SCEV fix. In general, Add/Mul expressions should not inherit NSW/NUW.
This reverts r139450, fixes r139453, and adds much needed comments and a
unit test.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@145367 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index a054801..ff85906 100644
--- a/lib/Analysis/ScalarEvolution.cpp
+++ b/lib/Analysis/ScalarEvolution.cpp
@@ -3592,6 +3592,12 @@
// because it leads to N-1 getAddExpr calls for N ultimate operands.
// Instead, gather up all the operands and make a single getAddExpr call.
// LLVM IR canonical form means we need only traverse the left operands.
+ //
+ // Don't apply this instruction's NSW or NUW flags to the new
+ // expression. The instruction may be guarded by control flow that the
+ // no-wrap behavior depends on. Non-control-equivalent instructions can be
+ // mapped to the same SCEV expression, and it would be incorrect to transfer
+ // NSW/NUW semantics to those operations.
SmallVector<const SCEV *, 4> AddOps;
AddOps.push_back(getSCEV(U->getOperand(1)));
for (Value *Op = U->getOperand(0); ; Op = U->getOperand(0)) {
@@ -3606,16 +3612,10 @@
AddOps.push_back(Op1);
}
AddOps.push_back(getSCEV(U->getOperand(0)));
- SCEV::NoWrapFlags Flags = SCEV::FlagAnyWrap;
- OverflowingBinaryOperator *OBO = cast<OverflowingBinaryOperator>(V);
- if (OBO->hasNoSignedWrap())
- Flags = setFlags(Flags, SCEV::FlagNSW);
- if (OBO->hasNoUnsignedWrap())
- Flags = setFlags(Flags, SCEV::FlagNUW);
- return getAddExpr(AddOps, Flags);
+ return getAddExpr(AddOps);
}
case Instruction::Mul: {
- // See the Add code above.
+ // Don't transfer NSW/NUW for the same reason as AddExpr.
SmallVector<const SCEV *, 4> MulOps;
MulOps.push_back(getSCEV(U->getOperand(1)));
for (Value *Op = U->getOperand(0);