[Bug middle-end/22141] [5/6/7 Regression] Missing optimization when storing structures

[etienne_lorrain at yahoo dot fr]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=22141

--- Comment #40 from etienne_lorrain at yahoo dot fr ---
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.