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[GMR] Be a bit smarter about which globals don't alias when doing recursive lookups

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Should hopefully fix the remainder of PR24288.

Differential Revision: http://reviews.llvm.org/D11900

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@244575 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Michael Kuperstein 2015-08-11 08:06:44 +00:00
parent f52c83762e
commit ea7c99472d
2 changed files with 30 additions and 11 deletions
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30
lib/Analysis/IPA/GlobalsModRef.cpp
View File

@ -717,12 +717,23 @@ bool GlobalsModRef::isNonEscapingGlobalNoAlias(const GlobalValue *GV,
if (InputGV == GV)
return false;
// FIXME: It would be good to handle other obvious no-alias cases here, but
// it isn't clear how to do so reasonbly without building a small version
// of BasicAA into this code. We could recurse into AliasAnalysis::alias
// here but that seems likely to go poorly as we're inside the
// implementation of such a query. Until then, just conservatievly retun
// false.
// Distinct GlobalVariables never alias, unless overriden or zero-sized.
// FIXME: The condition can be refined, but be conservative for now.
auto *GVar = dyn_cast<GlobalVariable>(GV);
auto *InputGVar = dyn_cast<GlobalVariable>(InputGV);
if (GVar && InputGVar &&
!GVar->isDeclaration() && !InputGVar->isDeclaration() &&
!GVar->mayBeOverridden() && !InputGVar->mayBeOverridden()) {
Type *GVType = GVar->getInitializer()->getType();
Type *InputGVType = InputGVar->getInitializer()->getType();
if (GVType->isSized() && InputGVType->isSized() &&
(DL->getTypeAllocSize(GVType) > 0) &&
(DL->getTypeAllocSize(InputGVType) > 0))
continue;
}
// Conservatively return false, even though we could be smarter
// (e.g. look through GlobalAliases).
return false;
}
@ -767,7 +778,12 @@ bool GlobalsModRef::isNonEscapingGlobalNoAlias(const GlobalValue *GV,
continue;
}
// Unknown instruction, bail.
// FIXME: It would be good to handle other obvious no-alias cases here, but
// it isn't clear how to do so reasonbly without building a small version
// of BasicAA into this code. We could recurse into AliasAnalysis::alias
// here but that seems likely to go poorly as we're inside the
// implementation of such a query. Until then, just conservatievly retun
// false.
return false;
} while (!Inputs.empty());

11
test/Analysis/GlobalsModRef/nonescaping-noalias.ll
View File

@ -61,7 +61,9 @@ entry:
ret i32 %v
}
define i32 @test4(i32* %param, i32 %n, i1 %c1, i1 %c2) {
@g3 = internal global i32 1
define i32 @test4(i32* %param, i32 %n, i1 %c1, i1 %c2, i1 %c3) {
; Ensure that we can fold a store to a load of a global across a store to
; the pointer loaded from that global even when the load is behind PHIs and
; selects, and there is a mixture of a load and another global or argument.
@ -77,14 +79,15 @@ entry:
store i32 42, i32* @g1
%ptr1 = load i32*, i32** @g2
%ptr2 = select i1 %c1, i32* %ptr1, i32* %param
%ptr3 = select i1 %c3, i32* %ptr2, i32* @g3
br label %loop
loop:
%iv = phi i32 [ 0, %entry ], [ %inc, %loop ]
%ptr = phi i32* [ %ptr2, %entry ], [ %ptr4, %loop ]
%ptr = phi i32* [ %ptr3, %entry ], [ %ptr5, %loop ]
store i32 7, i32* %ptr
%ptr3 = load i32*, i32** @g2
%ptr4 = select i1 %c2, i32* %ptr3, i32* %call
%ptr4 = load i32*, i32** @g2
%ptr5 = select i1 %c2, i32* %ptr4, i32* %call
%inc = add i32 %iv, 1
%test = icmp slt i32 %inc, %n
br i1 %test, label %loop, label %exit