re PR tree-optimization/60276 (-O3 autovectorizer breaks on a particular loop)

2014-02-21  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/60276
	* tree-vectorizer.h (struct _stmt_vec_info): Add min_neg_dist field.
	(STMT_VINFO_MIN_NEG_DIST): New macro.
	* tree-vect-data-refs.c (vect_analyze_data_ref_dependence): Record
	STMT_VINFO_MIN_NEG_DIST.
	* tree-vect-stmts.c (vectorizable_load): Verify if assumptions
	made for negative dependence distances still hold.

	* gcc.dg/vect/pr60276.c: New testcase.

From-SVN: r207992

gcc/ChangeLog

 2014-02-21  Richard Biener  <rguenther@suse.de>
 
+	PR tree-optimization/60276
+	* tree-vectorizer.h (struct _stmt_vec_info): Add min_neg_dist field.
+	(STMT_VINFO_MIN_NEG_DIST): New macro.
+	* tree-vect-data-refs.c (vect_analyze_data_ref_dependence): Record
+	STMT_VINFO_MIN_NEG_DIST.
+	* tree-vect-stmts.c (vectorizable_load): Verify if assumptions
+	made for negative dependence distances still hold.
+
+2014-02-21  Richard Biener  <rguenther@suse.de>
+
 	PR middle-end/60291
 	* tree-ssa-live.c (mark_all_vars_used_1): Do not walk
 	DECL_INITIAL for globals not in the current function context.

gcc/testsuite/ChangeLog

+2014-02-21  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/60276
+	* gcc.dg/vect/pr60276.c: New testcase.
+
 2014-02-21  Janus Weil  <janus@gcc.gnu.org>
 
 	PR fortran/60234

gcc/testsuite/gcc.dg/vect/pr60276.c

+/* { dg-do run } */
+
+extern void abort (void);
+
+static void 
+foo (int *out, const int *lp, unsigned samples)
+{
+  int x, target;
+  for (x = 0, target = 0; x < (int)samples; x += 2, target++)
+    {
+      out[x] = lp[target];
+      out[x - 1] = out[x - 2] + out[x];
+    }
+}
+
+static void 
+foo_novec (int *out, const int *lp, unsigned samples)
+{
+  int x, target;
+  for (x = 0, target = 0; x < (int)samples; x += 2, target++)
+    {
+      out[x] = lp[target];
+      out[x - 1] = out[x - 2] + out[x];
+      __asm__ volatile ("" : : : "memory");
+    }
+}
+
+int main(void)
+{
+  const int lp[25] = {
+      0, 2, 4, 6, 8,
+      10, 12, 14, 16,
+      18, 20, 22, 24,
+      26, 28, 30, 32,
+      34, 36, 38, 40,
+      42, 44, 46, 48,
+  };
+  int out[49] = {0};
+  int out2[49] = {0};
+  int s;
+
+  foo (out + 2, lp + 1, 48);
+  foo_novec (out2 + 2, lp + 1, 48);
+
+  for (s = 0; s < 49; s++)
+    if (out[s] != out2[s])
+      abort ();
+
+  return 0;
+}
+
+/* { dg-final { cleanup-tree-dump "vect" } } */

gcc/tree-vect-data-refs.c

@@ -403,6 +403,13 @@ vect_analyze_data_ref_dependence (struct data_dependence_relation *ddr,
 	  if (dump_enabled_p ())
 	    dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
 	                     "dependence distance negative.\n");
+	  /* Record a negative dependence distance to later limit the
+	     amount of stmt copying / unrolling we can perform.
+	     Only need to handle read-after-write dependence.  */
+	  if (DR_IS_READ (drb)
+	      && (STMT_VINFO_MIN_NEG_DIST (stmtinfo_b) == 0
+		  || STMT_VINFO_MIN_NEG_DIST (stmtinfo_b) > (unsigned)dist))
+	    STMT_VINFO_MIN_NEG_DIST (stmtinfo_b) = dist;
 	  continue;
 	}
 

gcc/tree-vect-stmts.c

@@ -5629,6 +5629,20 @@ vectorizable_load (gimple stmt, gimple_stmt_iterator *gsi, gimple *vec_stmt,
       return false;
     }
 
+  /* Invalidate assumptions made by dependence analysis when vectorization
+     on the unrolled body effectively re-orders stmts.  */
+  if (ncopies > 1
+      && STMT_VINFO_MIN_NEG_DIST (stmt_info) != 0
+      && ((unsigned)LOOP_VINFO_VECT_FACTOR (loop_vinfo)
+	  > STMT_VINFO_MIN_NEG_DIST (stmt_info)))
+    {
+      if (dump_enabled_p ())
+	dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
+			 "cannot perform implicit CSE when unrolling "
+			 "with negative dependence distance\n");
+      return false;
+    }
+
   if (!STMT_VINFO_RELEVANT_P (stmt_info) && !bb_vinfo)
     return false;
 
@@ -5686,6 +5700,20 @@ vectorizable_load (gimple stmt, gimple_stmt_iterator *gsi, gimple *vec_stmt,
 	  else if (!vect_grouped_load_supported (vectype, group_size))
 	    return false;
 	}
+
+      /* Invalidate assumptions made by dependence analysis when vectorization
+	 on the unrolled body effectively re-orders stmts.  */
+      if (!PURE_SLP_STMT (stmt_info)
+	  && STMT_VINFO_MIN_NEG_DIST (stmt_info) != 0
+	  && ((unsigned)LOOP_VINFO_VECT_FACTOR (loop_vinfo)
+	      > STMT_VINFO_MIN_NEG_DIST (stmt_info)))
+	{
+	  if (dump_enabled_p ())
+	    dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
+			     "cannot perform implicit CSE when performing "
+			     "group loads with negative dependence distance\n");
+	  return false;
+	}
     }
 
 

gcc/tree-vectorizer.h

@@ -622,6 +622,10 @@ typedef struct _stmt_vec_info {
      is 1.  */
   unsigned int gap;
 
+  /* The minimum negative dependence distance this stmt participates in
+     or zero if none.  */
+  unsigned int min_neg_dist;
+
   /* Not all stmts in the loop need to be vectorized. e.g, the increment
      of the loop induction variable and computation of array indexes. relevant
      indicates whether the stmt needs to be vectorized.  */
@@ -677,6 +681,7 @@ typedef struct _stmt_vec_info {
 #define STMT_VINFO_GROUP_SAME_DR_STMT(S)   (S)->same_dr_stmt
 #define STMT_VINFO_GROUPED_ACCESS(S)      ((S)->first_element != NULL && (S)->data_ref_info)
 #define STMT_VINFO_LOOP_PHI_EVOLUTION_PART(S) (S)->loop_phi_evolution_part
+#define STMT_VINFO_MIN_NEG_DIST(S)	(S)->min_neg_dist
 
 #define GROUP_FIRST_ELEMENT(S)          (S)->first_element
 #define GROUP_NEXT_ELEMENT(S)           (S)->next_element