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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.

llvm-svn: 185955
This commit is contained in:
Hal Finkel 2013-07-09 18:16:16 +00:00
parent a36d20b589
commit 9cb3ba300f
2 changed files with 19 additions and 1 deletions
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2
lib/Analysis/ScalarEvolution.cpp
View File

@ -3589,7 +3589,7 @@ ScalarEvolution::getSignedRange(const SCEV *S) {
if (!U->getValue()->getType()->isIntegerTy() && !TD) if (!U->getValue()->getType()->isIntegerTy() && !TD)
return setSignedRange(U, ConservativeResult); return setSignedRange(U, ConservativeResult);
unsigned NS = ComputeNumSignBits(U->getValue(), TD); unsigned NS = ComputeNumSignBits(U->getValue(), TD);
if (NS == 1) if (NS <= 1)
return setSignedRange(U, ConservativeResult); return setSignedRange(U, ConservativeResult);
return setSignedRange(U, ConservativeResult.intersectWith( return setSignedRange(U, ConservativeResult.intersectWith(
ConstantRange(APInt::getSignedMinValue(BitWidth).ashr(NS - 1), ConstantRange(APInt::getSignedMinValue(BitWidth).ashr(NS - 1),

18
test/CodeGen/PowerPC/ashr-neg1.ll Normal file
View File

@ -0,0 +1,18 @@
; RUN: llc -mtriple=powerpc64-unknown-linux-gnu -mcpu=pwr7 < %s
target triple = "powerpc64-unknown-linux-gnu"
define void @autogen_SD30723(i32) {
BB:
br label %CF80
CF80: ; preds = %CF80, %BB
%B = ashr i32 %0, -1
br i1 undef, label %CF80, label %CF84
CF84: ; preds = %CF84, %CF80
%Cmp62 = icmp sge i32 undef, %B
br i1 %Cmp62, label %CF84, label %CF85
CF85: ; preds = %CF85, %CF84
br label %CF85
}