Use df_read_modify_subreg_p in cprop.c

Use df_read_modify_subreg_p in cprop.c

[Richard Sandiford]

local_cprop_find_used_regs punted on all multiword registers,
with the comment:

      /* Setting a subreg of a register larger than word_mode leaves
         the non-written words unchanged.  */

But this only applies if the outer mode is smaller than the
inner mode.  If they're the same size then writes to the subreg
are a normal full update.

This patch uses df_read_modify_subreg_p instead.  A later patch
adds more uses of the same routine, but this part had a (positive)
effect on code generation for the testsuite whereas the others
seemed to be simple clean-ups.

Tested on aarch64-linux-gnu and x86_64-linux-gnu.  OK to install?

Thanks,
Richard


[ This patch is part of the SVE series posted here:
  https://gcc.gnu.org/ml/gcc/2016-11/msg00030.html ]

gcc/
2016-11-15  Richard Sandiford  <richard.sandiford@arm.com>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

	* cprop.c (local_cprop_find_used_regs): Use df_read_modify_subreg_p.

diff --git a/gcc/cprop.c b/gcc/cprop.c
index 6b4c0b8..31868a5 100644
--- a/gcc/cprop.c
+++ b/gcc/cprop.c
@@ -1161,9 +1161,7 @@ local_cprop_find_used_regs (rtx *xptr, void *data)
       return;
 
     case SUBREG:
-      /* Setting a subreg of a register larger than word_mode leaves
-	 the non-written words unchanged.  */
-      if (GET_MODE_BITSIZE (GET_MODE (SUBREG_REG (x))) > BITS_PER_WORD)
+      if (df_read_modify_subreg_p (x))
 	return;
       break;
 

Re: Use df_read_modify_subreg_p in cprop.c

[Jeff Law]

On 11/15/2016 09:27 AM, Richard Sandiford wrote:
> local_cprop_find_used_regs punted on all multiword registers,
> with the comment:
>
>       /* Setting a subreg of a register larger than word_mode leaves
>          the non-written words unchanged.  */
>
> But this only applies if the outer mode is smaller than the
> inner mode.  If they're the same size then writes to the subreg
> are a normal full update.
>
> This patch uses df_read_modify_subreg_p instead.  A later patch
> adds more uses of the same routine, but this part had a (positive)
> effect on code generation for the testsuite whereas the others
> seemed to be simple clean-ups.
>
> Tested on aarch64-linux-gnu and x86_64-linux-gnu.  OK to install?
>
> Thanks,
> Richard
>
>
> [ This patch is part of the SVE series posted here:
>   https://gcc.gnu.org/ml/gcc/2016-11/msg00030.html ]
>
> gcc/
> 2016-11-15  Richard Sandiford  <richard.sandiford@arm.com>
> 	    Alan Hayward  <alan.hayward@arm.com>
> 	    David Sherwood  <david.sherwood@arm.com>
>
> 	* cprop.c (local_cprop_find_used_regs): Use df_read_modify_subreg_p.
OK.
jeff