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SCEV fix. In general, Add/Mul expressions should not inherit NSW/NUW.

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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
This commit is contained in:
Andrew Trick 2011-11-29 02:16:38 +00:00
parent 121d78f7e7
commit ecb35ece5c
3 changed files with 33 additions and 11 deletions
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16
lib/Analysis/ScalarEvolution.cpp
View File

@ -3592,6 +3592,12 @@ const SCEV *ScalarEvolution::createSCEV(Value *V) {
// 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 @@ const SCEV *ScalarEvolution::createSCEV(Value *V) {
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);

8
lib/Transforms/Scalar/IndVarSimplify.cpp
View File

@ -944,9 +944,13 @@ const SCEVAddRecExpr* WidenIV::GetExtendedOperandRecurrence(NarrowIVDefUse DU) {
else
return 0;
// When creating this AddExpr, don't apply the current operations NSW or NUW
// flags. This 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.
const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(
SE->getAddExpr(SE->getSCEV(DU.WideDef), ExtendOperExpr,
IsSigned ? SCEV::FlagNSW : SCEV::FlagNUW));
SE->getAddExpr(SE->getSCEV(DU.WideDef), ExtendOperExpr));
if (!AddRec || AddRec->getLoop() != L)
return 0;

20
test/Analysis/ScalarEvolution/nsw.ll
View File

@ -103,4 +103,22 @@ for.body.i.i: ; preds = %entry, %for.body.i.
; CHECK: Loop %for.body.i.i: max backedge-taken count is ((-4 + (-1 * %begin) + %end) /u 4)
_ZSt4fillIPiiEvT_S1_RKT0_.exit: ; preds = %for.body.i.i, %entry
ret void
}
}
; A single AddExpr exists for (%a + %b), which is not always <nsw>.
; CHECK: @addnsw
; CHECK-NOT: --> (%a + %b)<nsw>
define i32 @addnsw(i32 %a, i32 %b) nounwind ssp {
entry:
%tmp = add i32 %a, %b
%cmp = icmp sgt i32 %tmp, 0
br i1 %cmp, label %greater, label %exit
greater:
%tmp2 = add nsw i32 %a, %b
br label %exit
exit:
%result = phi i32 [ %a, %entry ], [ %tmp2, %greater ]
ret i32 %result
}