https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116398
--- Comment #10 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
So, I've made an experiment
--- gcc/combine.cc.jj 2025-03-04 09:45:50.620584561 +0100
+++ gcc/combine.cc 2025-03-14 10:57:29.164681115 +0100
@@ -4204,7 +4204,8 @@ try_combine (rtx_insn *i3, rtx_insn *i2,
/* If I2 didn't change, this is not a combination (but a simplification or
canonicalisation with context), which should not be done here. Doing
it here explodes the algorithm. Don't. */
- if (rtx_equal_p (newi2pat, PATTERN (i2)))
+ if (rtx_equal_p (newi2pat, PATTERN (i2))
+ && DF_INSN_LUID (i3) - DF_INSN_LUID (i2) >= (getenv ("LUIDDIFF") ? atoi
(getenv ("LUIDDIFF")) : 0))
{
if (dump_file)
fprintf (dump_file, "i2 didn't change, not doing this\n");
On the #c0 testcase from this PR, LUIDDIFF=0 and LUIDDIFF=1 are the regression
case, LUIDDIFF=2 and above are the GCC 14 code.
On the
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101523#c10
testcase for s390x-linux I get (x86_64-linux -> s390x-linux cross, built with
-O2 and the above hack):
$ for i in 0 10 100 200 400 600 800 1000 1200 10000; do echo LUIDDIFF=$i time
./cc1plus -quiet -nostdinc -O2 pr101523.ii -mlong-double-128 -march=z196
-fpreprocessed -w; LUIDDIFF=$i time ./cc1plus -quiet -nostdinc -O2 pr101523.ii
-mlong-double-128 -march=z196 -fpreprocessed -w; done
LUIDDIFF=0 time ./cc1plus -quiet -nostdinc -O2 pr101523.ii -mlong-double-128
-march=z196 -fpreprocessed -w
13.77user 0.13system 0:13.97elapsed 99%CPU (0avgtext+0avgdata
320320maxresident)k
0inputs+776outputs (0major+105819minor)pagefaults 0swaps
LUIDDIFF=10 time ./cc1plus -quiet -nostdinc -O2 pr101523.ii -mlong-double-128
-march=z196 -fpreprocessed -w
13.88user 0.12system 0:14.05elapsed 99%CPU (0avgtext+0avgdata
319656maxresident)k
0inputs+784outputs (0major+106128minor)pagefaults 0swaps
LUIDDIFF=100 time ./cc1plus -quiet -nostdinc -O2 pr101523.ii -mlong-double-128
-march=z196 -fpreprocessed -w
14.22user 0.15system 0:14.44elapsed 99%CPU (0avgtext+0avgdata
322476maxresident)k
0inputs+800outputs (0major+106693minor)pagefaults 0swaps
LUIDDIFF=200 time ./cc1plus -quiet -nostdinc -O2 pr101523.ii -mlong-double-128
-march=z196 -fpreprocessed -w
14.05user 0.16system 0:14.25elapsed 99%CPU (0avgtext+0avgdata
315804maxresident)k
0inputs+816outputs (0major+109184minor)pagefaults 0swaps
LUIDDIFF=400 time ./cc1plus -quiet -nostdinc -O2 pr101523.ii -mlong-double-128
-march=z196 -fpreprocessed -w
15.44user 0.15system 0:15.66elapsed 99%CPU (0avgtext+0avgdata
360208maxresident)k
0inputs+816outputs (0major+120533minor)pagefaults 0swaps
LUIDDIFF=600 time ./cc1plus -quiet -nostdinc -O2 pr101523.ii -mlong-double-128
-march=z196 -fpreprocessed -w
17.47user 0.18system 0:17.70elapsed 99%CPU (0avgtext+0avgdata
412556maxresident)k
0inputs+816outputs (0major+133990minor)pagefaults 0swaps
LUIDDIFF=800 time ./cc1plus -quiet -nostdinc -O2 pr101523.ii -mlong-double-128
-march=z196 -fpreprocessed -w
18.75user 0.24system 0:19.07elapsed 99%CPU (0avgtext+0avgdata
498380maxresident)k
