On 26 March 2014 15:45, Jakub Jelinek <ja...@redhat.com> wrote:
> On Wed, Mar 26, 2014 at 03:30:44PM +0800, Zhenqiang Chen wrote:
>> Agree. CSE should never modify asm insns to drop some of the outputs.
>
> So the right fix is top prevent this from happening, not papering over about
> it.
>>
>> But in this case, CSE does not drop any of the outputs. It just takes
>> the SRC of a set and replace the reference of the set. And the
>> instruction validation tells CSE that it is legal instruction after
>> replacement. (The original correct asm insn is optimized away after
>> this replacement)
>>
>> I think it is common for most rtl-optimizations to do such kind of
>> validation. So to avoid such kind of bug, check_asm_operands must tell
>> the optimizer the asm is illegal.
>
> As it is wrong if CSE does that even with asm ("" : "=r" (i), "=r" (j));,
> your patch is not the right place to fix this. CSE just must check where
> the ASM_OPERANDS is coming from and if it comes from a PARALLEL with
> multiple outputs, either give up or duplicate all outputs (if it makes sense
> at all). Or just don't enter into the hash tables ASM_OPERANDS with
> multiple outputs.
Thanks for the comments. I will rework the patch to check it in CSE.
-Zhenqiang
> Jakub
