[gcc r13-1083] vect: Move suggested_unroll_factor applying [PR105940]

[gcc r13-1083] vect: Move suggested_unroll_factor applying [PR105940]

[Kewen Lin]

https://gcc.gnu.org/g:f907cf4c07cf51863dadbe90894e2ae3382bada5

commit r13-1083-gf907cf4c07cf51863dadbe90894e2ae3382bada5
Author: Kewen Lin <linkw@linux.ibm.com>
Date:   Tue Jun 14 00:57:01 2022 -0500

    vect: Move suggested_unroll_factor applying [PR105940]
    
    As PR105940 shown, when rs6000 port tries to assign
    m_suggested_unroll_factor by 4 or so, there will be ICE on:
    
      exact_div (LOOP_VINFO_VECT_FACTOR (loop_vinfo),
                 loop_vinfo->suggested_unroll_factor);
    
    In function vect_analyze_loop_2, the current place of
    suggested_unroll_factor applying can't guarantee it's
    applied for all cases.  As the case shows, vectorizer
    could retry with SLP forced off, the vf is reset by
    saved_vectorization_factor which isn't applied with
    suggested_unroll_factor before.  It means it can end
    up with one vf which neglects suggested_unroll_factor.
    I think it's off design, we should move the applying
    of suggested_unroll_factor after start_over.
    
            PR tree-optimization/105940
    
    gcc/ChangeLog:
    
            * tree-vect-loop.cc (vect_analyze_loop_2): Move the place of
            applying suggested_unroll_factor after start_over.

Diff:
---
 gcc/tree-vect-loop.cc | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
index 246347b9b08..e05f8e87f7d 100644
--- a/gcc/tree-vect-loop.cc
+++ b/gcc/tree-vect-loop.cc
@@ -2388,15 +2388,15 @@ vect_analyze_loop_2 (loop_vec_info loop_vinfo, bool &fatal,
      set of rgroups.  */
   gcc_assert (LOOP_VINFO_MASKS (loop_vinfo).is_empty ());
 
+  /* This is the point where we can re-start analysis with SLP forced off.  */
+start_over:
+
   /* Apply the suggested unrolling factor, this was determined by the backend
      during finish_cost the first time we ran the analyzis for this
      vector mode.  */
   if (loop_vinfo->suggested_unroll_factor > 1)
     LOOP_VINFO_VECT_FACTOR (loop_vinfo) *= loop_vinfo->suggested_unroll_factor;
 
-  /* This is the point where we can re-start analysis with SLP forced off.  */
-start_over:
-
   /* Now the vectorization factor is final.  */
   poly_uint64 vectorization_factor = LOOP_VINFO_VECT_FACTOR (loop_vinfo);
   gcc_assert (known_ne (vectorization_factor, 0U));