Open Radar

 
22-Aug-2011 05:46 PM Rob Napier:
'main.m' was successfully uploaded

22-Aug-2011 05:46 PM Rob Napier:
Summary:

When calling an IMP in a void context, ARC injects an extra _objc_retainAutoreleasedReturnValue and _objc_release, even though the result is thrown away. When using normal ObjC [foo bar], ARC correctly avoids this.

Steps to Reproduce:

See attached test program. Starred assembly should not be needed since the result is a void.

    for (count = 0; count < kTotalCount; ++count) {
      setStringMethod(string, selector, @"stuff");
    }

LBB0_5:                                 ## =>This Inner Loop Header: Depth=1
	cmpq	$100000000, -48(%rbp)   ## imm = 0x5F5E100
	jae	LBB0_8
## BB#6:                                ##   in Loop: Header=BB0_5 Depth=1
	leaq	L__unnamed_cfstring_(%rip), %rax
	.loc	1 35 7                  ## /Users/rnapier/src/TestIMP/TestIMP/main.m:35:7
Ltmp11:
	movq	-64(%rbp), %rcx
	movq	-24(%rbp), %rdx
	movq	-56(%rbp), %rsi
	movq	%rdx, %rdi
	movq	%rax, %rdx
	movb	$0, %al
	callq	*%rcx
*	movq	%rax, %rdi
*	callq	_objc_retainAutoreleasedReturnValue
*	movq	%rax, %rdi
*	callq	_objc_release
Ltmp12:
## BB#7:                                ##   in Loop: Header=BB0_5 Depth=1
	.loc	1 34 42                 ## /Users/rnapier/src/TestIMP/TestIMP/main.m:34:42
	movq	-48(%rbp), %rax
	addq	$1, %rax
	movq	%rax, -48(%rbp)
	jmp	LBB0_5



Expected Results:

The starred assembly should be optimized out as it is for the objc_msgSend case:

  for (count = 0; count < kTotalCount; ++count) {
    [string setString:@"stuff"];
  }

LBB0_1:                                 ## =>This Inner Loop Header: Depth=1
	cmpq	$100000000, -48(%rbp)   ## imm = 0x5F5E100
	jae	LBB0_4
## BB#2:                                ##   in Loop: Header=BB0_1 Depth=1
	leaq	L__unnamed_cfstring_(%rip), %rax
	.loc	1 23 7                  ## /Users/rnapier/src/TestIMP/TestIMP/main.m:23:7
Ltmp8:
	movq	-24(%rbp), %rcx
	movq	L_OBJC_SELECTOR_REFERENCES_5(%rip), %rsi
	movq	%rcx, %rdi
	movq	%rax, %rdx
	callq	_objc_msgSend
Ltmp9:
## BB#3:                                ##   in Loop: Header=BB0_1 Depth=1
	.loc	1 22 42                 ## /Users/rnapier/src/TestIMP/TestIMP/main.m:22:42
	movq	-48(%rbp), %rax
	addq	$1, %rax
	movq	%rax, -48(%rbp)
	jmp	LBB0_1


Actual Results:

Regression:

Notes: