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When merging MustAlias and PartialAlias, chose PartialAlias instead

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of conservatively choosing MayAlias.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@132579 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman 2011-06-03 20:17:36 +00:00
parent abb2512205
commit 965fefa1ad
2 changed files with 60 additions and 10 deletions
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31
lib/Analysis/BasicAliasAnalysis.cpp
View File

@ -949,6 +949,19 @@ BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, uint64_t V1Size,
return MayAlias;
}
static AliasAnalysis::AliasResult
MergeAliasResults(AliasAnalysis::AliasResult A, AliasAnalysis::AliasResult B) {
// If the results agree, take it.
if (A == B)
return A;
// A mix of PartialAlias and MustAlias is PartialAlias.
if ((A == AliasAnalysis::PartialAlias && B == AliasAnalysis::MustAlias) ||
(B == AliasAnalysis::PartialAlias && A == AliasAnalysis::MustAlias))
return AliasAnalysis::PartialAlias;
// Otherwise, we don't know anything.
return AliasAnalysis::MayAlias;
}
/// aliasSelect - Provide a bunch of ad-hoc rules to disambiguate a Select
/// instruction against another.
AliasAnalysis::AliasResult
@ -975,9 +988,7 @@ BasicAliasAnalysis::aliasSelect(const SelectInst *SI, uint64_t SISize,
AliasResult ThisAlias =
aliasCheck(SI->getFalseValue(), SISize, SITBAAInfo,
SI2->getFalseValue(), V2Size, V2TBAAInfo);
if (ThisAlias != Alias)
return MayAlias;
return Alias;
return MergeAliasResults(ThisAlias, Alias);
}
// If both arms of the Select node NoAlias or MustAlias V2, then returns
@ -994,9 +1005,7 @@ BasicAliasAnalysis::aliasSelect(const SelectInst *SI, uint64_t SISize,
AliasResult ThisAlias =
aliasCheck(V2, V2Size, V2TBAAInfo, SI->getFalseValue(), SISize, SITBAAInfo);
if (ThisAlias != Alias)
return MayAlias;
return Alias;
return MergeAliasResults(ThisAlias, Alias);
}
// aliasPHI - Provide a bunch of ad-hoc rules to disambiguate a PHI instruction
@ -1026,8 +1035,9 @@ BasicAliasAnalysis::aliasPHI(const PHINode *PN, uint64_t PNSize,
aliasCheck(PN->getIncomingValue(i), PNSize, PNTBAAInfo,
PN2->getIncomingValueForBlock(PN->getIncomingBlock(i)),
V2Size, V2TBAAInfo);
if (ThisAlias != Alias)
return MayAlias;
Alias = MergeAliasResults(ThisAlias, Alias);
if (Alias == MayAlias)
break;
}
return Alias;
}
@ -1065,8 +1075,9 @@ BasicAliasAnalysis::aliasPHI(const PHINode *PN, uint64_t PNSize,
AliasResult ThisAlias = aliasCheck(V2, V2Size, V2TBAAInfo,
V, PNSize, PNTBAAInfo);
if (ThisAlias != Alias || ThisAlias == MayAlias)
return MayAlias;
Alias = MergeAliasResults(ThisAlias, Alias);
if (Alias == MayAlias)
break;
}
return Alias;

39
test/Analysis/BasicAA/must-and-partial.ll Normal file
View File

@ -0,0 +1,39 @@
; RUN: opt < %s -basicaa -aa-eval -print-all-alias-modref-info |& FileCheck %s
; When merging MustAlias and PartialAlias, merge to PartialAlias
; instead of MayAlias.
target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
; CHECK: PartialAlias: i16* %bigbase0, i8* %phi
define i8 @test0(i8* %base, i1 %x) {
entry:
%baseplusone = getelementptr i8* %base, i64 1
br i1 %x, label %red, label %green
red:
br label %green
green:
%phi = phi i8* [ %baseplusone, %red ], [ %base, %entry ]
store i8 0, i8* %phi
%bigbase0 = bitcast i8* %base to i16*
store i16 -1, i16* %bigbase0
%loaded = load i8* %phi
ret i8 %loaded
}
; CHECK: PartialAlias: i16* %bigbase1, i8* %sel
define i8 @test1(i8* %base, i1 %x) {
entry:
%baseplusone = getelementptr i8* %base, i64 1
%sel = select i1 %x, i8* %baseplusone, i8* %base
store i8 0, i8* %sel
%bigbase1 = bitcast i8* %base to i16*
store i16 -1, i16* %bigbase1
%loaded = load i8* %sel
ret i8 %loaded
}