Re: [vect] Re-analyze all modes for epilogues

["Andre Vieira (lists)" <andre.simoesdiasvieira@arm.com>]

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Made the suggested changes.

Regarding the name change to partial vectors, I agree in the name change 
since that is the terminology we are using in the loop_vinfo members 
too, but is there an actual difference between predication/masking and 
partial vectors that I am missing?

OK for trunk?

gcc/ChangeLog:

         * tree-vect-loop.c (vect_better_loop_vinfo_p): Round factors up 
for epilogue costing.
         (vect_analyze_loop): Re-analyze all modes for epilogues, unless 
we are guaranteed that we can't
         have partial vectors.
         (genopinit.c) (partial_vectors_supported): Generate new function.

gcc/testsuite/ChangeLog:

         * gcc.target/aarch64/masked_epilogue.c: New test.

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diff --git a/gcc/genopinit.c b/gcc/genopinit.c
index 195ddf74fa2b7d89760622073dcec9d5d339a097..2bc7cdbf53337beae181afd7bb05b366ab068c6a 100644
--- a/gcc/genopinit.c
+++ b/gcc/genopinit.c
@@ -321,6 +321,7 @@ main (int argc, const char **argv)
 	   "  bool supports_vec_scatter_store_cached;\n"
 	   "};\n"
 	   "extern void init_all_optabs (struct target_optabs *);\n"
+	   "extern bool partial_vectors_supported_p (void);\n"
 	   "\n"
 	   "extern struct target_optabs default_target_optabs;\n"
 	   "extern struct target_optabs *this_fn_optabs;\n"
@@ -373,6 +374,33 @@ main (int argc, const char **argv)
     fprintf (s_file, "  ena[%u] = HAVE_%s;\n", i, p->name);
   fprintf (s_file, "}\n\n");
 
+  fprintf (s_file,
+	   "/* Returns TRUE if the target supports any of the partial vector\n"
+	   "   optabs: while_ult_optab, len_load_optab or len_store_optab,\n"
+	   "   for any mode.  */\n"
+	   "bool\npartial_vectors_supported_p (void)\n{\n");
+  bool any_match = false;
+  fprintf (s_file, "\treturn");
+  bool first = true;
+  for (i = 0; patterns.iterate (i, &p); ++i)
+    {
+#define CMP_NAME(N) !strncmp (p->name, (N), strlen ((N)))
+      if (CMP_NAME("while_ult") || CMP_NAME ("len_load")
+	  || CMP_NAME ("len_store"))
+	{
+	  if (first)
+	    fprintf (s_file, " HAVE_%s", p->name);
+	  else
+	    fprintf (s_file, " || HAVE_%s", p->name);
+	  first = false;
+	  any_match = true;
+	}
+    }
+  if (!any_match)
+    fprintf (s_file, " false");
+  fprintf (s_file, ";\n}\n");
+
+
   /* Perform a binary search on a pre-encoded optab+mode*2.  */
   /* ??? Perhaps even better to generate a minimal perfect hash.
      Using gperf directly is awkward since it's so geared to working
diff --git a/gcc/testsuite/gcc.target/aarch64/masked_epilogue.c b/gcc/testsuite/gcc.target/aarch64/masked_epilogue.c
new file mode 100644
index 0000000000000000000000000000000000000000..286a7be236f337fee4c4650f42da72000855c5e6
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/masked_epilogue.c
@@ -0,0 +1,10 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -ftree-vectorize -fdump-tree-vect-details -march=armv8-a+sve -msve-vector-bits=scalable" } */
+
+void f(unsigned char y[restrict],
+       unsigned char x[restrict], int n) {
+  for (int i = 0; i < n; ++i)
+    y[i] = (y[i] + x[i] + 1) >> 1;
+}
+
+/* { dg-final { scan-tree-dump {LOOP EPILOGUE VECTORIZED \(MODE=VNx} "vect" } } */
diff --git a/gcc/tree-vect-loop.c b/gcc/tree-vect-loop.c
index a28bb6321d76b8222bc8cfdade151ca9b4dca406..5af98a36678ae61e99f93beb90920e2d0940c53a 100644
--- a/gcc/tree-vect-loop.c
+++ b/gcc/tree-vect-loop.c
@@ -2824,11 +2824,13 @@ vect_better_loop_vinfo_p (loop_vec_info new_loop_vinfo,
 	{
 	  unsigned HOST_WIDE_INT main_vf_max
 	    = estimated_poly_value (main_poly_vf, POLY_VALUE_MAX);
+	  unsigned HOST_WIDE_INT old_vf_max
+	    = estimated_poly_value (old_vf, POLY_VALUE_MAX);
+	  unsigned HOST_WIDE_INT new_vf_max
+	    = estimated_poly_value (new_vf, POLY_VALUE_MAX);
 
-	  old_factor = main_vf_max / estimated_poly_value (old_vf,
-							   POLY_VALUE_MAX);
-	  new_factor = main_vf_max / estimated_poly_value (new_vf,
-							   POLY_VALUE_MAX);
+	  old_factor = CEIL (main_vf_max, old_vf_max);
+	  new_factor = CEIL (main_vf_max, new_vf_max);
 
