[RS6000] Fix PowerPC ICE due to secondary_reload ignoring reload replacements

[David Edelsohn]

On Wed, Sep 9, 2015 at 8:57 PM, Alan Modra <amodra@gmail.com> wrote:
> On Tue, Sep 08, 2015 at 02:46:58PM +0200, Ulrich Weigand wrote:
>> David Edelsohn wrote:
>> > On Mon, Sep 7, 2015 at 11:47 PM, Alan Modra <amodra@gmail.com> wrote:
>> > > In https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67378 analysis I show
>> > > the reason for this PR is that insns emitted by secondary reload
>> > > patterns are being generated without taking into account other reloads
>> > > that may have occurred.  We run into this problem when an insn has a
>> > > pseudo that doesn't get a hard reg, and the pseudo is used in a way
>> > > that requires a secondary reload.  In this case the secondary reload
>> > > is needed due to gcc generating a 64-bit gpr load from memory insn
>> > > with an address offset not a multiple of 4.
>> > >
>> > >         PR target/67378
>> > >         * config/rs6000/rs6000.c (rs6000_secondary_reload_gpr): Find
>> > >         reload replacement for PRE_MODIFY address reg.
>> >
>> > I'm okay with this patch, but I'd like Uli to double-check it when he
>> > has a moment.
>>
>> The patch looks OK to me.  We definitely need to check for replacements
>> in secondary reload in such cases.
>
> Thanks for reviewing!  I think rs6000_secondary_reload_inner needs the
> same.  (https://gcc.gnu.org/ml/gcc-patches/2014-11/msg01114.html
> removed a bunch of find_replacement calls that I'd added previously.)
>
> This patch reinstates some of the calls, a little more elegantly than
> in my original effort.  I've also corrected an obvious error with the
> PRE_DEC address offset.  Bootstrapped and regression tested
> powerpc64le-linux.  OK for mainline and gcc-5?

Alan,

You and Mike need to get on the same page.  I don't want ping-ponging
patches where you add a check and Mike knowingly or unknowingly
removes it, then you add it back.

Ideally I want a testcase.  Barring that, I want a comment at all of
these points explaining why find_replacement is necessary.

Thanks, David