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[PATCH] Make scatter/gather vectorization failures non-fatal (PR tree-optimization/91033)


Hi!

As mentioned in the PR, I'm afraid we can't easily move the scatter/gather
verification from vect_analyze_data_refs to vectorizable_{load,store},
because we need to process_use in between on the gsinfo.offset to determine
what statements need to be vectorized and that can be only determined with
the successful scatter/gather detection.

The following patch just makes sure that we don't mark failures to handle
scatter/gather as fatal, which means if there are multiple vectorization
factors, if there is a scatter/gather failure (but some scatter/gather is
supported, no scatter/gather support altogether is fatal), we keep trying
finding another suitable vectorization factors.

This matters e.g. on AVX512F without AVX512VL, where we can scatter only
when using 512-bit vectors but not other sizes; if we try say 256-bit
vectors first without simdlen, it would mean we don't vectorize even if we
could (with 512-bit vectors), if we try 512-bit vectors first with simdlen,
vectorization succeeds for that, but gets fatal when retrying with 256-bit
or 128-bit vectors to see if that doesn't match the simdlen and we have
asserts to make sure that the fatal failures are either for all vector sizes
or none.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2019-07-03  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/91033
	* tree-vectorizer.h (vect_mark_stmts_to_be_vectorized,
	vect_analyze_data_refs): Add bool * arguments.
	* tree-vect-data-refs.c (vect_analyze_data_refs): Add fatal argument,
	if failure is due to scatter/gather, set *fatal to false if non-NULL.
	* tree-vect-stmts.c (vect_mark_stmts_to_be_vectorized): Likewise.
	* tree-vect-loop.c (vect_analyze_loop_2): Adjust
	vect_mark_stmts_to_be_vectorized and vect_analyze_data_refs callers.
	* tree-vect-slp.c (vect_slp_analyze_bb_1): Adjust
	vect_analyze_data_refs caller.

	* gcc.target/i386/pr91033.c: New test.
	
--- gcc/tree-vectorizer.h.jj	2019-06-21 08:47:04.169673346 +0200
+++ gcc/tree-vectorizer.h	2019-07-02 18:35:45.759141160 +0200
@@ -1501,7 +1501,7 @@ extern unsigned record_stmt_cost (stmt_v
 extern stmt_vec_info vect_finish_replace_stmt (stmt_vec_info, gimple *);
 extern stmt_vec_info vect_finish_stmt_generation (stmt_vec_info, gimple *,
 						  gimple_stmt_iterator *);
-extern opt_result vect_mark_stmts_to_be_vectorized (loop_vec_info);
+extern opt_result vect_mark_stmts_to_be_vectorized (loop_vec_info, bool *);
 extern tree vect_get_store_rhs (stmt_vec_info);
 extern tree vect_get_vec_def_for_operand_1 (stmt_vec_info, enum vect_def_type);
 extern tree vect_get_vec_def_for_operand (tree, stmt_vec_info, tree = NULL);
@@ -1559,7 +1559,7 @@ extern bool vect_check_gather_scatter (s
 				       gather_scatter_info *);
 extern opt_result vect_find_stmt_data_reference (loop_p, gimple *,
 						 vec<data_reference_p> *);
-extern opt_result vect_analyze_data_refs (vec_info *, poly_uint64 *);
+extern opt_result vect_analyze_data_refs (vec_info *, poly_uint64 *, bool *);
 extern void vect_record_base_alignments (vec_info *);
 extern tree vect_create_data_ref_ptr (stmt_vec_info, tree, struct loop *, tree,
 				      tree *, gimple_stmt_iterator *,
--- gcc/tree-vect-data-refs.c.jj	2019-06-21 23:37:57.002962811 +0200
+++ gcc/tree-vect-data-refs.c	2019-07-02 18:34:03.225722070 +0200
@@ -4160,7 +4160,7 @@ vect_find_stmt_data_reference (loop_p lo
 */
 
