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Fix: CFLAA -- Mark no-args returns as unknown

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Prior to this patch, we hadn't been marking StratifiedSets with the
appropriate StratifiedAttrs when handling the result of no-args call
instructions. This caused us to report NoAlias when handed, for
example, an escaped alloca and a result from an opaque function. Now we
properly mark the return value of said functions.

Thanks again to Chandler, Richard, and Nick for pinging me about this.

Differential review: http://reviews.llvm.org/D12408

llvm-svn: 246240
This commit is contained in:
George Burgess IV 2015-08-28 00:16:18 +00:00
parent fa4ecb4b9a
commit 68b36e01da
2 changed files with 30 additions and 0 deletions
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10
llvm/lib/Analysis/CFLAliasAnalysis.cpp
View File

@ -398,6 +398,8 @@ public:
}
template <typename InstT> void visitCallLikeInst(InstT &Inst) {
// TODO: Add support for noalias args/all the other fun function attributes
// that we can tack on.
SmallVector<Function *, 4> Targets;
if (getPossibleTargets(&Inst, Targets)) {
if (tryInterproceduralAnalysis(Targets, &Inst, Inst.arg_operands()))
@ -406,8 +408,16 @@ public:
Output.clear();
}
// Because the function is opaque, we need to note that anything
// could have happened to the arguments, and that the result could alias
// just about anything, too.
// The goal of the loop is in part to unify many Values into one set, so we
// don't care if the function is void there.
for (Value *V : Inst.arg_operands())
Output.push_back(Edge(&Inst, V, EdgeType::Assign, AttrAll));
if (Inst.getNumArgOperands() == 0 &&
Inst.getType() != Type::getVoidTy(Inst.getContext()))
Output.push_back(Edge(&Inst, &Inst, EdgeType::Assign, AttrAll));
}
void visitCallInst(CallInst &Inst) { visitCallLikeInst(Inst); }

20
llvm/test/Analysis/CFLAliasAnalysis/opaque-call-alias.ll Normal file
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@ -0,0 +1,20 @@
; We previously had a case where we would put results from a no-args call in
; its own stratified set. This would make cases like the one in @test say that
; nothing (except %Escapes and %Arg) can alias
; RUN: opt < %s -cfl-aa -aa-eval -print-may-aliases -disable-output 2>&1 | FileCheck %s
; CHECK: Function: test
; CHECK: MayAlias: i8* %Arg, i8* %Escapes
; CHECK: MayAlias: i8* %Arg, i8* %Retrieved
; CHECK: MayAlias: i8* %Escapes, i8* %Retrieved
define void @test(i8* %Arg) {
%Noalias = alloca i8
%Escapes = alloca i8
call void @set_thepointer(i8* %Escapes)
%Retrieved = call i8* @get_thepointer()
ret void
}
declare void @set_thepointer(i8* %P)
declare i8* @get_thepointer()