On Mar 5, 2014, at 10:07 AM, Richard Henderson <[email protected]> wrote:
> On 03/04/2014 10:12 PM, Yury Gribov wrote:
>>>> Asms without outputs are automatically volatile. So there ought be zero
>>>> change
>>>> with and without the explicit use of the __volatile__ keyword.
>>>
>>> That’s what the documentation says but it wasn’t actually true
>>> as of a couple of releases ago, as I recall.
>>
>> Looks like 2005:
>>
>> $ git annotate gcc/c/c-typeck.c
>> ...
>> 89552023 ( bonzini 2005-10-05 12:17:16 +0000 9073) /* asm
>> statements without outputs, including simple ones, are treated
>> 89552023 ( bonzini 2005-10-05 12:17:16 +0000 9074) as
>> volatile. */
>> 89552023 ( bonzini 2005-10-05 12:17:16 +0000 9075)
>> ASM_INPUT_P (args) = simple;
>> 89552023 ( bonzini 2005-10-05 12:17:16 +0000 9076)
>> ASM_VOLATILE_P (args) = (noutputs == 0);
>
> Yep, that's the one. So, more than "a couple" of releases: gcc 4.2 and later.
Thanks gentlemen. That explains it — we ran into this in GCC 3.3.3 and then
upgraded from there straight to V4.6 or so.
paul
