abs insn with QI and HI mode

[Jim Wilson]

Ying Yi wrote:
> The generated codes do the following operations: 1) extend variable a_HI 
> (HImode) to temp variable SImode, and do abs operation with SImode 
> operators. I find the gimple intermedia represention as shown below:

abs is a standard library function that takes an int as an argument.  So 
if you call abs(), then gcc must convert the argument to type int before 
generating code for the abs.

To get your special char/short abs instructions, we need one of two things
1) Optimization support to recognize a sign-extend followed by an abs, 
where the target has an abs instruction that operates on the 
pre-extended value.  We can then optimize away the sign extend 
instruction.  This optimization support apparently does not exist at the 
moment, perhaps because no one has needed it before.
2)  Alternative abs function calls that accept short/char.  We already 
have abs (int), labs (long), llabs(long long), fabs (double), fabsf 
(float) and fabsl (long double).
-- 
Jim Wilson, GNU Tools Support, http://www.specifix.com