[Bug middle-end/55027] simplify vector multiplication by 1

[glisse at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55027

--- Comment #2 from Marc Glisse <glisse at gcc dot gnu.org> 2012-10-24 19:35:03 UTC ---
Created attachment 28525
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=28525
patch

Surprisingly enough, the attached patch doesn't cause any regression in the
testsuite (default languages). I'll add a simple testcase and submit it.

Some remaining predicates that don't handle vectors are integer_nonzerop,
integer_pow2p, but some adaptations are necessary in the users before they can
be changed (at least for pow2p).