CC_MODE and cc0

[Kazu Hirata]

Hi Paul,

> It sounds like i386 is supposed to be an example of how to do things.
> But looking at i386.md, the first thing I see is patterns that match
> compare/jump pairs.  That doesn't seem the way to optimal code, and
> sure enough, in a simple test program I end up with 
> 	cmpl	$4, %eax
> 	je	.L4
> 	cmpl	$4, %eax
> 	jle	.L3
> which looks like a redundant compare, unless I misunderstand i386
> machine code.  (By comparison, the pdp11 back end, which uses cc0,
> produces the desired result: one compare, two branches.)

This has just been fixed by Ian.  See PR 1532.

> Is there a recipe documented anywhere that shows how the move away
> from cc0 is supposed to happen, and in particular how to make it work
> in such a way that the code quality doesn't suffer?  It would be nice
> if this were captured in documentation somewhere that can be found...

I haven't seen any, but I am thinking about writing down my
experiences on H8 once that's done.

Kazu Hirata