On Thu, 11 Sept 2025 at 19:44, Jakub Jelinek <ja...@redhat.com> wrote: > > On Thu, Sep 11, 2025 at 07:14:51PM +0200, Richard Biener wrote: > > Yes, RTL expansion inserts an AND operation when !SHIFT_COUNT_TRUNCATED. > > What I was saying there's no way to get a negative shift count flip shift > > direction to RTL - it would require a target specific intrinsic that's a > > builtin > > call before RTL expansion and an UNSPEC after. > > Of course the target can have patterns like: > (set (match_operand:M 0) > (if_then_else:M > (lt:SI (match_operand:SI 2) (const_int 0)) > (ashiftrt:M (match_operand:M 1) (neg:SI (match_dup 2))) > (ashift:M (match_dup 1) (match_dup 2)))) > or so, it doesn't need to use UNSPEC for that. >
Hi! Thanks for all the feedback, that was very useful. I've implemented the suggestion above, but so far I couldn't make the 'if' condition match (the shift amount is never seen as negative with my tests). Since the constraint is "rPg", where "Pg" means "constant in range 1 to 32", out-of-range values are always passed in register: can the above if_then_else work when operand 2 is a register? Christophe > Jakub >
