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[Attributor] Implement "noalias" callsite argument deduction 

Summary: Now, `nocapture` is deduced in Attributor therefore, this patch introduces deduction for `noalias` callsite argument using `nocapture`.

Reviewers: jdoerfert, sstefan1

Reviewed By: jdoerfert

Subscribers: lebedev.ri, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D67286

llvm-svn: 371590
This commit is contained in:
Hideto Ueno 2019-09-11 07:00:33 +00:00
parent 3736764657
commit 1d68ed8c24
2 changed files with 126 additions and 4 deletions
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54
llvm/lib/Transforms/IPO/Attributor.cpp
View File

@ -1672,8 +1672,9 @@ struct AANoAliasFloating final : AANoAliasImpl {
/// See AbstractAttribute::initialize(...).
void initialize(Attributor &A) override {
// TODO: It isn't sound to initialize as the same with `AANoAliasImpl`
// because `noalias` may not be valid in the current position.
AANoAliasImpl::initialize(A);
if (isa<AllocaInst>(getAnchorValue()))
indicateOptimisticFixpoint();
}
/// See AbstractAttribute::updateImpl(...).
@ -1711,8 +1712,53 @@ struct AANoAliasCallSiteArgument final : AANoAliasImpl {
/// See AbstractAttribute::updateImpl(...).
ChangeStatus updateImpl(Attributor &A) override {
// TODO: Implement this.
return indicatePessimisticFixpoint();
// We can deduce "noalias" if the following conditions hold.
// (i) Associated value is assumed to be noalias in the definition.
// (ii) Associated value is assumed to be no-capture in all the uses
// possibly executed before this callsite.
// (iii) There is no other pointer argument which could alias with the
// value.
const Value &V = getAssociatedValue();
const IRPosition IRP = IRPosition::value(V);
// (i) Check whether noalias holds in the definition.
auto &NoAliasAA = A.getAAFor<AANoAlias>(*this, IRP);
if (!NoAliasAA.isAssumedNoAlias())
return indicatePessimisticFixpoint();
LLVM_DEBUG(dbgs() << "[Attributor][AANoAliasCSArg] " << V
<< " is assumed NoAlias in the definition\n");
// (ii) Check whether the value is captured in the scope using AANoCapture.
// FIXME: This is conservative though, it is better to look at CFG and
// check only uses possibly executed before this callsite.
auto &NoCaptureAA = A.getAAFor<AANoCapture>(*this, IRP);
if (!NoCaptureAA.isAssumedNoCaptureMaybeReturned())
return indicatePessimisticFixpoint();
// (iii) Check there is no other pointer argument which could alias with the
// value.
ImmutableCallSite ICS(&getAnchorValue());
for (unsigned i = 0; i < ICS.getNumArgOperands(); i++) {
if (getArgNo() == (int)i)
continue;
const Value *ArgOp = ICS.getArgOperand(i);
if (!ArgOp->getType()->isPointerTy())
continue;
// TODO: Use AliasAnalysis
// AAResults& AAR = ..;
// if(AAR.isNoAlias(&getAssociatedValue(), ArgOp))
// return indicatePessimitisicFixpoint();
return indicatePessimisticFixpoint();
}
return ChangeStatus::UNCHANGED;
}
/// See AbstractAttribute::trackStatistics()

76
llvm/test/Transforms/FunctionAttrs/noalias_returned.ll
View File

@ -191,3 +191,79 @@ define void @test11(i8* noalias %a) {
tail call void @test11_helper(i8* %a, i8* %a)
ret void
}
; TEST 12
; CallSite Argument
declare void @use_nocapture(i8* nocapture)
declare void @use(i8*)
define void @test12_1() {
; CHECK-LABEL: @test12_1(
; CHECK-NEXT: [[A:%.*]] = alloca i8, align 4
; CHECK-NEXT: [[B:%.*]] = tail call noalias i8* @malloc(i64 4)
; CHECK-NEXT: tail call void @use_nocapture(i8* noalias nonnull align 4 dereferenceable(1) [[A]])
; CHECK-NEXT: tail call void @use_nocapture(i8* noalias nonnull align 4 dereferenceable(1) [[A]])
; CHECK-NEXT: tail call void @use_nocapture(i8* noalias [[B]])
; CHECK-NEXT: tail call void @use_nocapture(i8* noalias [[B]])
; CHECK-NEXT: ret void
;
%A = alloca i8, align 4
%B = tail call noalias i8* @malloc(i64 4)
tail call void @use_nocapture(i8* %A)
tail call void @use_nocapture(i8* %A)
tail call void @use_nocapture(i8* %B)
tail call void @use_nocapture(i8* %B)
ret void
}
define void @test12_2(){
; CHECK-LABEL: @test12_2(
; CHECK-NEXT: [[A:%.*]] = tail call noalias i8* @malloc(i64 4)
; FIXME: This should be @use_nocapture(i8* noalias [[A]])
; CHECK-NEXT: tail call void @use_nocapture(i8* [[A]])
; FIXME: This should be @use_nocapture(i8* noalias [[A]])
; CHECK-NEXT: tail call void @use_nocapture(i8* [[A]])
; CHECK-NEXT: tail call void @use(i8* [[A]])
; CHECK-NEXT: tail call void @use_nocapture(i8* [[A]])
; CHECK-NEXT: ret void
;
%A = tail call noalias i8* @malloc(i64 4)
tail call void @use_nocapture(i8* %A)
tail call void @use_nocapture(i8* %A)
tail call void @use(i8* %A)
tail call void @use_nocapture(i8* %A)
ret void
}
declare void @two_args(i8* nocapture , i8* nocapture)
define void @test12_3(){
; CHECK-LABEL: @test12_3(
%A = tail call noalias i8* @malloc(i64 4)
; CHECK: tail call void @two_args(i8* %A, i8* %A)
tail call void @two_args(i8* %A, i8* %A)
ret void
}
define void @test12_4(){
; CHECK-LABEL: @test12_4(
%A = tail call noalias i8* @malloc(i64 4)
%B = tail call noalias i8* @malloc(i64 4)
%A_0 = getelementptr i8, i8* %A, i64 0
%A_1 = getelementptr i8, i8* %A, i64 1
%B_0 = getelementptr i8, i8* %B, i64 0
; FIXME: This should be @two_args(i8* noalias %A, i8* noalias %B)
; CHECK: tail call void @two_args(i8* %A, i8* %B)
tail call void @two_args(i8* %A, i8* %B)
; CHECK: tail call void @two_args(i8* %A, i8* %A_0)
tail call void @two_args(i8* %A, i8* %A_0)
; CHECK: tail call void @two_args(i8* %A, i8* %A_1)
tail call void @two_args(i8* %A, i8* %A_1)
; FIXME: This should be @two_args(i8* noalias %A_0, i8* noalias %B_0)
; CHECK: tail call void @two_args(i8* %A_0, i8* %B_0)
tail call void @two_args(i8* %A_0, i8* %B_0)
ret void
}