On Mar 23, 2012, at 3:01 AM, Richard Sandiford wrote:
> ...it doesn't mean that we interpret the value as a negative _rtx_.
> As with all rtx calculations, things like signedness and saturation are
> decided by the operation rather than the "type" ("type" == rtx mode).

Ah...  [ light goes on ]  Let me adjust the documentation to be exceptionally clear in this case.  Check out the new wording on const_int, const_double and on immed_double_const.  I fixed simplify_const_unary_operation to match your suggestion.

> Sorry for the rather rambling explanation :-)  I still think the
> version I suggested for this hunk is right though.

I agree.  I now see what I had wrong.  Thanks for your patience and explanations.  If you like the wording I used in the doc and on immed_double_const, I think we have now resolved all issues.  The previous version was bootstraped and regression tested on darwin, fortran, c, c++, objective-c++...  I'll do one more run with the update for simplify_const_unary_operation, as that can trip when before it would merely return 0.

Ok?