This is the mail archive of the
gcc-patches@gcc.gnu.org
mailing list for the GCC project.
Re: [PATCH][RFC] Fixing instability of -fschedule-insns for x86
On Tue, Aug 14, 2012 at 2:45 PM, Jakub Jelinek <jakub@redhat.com> wrote:
> On Tue, Aug 14, 2012 at 02:40:42PM +0200, Richard Guenther wrote:
>> On Tue, Aug 14, 2012 at 2:02 PM, Uros Bizjak <ubizjak@gmail.com> wrote:
>> > On Tue, Aug 14, 2012 at 1:51 PM, Yuri Rumyantsev <ysrumyan@gmail.com> wrote:
>> >
>> >> 2. Passing function arguments in HW registers.
>> >> The main problem here is that backward copy propagation phase (aka
>> >> combine instructions) can propagate HW argument registers to
>> >> instructions evaluating argument values (e.g. issue#46829). To
>> >> resolve this problem I decided to preserve an order of instructions
>> >> writing to HW function argument registers through additional output
>> >> dependencies between two adjacent instructions
>> >> (ix86_dependencies_evaluation_hook).
>> >
>> > Looking a bit deeper into PR46829 problem, it is actually the output
>> > of the divide instruction that gets combined with _called_ function
>> > argument (r8), before the call to "bar" function. So, this is similar,
>> > but separate issue from the propagation of function arguments into
>> > insn inputs.
>> >
>> > In any case, short of disabling propagation of hard registers,
>> > recog_for_combine should somehow check if the insn that combines hard
>> > regs is still valid.
>>
>> Yes, that sounds reasonable.
>
> What kind of checks do you have in mind though? Combiner already tries to
> recog the insn, which involves testing all the predicates on the insn. What
> else it could do? You mean that for hard registers it should check
> constraints too?
Yes. Do the same checks reload would do.
Richard.
> Jakub