0inputs+832outputs (0major+156165minor)pagefaults 0swaps
LUIDDIFF=1000 time ./cc1plus -quiet -nostdinc -O2 pr101523.ii -mlong-double-128
-march=z196 -fpreprocessed -w
21.60user 0.26system 0:21.92elapsed 99%CPU (0avgtext+0avgdata
599660maxresident)k
0inputs+840outputs (0major+181821minor)pagefaults 0swaps
LUIDDIFF=1200 time ./cc1plus -quiet -nostdinc -O2 pr101523.ii -mlong-double-128
-march=z196 -fpreprocessed -w
23.00user 0.27system 0:23.36elapsed 99%CPU (0avgtext+0avgdata
670684maxresident)k
0inputs+824outputs (0major+199625minor)pagefaults 0swaps
LUIDDIFF=10000 time ./cc1plus -quiet -nostdinc -O2 pr101523.ii
-mlong-double-128 -march=z196 -fpreprocessed -w
149.81user 3.26system 2:33.68elapsed 99%CPU (0avgtext+0avgdata
7216920maxresident)k
0inputs+912outputs (0major+1844663minor)pagefaults 0swaps
$ rm pr101523.ii.*; LUIDDIFF=0 ./cc1plus -quiet -nostdinc -O2 pr101523.ii
-mlong-double-128 -march=z196 -fpreprocessed -w -fdump-rtl-combine-stats; awk
'/^attempts:/{attempts+=$2}/^merges:/{merges+=$2}/^extras:/{extras+=$2}/^successes/{successes+=$2}/^two-insn
combine:/{two+=$3}/^three-insn combine:/{three+=$3}/^four-insn
combine:/{four+=$3}/^insn-with-note combine/{note+=$3}END{printf "attempts:
%d\nmerges: %d\nextras: %d\nsuccesses: %d\ntwo-insn combine: %d\nthree-insn
combine: %d\nfour-insn combine: %d\ninsn-with-note combine: %d\n", attempts,
merges, extras, successes, two, three, four, note}' pr101523.ii.*combine*
attempts: 22982
merges: 21955
extras: 5419
successes: 115
two-insn combine: 113
three-insn combine: 2
four-insn combine: 0
insn-with-note combine: 0
$ rm pr101523.ii.*; LUIDDIFF=10 ./cc1plus -quiet -nostdinc -O2 pr101523.ii
-mlong-double-128 -march=z196 -fpreprocessed -w -fdump-rtl-combine-stats; awk
'/^attempts:/{attempts+=$2}/^merges:/{merges+=$2}/^extras:/{extras+=$2}/^successes/{successes+=$2}/^two-insn
combine:/{two+=$3}/^three-insn combine:/{three+=$3}/^four-insn
combine:/{four+=$3}/^insn-with-note combine/{note+=$3}END{printf "attempts:
%d\nmerges: %d\nextras: %d\nsuccesses: %d\ntwo-insn combine: %d\nthree-insn
combine: %d\nfour-insn combine: %d\ninsn-with-note combine: %d\n", attempts,
merges, extras, successes, two, three, four, note}' pr101523.ii.*combine*
attempts: 23474
merges: 22422
extras: 5587
successes: 167
two-insn combine: 166
three-insn combine: 1
four-insn combine: 0
insn-with-note combine: 0
$ rm pr101523.ii.*; LUIDDIFF=100 ./cc1plus -quiet -nostdinc -O2 pr101523.ii
-mlong-double-128 -march=z196 -fpreprocessed -w -fdump-rtl-combine-stats; awk
'/^attempts:/{attempts+=$2}/^merges:/{merges+=$2}/^extras:/{extras+=$2}/^successes/{successes+=$2}/^two-insn
combine:/{two+=$3}/^three-insn combine:/{three+=$3}/^four-insn
combine:/{four+=$3}/^insn-with-note combine/{note+=$3}END{printf "attempts:
%d\nmerges: %d\nextras: %d\nsuccesses: %d\ntwo-insn combine: %d\nthree-insn
combine: %d\nfour-insn combine: %d\ninsn-with-note combine: %d\n", attempts,
merges, extras, successes, two, three, four, note}' pr101523.ii.*combine*
attempts: 76272
merges: 74913
extras: 21116
successes: 801
