[Bug target/126328] x86 costing rejects forming of *sse3_haddv2df3_low from vec_select of sse3_haddv2df

[segher at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126328

--- Comment #5 from Segher Boessenkool <segher at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #3)
> so we are back to a cost of 4, because combine_validate_cost doesn't
> re-recog before costing :/

What does this mean?  The result of recog () should depend only on the RTL of
the insn, always.  So why would you ever want to run recog () more often than
required?