[Bug tree-optimization/77848] Gimple if-conversion results in redundant comparisons

["rguenther at suse dot de" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77848

--- Comment #9 from rguenther at suse dot de <rguenther at suse dot de> ---
On Fri, 4 Nov 2016, wschmidt at gcc dot gnu.org wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77848
> 
> --- Comment #7 from Bill Schmidt <wschmidt at gcc dot gnu.org> ---
> OK, I will try to get some machine time to do performance testing of the
> existing patch as soon as possible.
> 
> Here is the list of failures:
> 
> > FAIL: gcc.dg/vect/bb-slp-cond-1.c -flto -ffat-lto-objects  scan-tree-dump-times slp1 "basic block vectorized" 1
> > FAIL: gcc.dg/vect/bb-slp-cond-1.c scan-tree-dump-times slp1 "basic block vectorized" 1
> 66a69,76
> > FAIL: gcc.dg/vect/vect-cond-1.c -flto -ffat-lto-objects  scan-tree-dump-times vect "OUTER LOOP VECTORIZED" 1
> > FAIL: gcc.dg/vect/vect-cond-1.c scan-tree-dump-times vect "OUTER LOOP VECTORIZED" 1
> > FAIL: gcc.dg/vect/vect-cond-3.c -flto -ffat-lto-objects  scan-tree-dump-times vect "OUTER LOOP VECTORIZED" 1
> > FAIL: gcc.dg/vect/vect-cond-3.c scan-tree-dump-times vect "OUTER LOOP VECTORIZED" 1
> > FAIL: gcc.dg/vect/vect-cond-4.c -flto -ffat-lto-objects  scan-tree-dump-times vect "OUTER LOOP VECTORIZED" 1
> > FAIL: gcc.dg/vect/vect-cond-4.c scan-tree-dump-times vect "OUTER LOOP VECTORIZED" 1
> > FAIL: gcc.dg/vect/vect-cond-6.c -flto -ffat-lto-objects  scan-tree-dump-times vect "OUTER LOOP VECTORIZED" 1
> > FAIL: gcc.dg/vect/vect-cond-6.c scan-tree-dump-times vect "OUTER LOOP VECTORIZED" 1

Ok, so that's outer loop vect not handling the if (LOOP_VECTORIZED ()) 
case -- if-conversion only handles innermost loops but the vectorizer
handles a single outer loop.  This means the if (LOOP_VECTORIZED ())
would need to be put on the outer loop or outer loop vectorization
would need to handle it in some way.  I think we already disable
outer loop vectorization when sth forces LOOP_VECTORIZED () for
if-conversion.  I think "ignoring" LOOP_VECTORIZED and its associated
CFG in outer loop vectorization and folding it away before transform
might work...  (we also fail to if-convert the "outer" loop btw).
See vect_analyze_loop_form_1 for what loop form we expect for outer
loop vectorization.