Since this came up the other day in the "post-reload compare optimization pass" discussion, I thought better comment on this old post in case someone is tempted to do something...
On Wed, 2 Nov 2011, Richard Henderson wrote: > Frankly, I'd prefer to flip the default. It does seem to make the most sense. > We shan't do that until we tackle... > > On 11/01/2011 02:59 PM, Hans-Peter Nilsson wrote: > > I'm still thinking of a generic md iterator mechanism (one that > > doesn't restrict the form of the expansion in ways getting in > > the way with expanding to both a clobber and a set, and in > > swapped locations as above), to make the troubles go away... > > But maybe expanding them by a pass through e.g. m4 would be > > better than cooking up something new there. > > ... this, so that it can all be done automatically. > > I think some sort of iterator mechanism is best, much like we > automate cond_exec and other sorts of macro-izations. > > I can imagine a sort of > > (define_insn_with_flags "name" > [(set ...) > (set (reg:cc) (...)] > "" > ...) > > where we automatically expand to > > (define_insn "name" > [(set ...) > (clobber (reg:cc))] > ...) > > (define_insn "name_flags" > [(set ...) > (set (reg:cc) (...)] > ...) > > or something like that. Of equal value would be an optional third expansion for that define_insn_with_flags thing with just the plain "main" set, for the cases where (for some alternatives) the plain set can be emitted without CC side effects. brgds, H-P
