[Bug tree-optimization/56522] [4.8 Regression] Bytemark ASSIGNMENT 9% / 11% slower

[jakub at gcc dot gnu.org]

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.