[SCEV] Make getUDivExactExpr handle non-nuw multiplies correctly.
To avoid regressions, make ScalarEvolution::createSCEV a bit more
clever.
Also get rid of some useless code in ScalarEvolution::howFarToZero
which was hiding this bug.
No new testcase because it's impossible to actually expose this bug:
we don't have any in-tree users of getUDivExactExpr besides the two
functions I just mentioned, and they both dodged the problem. I'll
try to add some interesting users in a followup.
Differential Revision: https://reviews.llvm.org/D28587
llvm-svn: 292449
diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 8164852..18fcb0e 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -2888,7 +2888,7 @@
// end of this file for inspiration.
const SCEVMulExpr *Mul = dyn_cast<SCEVMulExpr>(LHS);
- if (!Mul)
+ if (!Mul || !Mul->hasNoUnsignedWrap())
return getUDivExpr(LHS, RHS);
if (const SCEVConstant *RHSCst = dyn_cast<SCEVConstant>(RHS)) {
@@ -5147,12 +5147,27 @@
APInt EffectiveMask =
APInt::getLowBitsSet(BitWidth, BitWidth - LZ - TZ).shl(TZ);
if ((LZ != 0 || TZ != 0) && !((~A & ~KnownZero) & EffectiveMask)) {
- const SCEV *MulCount = getConstant(ConstantInt::get(
- getContext(), APInt::getOneBitSet(BitWidth, TZ)));
+ const SCEV *MulCount = getConstant(APInt::getOneBitSet(BitWidth, TZ));
+ const SCEV *LHS = getSCEV(BO->LHS);
+ const SCEV *ShiftedLHS = nullptr;
+ if (auto *LHSMul = dyn_cast<SCEVMulExpr>(LHS)) {
+ if (auto *OpC = dyn_cast<SCEVConstant>(LHSMul->getOperand(0))) {
+ // For an expression like (x * 8) & 8, simplify the multiply.
+ unsigned MulZeros = OpC->getAPInt().countTrailingZeros();
+ unsigned GCD = std::min(MulZeros, TZ);
+ APInt DivAmt = APInt::getOneBitSet(BitWidth, TZ - GCD);
+ SmallVector<const SCEV*, 4> MulOps;
+ MulOps.push_back(getConstant(OpC->getAPInt().lshr(GCD)));
+ MulOps.append(LHSMul->op_begin() + 1, LHSMul->op_end());
+ auto *NewMul = getMulExpr(MulOps, LHSMul->getNoWrapFlags());
+ ShiftedLHS = getUDivExpr(NewMul, getConstant(DivAmt));
+ }
+ }
+ if (!ShiftedLHS)
+ ShiftedLHS = getUDivExpr(LHS, MulCount);
return getMulExpr(
getZeroExtendExpr(
- getTruncateExpr(
- getUDivExactExpr(getSCEV(BO->LHS), MulCount),
+ getTruncateExpr(ShiftedLHS,
IntegerType::get(getContext(), BitWidth - LZ - TZ)),
BO->LHS->getType()),
MulCount);
@@ -7276,17 +7291,7 @@
// E.g. if Val is i8 -127 then the smallest value of X that satisfies (3)
// is i8 1, not i8 -127
- const auto *ModuloResult = getUDivExactExpr(Distance, Step);
-
- // Since SCEV does not have a URem node, we construct one using a truncate
- // and a zero extend.
-
- unsigned NarrowWidth = StepV.getBitWidth() - StepV.countTrailingZeros();
- auto *NarrowTy = IntegerType::get(getContext(), NarrowWidth);
- auto *WideTy = Distance->getType();
-
- const SCEV *Limit =
- getZeroExtendExpr(getTruncateExpr(ModuloResult, NarrowTy), WideTy);
+ const auto *Limit = getUDivExactExpr(Distance, Step);
return ExitLimit(Limit, Limit, false, Predicates);
}
}