two-insn combine: 800
three-insn combine: 1
four-insn combine: 0
insn-with-note combine: 0
$ rm pr101523.ii.*; LUIDDIFF=200 ./cc1plus -quiet -nostdinc -O2 pr101523.ii
-mlong-double-128 -march=z196 -fpreprocessed -w -fdump-rtl-combine-stats; awk
'/^attempts:/{attempts+=$2}/^merges:/{merges+=$2}/^extras:/{extras+=$2}/^successes/{successes+=$2}/^two-insn
combine:/{two+=$3}/^three-insn combine:/{three+=$3}/^four-insn
combine:/{four+=$3}/^insn-with-note combine/{note+=$3}END{printf "attempts:
%d\nmerges: %d\nextras: %d\nsuccesses: %d\ntwo-insn combine: %d\nthree-insn
combine: %d\nfour-insn combine: %d\ninsn-with-note combine: %d\n", attempts,
merges, extras, successes, two, three, four, note}' pr101523.ii.*combine*
attempts: 225950
merges: 223585
extras: 60074
successes: 1457
two-insn combine: 1456
three-insn combine: 1
four-insn combine: 0
insn-with-note combine: 0
$ rm pr101523.ii.*; LUIDDIFF=400 ./cc1plus -quiet -nostdinc -O2 pr101523.ii
-mlong-double-128 -march=z196 -fpreprocessed -w -fdump-rtl-combine-stats; awk
'/^attempts:/{attempts+=$2}/^merges:/{merges+=$2}/^extras:/{extras+=$2}/^successes/{successes+=$2}/^two-insn
combine:/{two+=$3}/^three-insn combine:/{three+=$3}/^four-insn
combine:/{four+=$3}/^insn-with-note combine/{note+=$3}END{printf "attempts:
%d\nmerges: %d\nextras: %d\nsuccesses: %d\ntwo-insn combine: %d\nthree-insn
combine: %d\nfour-insn combine: %d\ninsn-with-note combine: %d\n", attempts,
merges, extras, successes, two, three, four, note}' pr101523.ii.*combine*
attempts: 562238
merges: 558672
extras: 142181
successes: 2223
two-insn combine: 2222
three-insn combine: 1
four-insn combine: 0
insn-with-note combine: 0
$ rm pr101523.ii.*; LUIDDIFF=600 ./cc1plus -quiet -nostdinc -O2 pr101523.ii
-mlong-double-128 -march=z196 -fpreprocessed -w -fdump-rtl-combine-stats; awk
'/^attempts:/{attempts+=$2}/^merges:/{merges+=$2}/^extras:/{extras+=$2}/^successes/{successes+=$2}/^two-insn
combine:/{two+=$3}/^three-insn combine:/{three+=$3}/^four-insn
combine:/{four+=$3}/^insn-with-note combine/{note+=$3}END{printf "attempts:
%d\nmerges: %d\nextras: %d\nsuccesses: %d\ntwo-insn combine: %d\nthree-insn
combine: %d\nfour-insn combine: %d\ninsn-with-note combine: %d\n", attempts,
merges, extras, successes, two, three, four, note}' pr101523.ii.*combine*
attempts: 949334
merges: 943646
extras: 232455
successes: 2720
two-insn combine: 2719
three-insn combine: 1
four-insn combine: 0
insn-with-note combine: 0
$ rm pr101523.ii.*; LUIDDIFF=800 ./cc1plus -quiet -nostdinc -O2 pr101523.ii
-mlong-double-128 -march=z196 -fpreprocessed -w -fdump-rtl-combine-stats; awk
'/^attempts:/{attempts+=$2}/^merges:/{merges+=$2}/^extras:/{extras+=$2}/^successes/{successes+=$2}/^two-insn
combine:/{two+=$3}/^three-insn combine:/{three+=$3}/^four-insn
combine:/{four+=$3}/^insn-with-note combine/{note+=$3}END{printf "attempts:
%d\nmerges: %d\nextras: %d\nsuccesses: %d\ntwo-insn combine: %d\nthree-insn
combine: %d\nfour-insn combine: %d\ninsn-with-note combine: %d\n", attempts,
merges, extras, successes, two, three, four, note}' pr101523.ii.*combine*
