[PATCH][RFC] Fixing instability of -fschedule-insns for x86

[Richard Guenther]

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.

Richard.

> Uros.