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Don't crash in SE dealing with ashr x, -1

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ScalarEvolution::getSignedRange uses ComputeNumSignBits from ValueTracking on
ashr instructions. ComputeNumSignBits can return zero, but this case was not
handled correctly by the code in getSignedRange which was calling:
  APInt::getSignedMinValue(BitWidth).ashr(NS - 1)
with NS = 0, resulting in an assertion failure in APInt::ashr.

Now, we just return the conservative result (as with NS == 1).

Another bug found by llvm-stress.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185955 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Hal Finkel
2013-07-09 18:16:16 +00:00
parent ab6ceab8a6
commit 033e0a94cb
2 changed files with 19 additions and 1 deletions
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lib/Analysis/ScalarEvolution.cpp
+1 -1
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@@ -3589,7 +3589,7 @@ ScalarEvolution::getSignedRange(const SCEV *S) {
if (!U->getValue()->getType()->isIntegerTy() && !TD)
return setSignedRange(U, ConservativeResult);
unsigned NS = ComputeNumSignBits(U->getValue(), TD);
if (NS == 1)
if (NS <= 1)
return setSignedRange(U, ConservativeResult);
return setSignedRange(U, ConservativeResult.intersectWith(
ConstantRange(APInt::getSignedMinValue(BitWidth).ashr(NS - 1),