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[SimplifyIndvar] Replace the srem used by IV if we can prove both of its operands are non-negative 

Since now SCEV can handle 'urem', an 'urem' is a better canonical form than an 'srem' because it has well-defined behavior

This is a follow up of D34598

Differential Revision: https://reviews.llvm.org/D38072

llvm-svn: 314125
This commit is contained in:
Hongbin Zheng 2017-09-25 17:39:40 +00:00
parent 3103896914
commit f0093e45c4
3 changed files with 200 additions and 49 deletions
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134
llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
View File

@ -39,6 +39,9 @@ STATISTIC(NumElimRem , "Number of IV remainder operations eliminated");
STATISTIC(
NumSimplifiedSDiv,
"Number of IV signed division operations converted to unsigned division");
STATISTIC(
NumSimplifiedSRem,
"Number of IV signed remainder operations converted to unsigned remainder");
STATISTIC(NumElimCmp , "Number of IV comparisons eliminated");
namespace {
@ -77,8 +80,11 @@ namespace {
bool eliminateOverflowIntrinsic(CallInst *CI);
bool eliminateIVUser(Instruction *UseInst, Instruction *IVOperand);
void eliminateIVComparison(ICmpInst *ICmp, Value *IVOperand);
void eliminateIVRemainder(BinaryOperator *Rem, Value *IVOperand,
bool IsSigned);
void simplifyIVRemainder(BinaryOperator *Rem, Value *IVOperand,
bool IsSigned);
void replaceRemWithNumerator(BinaryOperator *Rem);
void replaceRemWithNumeratorOrZero(BinaryOperator *Rem);
void replaceSRemWithURem(BinaryOperator *Rem);
bool eliminateSDiv(BinaryOperator *SDiv);
bool strengthenOverflowingOperation(BinaryOperator *OBO, Value *IVOperand);
bool strengthenRightShift(BinaryOperator *BO, Value *IVOperand);
@ -309,56 +315,92 @@ bool SimplifyIndvar::eliminateSDiv(BinaryOperator *SDiv) {
return false;
}
/// SimplifyIVUsers helper for eliminating useless
/// remainder operations operating on an induction variable.
void SimplifyIndvar::eliminateIVRemainder(BinaryOperator *Rem,
Value *IVOperand,
bool IsSigned) {
// We're only interested in the case where we know something about
// the numerator.
if (IVOperand != Rem->getOperand(0))
return;
// Get the SCEVs for the ICmp operands.
const SCEV *S = SE->getSCEV(Rem->getOperand(0));
const SCEV *X = SE->getSCEV(Rem->getOperand(1));
// Simplify unnecessary loops away.
const Loop *ICmpLoop = LI->getLoopFor(Rem->getParent());
S = SE->getSCEVAtScope(S, ICmpLoop);
X = SE->getSCEVAtScope(X, ICmpLoop);
// i % n --> i if i is in [0,n).
if ((!IsSigned || SE->isKnownNonNegative(S)) &&
SE->isKnownPredicate(IsSigned ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
S, X))
Rem->replaceAllUsesWith(Rem->getOperand(0));
else {
// (i+1) % n --> (i+1)==n?0:(i+1) if i is in [0,n).
const SCEV *LessOne = SE->getMinusSCEV(S, SE->getOne(S->getType()));
if (IsSigned && !SE->isKnownNonNegative(LessOne))
return;
if (!SE->isKnownPredicate(IsSigned ?
ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
LessOne, X))
return;
ICmpInst *ICmp = new ICmpInst(Rem, ICmpInst::ICMP_EQ,
Rem->getOperand(0), Rem->getOperand(1));
SelectInst *Sel =
SelectInst::Create(ICmp,
ConstantInt::get(Rem->getType(), 0),
Rem->getOperand(0), "tmp", Rem);
Rem->replaceAllUsesWith(Sel);
}
// i %s n -> i %u n if i >= 0 and n >= 0
void SimplifyIndvar::replaceSRemWithURem(BinaryOperator *Rem) {
auto *N = Rem->getOperand(0), *D = Rem->getOperand(1);
