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[BasicAA] Compare GEP indices based on value (Fix PR27418)

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Equivalent GEP indices with different types are treated as different
indices altogether, leading to an incorrect AA result. Fix the issue
by comparing indices based on their values.

Thanks to Mikael Holmén for reporting the issue!

Differential Revision: http://reviews.llvm.org/D19935

llvm-svn: 269197
This commit is contained in:
Vedant Kumar 2016-05-11 15:45:43 +00:00
parent b13f3435de
commit 641c55ebd0
2 changed files with 10 additions and 1 deletions
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2
lib/Analysis/BasicAliasAnalysis.cpp
View File

@ -847,7 +847,7 @@ static AliasResult aliasSameBasePointerGEPs(const GEPOperator *GEP1,
// If the last (struct) indices are constants and are equal, the other indices
// might be also be dynamically equal, so the GEPs can alias.
if (C1 && C2 && C1 == C2)
if (C1 && C2 && C1->getSExtValue() == C2->getSExtValue())
return MayAlias;
// Find the last-indexed type of the GEP, i.e., the type you'd get if

9
test/Analysis/BasicAA/struct-geps.ll
View File

@ -162,3 +162,12 @@ define void @test_struct_in_array(%struct2* %st, i64 %i, i64 %j, i64 %k) {
%y = getelementptr %struct2, %struct2* %st, i32 0, i32 0, i32 1, i32 1
ret void
}
; PR27418 - Treat GEP indices with the same value but different types the same
; CHECK-LABEL: test_different_index_types
; CHECK: MustAlias: i16* %tmp1, i16* %tmp2
define void @test_different_index_types([2 x i16]* %arr) {
%tmp1 = getelementptr [2 x i16], [2 x i16]* %arr, i16 0, i32 1
%tmp2 = getelementptr [2 x i16], [2 x i16]* %arr, i16 0, i16 1
ret void
}