[Bug target/44551] [missed optimization] AVX vextractf128 after vinsertf128

[glisse at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=44551

--- Comment #13 from Marc Glisse <glisse at gcc dot gnu.org> ---
Created attachment 32915
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=32915&action=edit
simplify vec_select(vec_concat)

A simpler/safer version of the patch linked in comment #12 (untested). It
optimizes the example in comment #11, but fails to optimize the original
testcase because simplify-rtx operations are only done on single-use operands,
and I don't know where in the RTL optimizers we can apply transformations
without this constraint.