auto *URem = BinaryOperator::Create(BinaryOperator::URem, N, D,
Rem->getName() + ".urem", Rem);
Rem->replaceAllUsesWith(URem);
DEBUG(dbgs() << "INDVARS: Simplified srem: " << *Rem << '\n');
++NumSimplifiedSRem;
DeadInsts.emplace_back(Rem);
}
// i % n --> i if i is in [0,n).
void SimplifyIndvar::replaceRemWithNumerator(BinaryOperator *Rem) {
Rem->replaceAllUsesWith(Rem->getOperand(0));
DEBUG(dbgs() << "INDVARS: Simplified rem: " << *Rem << '\n');
++NumElimRem;
Changed = true;
DeadInsts.emplace_back(Rem);
}
// (i+1) % n --> (i+1)==n?0:(i+1) if i is in [0,n).
void SimplifyIndvar::replaceRemWithNumeratorOrZero(BinaryOperator *Rem) {
auto *T = Rem->getType();
auto *N = Rem->getOperand(0), *D = Rem->getOperand(1);
ICmpInst *ICmp = new ICmpInst(Rem, ICmpInst::ICMP_EQ, N, D);
SelectInst *Sel =
SelectInst::Create(ICmp, ConstantInt::get(T, 0), N, "iv.rem", Rem);
Rem->replaceAllUsesWith(Sel);
DEBUG(dbgs() << "INDVARS: Simplified rem: " << *Rem << '\n');
++NumElimRem;
Changed = true;
DeadInsts.emplace_back(Rem);
}
/// SimplifyIVUsers helper for eliminating useless remainder operations
/// operating on an induction variable or replacing srem by urem.
void SimplifyIndvar::simplifyIVRemainder(BinaryOperator *Rem, Value *IVOperand,
bool IsSigned) {
auto *NValue = Rem->getOperand(0);
auto *DValue = Rem->getOperand(1);
// We're only interested in the case where we know something about
// the numerator, unless it is a srem, because we want to replace srem by urem
// in general.
bool UsedAsNumerator = IVOperand == NValue;
if (!UsedAsNumerator && !IsSigned)
return;
const SCEV *N = SE->getSCEV(NValue);
// Simplify unnecessary loops away.
const Loop *ICmpLoop = LI->getLoopFor(Rem->getParent());
N = SE->getSCEVAtScope(N, ICmpLoop);
bool IsNumeratorNonNegative = !IsSigned || SE->isKnownNonNegative(N);
// Do not proceed if the Numerator may be negative
if (!IsNumeratorNonNegative)
return;
const SCEV *D = SE->getSCEV(DValue);
D = SE->getSCEVAtScope(D, ICmpLoop);
if (UsedAsNumerator) {
auto LT = IsSigned ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT;
if (SE->isKnownPredicate(LT, N, D)) {
replaceRemWithNumerator(Rem);
return;
}
auto *T = Rem->getType();
const auto *NLessOne = SE->getMinusSCEV(N, SE->getOne(T));
if (SE->isKnownPredicate(LT, NLessOne, D)) {
replaceRemWithNumeratorOrZero(Rem);
return;
}
}
// Try to replace SRem with URem, if both N and D are known non-negative.
// Since we had already check N, we only need to check D now
if (!IsSigned || !SE->isKnownNonNegative(D))
return;
replaceSRemWithURem(Rem);
Changed = true;
}
bool SimplifyIndvar::eliminateOverflowIntrinsic(CallInst *CI) {
auto *F = CI->getCalledFunction();
if (!F)
@ -474,7 +516,7 @@ bool SimplifyIndvar::eliminateIVUser(Instruction *UseInst,
if (BinaryOperator *Bin = dyn_cast<BinaryOperator>(UseInst)) {
bool IsSRem = Bin->getOpcode() == Instruction::SRem;
if (IsSRem || Bin->getOpcode() == Instruction::URem) {
eliminateIVRemainder(Bin, IVOperand, IsSRem);
simplifyIVRemainder(Bin, IVOperand, IsSRem);
return true;
}

6
llvm/test/Transforms/IndVarSimplify/eliminate-rem.ll
View File

@ -33,9 +33,9 @@ bb12: ; preds = %bb11, %bb
; Indvars should be able to eliminate the (i+1)%n.
; CHECK-LABEL: @f(
; CHECK-NOT: rem
; CHECK: rem
; CHECK-NOT: rem
; CHECK-NOT: {{[us]}}rem
; CHECK: {{[us]}}rem
; CHECK-NOT: {{[us]}}rem
; CHECK: ret
define i32 @f(i64* %arg, i64 %arg1, i64 %arg2, i64 %arg3) nounwind {