attempts: 1584155
merges: 1576840
extras: 375785
successes: 3305
two-insn combine: 3304
three-insn combine: 1
four-insn combine: 0
insn-with-note combine: 0
$ rm pr101523.ii.*; LUIDDIFF=1000 ./cc1plus -quiet -nostdinc -O2 pr101523.ii
-mlong-double-128 -march=z196 -fpreprocessed -w -fdump-rtl-combine-stats; awk
'/^attempts:/{attempts+=$2}/^merges:/{merges+=$2}/^extras:/{extras+=$2}/^successes/{successes+=$2}/^two-insn
combine:/{two+=$3}/^three-insn combine:/{three+=$3}/^four-insn
combine:/{four+=$3}/^insn-with-note combine/{note+=$3}END{printf "attempts:
%d\nmerges: %d\nextras: %d\nsuccesses: %d\ntwo-insn combine: %d\nthree-insn
combine: %d\nfour-insn combine: %d\ninsn-with-note combine: %d\n", attempts,
merges, extras, successes, two, three, four, note}' pr101523.ii.*combine*
attempts: 2302888
merges: 2294229
extras: 536374
successes: 3836
two-insn combine: 3835
three-insn combine: 1
four-insn combine: 0
insn-with-note combine: 0
$ rm pr101523.ii.*; LUIDDIFF=1200 ./cc1plus -quiet -nostdinc -O2 pr101523.ii
-mlong-double-128 -march=z196 -fpreprocessed -w -fdump-rtl-combine-stats; awk
'/^attempts:/{attempts+=$2}/^merges:/{merges+=$2}/^extras:/{extras+=$2}/^successes/{successes+=$2}/^two-insn
combine:/{two+=$3}/^three-insn combine:/{three+=$3}/^four-insn
combine:/{four+=$3}/^insn-with-note combine/{note+=$3}END{printf "attempts:
%d\nmerges: %d\nextras: %d\nsuccesses: %d\ntwo-insn combine: %d\nthree-insn
combine: %d\nfour-insn combine: %d\ninsn-with-note combine: %d\n", attempts,
merges, extras, successes, two, three, four, note}' pr101523.ii.*combine*
attempts: 2805076
merges: 2795853
extras: 648411
successes: 4138
two-insn combine: 4137
three-insn combine: 1
four-insn combine: 0
insn-with-note combine: 0
$ rm pr101523.ii.*; LUIDDIFF=10000 ./cc1plus -quiet -nostdinc -O2 pr101523.ii
-mlong-double-128 -march=z196 -fpreprocessed -w -fdump-rtl-combine-stats; awk
'/^attempts:/{attempts+=$2}/^merges:/{merges+=$2}/^extras:/{extras+=$2}/^successes/{successes+=$2}/^two-insn
combine:/{two+=$3}/^three-insn combine:/{three+=$3}/^four-insn
combine:/{four+=$3}/^insn-with-note combine/{note+=$3}END{printf "attempts:
%d\nmerges: %d\nextras: %d\nsuccesses: %d\ntwo-insn combine: %d\nthree-insn
combine: %d\nfour-insn combine: %d\ninsn-with-note combine: %d\n", attempts,
merges, extras, successes, two, three, four, note}' pr101523.ii.*combine*
attempts: 31960714
merges: 31936996
extras: 7194023
successes: 8924
two-insn combine: 8923
three-insn combine: 1
four-insn combine: 0
insn-with-note combine: 0
So, I'd think punting only if the DF_INSN_LUID difference is >= something in
between 600 and 1200 is IMHO reasonable, say for 1000 the compiler will need
less than twice compiler memory than vanilla trunk and around 1.5x longer to
compile, but bet (haven't done full bootstraps/regtests with statistics
gathering) that most of the real-world cases on most arches are within 1000
insns.
But, do DEBUG_INSNs have their DF_INSN_LUID as well, so would that DF_INSN_LUID
difference cause -fcompare-debug issues?
