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[Lint] Don't warn about noalias argument aliasing if other argument is byval 

Summary:
When using byval, the data is effectively copied as part of the call
anyway, so we aren't actually passing the pointer and thus there is no
reason to issue a warning.

Reviewers: rnk

Reviewed By: rnk

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D40118

llvm-svn: 321478
This commit is contained in:
Mikael Holmen 2017-12-27 08:48:33 +00:00
parent f4811ebc39
commit fb2fd20f50
2 changed files with 58 additions and 2 deletions
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12
llvm/lib/Analysis/Lint.cpp
View File

@ -265,13 +265,21 @@ void Lint::visitCallSite(CallSite CS) {
// Check that noalias arguments don't alias other arguments. This is
// not fully precise because we don't know the sizes of the dereferenced
// memory regions.
if (Formal->hasNoAliasAttr() && Actual->getType()->isPointerTy())
for (CallSite::arg_iterator BI = CS.arg_begin(); BI != AE; ++BI)
if (Formal->hasNoAliasAttr() && Actual->getType()->isPointerTy()) {
AttributeList PAL = CS.getAttributes();
unsigned ArgNo = 0;
for (CallSite::arg_iterator BI = CS.arg_begin(); BI != AE; ++BI) {
// Skip ByVal arguments since they will be memcpy'd to the callee's
// stack so we're not really passing the pointer anyway.
if (PAL.hasParamAttribute(ArgNo++, Attribute::ByVal))
continue;
if (AI != BI && (*BI)->getType()->isPointerTy()) {
AliasResult Result = AA->alias(*AI, *BI);
Assert(Result != MustAlias && Result != PartialAlias,
"Unusual: noalias argument aliases another argument", &I);
}
}
}
// Check that an sret argument points to valid memory.
if (Formal->hasStructRetAttr() && Actual->getType()->isPointerTy()) {

48
llvm/test/Analysis/Lint/noalias-byval.ll Normal file
View File

@ -0,0 +1,48 @@
; RUN: opt < %s -lint -disable-output 2>&1 | FileCheck %s
%s = type { i8 }
; Function Attrs: argmemonly nounwind
declare void @llvm.memcpy.p0i8.p0i8.i32(i8* nocapture writeonly, i8* nocapture readonly, i32, i32, i1) #0
; Function Attrs: argmemonly nounwind
declare void @llvm.memset.p0i8.i8.i32(i8* nocapture writeonly, i8, i32, i32, i1) #0
declare void @f1(%s* noalias nocapture sret, %s* nocapture readnone)
define void @f2() {
entry:
%c = alloca %s
%tmp = alloca %s
%0 = bitcast %s* %c to i8*
%1 = bitcast %s* %tmp to i8*
call void @llvm.memset.p0i8.i8.i32(i8* %0, i8 0, i32 1, i32 1, i1 false)
call void @f1(%s* sret %c, %s* %c)
ret void
}
; Lint should complain about us passing %c to both arguments since one of them
; is noalias.
; CHECK: Unusual: noalias argument aliases another argument
; CHECK-NEXT: call void @f1(%s* sret %c, %s* %c)
declare void @f3(%s* noalias nocapture sret, %s* byval nocapture readnone)
define void @f4() {
entry:
%c = alloca %s
%tmp = alloca %s
%0 = bitcast %s* %c to i8*
%1 = bitcast %s* %tmp to i8*
call void @llvm.memset.p0i8.i8.i32(i8* %0, i8 0, i32 1, i32 1, i1 false)
call void @f3(%s* sret %c, %s* byval %c)
ret void
}
; Lint should not complain about passing %c to both arguments even if one is
; noalias, since the other one is byval, effectively copying the data to the
; stack instead of passing the pointer itself.
; CHECK-NOT: Unusual: noalias argument aliases another argument
; CHECK-NOT: call void @f3(%s* sret %c, %s* %c)
attributes #0 = { argmemonly nounwind }