109
llvm/test/Transforms/IndVarSimplify/replace-srem-by-urem.ll Normal file
View File

@ -0,0 +1,109 @@
; RUN: opt < %s -indvars -S | FileCheck %s
define void @test0(i32* %a) {
; CHECK-LABEL: @test0(
entry:
br label %for.body
for.body: ; preds = %entry, %for.body
%i.01 = phi i32 [ 0, %entry ], [ %inc, %for.body ]
%rem = srem i32 %i.01, 2
; CHECK-NOT: srem
; CHECK: urem
%idxprom = sext i32 %rem to i64
%arrayidx = getelementptr inbounds i32, i32* %a, i64 %idxprom
store i32 %i.01, i32* %arrayidx, align 4
%inc = add nsw i32 %i.01, 1
%cmp = icmp slt i32 %inc, 64
br i1 %cmp, label %for.body, label %for.end
for.end: ; preds = %for.body
ret void
}
define void @test2(i32* %a, i32 %d) {
; CHECK-LABEL: @test2(
entry:
br label %for.body
for.body: ; preds = %entry, %for.body
%i.01 = phi i32 [ 0, %entry ], [ %inc, %for.body ]
%mul = mul nsw i32 %i.01, 64
%rem = srem i32 %mul, %d
; CHECK-NOT: urem
%idxprom = sext i32 %rem to i64
%arrayidx = getelementptr inbounds i32, i32* %a, i64 %idxprom
store i32 %i.01, i32* %arrayidx, align 4
%inc = add nsw i32 %i.01, 1
%cmp = icmp slt i32 %inc, 64
br i1 %cmp, label %for.body, label %for.end
for.end: ; preds = %for.body
ret void
}
define void @test3(i32* %a) {
; CHECK-LABEL: @test3(
entry:
br label %for.body
for.body: ; preds = %entry, %for.body
%i.01 = phi i32 [ 0, %entry ], [ %inc, %for.body ]
%rem = srem i32 2048, %i.01
; CHECK: urem
; CHECK-NOT: srem
%idxprom = sext i32 %rem to i64
%arrayidx = getelementptr inbounds i32, i32* %a, i64 %idxprom
store i32 %i.01, i32* %arrayidx, align 4
%inc = add nsw i32 %i.01, 1
%cmp = icmp slt i32 %inc, 64
br i1 %cmp, label %for.body, label %for.end
for.end: ; preds = %for.body
ret void
}
define void @test4(i32* %a) {
; CHECK-LABEL: @test4(
entry:
br label %for.body
for.body: ; preds = %entry, %for.body
%i.01 = phi i32 [ 0, %entry ], [ %inc, %for.body ]
%mul = mul nsw i32 %i.01, 64
%rem = srem i32 %mul, 8
; CHECK: urem
; CHECK-NOT: srem
%idxprom = sext i32 %rem to i64
%arrayidx = getelementptr inbounds i32, i32* %a, i64 %idxprom
store i32 %i.01, i32* %arrayidx, align 4
%inc = add nsw i32 %i.01, 1
%cmp = icmp slt i32 %inc, 64
br i1 %cmp, label %for.body, label %for.end
for.end: ; preds = %for.body
ret void
}
define void @test5(i32* %a) {
; CHECK-LABEL: @test5(
entry:
br label %for.body
for.body: ; preds = %entry, %for.body
%i.01 = phi i32 [ 0, %entry ], [ %inc, %for.body ]
%mul = mul nsw i32 %i.01, 64
%rem = srem i32 %mul, 6
; CHECK: urem
; CHECK-NOT: srem
%idxprom = sext i32 %rem to i64
%arrayidx = getelementptr inbounds i32, i32* %a, i64 %idxprom
store i32 %i.01, i32* %arrayidx, align 4
%inc = add nsw i32 %i.01, 1
%cmp = icmp slt i32 %inc, 64
br i1 %cmp, label %for.body, label %for.end
for.end: ; preds = %for.body
ret void
}