 	  /* If the loop is not using partial vectors then it will iterate one
 	     time less than one that does.  It is safe to subtract one here,
@@ -3069,8 +3071,6 @@ vect_analyze_loop (class loop *loop, vec_info_shared *shared)
   machine_mode autodetected_vector_mode = VOIDmode;
   opt_loop_vec_info first_loop_vinfo = opt_loop_vec_info::success (NULL);
   unsigned int mode_i = 0;
-  unsigned int first_loop_i = 0;
-  unsigned int first_loop_next_i = 0;
   unsigned HOST_WIDE_INT simdlen = loop->simdlen;
 
   /* First determine the main loop vectorization mode, either the first
@@ -3079,7 +3079,6 @@ vect_analyze_loop (class loop *loop, vec_info_shared *shared)
      lowest cost if pick_lowest_cost_p.  */
   while (1)
     {
-      unsigned int loop_vinfo_i = mode_i;
       bool fatal;
       opt_loop_vec_info loop_vinfo
 	= vect_analyze_loop_1 (loop, shared, &loop_form_info,
@@ -3108,11 +3107,7 @@ vect_analyze_loop (class loop *loop, vec_info_shared *shared)
 	      first_loop_vinfo = opt_loop_vec_info::success (NULL);
 	    }
 	  if (first_loop_vinfo == NULL)
-	    {
-	      first_loop_vinfo = loop_vinfo;
-	      first_loop_i = loop_vinfo_i;
-	      first_loop_next_i = mode_i;
-	    }
+	    first_loop_vinfo = loop_vinfo;
 	  else
 	    {
 	      delete loop_vinfo;
@@ -3158,32 +3153,37 @@ vect_analyze_loop (class loop *loop, vec_info_shared *shared)
   /* Now analyze first_loop_vinfo for epilogue vectorization.  */
   poly_uint64 lowest_th = LOOP_VINFO_VERSIONING_THRESHOLD (first_loop_vinfo);
 
-  /* Handle the case that the original loop can use partial
-     vectorization, but want to only adopt it for the epilogue.
-     The retry should be in the same mode as original.  */
-  if (LOOP_VINFO_EPIL_USING_PARTIAL_VECTORS_P (first_loop_vinfo))
+  /* For epilogues start the analysis from the first mode.  The motivation
+     behind starting from the beginning comes from cases where the VECTOR_MODES
+     array may contain length-agnostic and length-specific modes.  Their
+     ordering is not guaranteed, so we could end up picking a mode for the main
+     loop that is after the epilogue's optimal mode.  */
+  mode_i = 1;
+  bool supports_partial_vectors = partial_vectors_supported_p ();
+  poly_uint64 first_vinfo_vf = LOOP_VINFO_VECT_FACTOR (first_loop_vinfo);
+
+  while (1)
     {
-      gcc_assert (LOOP_VINFO_CAN_USE_PARTIAL_VECTORS_P (first_loop_vinfo)
-		  && !LOOP_VINFO_USING_PARTIAL_VECTORS_P (first_loop_vinfo));
+      /* If the target does not support partial vectors we can shorten the
+	 number of modes to analyze for the epilogue as we know we can't pick a
+	 mode that has at least as many NUNITS as the main loop's vectorization
+	 factor, since that would imply the epilogue's vectorization factor
+	 would be at least as high as the main loop's and we would be
+	 vectorizing for more scalar iterations than there would be left.  */
+      if (!supports_partial_vectors
+	  && maybe_ge (GET_MODE_NUNITS (vector_modes[mode_i]), first_vinfo_vf))
+	{
+	  mode_i++;
+	  if (mode_i == vector_modes.length ())
+	    break;
+	  continue;
+	}
+
       if (dump_enabled_p ())
 	dump_printf_loc (MSG_NOTE, vect_location,
-			 "***** Re-trying analysis with same vector mode"
-			 " %s for epilogue with partial vectors.\n",
-			 GET_MODE_NAME (first_loop_vinfo->vector_mode));
-      mode_i = first_loop_i;
-    }
-  else
-    {
-      mode_i = first_loop_next_i;
-      if (mode_i == vector_modes.length ())
-	return first_loop_vinfo;
-    }
-
-  /* ???  If first_loop_vinfo was using VOIDmode then we probably
-     want to instead search for the corresponding mode in vector_modes[].  */
+			 "***** Re-trying epilogue analysis with vector "
+			 "mode %s\n", GET_MODE_NAME (vector_modes[mode_i]));
 
-  while (1)
-    {
       bool fatal;
       opt_loop_vec_info loop_vinfo
 	= vect_analyze_loop_1 (loop, shared, &loop_form_info,
@@ -3235,11 +3235,6 @@ vect_analyze_loop (class loop *loop, vec_info_shared *shared)
       if (mode_i == vector_modes.length ())
 	break;
 
-      /* Try the next biggest vector size.  */
-      if (dump_enabled_p ())
-	dump_printf_loc (MSG_NOTE, vect_location,
-			 "***** Re-trying epilogue analysis with vector "
-			 "mode %s\n", GET_MODE_NAME (vector_modes[mode_i]));
     }
 
   if (!first_loop_vinfo->epilogue_vinfos.is_empty ())