https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106187
Richard Earnshaw <rearnsha at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |rguenth at gcc dot gnu.org
--- Comment #26 from Richard Earnshaw <rearnsha at gcc dot gnu.org> ---
git bisect points to commit r11-9688 resolving the issue. Before that commit
the ivopts pass generates:
ivtmp.761_217 = (unsigned int) &au;
_222 = &bu + 4;
ivtmp.767_220 = (unsigned int) _222;
_225 = (unsigned int) &au;
_228 = _225 + 16;
<bb 9> [local count: 858993457]:
# prephitmp_136 = PHI <pretmp_120(10), 1073741824(8)>
# prephitmp_32 = PHI <pretmp_18(10), 2147483648(8)>
# ivtmp.761_278 = PHI <ivtmp.761_216(10), ivtmp.761_217(8)>
# ivtmp.767_218 = PHI <ivtmp.767_219(10), ivtmp.767_220(8)>
_16 = prephitmp_32 ^ prephitmp_136;
_223 = (void *) ivtmp.761_278;
MEM[(unsigned int *)_223] = _16;
ivtmp.761_216 = ivtmp.761_278 + 4;
if (ivtmp.761_216 != _228)
goto <bb 10>; [75.00%]
else
goto <bb 11>; [25.00%]
<bb 10> [local count: 644245086]:
_230 = (void *) ivtmp.761_216;
pretmp_120 = MEM[(unsigned int *)_230];
_229 = (void *) ivtmp.767_218;
pretmp_18 = MEM[(unsigned int *)_229];
ivtmp.767_219 = ivtmp.767_218 + 4;
goto <bb 9>; [100.00%]
And once that patch is applied we get:
ivtmp.761_217 = (unsigned int) &au;
ivtmp.766_220 = (unsigned int) &bu;
_223 = (unsigned int) &au;
_225 = _223 + 16;
<bb 9> [local count: 858993457]:
# prephitmp_136 = PHI <pretmp_120(10), 1073741824(8)>
# prephitmp_32 = PHI <pretmp_18(10), 2147483648(8)>
# ivtmp.761_278 = PHI <ivtmp.761_216(10), ivtmp.761_217(8)>
# ivtmp.766_218 = PHI <ivtmp.766_219(10), ivtmp.766_220(8)>
_16 = prephitmp_32 ^ prephitmp_136;
_222 = (void *) ivtmp.761_278;
MEM[(unsigned int *)_222] = _16;
ivtmp.761_216 = ivtmp.761_278 + 4;
if (ivtmp.761_216 != _225)
goto <bb 10>; [75.00%]
else
goto <bb 11>; [25.00%]
The main difference being that in the 'bad' code we start with &bu + 4, while
in the good code we start with &bu.
I'm afraid I don't know enough about this code to take this further. Richi?
