[PATCH] rtlanal: fix subreg handling in set_noop_p ()

[Richard Sandiford]

Ilya Leoshkevich <iii@linux.ibm.com> writes:
> Bootstrapped and regtested on x86_64-redhat-linux.  Ok for master?
>
>
>
> The following s390 rtx is errneously considered a no-op:
>
> (set (subreg:DF (reg:TF %f0) 8) (subreg:DF (reg:V1TF %f0) 8))
>
> Here, SET_DEST is a second register in a floating-point register pair,
> and SET_SRC is the second half of a vector register, so they refer to
> different bits.
>
> Fix by treating subregs of registers in different modes conservatively.
>
> gcc/ChangeLog:
>
> 2020-09-11  Ilya Leoshkevich  <iii@linux.ibm.com>
>
> 	* rtlanal.c (set_noop_p): Treat subregs of registers in
> 	different modes conservatively.
> ---
>  gcc/rtlanal.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/gcc/rtlanal.c b/gcc/rtlanal.c
> index 5ae38b7966d..ed3360562d5 100644
> --- a/gcc/rtlanal.c
> +++ b/gcc/rtlanal.c
> @@ -1619,6 +1619,10 @@ set_noop_p (const_rtx set)
>  	return 0;
>        src = SUBREG_REG (src);
>        dst = SUBREG_REG (dst);
> +      if (GET_MODE (src) != GET_MODE (dst))
> +	/* It is hard to tell whether subregs refers to the same bits, so act
> +	 * conservatively and return 0.  */

Sorry for the nit, but GCC style is not to have leading “*”s on second
and subsequent lines, so just;

	/* It is hard to tell whether subregs refers to the same bits, so act
	   conservatively and return 0.  */

OK with that change, thanks.

Richard

> +	return 0;
>      }
>  
>    /* It is a NOOP if destination overlaps with selected src vector