[clang] 874b0a0 - [CodeGen] Mark calls to objc_autorelease as tail

[Akira Hatanaka via cfe-commits]

Author: Akira Hatanaka
Date: 2020-11-10T13:48:25-08:00
New Revision: 874b0a0b9db93f5d3350ffe6b5efda2d908415d0

URL: https://github.com/llvm/llvm-project/commit/874b0a0b9db93f5d3350ffe6b5efda2d908415d0
DIFF: https://github.com/llvm/llvm-project/commit/874b0a0b9db93f5d3350ffe6b5efda2d908415d0.diff

LOG: [CodeGen] Mark calls to objc_autorelease as tail

This enables a method sending an autorelease message to an object and
returning the object in MRR to avoid adding the object to an autorelease
pool if a call to objc_retainAutoreleasedReturnValue in the caller
function accepts the hand off of the retain count.

rdar://problem/50678052

Differential Revision: https://reviews.llvm.org/D91111

Added: 
    

Modified: 
    clang/lib/CodeGen/CGObjC.cpp
    clang/test/CodeGenObjC/convert-messages-to-runtime-calls.m

Removed: 
    


################################################################################
diff  --git a/clang/lib/CodeGen/CGObjC.cpp b/clang/lib/CodeGen/CGObjC.cpp
index 89bf402c19f8..bdb9f4002f3c 100644
--- a/clang/lib/CodeGen/CGObjC.cpp
+++ b/clang/lib/CodeGen/CGObjC.cpp
@@ -2221,6 +2221,12 @@ static llvm::Value *emitObjCValueOperation(CodeGenFunction &CGF,
   // Call the function.
   llvm::CallBase *Inst = CGF.EmitCallOrInvoke(fn, value);
 
+  // Mark calls to objc_autorelease as tail on the assumption that methods
+  // overriding autorelease do not touch anything on the stack.
+  if (fnName == "objc_autorelease")
+    if (auto *Call = dyn_cast<llvm::CallInst>(Inst))
+      Call->setTailCall();
+
   // Cast the result back to the original type.
   return CGF.Builder.CreateBitCast(Inst, origType);
 }

diff  --git a/clang/test/CodeGenObjC/convert-messages-to-runtime-calls.m b/clang/test/CodeGenObjC/convert-messages-to-runtime-calls.m
index c51b56b66fff..4a415be21cb0 100644
--- a/clang/test/CodeGenObjC/convert-messages-to-runtime-calls.m
+++ b/clang/test/CodeGenObjC/convert-messages-to-runtime-calls.m
@@ -30,7 +30,7 @@ void test1(id x) {
   // CALLS: {{call.*@objc_allocWithZone}}
   // CALLS: {{call.*@objc_retain}}
   // CALLS: {{call.*@objc_release}}
-  // CALLS: {{call.*@objc_autorelease}}
+  // CALLS: {{tail call.*@objc_autorelease}}
   [NSObject alloc];
   [NSObject allocWithZone:nil];
   [x retain];
@@ -121,7 +121,7 @@ void test_alloc_instance(A *a) {
 // call will return i8* which we have to cast to A*
 // CHECK-LABEL: define {{.*}}void @test_autorelease_class_ptr
 A* test_autorelease_class_ptr(B *b) {
-  // CALLS: {{call.*@objc_autorelease}}
+  // CALLS: {{tail call.*@objc_autorelease}}
   // CALLS-NEXT: bitcast i8*
   // CALLS-NEXT: ret
   return [b autorelease];