On Tue, Jul 14, 2020 at 04:33:42PM -0500, Segher Boessenkool wrote:
> > If combine only did lower-cost combinations (perhaps with
> > Richard Sandifords lower-size-when-tied suggestion), I guess
> > this wouldn't happen. 0:-)
>
> And we would regress (a LOT).
Like this. C0 is an unmodified compiler. C1 is with the single_set
modification to is_just_move I committed a minute ago (84c5396d4bdb).
C2 is with this patch:
-- 8< --
diff --git a/gcc/combine.c b/gcc/combine.c
index 3a81bb6..619ba77 100644
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -939,7 +939,7 @@ combine_validate_cost (rtx_insn *i0, rtx_insn *i1, rtx_insn
/* Disallow this combination if both new_cost and old_cost are greater than
zero, and new_cost is greater than old cost. */
- int reject = old_cost > 0 && new_cost > old_cost;
+ int reject = old_cost > 0 && new_cost >= old_cost;
if (dump_file)
{
-- 8< --
[segher@gcc135 buildall]$ perl sizes.pl --percent C[012]
C0 C1 C2
alpha 6045560 100.000% 100.518%
arc 3529016 100.000% 99.933%
arm 14173370 100.000% 101.607%
arm64 12958466 100.000% 100.477%
c6x 2341205 100.000% 100.154%
csky 3320386 100.000% 100.838%
h8300 1163584 100.000% 100.331%
i386 0 0 0
ia64 18079744 100.000% 100.857%
m68k 3711195 100.000% 100.327%
microblaze 4930937 100.000% 100.054%
mips 8403293 100.000% 100.049%
mips64 6975860 100.000% 99.986%
nds32 4450951 100.000% 99.992%
nios2 3641733 100.000% 100.206%
openrisc 4182260 100.000% 100.025%
parisc 7706299 100.000% 101.500%
parisc64 8677365 100.000% 101.491%
powerpc 10016575 100.000% 100.001%
powerpc64 17331518 100.000% 99.974%
powerpc64le 17331518 100.000% 99.974%
riscv32 0 0 0
riscv64 0 0 0
s390 13091897 100.000% 100.396%
sh 3213207 100.000% 100.031%
shnommu 1610444 100.000% 100.031%
sparc 4356641 100.000% 101.521%
sparc64 6745123 100.000% 101.450%
x86_64 19663507 100.000% 100.007%
xtensa 2105610 100.000% 100.425%
Segher
