On Mon, May 19, 2014 at 5:51 PM, Michael Matz <m...@suse.de> wrote: > Hi, > > On Thu, 15 May 2014, Richard Biener wrote: > >> To me predicate (and capture without expression or predicate) >> differs from expression in that predicate is clearly a leaf of the >> expression tree while we have to recurse into expression operands. >> >> Now, if we want to support applying predicates to the midst of an >> expression, like >> >> (plus predicate(minus @0 @1) >> @2) >> (...) >> >> then this would no longer be true. At the moment you'd write >> >> (plus (minus@3 @0 @1) >> @2) >> if (predicate (@3)) >> (...) >> >> which makes it clearer IMHO (with the decision tree building >> you'd apply the predicates after matching the expression tree >> anyway I suppose, so code generation would be equivalent). > > Syntaxwise I had this idea for adding generic predicates to expressions: > > (plus (minus @0 @1):predicate > @2) > (...)
So you'd write (plus @0 :integer_zerop) instead of (plus @0 integer_zerop) ? > If prefix or suffix doesn't matter much, but using a different syntax > to separate expression from predicate seems to make things clearer. > Optionally adding things like and/or for predicates might also make sense: > > (plus (minus @0 @1):positive_p(@0) || positive_p(@1) > @2) > (...) negation whould be more useful I guess. You open up a can of worms with ordering though: (plus (minus @0 @1) @2:operand_equal_p (@1, @2, 0)) which might be declared invalid or is equivalent to (plus (minus @0 @1) @2):operand_equal_p (@1, @2, 0) ? Note that your predicate placement doesn't match placement of captures for non-innermost expressions. capturing the outer plus would be (plus@3 (minus @0 @1) @2) not (plus (minus @0 @1) @2)@3 so maybe apply predicates there as well: (plus:operand_equal_p (@1, @2, 0) (minus @0 @1) @2) But I still think that doing all predicates within a if-expr makes the pattern less convoluted. Enabling/disabling a whole set of patterns with a common condition might still be a worthwhile addition. Richard. > > Ciao, > Michael.
