[Mesa-dev] GLSL compiler function call cleaning

[Kenneth Graunke]

I finally resurrected this work I started back in September.  I think
I've included most of the old feedback, and done a bunch more cleaning.

This series changes ir_call from a value (which can be nested inside
expression trees) to a statement which can only appear in the instruction
stream.  This makes expression trees pure (free from side-effects), which
ought to make optimization passes easier to write and less error-prone.

It also resolves the ugliness where ir_call was the _only_ ir_rvalue
that could appear in an instruction stream, which was bizarre.

It also includes some AST->IR clean-ups, because...well.  It was a mess.

The one outstanding concern I have is IR->Mesa and IR->TGSI: both seem
to support function calls, but I'm not sure how that all works.  IMHO
Mesa IR really shouldn't support them---we should just rely on the GLSL
compiler's inliner.  I'm incredibly skeptical that the code in IR->Mesa
actually works, since it has a comment that functions other than main()
should never been seen.  Maybe that's just old.  Can we delete this?

I suspect IR->TGSI needs to support real function calls.  The code there
still compiles, but it probably breaks.  I probably need help adapting it.

No piglit regressions on i965.  Nothing else was tested.