Re: [PATCH] combine: Do not combine moves from hard registers

[Jeff Law <law at redhat dot com>]

On 11/2/18 5:54 PM, Segher Boessenkool wrote:
> On Fri, Nov 02, 2018 at 06:03:20PM -0500, Segher Boessenkool wrote:
>>> The original rtx is generated by expand_builtin_setjmp_receiver to adjust 
>>> the frame pointer.
>>>
>>> And later in LRA, it will try to eliminate frame_pointer with hard frame 
>>> pointer which is
>>> defined the ELIMINABLE_REGS.
>>>
>>> Your change split the insn into two.
>>> This makes it doesn't match the "from" and "to" regs defined in 
>>> ELIMINABLE_REGS.
>>> The if statement to generate the adjustment insn is been skipt.
>>> And the original instruction is just been deleted!
>> I don't follow why, or what should have prevented it from being deleted.
>>
>>> Probably, we don't want to split the move rtx if they are related to 
>>> entries defined in ELIMINABLE_REGS?
>> One thing I can easily do is not making an intermediate pseudo when copying
>> *to* a fixed reg, which sfp is.  Let me try if that helps the testcase I'm
>> looking at (setjmp-4.c).
> This indeed helps, see patch below.  Could you try that on the whole
> testsuite?
> 
> Thanks,
> 
> 
> Segher
> 
> 
> p.s. It still is a problem in the arm backend, but this won't hurt combine,
> so why not.
> 
> 
> From 814ca23ce05384d017b3c2bff41ab61cf5446e46 Mon Sep 17 00:00:00 2001
> Message-Id: <814ca23ce05384d017b3c2bff41ab61cf5446e46.1541202704.git.segher@kernel.crashing.org>
> From: Segher Boessenkool <segher@kernel.crashing.org>
> Date: Fri, 2 Nov 2018 23:33:32 +0000
> Subject: [PATCH] combine: Don't break up copy from hard to fixed reg
> 
> ---
>  gcc/combine.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/gcc/combine.c b/gcc/combine.c
> index dfb0b44..15e941a 100644
> --- a/gcc/combine.c
> +++ b/gcc/combine.c
> @@ -14998,6 +14998,8 @@ make_more_copies (void)
>  	    continue;
>  	  if (TEST_HARD_REG_BIT (fixed_reg_set, REGNO (src)))
>  	    continue;
> +	  if (REG_P (dest) && TEST_HARD_REG_BIT (fixed_reg_set, REGNO (dest)))
> +	    continue;
>  
>  	  rtx new_reg = gen_reg_rtx (GET_MODE (dest));
>  	  rtx_insn *new_insn = gen_move_insn (new_reg, src);
> -- 1.8.3.1
It certainly helps the armeb test results.

Jeff