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combine: Query can_change_dest_mode before changing dest mode 

As reported in https://gcc.gnu.org/ml/gcc-patches/2016-11/msg02388.html .

Changing the mode of a hard register can lead to problems, or at least
it can make worse code if the result will need reloads.


	* combine.c (change_zero_ext): Only change the mode of a hard register
	destination if can_change_dest_mode holds for that.

From-SVN: r242812
This commit is contained in:
Segher Boessenkool 2016-11-24 00:30:38 +01:00 committed by Segher Boessenkool
parent 188a209119
commit 469585df2d
2 changed files with 7 additions and 1 deletions
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5
gcc/ChangeLog
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@ -1,3 +1,8 @@
2016-11-23 Segher Boessenkool <segher@kernel.crashing.org>
* combine.c (change_zero_ext): Only change the mode of a hard register
destination if can_change_dest_mode holds for that.
2016-11-23 Jeff Law <law@redhat.com>
* varasm.c (assemble_name): Increase buffer size for name.

3
gcc/combine.c
View File

@ -11230,7 +11230,8 @@ change_zero_ext (rtx pat)
else if (GET_CODE (x) == ZERO_EXTEND
&& SCALAR_INT_MODE_P (mode)
&& REG_P (XEXP (x, 0))
&& HARD_REGISTER_P (XEXP (x, 0)))
&& HARD_REGISTER_P (XEXP (x, 0))
&& can_change_dest_mode (XEXP (x, 0), 0, mode))
{
size = GET_MODE_PRECISION (GET_MODE (XEXP (x, 0)));
x = gen_rtx_REG (mode, REGNO (XEXP (x, 0)));