[Bug tree-optimization/29777] missed optimization: model missing widen_mult* idioms for SSE

["dorit at il dot ibm dot com" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #2 from dorit at il dot ibm dot com  2006-11-09 20:26 -------
> But these files can be succesfully vectorized using current (gcc version 4.3.0
> 20061109) version on i686:
> gcc -O2 -msse2 -ftree-vectorize -fdump-tree-vect-all vect-widen-mult-sum.c
> vect-widen-mult-sum.c:16: note: LOOP VECTORIZED.
> vect-widen-mult-sum.c:12: note: vectorized 1 loops in function.

Probably because the i386 port models the "vect_unpack" and "vect_int_mult"
idioms (see
target-supports.exp:check_effective_target_vect_widen_mult_hi_to_si()): i.e.,
instead of recognizing it's a widening multiplication and vectorizing it as
such, it's vectorized by first unpacking (widening) the shorts to ints, and
then doing int multiplication, which is probably less efficient. Sorry for the
unclarity

> > The missing insns (that should be merged from autovect-branch and debugged):
> > vec_widen_umult_hi_v8hi
> > vec_widen_umult_lo_v8hi
> These patterns _are_ present in gcc version 4.3.0 20061109 (experimental) in
> sse.md.

I'm sorry - I meant vec_widen_smult_hi_v8hi and vec_widen_smult_lo_v8hi.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29777