[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

llvm/lib/Analysis/BasicAliasAnalysis.cpp

@@ -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

llvm/lib/Analysis/CaptureTracking.cpp

@@ -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;

llvm/test/Analysis/BasicAA/invariant_group.ll

@@ -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*)