Re: [PATCH] xtensa: Prevent emitting integer additions of constant zero

[Takayuki 'January June' Suwa <jjsuwa_sys3175@yahoo.co.jp>]

On 2022/08/17 4:58, Max Filippov wrote:
> Hi Suwa-san,
Hi!

> 
> On Tue, Aug 16, 2022 at 5:42 AM Takayuki 'January June' Suwa
> <jjsuwa_sys3175@yahoo.co.jp> wrote:
>>
>> In a few cases, obviously omitable add instructions can be emitted via
>> invoking gen_addsi3.
>>
>> gcc/ChangeLog:
>>
>>         * config/xtensa/xtensa.md (addsi3_internal): Rename from "addsi3".
>>         (addsi3): New define_expand in order to reject integer additions of
>>         constant zero.
>> ---
>>  gcc/config/xtensa/xtensa.md | 14 +++++++++++++-
>>  1 file changed, 13 insertions(+), 1 deletion(-)
> 
> with this change a bunch of tests fail to build with the following error:

Ah, sorry, I want to withdraw this patch.

>> In a few cases

As a matter of fact, "in a few cases" is just only one:

[xtensa_expand_epilogue() in /gcc/config/xtensa/xtensa.cc]
>      if (cfun->machine->current_frame_size > 0)
>	{
>	  if (frame_pointer_needed || /* always reachable with addi */
>	      cfun->machine->current_frame_size > 1024 ||
>	      cfun->machine->current_frame_size <= 127)
>	    {
>	      if (cfun->machine->current_frame_size <= 127)
>		offset = cfun->machine->current_frame_size;
>	      else
>		offset = cfun->machine->callee_save_size;
>
>	      emit_insn (gen_addsi3 (stack_pointer_rtx,
>				     stack_pointer_rtx,
>				     GEN_INT (offset)));	// offset can be zero!
>	    }

And adding "define_expand" only to deal with one rare case had too much impact, as you saw...

>   undefined reference to `__addsi3'
> 
> E.g. gcc.c-torture/execute/20000519-1.c
> or gcc.c-torture/execute/20070919-1.c
>