On Dec 11, 2009, at 12:28 PM, Mike Stump wrote:
> On Dec 10, 2009, at 7:37 PM, Eli Friedman wrote:
>>> It is annoying when
>>>
>>> int foo() {
>>> asm xor eax, eax
>>> }
>>>
>>> gives a warning.
>>
>> If that actually works,
>
> Yes, that works.
No it doesn't. It happens to get lucky in many cases, but it doesn't work.
>> it's pure luck.
>
> I'd call it careful engineering.
If you look at the IR generated by llvm-gcc, there is nothing that prevents the
compiler from clobbering EAX after the asm. There is nothing 'careful' about
this.
Please revert r91073.
>>> Bear in mind, gcc's policy for:
>>>
>>> asm int foo() {
>>> xor eax, eax
>>> }
>>>
>>> is to _not_ give the warning.
>>
>> Yes; we should follow gcc's lead here.
>
> :-)
Whole function asm blocks are a completely different thing. Your patch is
wrong, please revert it.
-Chris
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