RE: [PATCH] Check hard_regno_mode_ok before setting lowest memory move cost for the mode with different reg classes.

[Liu, Hongtao via Gcc-patches]

> -----Original Message-----
> From: Vladimir Makarov <vmaka...@redhat.com>
> Sent: Wednesday, April 5, 2023 8:59 PM
> To: Jeff Law <jeffreya...@gmail.com>; Liu, Hongtao
> <hongtao....@intel.com>; gcc-patches@gcc.gnu.org
> Subject: Re: [PATCH] Check hard_regno_mode_ok before setting lowest
> memory move cost for the mode with different reg classes.
> 
> 
> On 4/4/23 21:29, Jeff Law wrote:
> >
> >
> > On 4/3/23 23:13, liuhongt via Gcc-patches wrote:
> >> There's a potential performance issue when backend returns some
> >> unreasonable value for the mode which can be never be allocate with
> >> reg class.
> >>
> >> Bootstrapped and regtested on x86_64-pc-linux-gnu{-m32,}.
> >> Ok for trunk(or GCC14 stage1)?
> >>
> >> gcc/ChangeLog:
> >>
> >>     PR rtl-optimization/109351
> >>     * ira.cc (setup_class_subset_and_memory_move_costs): Check
> >>     hard_regno_mode_ok before setting lowest memory move cost for
> >>     the mode with different reg classes.
> > Not a regression *and* changing register allocation.  This seems like
> > it should defer to gcc-14.
> >
> Yes, I am agree.  It should wait for gcc-14, especially when we are close to 
> the
> release. Also the testing x86-64 is not enough for such changes (although I
> tried ppc64le and did not find any problem).
> 
> Cost related patches for RA frequently result in new testsuite failures on
> some targets.  Even if the change seems obvious and expected to improve
> the generated code.
> 
> Target dependent code sometimes defines correctly the costs only for some
> possible cases and making less dependent from this pitfall is good.  So I 
> think
> the patch moves us to the right direction.
> 
> The patch is ok for me to commit it to the trunk after the gcc-13 release and 
> if
> arm64 testing shows no GCC testsuite regression.
Bootstrapped and regtested on aarch64-unknown-linux-gnu.
Waiting for GCC14.
> 
> Thank you for working on this issue.
>