[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
diff --git a/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp b/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
index 6d90e6b..deaddcb 100644
--- a/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
@@ -39,6 +39,9 @@
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 @@
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 @@
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;
+// 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);
+}
- // 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 % 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 @@
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;
}