Generating gimple assign stmt that changes sign

[Kugan Vivekanandarajah <kugan dot vivekanandarajah at linaro dot org>]

Hi,

I am looking to introduce ABSU_EXPR and that would create:

unsigned short res = ABSU_EXPR (short);

Note that the argument is signed and result is unsigned. As per the
review, I have a match.pd entry to generate this as:
(simplify (abs (convert @0))
 (if (ANY_INTEGRAL_TYPE_P (TREE_TYPE (@0)))
  (convert (absu @0))))


Now when gimplifying the converted tree, how do we tell that ABSU_EXPR
will take a signed arg and return unsigned. I will have other match.pd
entries so this will be generated while in gimple.passes too. Should I
add new functions in gimple.[h|c] for this.

Is there any examples I can refer to. Conversion expressions seems to
be the only place where sign can change in gimple assignment but they
are very specific.

Thanks,
Kugan