From 4bd9c52fadd800122f3b3756c9621da387496d77 Mon Sep 17 00:00:00 2001
From: Akira Hatanaka <ahatanaka@apple.com>
Date: Mon, 16 Oct 2017 16:46:59 +0000
Subject: [PATCH] [ObjCARC] Do not move a release that has the
 clang.imprecise_release tag above PHI instructions.

ARC optimizer has an optimization that moves a call to an ObjC runtime
function above a phi instruction when the phi has a null operand and is
an argument passed to the function call. This optimization should not
kick in when the runtime function is an objc_release that releases an
object with precise lifetime semantics.

rdar://problem/34959669

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@315914 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/ObjCARC/ObjCARCOpts.cpp | 11 ++++++++---
 test/Transforms/ObjCARC/basic.ll       | 20 ++++++++++++++++++++
 2 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/lib/Transforms/ObjCARC/ObjCARCOpts.cpp b/lib/Transforms/ObjCARC/ObjCARCOpts.cpp
index 8c0a90843ef..6692d950da2 100644
--- a/lib/Transforms/ObjCARC/ObjCARCOpts.cpp
+++ b/lib/Transforms/ObjCARC/ObjCARCOpts.cpp
@@ -808,9 +808,14 @@ void ObjCARCOpt::OptimizeIndividualCalls(Function &F) {
 
     // If Arg is a PHI, and one or more incoming values to the
     // PHI are null, and the call is control-equivalent to the PHI, and there
-    // are no relevant side effects between the PHI and the call, the call
-    // could be pushed up to just those paths with non-null incoming values.
-    // For now, don't bother splitting critical edges for this.
+    // are no relevant side effects between the PHI and the call, and the call
+    // is not a release that doesn't have the clang.imprecise_release tag, the
+    // call could be pushed up to just those paths with non-null incoming
+    // values. For now, don't bother splitting critical edges for this.
+    if (Class == ARCInstKind::Release &&
+        !Inst->getMetadata(MDKindCache.get(ARCMDKindID::ImpreciseRelease)))
+      continue;
+
     SmallVector<std::pair<Instruction *, const Value *>, 4> Worklist;
     Worklist.push_back(std::make_pair(Inst, Arg));
     do {
diff --git a/test/Transforms/ObjCARC/basic.ll b/test/Transforms/ObjCARC/basic.ll
index cecaa3f2b4d..70b83b93138 100644
--- a/test/Transforms/ObjCARC/basic.ll
+++ b/test/Transforms/ObjCARC/basic.ll
@@ -1342,6 +1342,26 @@ A:
   br label %C
 B:
   br label %C
+C:
+  %h = phi double* [ null, %A ], [ %p, %B ]
+  %c = bitcast double* %h to i8*
+  call void @objc_release(i8* %c), !clang.imprecise_release !0
+  ret void
+}
+
+; Do not move an objc_release that doesn't have the clang.imprecise_release tag.
+
+; CHECK-LABEL: define void @test22_precise(
+; CHECK: %[[P0:.*]] = phi double*
+; CHECK: %[[V0:.*]] = bitcast double* %[[P0]] to i8*
+; CHECK: call void @objc_release(i8* %[[V0]])
+; CHECK: ret void
+define void @test22_precise(double* %p, i1 %a) {
+  br i1 %a, label %A, label %B
+A:
+  br label %C
+B:
+  br label %C
 C:
   %h = phi double* [ null, %A ], [ %p, %B ]
   %c = bitcast double* %h to i8*
-- 
2.50.1