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Fixes PR2395. Looking for a constant in a GEP tail (when the first GEP

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is longer than the second one) should stop after finding one. Added break 
instruction guarantees it. It also changes difference between offsets to 
absolute value of this difference in the condition.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@51875 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Wojciech Matyjewicz 2008-06-02 17:26:12 +00:00
parent 370a25c16a
commit 98e3a6829a
2 changed files with 22 additions and 1 deletions
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8
lib/Analysis/BasicAliasAnalysis.cpp
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@ -687,7 +687,7 @@ BasicAliasAnalysis::CheckGEPInstructions(
if (isa<ConstantInt>(GEP1Ops[i]) &&
!cast<ConstantInt>(GEP1Ops[i])->isZero()) {
// Yup, there's a constant in the tail. Set all variables to
// constants in the GEP instruction to make it suiteable for
// constants in the GEP instruction to make it suitable for
// TargetData::getIndexedOffset.
for (i = 0; i != MaxOperands; ++i)
if (!isa<ConstantInt>(GEP1Ops[i]))
@ -702,9 +702,15 @@ BasicAliasAnalysis::CheckGEPInstructions(
int64_t Offset2 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
MinOperands);
// Make sure we compare the absolute difference.
if (Offset1 > Offset2)
std::swap(Offset1, Offset2);
// If the tail provided a bit enough offset, return noalias!
if ((uint64_t)(Offset2-Offset1) >= SizeMax)
return NoAlias;
// Otherwise break - we don't look for another constant in the tail.
break;
}
}

15
test/Analysis/BasicAA/2008-06-02-GEPTailCrash.ll Normal file
View File

@ -0,0 +1,15 @@
; RUN: llvm-as < %s | opt -gvn -disable-output
; PR2395
target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:32:32"
target triple = "i686-pc-linux-gnu"
%struct.S291 = type <{ %union.anon, i32 }>
%union.anon = type { }
@a291 = external global [5 x %struct.S291] ; <[5 x %struct.S291]*> [#uses=2]
define void @test291() nounwind {
entry:
store i32 1138410269, i32* getelementptr ([5 x %struct.S291]* @a291, i32 0, i32 2, i32 1)
%tmp54 = load i32* bitcast (%struct.S291* getelementptr ([5 x %struct.S291]* @a291, i32 0, i32 2) to i32*), align 4 ; <i32> [#uses=0]
unreachable
}