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[BasicAA] Treat llvm.assume as not accessing memory in getModRefBehavior(Function)

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Reviewers: dberlin, chandlerc, hfinkel, reames, sanjoy

Subscribers: mcrosier, llvm-commits

Differential Revision: http://reviews.llvm.org/D19730

llvm-svn: 268068
This commit is contained in:
Geoff Berry 2016-04-29 17:18:28 +00:00
parent 8340e109f7
commit 9481cf55ae
2 changed files with 23 additions and 0 deletions
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6
lib/Analysis/BasicAliasAnalysis.cpp
View File

@ -575,6 +575,12 @@ FunctionModRefBehavior BasicAAResult::getModRefBehavior(const Function *F) {
if (F->doesNotAccessMemory())
return FMRB_DoesNotAccessMemory;
// While the assume intrinsic is marked as arbitrarily writing so that
// proper control dependencies will be maintained, it never aliases any
// particular memory location.
if (F->getIntrinsicID() == Intrinsic::assume)
return FMRB_DoesNotAccessMemory;
FunctionModRefBehavior Min = FMRB_UnknownModRefBehavior;
// If the function declares it only reads memory, go with that.

17
test/Transforms/Util/MemorySSA/assume.ll Normal file
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@ -0,0 +1,17 @@
; RUN: opt -basicaa -print-memoryssa -verify-memoryssa -analyze < %s 2>&1 | FileCheck %s
;
; Ensures that assumes are treated as not reading or writing memory.
declare void @llvm.assume(i1)
define i32 @foo(i32* %a, i32* %b, i1 %c) {
; CHECK: 1 = MemoryDef(liveOnEntry)
; CHECK-NEXT: store i32 4
store i32 4, i32* %a, align 4
; CHECK: call void @llvm.assume
call void @llvm.assume(i1 %c)
; CHECK: MemoryUse(1)
; CHECK-NEXT: %1 = load i32
%1 = load i32, i32* %a, align 4
ret i32 %1
}