Re: [PATCH] Fixing PR59006 and PR58921 by delaying loop invariant hoisting in vectorizer.

[Jakub Jelinek <jakub at redhat dot com>]

On Tue, Jan 14, 2014 at 10:01:06AM +0100, Richard Biener wrote:
> Jakub, adding the new flag is ok with me.

So like this?

2014-01-14  Jakub Jelinek  <jakub@redhat.com>

	* tree-vectorizer.h (struct _loop_vec_info): Add no_data_dependencies
	field.
	(LOOP_VINFO_NO_DATA_DEPENDENCIES): Define.
	* tree-vect-data-refs.c (vect_analyze_data_ref_dependence): Clear it
	when not giving up or versioning for alias only because of
	loop->safelen.
	(vect_analyze_data_ref_dependences): Set to true.
	* tree-vect-stmts.c (vectorizable_load): Use
	LOOP_VINFO_NO_DATA_DEPENDENCIES instead of
	LOOP_REQUIRES_VERSIONING_FOR_ALIAS.

--- gcc/tree-vectorizer.h.jj	2014-01-03 11:40:57.000000000 +0100
+++ gcc/tree-vectorizer.h	2014-01-14 13:10:00.477989924 +0100
@@ -347,6 +347,25 @@ typedef struct _loop_vec_info {
      fix it up.  */
   bool operands_swapped;
 
+  /* True if there are no loop carried data dependencies in the loop.
+     If loop->safelen <= 1, then this is always true, either the loop
+     didn't have any loop carried data dependencies, or the loop is being
+     vectorized guarded with some runtime alias checks, or couldn't
+     be vectorized at all, but then this field shouldn't be used.
+     For loop->safelen >= 2, the user has asserted that there are no
+     backward dependencies, but there still could be loop carried forward
+     dependencies in such loops.  This flag will be false if normal
+     vectorizer data dependency analysis would fail or require versioning
+     for alias, but because of loop->safelen >= 2 it has been vectorized
+     even without versioning for alias.  E.g. in:
+     #pragma omp simd
+     for (int i = 0; i < m; i++)
+       a[i] = a[i + k] * c;
+     (or #pragma simd or #pragma ivdep) we can vectorize this and it will
+     DTRT even for k > 0 && k < m, but without safelen we would not
+     vectorize this, so this field would be false.  */
+  bool no_data_dependencies;
+
   /* If if-conversion versioned this loop before conversion, this is the
      loop version without if-conversion.  */
   struct loop *scalar_loop;
@@ -385,6 +404,7 @@ typedef struct _loop_vec_info {
 #define LOOP_VINFO_PEELING_FOR_GAPS(L)     (L)->peeling_for_gaps
 #define LOOP_VINFO_OPERANDS_SWAPPED(L)     (L)->operands_swapped
 #define LOOP_VINFO_PEELING_FOR_NITER(L)    (L)->peeling_for_niter
+#define LOOP_VINFO_NO_DATA_DEPENDENCIES(L) (L)->no_data_dependencies
 #define LOOP_VINFO_SCALAR_LOOP(L)	   (L)->scalar_loop
 
 #define LOOP_REQUIRES_VERSIONING_FOR_ALIGNMENT(L) \
--- gcc/tree-vect-data-refs.c.jj	2014-01-10 00:38:26.000000000 +0100
+++ gcc/tree-vect-data-refs.c	2014-01-14 13:12:06.056342116 +0100
@@ -244,6 +244,7 @@ vect_analyze_data_ref_dependence (struct
 	{
 	  if (loop->safelen < *max_vf)
 	    *max_vf = loop->safelen;
+	  LOOP_VINFO_NO_DATA_DEPENDENCIES (loop_vinfo) = false;
 	  return false;
 	}
 
@@ -291,6 +292,7 @@ vect_analyze_data_ref_dependence (struct
 	{
 	  if (loop->safelen < *max_vf)
 	    *max_vf = loop->safelen;
+	  LOOP_VINFO_NO_DATA_DEPENDENCIES (loop_vinfo) = false;
 	  return false;
 	}
 
@@ -447,6 +449,7 @@ vect_analyze_data_ref_dependences (loop_
     dump_printf_loc (MSG_NOTE, vect_location,
                      "=== vect_analyze_data_ref_dependences ===\n");
 
+  LOOP_VINFO_NO_DATA_DEPENDENCIES (loop_vinfo) = true;
   if (!compute_all_dependences (LOOP_VINFO_DATAREFS (loop_vinfo),
 				&LOOP_VINFO_DDRS (loop_vinfo),
 				LOOP_VINFO_LOOP_NEST (loop_vinfo), true))
--- gcc/tree-vect-stmts.c.jj	2014-01-14 10:33:21.000000000 +0100
+++ gcc/tree-vect-stmts.c	2014-01-14 13:14:15.157677243 +0100
@@ -6381,10 +6381,11 @@ vectorizable_load (gimple stmt, gimple_s
 	      if (inv_p && !bb_vinfo)
 		{
 		  gcc_assert (!grouped_load);
-		  /* If we have versioned for aliasing then we are sure
-		     this is a loop invariant load and thus we can insert
-		     it on the preheader edge.  */
-		  if (LOOP_REQUIRES_VERSIONING_FOR_ALIAS (loop_vinfo))
+		  /* If we have versioned for aliasing or the loop doesn't
+		     have any data dependencies that would preclude this,
+		     then we are sure this is a loop invariant load and
+		     thus we can insert it on the preheader edge.  */
+		  if (LOOP_VINFO_NO_DATA_DEPENDENCIES (loop_vinfo))
 		    {
 		      if (dump_enabled_p ())
 			{


	Jakub