http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56522
--- Comment #3 from rguenther at suse dot de <rguenther at suse dot de> 2013-03-07 08:33:10 UTC --- On Wed, 6 Mar 2013, jakub at gcc dot gnu.org wrote: > > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56522 > > --- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-03-06 > 15:06:41 UTC --- > Created attachment 29598 > --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29598 > assign.c > > With -O3 -march=corei7 -fomit-frame-pointer -funroll-loops -ffast-math > the different in *.optimized dump from r196262 to r196263 is just: > @@ -176,7 +176,6 @@ Assignment (long int[101] * x) > short int[101][101] * pretmp_418; > long int _429; > long int _431; > - unsigned long _432; > long unsigned int patt_438; > unsigned int _440; > long unsigned int patt_441; > @@ -293,8 +292,7 @@ Assignment (long int[101] * x) > _108 = _130 >> 3; > _89 = -_108; > _72 = (short unsigned int) _89; > - _432 = _89 & 1; > - prolog_loop_niters.59_193 = (short unsigned int) _432; > + prolog_loop_niters.59_193 = _72 & 1; > if (prolog_loop_niters.59_193 == 0) > goto <bb 19>; > else > @@ -307,7 +305,7 @@ Assignment (long int[101] * x) > <bb 19>: > # j_288 = PHI <1(18), 0(17)> > # c_287 = PHI <c_141(18), 9223372036854775807(17)> > - prolog_loop_adjusted_niters.60_357 = _89 & 1; > + prolog_loop_adjusted_niters.60_357 = (sizetype) prolog_loop_niters.59_193; > niters.61_359 = 101 - prolog_loop_niters.59_193; > base_off.68_53 = prolog_loop_adjusted_niters.60_357 * 8; > vect_p.69_48 = pretmp_386 + base_off.68_53; > > From the bugreport, it isn't clear if you were measuring -m32 or -m64 > performance, but I guess the *.optimized dump change could just increase > register pressure and pessimize the loop RA or something. Yeah, I don't see anything wrong with the change otherwise. Note that forwprop's tree combiner doesn't seem to restrict itself to single-use defs in all cases.
