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

[Vladimir Makarov <vmakarov@redhat.com>]

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.

Thank you for working on this issue.