[ObjC][ARC] Don't remove autoreleaseRV/retainRV pairs if the call isn't

a tail call

Previosly ARC optimizer removed the autoreleaseRV/retainRV pair in the
following code, which caused the object returned by @something to be
placed in the autorelease pool because the call to @something isn't a
tail call:

```
  %call = call i8* @something(...)
  %2 = call i8* @objc_retainAutoreleasedReturnValue(i8* %call)
  %3 = call i8* @objc_autoreleaseReturnValue(i8* %2)
  ret i8* %3
```

Fix the bug by checking whether @something is a tail call.

rdar://problem/59275894

2 files changed, 23 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/ObjCARC/ObjCARCOpts.cpp b/llvm/lib/Transforms/ObjCARC/ObjCARCOpts.cpp
index 577a744..9a029cc 100644
--- a/llvm/lib/Transforms/ObjCARC/ObjCARCOpts.cpp
+++ b/llvm/lib/Transforms/ObjCARC/ObjCARCOpts.cpp
@@ -2296,7 +2296,7 @@ FindPredecessorAutoreleaseWithSafePath(const Value *Arg, BasicBlock *BB,
 
 /// Look for this pattern:
 /// \code
-///    %call = call i8* @something(...)
+///    %call = tail call i8* @something(...)
 ///    %2 = call i8* @objc_retain(i8* %call)
 ///    %3 = call i8* @objc_autorelease(i8* %2)
 ///    ret i8* %3
@@ -2344,6 +2344,13 @@ void ObjCARCOpt::OptimizeReturns(Function &F) {
     bool HasSafePathToCall = HasSafePathToPredecessorCall(Arg, Retain,
                                                           DependingInstructions,
                                                           Visited, PA);
+
+    // Don't remove retainRV/autoreleaseRV pairs if the call isn't a tail call.
+    if (GetBasicARCInstKind(Retain) == ARCInstKind::RetainRV &&
+        GetBasicARCInstKind(Autorelease) == ARCInstKind::AutoreleaseRV &&
+        !cast<CallInst>(*DependingInstructions.begin())->isTailCall())
+      continue;
+
     DependingInstructions.clear();
     Visited.clear();
 
diff --git a/llvm/test/Transforms/ObjCARC/rv.ll b/llvm/test/Transforms/ObjCARC/rv.ll
index 3d0d56c..ea06b38 100644
--- a/llvm/test/Transforms/ObjCARC/rv.ll
+++ b/llvm/test/Transforms/ObjCARC/rv.ll
@@ -77,7 +77,7 @@ define void @test2() {
 ; CHECK-NEXT: ret i8* %call
 define i8* @test3() {
 entry:
-  %call = call i8* @returner()
+  %call = tail call i8* @returner()
   %0 = call i8* @llvm.objc.retainAutoreleasedReturnValue(i8* %call) nounwind
   %1 = call i8* @llvm.objc.autoreleaseReturnValue(i8* %0) nounwind
   ret i8* %1
@@ -387,6 +387,20 @@ bb3:
   ret i32* %retval
 }
 
+; Don't eliminate the retainRV/autoreleaseRV pair if the call isn't a tail call.
+
+; CHECK-LABEL: define i8* @test28(
+; CHECK: call i8* @returner()
+; CHECK: call i8* @llvm.objc.retainAutoreleasedReturnValue(
+; CHECK: call i8* @llvm.objc.autoreleaseReturnValue(
+define i8* @test28() {
+entry:
+  %call = call i8* @returner()
+  %0 = call i8* @llvm.objc.retainAutoreleasedReturnValue(i8* %call) nounwind
+  %1 = call i8* @llvm.objc.autoreleaseReturnValue(i8* %0) nounwind
+  ret i8* %1
+}
+
 !0 = !{}
 
 ; CHECK: attributes [[NUW]] = { nounwind }