From 58b46683bd70c20c2543d60ca28af4dec4ec0443 Mon Sep 17 00:00:00 2001 From: Segher Boessenkool Date: Fri, 17 Nov 2017 15:46:04 +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 (although 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: r254874 --- gcc/ChangeLog | 6 ++++++ gcc/combine.c | 3 ++- 2 files changed, 8 insertions(+), 1 deletion(-) diff --git a/gcc/ChangeLog b/gcc/ChangeLog index 993ac9bba24..c0249e81aa5 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,3 +1,9 @@ +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. + 2017-11-17 Richard Biener PR fortran/83017 diff --git a/gcc/combine.c b/gcc/combine.c index eab10c599a6..404cf33e9d0 100644 --- a/gcc/combine.c +++ b/gcc/combine.c @@ -3010,7 +3010,8 @@ 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; -- 2.30.2