On 06/16/2011 05:44 AM, Bernd Schmidt wrote:
> +@deftypefn {Built-in Function} int __builtin_clrsb (unsigned int x)
> +Returns the number of leading redundant sign bits in @var{x}, starting
> +at the most significant bit position.
> +@end deftypefn
Do we want a signed argument, since we're talking about signs?
It would seem that unlike clz, this function is not undefined for zero.
What about INT_MIN? Do all cpus handle those edge cases the same way?
Both should probably be documented both for the builtin and the rtx code.
> + if (x == 0 || x == (Wtype)-1)
> + return W_TYPE_SIZE - 1;
> + if (x > 0)
> + count_leading_zeros (ret, x);
> + else
> + count_leading_zeros (ret, ~x);
> + return ret - 1;
Do you get smaller code in general from
if (x < 0)
x = ~x;
if (x == 0)
return W_TYPE_SIZE - 1;
count_leading_zeros(ret, x);
return ret - 1;
?
> -(define_insn "signbitssi2"
> +(define_insn "clrsbsi2"
> [(set (match_operand:HI 0 "register_operand" "=d")
> (if_then_else:HI
> (lt (match_operand:SI 1 "register_operand" "d") (const_int 0))
No use of the new rtx code? Not that this couldn't be handled
with a different patch, but I don't see how you're testing the
code in simplify-rtx without at least one such use.
r~
