On Fri, 10 Feb 2012, Richard Henderson wrote:
> Seeing as how Uros is starting to go down the path of cleaning up the
> flags handling for x86, I thought I'd go ahead and knock up the idea
> that I've been tossing around to help automate the process of building
> patterns that match both clobbering the flags and setting the flags to
> a comparison.
Sometimes the destination too unless there's overlap, but I
don't know how often that matters.
> This is far from complete, but it at least shows the direction.
Yes, nice!
> What I know is missing off the top of my head are:
> (2) Can't be usefully used with define_insn_and_split, and no way to tell.
> This problem should simply be documented in the .texi file as user error.
Not sure I see the problem or the impact of the absence. Would
it help if there was a way to match_dup the clobber/set? Maybe
as a match_op_flags, the same as match_flags but with the first
argument being an assigning operand number. You probably
wouldn't want to use this very often.)
> (3) Can't be used for x86 add patterns, as the "clobber" version wants the
> freedom to use "lea" and the "set flags" version cannot. And there are
> different sets of constraints if lea may be used or not.
Other targets too, but as it's warty for x86 I hope eventually
this'll see improvement...
> Comments?
Er... very interesting! (The kind of patch you want to play
around with to have any further insightful comments.)
So I can use match_{operand,whatever} in the second, optional
operand to match_flags? No, wait, no use to have anything but
a match_dup, hm.
I don't see where it'd make sense to have anything else but the
default, absent argument. Example?
brgds, H-P
