[PATCH] Fix mult expansion ICE (PR middle-end/82875)

[Richard Sandiford]

Richard Biener <rguenther@suse.de> writes:
> On Wed, 22 Nov 2017, Jakub Jelinek wrote:
>
>> On Wed, Nov 22, 2017 at 10:41:19AM +0100, Richard Biener wrote:
>> > How much churn would it be to pass down a mode alongside the operands
>> > in expand_binop?  Can't find it right now but didn't we introduce
>> > some rtx_with_mode pair-like stuff somewhen?
>> 
>> We have rtx_mode_t for that.  But there are 240+ calls to expand_binop,
>> and even if we add an overload that will transform it, unless we forcefully
>> inline it wouldn't that slow down all the spots a little bit?
>> The thing is, for the vast majority of binary ops we don't need the operand
>> modes, it is mainly comparisons, second arg of shifts/rotates and this
>> widening case.
>
> Ok, so maybe split expand_binop then to the class of cases where we do
> need the mode and a class where we don't then?
>
> We don't have to use rtx_mode_t we can just pass two arguments.  Not
> sure what is more convenient to use.

FWIW, rtx_mode_t was only really added so that we have a single blob
for wi:: calls (with the hope that it would eventually be replaced
with just the rtx once CONST_INTs have a mode).  I think it'd be
more consistent to use separate arguments for other cases.

Thanks,
Richard

> Anyway, this doesn't have to happen in stage3, just as a general
> note on how I believe we changed things in other places.  Richard S.
> may remember more here.
>
> Richard.