https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103675
Bug ID: 103675
Summary: gather is a loss for floats and win for doubles at
zen3
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: hubicka at gcc dot gnu.org
Target Milestone: ---
Currently we disable gather on zen1/2 and enable it for zen3. This was based
on testing I did before Richard's code for open coding it. Testing the only
kernels using gather in zen3 with double I get:
jh@ryzen3:~/tsvc/src> ~/trunk-install/bin/gcc tsvc.c -Ofast -march=native
common.c dummy.c -lm -mtune-ctrl=use_gather
jh@ryzen3:~/tsvc/src> ./a.out
Loop Time(sec) Checksum
s352 7.529 1.644903
s4112 1.317 1127072.247160
s4114 1.377 32000.000684
s4115 1.250 1.038812
s4116 0.873 0.753265
s4117 1.283 32002.208699
s4121 0.583 196490.281734
jh@ryzen3:~/tsvc/src> ~/trunk-install/bin/gcc tsvc.c -Ofast -march=native
common.c dummy.c -lm -mtune-ctrl=^use_gather
jh@ryzen3:~/tsvc/src> ./a.out
Loop Time(sec) Checksum
s352 7.618 1.644903
s4112 1.223 1127072.247160
s4114 1.523 32000.000684
s4115 2.019 1.038812
s4116 1.531 0.753265
s4117 1.388 32002.208699
s4121 0.549 196490.281734
So it using gather is a win. For floats I get:
jh@ryzen3:~/tsvc/src> ~/trunk-install/bin/gcc tsvc.c -Ofast -march=native
common.c dummy.c -lm -mtune-ctrl=use_gather ; ./a.out
Loop Time(sec) Checksum
s352 7.419 1.644808
s4112 1.183 1127128.875000
s4114 1.198 32000.000000
s4115 1.056 1.038788
s4116 0.817 0.753265
s4117 1.179 32002.205078
s4121 0.264 196500.265625
jh@ryzen3:~/tsvc/src> ~/trunk-install/bin/gcc tsvc.c -Ofast -march=native
common.c dummy.c -lm -mtune-ctrl=^use_gather ; ./a.out
Loop Time(sec) Checksum
s352 7.435 1.644808
s4112 0.742 1127128.875000
s4114 1.078 32000.000000
s4115 0.673 1.038788
s4116 0.532 0.753264
s4117 1.044 32002.205078
s4121 0.266 196500.265625
so using gather is loss. For long I get:
jh@ryzen3:~/tsvc/src> ~/trunk-install/bin/gcc tsvc.c -Ofast -march=native
common.c dummy.c -lm -mtune-ctrl=use_gather ; ./a.out
Loop Time(sec) Checksum
s352 4.327 1.000000
s4112 1.576 132000.000000
s4114 1.603 32000.000000
s4115 1.453 0.000000
s4116 1.131 0.000000
s4117 1.432 32001.000000
s4121 0.629 132000.000000
jh@ryzen3:~/tsvc/src> ~/trunk-install/bin/gcc tsvc.c -Ofast -march=native
common.c dummy.c -lm -mtune-ctrl=^use_gather ; ./a.out
Loop Time(sec) Checksum
s352 4.532 1.000000
s4112 1.630 132000.000000
s4114 1.808 32000.000000
s4115 1.431 0.000000
s4116 1.130 0.000000
s4117 1.646 32001.000000
s4121 0.638 132000.000000
so gather is a win
For int I get:
jh@ryzen3:~/tsvc/src> ~/trunk-install/bin/gcc tsvc.c -Ofast -march=native
common.c dummy.c -lm -mtune-ctrl=use_gather ; ./a.out
Loop Time(sec) Checksum
s352 1.345 1.000000
s4112 1.057 132000.000000
s4114 1.095 32000.000000
s4115 1.055 0.000000
s4116 0.817 0.000000
s4117 1.022 32001.000000
s4121 0.266 132000.000000
jh@ryzen3:~/tsvc/src> ~/trunk-install/bin/gcc tsvc.c -Ofast -march=native
common.c dummy.c -lm -mtune-ctrl=^use_gather ; ./a.out
Loop Time(sec) Checksum
s352 1.345 1.000000
s4112 0.730 132000.000000
s4114 1.089 32000.000000
s4115 0.679 0.000000
s4116 0.528 0.000000
s4117 1.013 32001.000000
s4121 0.262 132000.000000
so gather is a loss. So i suppose we want to disable gathers for 32bit and
smaller datatypes?
