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BasicAA: We need to check both access sizes when comparing a gep and an
underlying object of unknown size. Fixes PR18460. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@199351 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -1009,7 +1009,15 @@ BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, uint64_t V1Size,
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return NoAlias;
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return NoAlias;
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}
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}
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} else {
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} else {
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if (V1Size != UnknownSize) {
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// We have the situation where:
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// + +
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// | BaseOffset |
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// ---------------->|
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// |-->V1Size |-------> V2Size
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// GEP1 V2
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// We need to know that V2Size is not unknown, otherwise we might have
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// stripped a gep with negative index ('gep <ptr>, -1, ...).
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if (V1Size != UnknownSize && V2Size != UnknownSize) {
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if (-(uint64_t)GEP1BaseOffset < V1Size)
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if (-(uint64_t)GEP1BaseOffset < V1Size)
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return PartialAlias;
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return PartialAlias;
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return NoAlias;
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return NoAlias;
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33
test/Analysis/BasicAA/noalias-bugs.ll
Normal file
33
test/Analysis/BasicAA/noalias-bugs.ll
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@ -0,0 +1,33 @@
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; RUN: opt -S -basicaa -dse < %s | FileCheck %s
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target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
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target triple = "x86_64-unknown-linux-gnu"
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; We incorrectly returned noalias in the example below for "ptr.64" and
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; "either_ptr.64".
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; PR18460
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%nested = type { %nested.i64 }
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%nested.i64 = type { i64 }
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define i64 @testcase(%nested * noalias %p1, %nested * noalias %p2,
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i32 %a, i32 %b) {
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%ptr = getelementptr inbounds %nested* %p1, i64 -1, i32 0
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%ptr.64 = getelementptr inbounds %nested.i64* %ptr, i64 0, i32 0
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%ptr2= getelementptr inbounds %nested* %p2, i64 0, i32 0
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%cmp = icmp ult i32 %a, %b
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%either_ptr = select i1 %cmp, %nested.i64* %ptr2, %nested.i64* %ptr
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%either_ptr.64 = getelementptr inbounds %nested.i64* %either_ptr, i64 0, i32 0
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; Because either_ptr.64 and ptr.64 can alias (we used to return noalias)
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; elimination of the first store is not valid.
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; CHECK: store i64 2
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; CHECK: load
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; CHECK; store i64 1
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store i64 2, i64* %ptr.64, align 8
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%r = load i64* %either_ptr.64, align 8
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store i64 1, i64* %ptr.64, align 8
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ret i64 %r
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}
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