http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40436
--- Comment #45 from rguenther at suse dot de <rguenther at suse dot de> 2010-11-14 17:38:46 UTC --- On Sun, 14 Nov 2010, hubicka at gcc dot gnu.org wrote: > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40436 > > --- Comment #44 from Jan Hubicka <hubicka at gcc dot gnu.org> 2010-11-14 > 16:16:35 UTC --- > OK, ialloc is because 4.3 folds: > oldbit_430 = 0; > D.12699_431 = oldbit_430 & 1; > D.12698_462 = D.12699_431; > D.12095_241 = D.12698_462; > if (D.12095_241 != 0) > goto <bb 71>; > else > goto <bb 72>; > > In mainline the same sequence misses oldbit_430 = 0. > > static __inline__ int > test_and_set_bit_simple(unsigned long nr, volatile void * addr) > { > unsigned long reg1, reg2; > int oldbit; > > return oldbit & 1; > } > > > > > > static __inline__ int > test_and_clear_bit_simple(unsigned long nr, volatile void * addr) > { > unsigned long reg1, reg2; > int oldbit; > > > return oldbit & 1; > } > > > > > > static __inline__ int > test_and_change_bit_simple(unsigned long nr, volatile void * addr) > { > unsigned long reg1, reg2; > int oldbit; > > > return oldbit & 1; > } > > So another source code bug. > Richard, do you remember if we dropped initialization by zero for > uninitialized > vars? I don't even remember that we did that. Btw, CCP should be able to fold it with UNDEFINED given that & 1 cannot yield zero (but we're very conservative here now due to past bugs ...)
