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fwprop.c (forward_propagate_subreg): Skip the SIGN/ZERO_EXTEND optimization if the source register is already extended. 

gcc/
	* fwprop.c (forward_propagate_subreg): Skip the SIGN/ZERO_EXTEND
	optimization if the source register is already extended.

From-SVN: r182504
This commit is contained in:
Richard Sandiford 2011-12-19 22:05:28 +00:00 committed by Richard Sandiford
parent 373203331a
commit 7a61392921
2 changed files with 19 additions and 1 deletions
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5
gcc/ChangeLog
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@ -1,3 +1,8 @@
2011-12-19 Richard Sandiford <rdsandiford@googlemail.com>
* fwprop.c (forward_propagate_subreg): Skip the SIGN/ZERO_EXTEND
optimization if the source register is already extended.
2011-12-19 Richard Sandiford <rdsandiford@googlemail.com>
* lower-subreg.c (can_decompose_p): Check every word of a hard

15
gcc/fwprop.c
View File

@ -1112,7 +1112,18 @@ forward_propagate_subreg (df_ref use, rtx def_insn, rtx def_set)
/* If this is a SUBREG of a ZERO_EXTEND or SIGN_EXTEND, and the SUBREG
is the low part of the reg being extended then just use the inner
operand. Don't do this if the ZERO_EXTEND or SIGN_EXTEND insn will
be removed due to it matching a LOAD_EXTEND_OP load from memory. */
be removed due to it matching a LOAD_EXTEND_OP load from memory,
or due to the operation being a no-op when applied to registers.
For example, if we have:
A: (set (reg:DI X) (sign_extend:DI (reg:SI Y)))
B: (... (subreg:SI (reg:DI X)) ...)
and mode_rep_extended says that Y is already sign-extended,
the backend will typically allow A to be combined with the
definition of Y or, failing that, allow A to be deleted after
reload through register tying. Introducing more uses of Y
prevents both optimisations. */
else if (subreg_lowpart_p (use_reg))
{
use_insn = DF_REF_INSN (use);
@ -1123,6 +1134,8 @@ forward_propagate_subreg (df_ref use, rtx def_insn, rtx def_set)
&& REGNO (XEXP (src, 0)) >= FIRST_PSEUDO_REGISTER
&& GET_MODE (XEXP (src, 0)) == use_mode
&& !free_load_extend (src, def_insn)
&& (targetm.mode_rep_extended (use_mode, GET_MODE (src))
!= (int) GET_CODE (src))
&& all_uses_available_at (def_insn, use_insn))
return try_fwprop_subst (use, DF_REF_LOC (use), XEXP (src, 0),
def_insn, false);