Commit c0682840 authored by Bjorn Pettersson's avatar Bjorn Pettersson
Browse files

[Lint] Permit aliasing noalias and readnone arguments 

If an argument is readnone we know that it isn't dereferenced. Then
it should be OK if that argument alias with a noalias argument.

Differential Revision: https://reviews.llvm.org/D157737
parent a5925eee

llvm/lib/Analysis/Lint.cpp

+4 −0
Original line number Diff line number Diff line
@@ -235,6 +235,10 @@ void Lint::visitCallBase(CallBase &I) { 
            // If both arguments are readonly, they have no dependence.

            if (Formal->onlyReadsMemory() && I.onlyReadsMemory(ArgNo))

              continue;

            // Skip readnone arguments since those are guaranteed not to be

            // dereferenced anyway.

            if (I.doesNotAccessMemory(ArgNo))

              continue;

            if (AI != BI && (*BI)->getType()->isPointerTy()) {

              AliasResult Result = AA->alias(*AI, *BI);

              Check(Result != AliasResult::MustAlias &&

llvm/test/Analysis/Lint/noalias-byval.ll

+1 −1
Original line number Diff line number Diff line
@@ -8,7 +8,7 @@ declare void @llvm.memcpy.p0.p0.i32(ptr nocapture writeonly, ptr nocapture reado 
; Function Attrs: argmemonly nounwind

declare void @llvm.memset.p0.i32(ptr nocapture writeonly, i8, i32, i1) #0



declare void @f1(ptr noalias nocapture sret(%s), ptr nocapture readnone)

declare void @f1(ptr noalias nocapture sret(%s), ptr nocapture)



define void @f2() {

entry:

llvm/test/Analysis/Lint/noalias-readnone.ll

0 → 100644
+14 −0
Original line number Diff line number Diff line 
; RUN: opt < %s -passes=lint -disable-output 2>&1 | FileCheck --allow-empty %s



declare void @foo1(ptr noalias, ptr readnone)



define void @test1(ptr %a) {

entry:

  call void @foo1(ptr %a, ptr %a)

  ret void

}



; Lint should not complain about passing %a to both arguments even if one is

; noalias, since the second argument is readnone.

; CHECK-NOT: Unusual: noalias argument aliases another argument

; CHECK-NOT: call void @foo1(ptr %a, ptr %a)