Use df_read_modify_subreg_p in cprop.c

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.

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.

Co-Authored-By: Alan Hayward <alan.hayward@arm.com>
Co-Authored-By: David Sherwood <david.sherwood@arm.com>
From-SVN: r242488

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index a49e02492362fe0caafd25f5702c253a9495b962..fe32d0f7d3129ea018b731eeba20ef307dc1d393 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2016-11-16  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.
+
 2016-11-16  Richard Biener  <rguenther@suse.de>
 
        PR middle-end/78333

diff --git a/gcc/cprop.c b/gcc/cprop.c
index 6b4c0b8fa389f3f2ab065f4dbc7044c72fcd0338..31868a5c6bb4f5110276eb285d0ace01a61fb820 100644 (file)
--- 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;