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[BasicAA] Fix handling of invariant group launders 

Summary:
A recent patch ([[ https://reviews.llvm.org/rL331587 | rL331587 ]]) to Capture Tracking taught it that the `launder_invariant_group` intrinsic captures its argument only by returning it. Unfortunately, BasicAA still considered every call instruction as a possible escape source and hence concluded that the result of a `launder_invariant_group` call cannot alias any local non-escaping value. This led to [[ https://bugs.llvm.org/show_bug.cgi?id=37458 | bug 37458 ]].

This patch updates the relevant check for escape sources in BasicAA.

Reviewers: Prazek, kuhar, rsmith, hfinkel, sanjoy, xbolva00

Reviewed By: hfinkel, xbolva00

Subscribers: JDevlieghere, hiraditya, llvm-commits

Differential Revision: https://reviews.llvm.org/D46900

llvm-svn: 332466
This commit is contained in:
Krzysztof Pszeniczny 2018-05-16 13:16:54 +00:00
parent 0c8f451a1b
commit 2ba8fd4914
3 changed files with 62 additions and 1 deletions
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13
llvm/lib/Analysis/BasicAliasAnalysis.cpp
View File

@ -132,7 +132,18 @@ static bool isNonEscapingLocalObject(const Value *V) {
/// Returns true if the pointer is one which would have been considered an
/// escape by isNonEscapingLocalObject.
static bool isEscapeSource(const Value *V) {
if (isa<CallInst>(V) || isa<InvokeInst>(V) || isa<Argument>(V))
if (auto CS = ImmutableCallSite(V)) {
// launder_invariant_group captures its argument only by returning it,
// so it might not be considered an escape by isNonEscapingLocalObject.
// Note that adding similar special cases for intrinsics in CaptureTracking
// requires handling them here too.
if (CS.getIntrinsicID() == Intrinsic::launder_invariant_group)
return false;
return true;
}
if (isa<Argument>(V))
return true;
// The load case works because isNonEscapingLocalObject considers all

2
llvm/lib/Analysis/CaptureTracking.cpp
View File

@ -249,6 +249,8 @@ void llvm::PointerMayBeCaptured(const Value *V, CaptureTracker *Tracker) {
// launder.invariant.group only captures pointer by returning it,
// so the pointer wasn't captured if returned pointer is not captured.
// Note that adding similar special cases for intrinsics requires handling
// them in 'isEscapeSource' in BasicAA.
if (CS.getIntrinsicID() == Intrinsic::launder_invariant_group) {
AddUses(I);
break;

48
llvm/test/Analysis/BasicAA/invariant_group.ll Normal file
View File

@ -0,0 +1,48 @@
; RUN: opt < %s -basicaa -aa-eval -print-all-alias-modref-info -disable-output 2>&1 | FileCheck %s
; RUN: opt < %s -basicaa -gvn -S | FileCheck -check-prefix=CHECK-GVN %s
; The input *.ll had been adapted from bug 37458:
;
; struct A { virtual void f(); int n; };
;
; int h() {
; A a;
; a.n = 42;
; return __builtin_launder(&a)->n;
; }
%struct.A = type <{ i8*, i8 }>
; CHECK: testLaunderInvariantGroupIsNotEscapeSource
; CHECK-GVN: testLaunderInvariantGroupIsNotEscapeSource
define i8 @testLaunderInvariantGroupIsNotEscapeSource() {
; CHECK-DAG: MustAlias: %struct.A* %a, i8* %a.bitcast
; CHECK-DAG: PartialAlias: %struct.A* %a, i8* %n
; CHECK-DAG: NoAlias: i8* %a.bitcast, i8* %n
; CHECK-DAG: MustAlias: %struct.A* %a, i8* %a.laundered
; CHECK-DAG: MustAlias: i8* %a.bitcast, i8* %a.laundered
; CHECK-DAG: NoAlias: i8* %a.laundered, i8* %n
; CHECK-DAG: PartialAlias: %struct.A* %a, i8* %n.laundered
; CHECK-DAG: NoAlias: i8* %a.bitcast, i8* %n.laundered
; CHECK-DAG: MustAlias: i8* %n, i8* %n.laundered
; CHECK-DAG: NoAlias: i8* %a.laundered, i8* %n.laundered
; CHECK-DAG: NoModRef: Ptr: %struct.A* %a <-> %a.laundered = call i8* @llvm.launder.invariant.group.p0i8(i8* nonnull %a.bitcast)
; CHECK-DAG: NoModRef: Ptr: i8* %a.bitcast <-> %a.laundered = call i8* @llvm.launder.invariant.group.p0i8(i8* nonnull %a.bitcast)
; CHECK-DAG: NoModRef: Ptr: i8* %n <-> %a.laundered = call i8* @llvm.launder.invariant.group.p0i8(i8* nonnull %a.bitcast)
; CHECK-DAG: NoModRef: Ptr: i8* %a.laundered <-> %a.laundered = call i8* @llvm.launder.invariant.group.p0i8(i8* nonnull %a.bitcast)
; CHECK-DAG: NoModRef: Ptr: i8* %n.laundered <-> %a.laundered = call i8* @llvm.launder.invariant.group.p0i8(i8* nonnull %a.bitcast)
entry:
%a = alloca %struct.A, align 8
%a.bitcast = bitcast %struct.A* %a to i8*
%n = getelementptr inbounds %struct.A, %struct.A* %a, i64 0, i32 1
store i8 42, i8* %n
%a.laundered = call i8* @llvm.launder.invariant.group.p0i8(i8* nonnull %a.bitcast)
%n.laundered = getelementptr inbounds i8, i8* %a.laundered, i64 8
%v = load i8, i8* %n.laundered
; make sure that the load from %n.laundered to %v aliases the store of 42 to %n
; CHECK-GVN: ret i8 42
ret i8 %v
}
declare i8* @llvm.launder.invariant.group.p0i8(i8*)