From 269af9105524e4c5a8af43e3e4750c16f742a0db Mon Sep 17 00:00:00 2001 From: Segher Boessenkool Date: Fri, 24 Nov 2017 18:03:04 +0100 Subject: [PATCH] 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: r255143 --- gcc/ChangeLog | 9 +++++++++ gcc/combine.c | 3 ++- 2 files changed, 11 insertions(+), 1 deletion(-) diff --git a/gcc/ChangeLog b/gcc/ChangeLog index b0e03768700f..42162dc2715b 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,3 +1,12 @@ +2017-11-24 Segher Boessenkool + + Backport from mainline + 2017-11-17 Segher Boessenkool + + 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. + 2017-11-21 Pat Haugen Backport from mainline diff --git a/gcc/combine.c b/gcc/combine.c index a989659f2888..24f2af12b899 100644 --- a/gcc/combine.c +++ b/gcc/combine.c @@ -2947,7 +2947,8 @@ 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; -- 2.47.2