1, label %trap, label %cont, !nosanitize !{}
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trap: ; preds = %for.body
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tail call void @llvm.trap(), !nosanitize !{}
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unreachable, !nosanitize !{}
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cont: ; preds = %for.body
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%2 = extractvalue { i32, i1 } %0, 0
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%cmp = icmp slt i32 %2, 16
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br i1 %cmp, label %for.body, label %for.cond.cleanup
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}
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define void @f_ssub(i8* nocapture %a) {
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; CHECK-LABEL: @f_ssub(
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entry:
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br label %for.body
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for.cond.cleanup: ; preds = %cont
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ret void
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for.body: ; preds = %entry, %cont
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%i.04 = phi i32 [ 15, %entry ], [ %2, %cont ]
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%idxprom = sext i32 %i.04 to i64
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%arrayidx = getelementptr inbounds i8, i8* %a, i64 %idxprom
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store i8 0, i8* %arrayidx, align 1
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%0 = tail call { i32, i1 } @llvm.ssub.with.overflow.i32(i32 %i.04, i32 1)
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%1 = extractvalue { i32, i1 } %0, 1
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; CHECK: for.body:
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; CHECK-NOT: @llvm.ssub.with.overflow.i32
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; CHECK: br i1 false, label %trap, label %cont, !nosanitize !0
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br i1 %1, label %trap, label %cont, !nosanitize !{}
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trap: ; preds = %for.body
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tail call void @llvm.trap(), !nosanitize !{}
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unreachable, !nosanitize !{}
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cont: ; preds = %for.body
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%2 = extractvalue { i32, i1 } %0, 0
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%cmp = icmp sgt i32 %2, -1
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br i1 %cmp, label %for.body, label %for.cond.cleanup
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}
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define void @f_usub(i8* nocapture %a) {
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; CHECK-LABEL: @f_usub(
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entry:
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br label %for.body
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for.cond.cleanup: ; preds = %cont
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ret void
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for.body: ; preds = %entry, %cont
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%i.04 = phi i32 [ 15, %entry ], [ %2, %cont ]
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%idxprom = sext i32 %i.04 to i64
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%arrayidx = getelementptr inbounds i8, i8* %a, i64 %idxprom
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store i8 0, i8* %arrayidx, align 1
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%0 = tail call { i32, i1 } @llvm.usub.with.overflow.i32(i32 %i.04, i32 1)
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%1 = extractvalue { i32, i1 } %0, 1
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; It is theoretically possible to prove this, but SCEV cannot
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; represent non-unsigned-wrapping subtraction operations.
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; CHECK: for.body:
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; CHECK: [[COND:%[^ ]+]] = extractvalue { i32, i1 } %1, 1
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; CHECK-NEXT: br i1 [[COND]], label %trap, label %cont, !nosanitize !0
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br i1 %1, label %trap, label %cont, !nosanitize !{}
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trap: ; preds = %for.body
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tail call void @llvm.trap(), !nosanitize !{}
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unreachable, !nosanitize !{}
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cont: ; preds = %for.body
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%2 = extractvalue { i32, i1 } %0, 0
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%cmp = icmp sgt i32 %2, -1
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br i1 %cmp, label %for.body, label %for.cond.cleanup
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}
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declare { i32, i1 } @llvm.sadd.with.overflow.i32(i32, i32) nounwind readnone
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declare { i32, i1 } @llvm.uadd.with.overflow.i32(i32, i32) nounwind readnone
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declare { i32, i1 } @llvm.ssub.with.overflow.i32(i32, i32) nounwind readnone
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declare { i32, i1 } @llvm.usub.with.overflow.i32(i32, i32) nounwind readnone
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declare { i32, i1 } @llvm.smul.with.overflow.i32(i32, i32) nounwind readnone
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declare { i32, i1 } @llvm.umul.with.overflow.i32(i32, i32) nounwind readnone
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declare void @llvm.trap() #2
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@ -10,7 +10,7 @@ target triple = "x86_64-apple-macosx"
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; CHECK-LABEL: loop2:
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; CHECK-NOT: extractvalue
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; CHECK: add nuw
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; CHECK: @llvm.sadd.with.overflow
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; CHECK-NOT: @llvm.sadd.with.overflow
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; CHECK-LABEL: loop3:
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; CHECK-NOT: extractvalue
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; CHECK: ret
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