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[Lint] Permit aliasing noalias readonly arguments

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Summary:
If two arguments are both readonly, then they have no memory dependency
that would violate noalias, even if they do actually overlap.

Reviewers: hfinkel, efriedma

Reviewed By: efriedma

Subscribers: efriedma, hiraditya, llvm-commits, tstellar

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D60239

llvm-svn: 359047
This commit is contained in:
Josh Stone 2019-04-23 23:43:47 +00:00
parent a799766d83
commit 5f651d5aba
2 changed files with 46 additions and 2 deletions
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8
lib/Analysis/Lint.cpp
View File

@ -267,10 +267,14 @@ void Lint::visitCallSite(CallSite CS) {
if (Formal->hasNoAliasAttr() && Actual->getType()->isPointerTy()) {
AttributeList PAL = CS.getAttributes();
unsigned ArgNo = 0;
for (CallSite::arg_iterator BI = CS.arg_begin(); BI != AE; ++BI) {
for (CallSite::arg_iterator BI = CS.arg_begin(); BI != AE;
++BI, ++ArgNo) {
// 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))
if (PAL.hasParamAttribute(ArgNo, Attribute::ByVal))
continue;
// If both arguments are readonly, they have no dependence.
if (Formal->onlyReadsMemory() && CS.onlyReadsMemory(ArgNo))
continue;
if (AI != BI && (*BI)->getType()->isPointerTy()) {
AliasResult Result = AA->alias(*AI, *BI);

40
test/Analysis/Lint/noalias-readonly.ll Normal file
View File

@ -0,0 +1,40 @@
; RUN: opt < %s -lint -disable-output 2>&1 | FileCheck %s
declare void @f1(i8* noalias readonly, i8*)
define void @f2(i8* %a) {
entry:
call void @f1(i8* %a, i8* %a)
ret void
}
; Lint should complain about us passing %a to both arguments, since the noalias
; argument may depend on writes to the other.
; CHECK: Unusual: noalias argument aliases another argument
; CHECK-NEXT: call void @f1(i8* %a, i8* %a)
declare void @f3(i8* noalias, i8* readonly)
define void @f4(i8* %a) {
entry:
call void @f3(i8* %a, i8* %a)
ret void
}
; Lint should complain about us passing %a to both arguments, since writes to
; the noalias argument may cause a dependency for the other.
; CHECK: Unusual: noalias argument aliases another argument
; CHECK-NEXT: call void @f3(i8* %a, i8* %a)
declare void @f5(i8* noalias readonly, i8* readonly)
define void @f6(i8* %a) {
entry:
call void @f5(i8* %a, i8* %a)
ret void
}
; Lint should not complain about passing %a to both arguments even if one is
; noalias, since they are both readonly and thus have no dependence.
; CHECK-NOT: Unusual: noalias argument aliases another argument
; CHECK-NOT: call void @f5(i8* %a, i8* %a)