 opt_result
-vect_analyze_data_refs (vec_info *vinfo, poly_uint64 *min_vf)
+vect_analyze_data_refs (vec_info *vinfo, poly_uint64 *min_vf, bool *fatal)
 {
   struct loop *loop = NULL;
   unsigned int i;
@@ -4386,12 +4386,16 @@ vect_analyze_data_refs (vec_info *vinfo,
 					  as_a <loop_vec_info> (vinfo),
 					  &gs_info)
 	      || !get_vectype_for_scalar_type (TREE_TYPE (gs_info.offset)))
-	    return opt_result::failure_at
-	      (stmt_info->stmt,
-	       (gatherscatter == GATHER) ?
-	       "not vectorized: not suitable for gather load %G" :
-	       "not vectorized: not suitable for scatter store %G",
-	       stmt_info->stmt);
+	    {
+	      if (fatal)
+		*fatal = false;
+	      return opt_result::failure_at
+			(stmt_info->stmt,
+			 (gatherscatter == GATHER)
+			 ? "not vectorized: not suitable for gather load %G"
+			 : "not vectorized: not suitable for scatter store %G",
+			 stmt_info->stmt);
+	    }
 	  STMT_VINFO_GATHER_SCATTER_P (stmt_info) = gatherscatter;
 	}
     }
--- gcc/tree-vect-stmts.c.jj	2019-06-27 23:22:40.801471237 +0200
+++ gcc/tree-vect-stmts.c	2019-07-02 18:35:35.244303277 +0200
@@ -608,7 +608,7 @@ process_use (stmt_vec_info stmt_vinfo, t
    This pass detects such stmts.  */
 
 opt_result
-vect_mark_stmts_to_be_vectorized (loop_vec_info loop_vinfo)
+vect_mark_stmts_to_be_vectorized (loop_vec_info loop_vinfo, bool *fatal)
 {
   struct loop *loop = LOOP_VINFO_LOOP (loop_vinfo);
   basic_block *bbs = LOOP_VINFO_BBS (loop_vinfo);
@@ -778,7 +778,11 @@ vect_mark_stmts_to_be_vectorized (loop_v
 	    = process_use (stmt_vinfo, gs_info.offset, loop_vinfo, relevant,
 			   &worklist, true);
 	  if (!res)
-	    return res;
+	    {
+	      if (fatal)
+		*fatal = false;
+	      return res;
+	    }
 	}
     } /* while worklist */
 
--- gcc/tree-vect-loop.c.jj	2019-06-27 23:22:14.380884386 +0200
+++ gcc/tree-vect-loop.c	2019-07-02 18:36:41.581280458 +0200
@@ -1901,7 +1901,7 @@ vect_analyze_loop_2 (loop_vec_info loop_
   /* Analyze the data references and also adjust the minimal
      vectorization factor according to the loads and stores.  */
 
-  ok = vect_analyze_data_refs (loop_vinfo, &min_vf);
+  ok = vect_analyze_data_refs (loop_vinfo, &min_vf, &fatal);
   if (!ok)
     {
       if (dump_enabled_p ())
@@ -1932,7 +1932,7 @@ vect_analyze_loop_2 (loop_vec_info loop_
 
   /* Data-flow analysis to detect stmts that do not need to be vectorized.  */
 
-  ok = vect_mark_stmts_to_be_vectorized (loop_vinfo);
+  ok = vect_mark_stmts_to_be_vectorized (loop_vinfo, &fatal);
   if (!ok)
     {
       if (dump_enabled_p ())
--- gcc/tree-vect-slp.c.jj	2019-06-05 09:34:02.393372307 +0200
+++ gcc/tree-vect-slp.c	2019-07-02 18:37:15.150762867 +0200
@@ -2861,7 +2861,7 @@ vect_slp_analyze_bb_1 (gimple_stmt_itera
 
   /* Analyze the data references.  */
 
-  if (!vect_analyze_data_refs (bb_vinfo, &min_vf))
+  if (!vect_analyze_data_refs (bb_vinfo, &min_vf, NULL))
     {
       if (dump_enabled_p ())
         dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
--- gcc/testsuite/gcc.target/i386/pr91033.c.jj	2019-07-02 19:49:02.300365110 +0200
+++ gcc/testsuite/gcc.target/i386/pr91033.c	2019-07-02 19:48:56.219458810 +0200
@@ -0,0 +1,15 @@
+/* PR tree-optimization/91033 */
+/* { dg-do compile { target pthread } } */
+/* { dg-options "-march=knl -O2 -fopenmp-simd -ftree-parallelize-loops=2" } */
+
+#define N 1024
+int a[N];
+
+void
+foo (void)
+{
+  int i;
+  #pragma omp simd simdlen (4)
+  for (i = 0; i < N; ++i)
+    a[i] = a[i] + 1;
+}

	Jakub


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