On 1/18/07, Richard Kenner <[EMAIL PROTECTED]> wrote:
> I'm not immediately aware of too many cases where lowering the IL is
> going to expose new opportunities to track and optimize nonzero/zero
> bits stuff.
Bitfield are the big one. If you have both bitfield and logical operations,
you can often merge the logical operations with those used to retrieve
and/or store the field.
Things such as
x.y |= 1;
where Y is a bitfield and X non-BLKmode would be a large sequence of logical
operations that can all be replaced by a single OR insn at the RTL level
but presents no optimization opportunities at the tree level.
I have found another case where a zero / sign extend is inhibiting optimization
extern char b;
extern char c;
int main()
{
b <<= 1;
b <<= 1;
b <<= 1;
c = b;
return 0;
}
Here again a zero extend gets generated after every 'ashift' whereas
we are interested only in the lower order 8 bits. However when i try
the same thing with int instead of char i.e. there is no need for
extension then the operations get converted into b<<=3 instead of 3
instructions.
regards,
Pranav
