[gcc r15-4225] Enable vectorization for unknown tripcount in very cheap cost model but disable epilog vectorization

[hongtao Liu via Gcc-cvs]

https://gcc.gnu.org/g:70c3db511ba14ff5fa68cb41d0714a9fb957ea5d

commit r15-4225-g70c3db511ba14ff5fa68cb41d0714a9fb957ea5d
Author: liuhongt <hongtao....@intel.com>
Date:   Mon Mar 25 21:28:14 2024 -0700

    Enable vectorization for unknown tripcount in very cheap cost model but 
disable epilog vectorization.
    
    gcc/ChangeLog:
    
            * tree-vect-loop.cc (vect_analyze_loop_costing): Enable
            vectorization for LOOP_VINFO_PEELING_FOR_NITER in very cheap
            cost model.
            (vect_analyze_loop): Disable epilogue vectorization in very
            cheap cost model.
            * doc/invoke.texi: Adjust documents for very-cheap cost model.

Diff:
---
 gcc/doc/invoke.texi   | 11 ++++-------
 gcc/tree-vect-loop.cc |  6 +++---
 2 files changed, 7 insertions(+), 10 deletions(-)

diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index c0c8bf1c29a9..12477e6f9df3 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -14315,13 +14315,10 @@ counts that will likely execute faster than when 
executing the original
 scalar loop.  The @samp{cheap} model disables vectorization of
 loops where doing so would be cost prohibitive for example due to
 required runtime checks for data dependence or alignment but otherwise
-is equal to the @samp{dynamic} model.  The @samp{very-cheap} model only
-allows vectorization if the vector code would entirely replace the
-scalar code that is being vectorized.  For example, if each iteration
-of a vectorized loop would only be able to handle exactly four iterations
-of the scalar loop, the @samp{very-cheap} model would only allow
-vectorization if the scalar iteration count is known to be a multiple
-of four.
+is equal to the @samp{dynamic} model.  The @samp{very-cheap} model disables
+vectorization of loops when any runtime check for data dependence or alignment
+is required, it also disables vectorization of epilogue loops but otherwise is
+equal to the @samp{cheap} model.
 
 The default cost model depends on other optimization flags and is
 either @samp{dynamic} or @samp{cheap}.
diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
index 9be50aaa621c..ade72a5124f7 100644
--- a/gcc/tree-vect-loop.cc
+++ b/gcc/tree-vect-loop.cc
@@ -2375,8 +2375,7 @@ vect_analyze_loop_costing (loop_vec_info loop_vinfo,
      a copy of the scalar code (even if we might be able to vectorize it).  */
   if (loop_cost_model (loop) == VECT_COST_MODEL_VERY_CHEAP
       && (LOOP_VINFO_PEELING_FOR_ALIGNMENT (loop_vinfo)
-         || LOOP_VINFO_PEELING_FOR_GAPS (loop_vinfo)
-         || LOOP_VINFO_PEELING_FOR_NITER (loop_vinfo)))
+         || LOOP_VINFO_PEELING_FOR_GAPS (loop_vinfo)))
     {
       if (dump_enabled_p ())
        dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
@@ -3683,7 +3682,8 @@ vect_analyze_loop (class loop *loop, gimple 
*loop_vectorized_call,
                           /* No code motion support for multiple epilogues so 
for now
                              not supported when multiple exits.  */
                         && !LOOP_VINFO_EARLY_BREAKS (first_loop_vinfo)
-                        && !loop->simduid);
+                        && !loop->simduid
+                        && loop_cost_model (loop) > 
VECT_COST_MODEL_VERY_CHEAP);
   if (!vect_epilogues)
     return first_loop_vinfo;