Jan Hubicka <hubi...@ucw.cz> writes:
>> MIPS16 code can't do atomic operations directly, so it calls into out-of-line
>> versions that are compiled as -mno-mips16. These out-of-line versions use
>> the same open-coded implementation as you'd get in normal -mno-mips16 code.
>
> Hmm, and I assume you don't want to use target attribute for this...
You mean so that any code that calls a __sync function would become
-mno-mips16? Yeah, we want to avoid that. There are specific mips16
and nomips16 attributes for setting the ISA mode, but the idea is to
allow functions to be compiled as -mips16 wherever possible.
>> This is done by libgcc/sync.c, which contains code like like:
>>
>> static void
>> sync_synchronize (void)
>> {
>> __sync_synchronize ();
>> }
>> typeof (sync_synchronize) __sync_synchronize
>> __attribute__((alias ("sync_synchronize")));
>>
>> With the recent cgraph changes, we follow the alias and the function becomes
>> an infinite loop.
>
> Yep, here you define two symbols of same assembler name, so they will be
> identified.
> How exactly the code worked before?
You'd know better than me how it worked before. :-) All I know is
that until the recent changes, the gimple optimisers didn't redirect
__sync_synchronize() to sync_synchronize(), so the original call
survived until expand and so got replaced with a sync instruction.
This is in contrast to:
void
__sync_synchronize (void)
{
__sync_synchronize ();
}
which the compiler always treated as an infinite loop. That's why
the alias indirect was used.
Thanks,
Richard
