https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70557
--- Comment #5 from Albert Cahalan <acahalan at gmail dot com> ---
This example shows the most simple form of the problem:
unsigned long long ull;
void simple64(void){
ull = 0;
}
NOTE: In the assembly below, I might have missing/excess parentheses. Assembler
syntax varies.
gcc generates:
clr.L %d0
clr.L %d1
move.L %d0,ull
move.L %d1,ull+4
As you can see, two registers are set to the same value. It's better to set
just one, and even better to directly address memory with a clr.L instruction.
Also, given that this code was optimized for size and there was an address
register free, gcc should have put the address of ull into a register and then
used that, preferably with autoincrement addressing.
I'd like to see something like this:
movea.L ull, %a0
clr.L (%a0)+
clr.L (%a0)
When optimizing for speed and registers are not available, maybe this:
clr.L ull
clr.L ull+4
(the code is larger with those 6-byte instructions though, and it might
actually run slower especially considering the small cache)
