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.sandif...@arm.com>
Alan Hayward <alan.hayw...@arm.com>
David Sherwood <david.sherw...@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;
