[llvm-commits] PATCH: Tailcallopt x86 byval argument handling

[Evan Cheng]

And please add the test case to our dejagnu tests.

Evan

On Apr 11, 2008, at 9:57 AM, Evan Cheng wrote:

> Looks good. Thanks!
>
> Evan
>
> On Apr 10, 2008, at 5:52 PM, Arnold Schwaighofer wrote:
>
>> On Fri, Apr 11, 2008 at 2:10 AM, Evan Cheng <evan.cheng at apple.com>
>> wrote:
>>> Thanks. The patch looks good. Have you verified the register
>>> allocator
>>> does eliminate the unnecessary copies?
>> Depends on what your notion of verify is. I checked with a few
>> examples. :)
>>
>> The copying of arguments for register parameters to virtual registers
>> and back to the parameter's register  is only emitted in cases where
>> tail call opt is on and the function call contains a byval argument.
>> So tail calls without byval arguments would not pay the price. So  
>> even
>> in this case i wouldn't be so bad?
>>
>> take for example the following call:
>>
>> define  fastcc i64 @tailcaller(i64 %b, %struct.s* byval %a) {
>> entry:
>>       %tmp2 = getelementptr %struct.s* %a, i32 0, i32 1
>>       %tmp3 = load i64* %tmp2, align 8
>>       %tmp4 = tail call fastcc i64 @tailcallee(%struct.s* %a byval,
>> i64 %tmp3, i64 %b, i64 7, i64 13, i64 17)
>>       ret i64 %tmp4
>> }
>>
>> as you can see 3rd (7) and 5th (17) argument are directly moved to
>> their corresponding argument register (rdx,r8). only rsi, rdi, rcx  
>> are
>> moved to intermediate registers as expected (killed by byval
>> lowering). as note that when i say 3rd i really mean 4th (b) but  
>> since
>> the first argument is byval and passed on the stack it i do not take
>> into account. so it seems the allocator is doing it's job nicely.
>>
>> tailcaller:
>> 	pushq	%rbx
>> 	subq	$32, %rsp
>> 	movq	%rdi, %rax
>> 	movq	56(%rsp), %r9
>> 	movl	$6, %r10d
>> 	leaq	48(%rsp), %rsi
>> 	movq	%r10, %rcx
>> 	movq	%rsp, %rdi
>> 	rep;movsl
>> 	leaq	48(%rsp), %rdi
>> 	movl	$13, %ebx
>> 	movl	$7, %edx
>> 	movl	$17, %r8d
>> 	movq	%r10, %rcx
>> 	movq	%rsp, %rsi
>> 	rep;movsl
>> 	movq	%r9, %rdi
>> 	movq	%rax, %rsi
>> 	movq	%rbx, %rcx
>> 	addq	$32, %rsp
>> 	popq	%rbx
>> 	jmp	tailcallee  # TAILCALL
>> 	.size	tailcaller, .-tailcaller
>>
>> okay to commit?
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>
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