https://gcc.gnu.org/bugzilla/show_bug.cgi?id=22141
--- Comment #41 from ktkachov at gcc dot gnu.org --- (In reply to etienne_lorrain from comment #40) > Following my comment No 17, the optimisation could also be done for reads - > we still have (https://gcc.godbolt.org/ -O2 -m32) that: > struct S > { > char a; > char b; > char c; > char d; > } u, v; > > void fct (void) { > u.a = v.a; > u.b = v.b; > u.c = v.c; > u.d = v.d; > } > > compiled into: > fct(): > movzbl v, %eax > movb %al, u > movzbl v+1, %eax > movb %al, u+1 > movzbl v+2, %eax > movb %al, u+2 > movzbl v+3, %eax > movb %al, u+3 > ret > > Same if fct() contains "u = (struct S) {v.a, v.b, v.c, v.d};" > Where a single read32 / write32 could be used... > > Having fct() only do "u = v;" is compiled with a single read32 / write32. > I do not know if it is important enough, if it needs another bugzilla > number... > Thanks. Yeah, I separate bugzilla entry would be good here
