combine: Don't split insns if half is unused (PR82621)
If we have a PARALLEL of two SETs, and one half is unused, we currently happily split that into two instructions (albeit the unused one is useless). Worse, as PR82621 shows, combine will happily merge this insn into I3 even if some intervening insn sets the same register again, which is wrong. This fixes it by not splitting PARALLELs with REG_UNUSED notes. It all is handled fine by combine in that case; just the "single set that is unused" case isn't handled properly. This also results in better code: combine will now actually throw away the unused SET. (It still won't do that in an I3). PR rtl-optimization/82621 * combine.c (try_combine): Do not split PARALLELs of two SETs if the dest of one of those SETs is unused. From-SVN: r255142
This commit is contained in:
parent
0dc933f4f5
commit
6b856e6c31
|
@ -1,3 +1,12 @@
|
|||
2017-11-24 Segher Boessenkool <segher@kernel.crashing.org>
|
||||
|
||||
Backport from mainline
|
||||
2017-11-17 Segher Boessenkool <segher@kernel.crashing.org>
|
||||
|
||||
PR rtl-optimization/82621
|
||||
* combine.c (try_combine): Do not split PARALLELs of two SETs if the
|
||||
dest of one of those SETs is unused.
|
||||
|
||||
2017-11-23 Oleg Endo <olegendo@gcc.gnu.org>
|
||||
|
||||
Backport from mainline
|
||||
|
|
|
@ -2964,7 +2964,8 @@ try_combine (rtx_insn *i3, rtx_insn *i2, rtx_insn *i1, rtx_insn *i0,
|
|||
&& is_parallel_of_n_reg_sets (PATTERN (i2), 2)
|
||||
&& can_split_parallel_of_n_reg_sets (i2, 2)
|
||||
&& !reg_used_between_p (SET_DEST (XVECEXP (PATTERN (i2), 0, 0)), i2, i3)
|
||||
&& !reg_used_between_p (SET_DEST (XVECEXP (PATTERN (i2), 0, 1)), i2, i3))
|
||||
&& !reg_used_between_p (SET_DEST (XVECEXP (PATTERN (i2), 0, 1)), i2, i3)
|
||||
&& !find_reg_note (i2, REG_UNUSED, 0))
|
||||
{
|
||||
/* If there is no I1, there is no I0 either. */
|
||||
i0 = i1;
|
||||
|
|
Loading…
Reference in New Issue