Re: approaches to carry-flag modelling in RTL

[Joern Rennecke <amylaar at spamcop dot net>]

Quoting Hans-Peter Nilsson <hp@bitrange.com>:

> I came to the somewhat the same conclusion for CRIS where all
> insns set condition codes except move to memory and a "add
> reg1,reg2" (no immediate operand) and to/from special registers:
> there'll one clobbering and one CC_REG-setting pattern plus a
> load of others (peephole2's mostly) to get an exact match.
>
> What would help is a kind of iterator that (also) affects the
> form of the insn, so you could match the clobbering and the
> cc0-setting insn in the same (iterator-using) pattern.

match_parallel is useful for recognizing insns with varying clobbers.
Unfortunately, it is absolutely useless when you want a reasonable expander,
so then you end up having a separate expander pattern, even if all you want to
do is have structure of the patch_parallel without extra clobbers.
Repeat for a dozen similar instructions, and it gets really annoying.