[PATCH] Fix PR81354 (SLSR, insert on edges)

[Bill Schmidt <wschmidt at linux dot vnet dot ibm dot com>]

Hi,

PR81354 describes an ICE in SLSR that occurs when a GIMPLE PHI statement changes
address during the SLSR pass.  SLSR contains a mapping table from GIMPLE statements
to entries in the candidate table that relies on this address remaining constant.

The address change occurs during gimple_split_edge (), as the PHIs in the dest
block of the edge first have their number of predecessors grow by 1 and then
shrink back to their original size.  The growth causes the PHIs to usually be
reallocated.  We've discussed some attempts to fix this in gimple_split_edge,
but the simplest solution is to fix this directly in SLSR by deferring the splitting
of the edge until the end of the pass, using gsi_insert_on_edge and
gsi_commit_edge_inserts.  That's what this patch does.

Bootstrapped and tested on powerpc64le-linux-gnu with no regressions.  Is this ok
for trunk, and for backports to GCC 5, 6, and 7 after burn-in?

Thanks,
Bill


[gcc]

2017-08-07  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>

	PR tree-optimization/81354
	* gimple-ssa-strength-reduction.c (create_add_on_incoming_edge):
	Insert on edges rather than explicitly creating landing pads.
	(analyze_candidates_and_replace): Commit edge inserts.


[gcc/testsuite]

2017-08-07  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>

	PR tree-optimization/81354
	* g++.dg/torture/pr81354.C: New file.


Index: gcc/gimple-ssa-strength-reduction.c
===================================================================
--- gcc/gimple-ssa-strength-reduction.c	(revision 250791)
+++ gcc/gimple-ssa-strength-reduction.c	(working copy)
@@ -2224,8 +2224,6 @@ create_add_on_incoming_edge (slsr_cand_t c, tree b
 			     widest_int increment, edge e, location_t loc,
 			     bool known_stride)
 {
-  basic_block insert_bb;
-  gimple_stmt_iterator gsi;
   tree lhs, basis_type;
   gassign *new_stmt, *cast_stmt = NULL;
 
@@ -2294,39 +2292,25 @@ create_add_on_incoming_edge (slsr_cand_t c, tree b
       }
     }
 
-  insert_bb = single_succ_p (e->src) ? e->src : split_edge (e);
-  gsi = gsi_last_bb (insert_bb);
-
-  if (!gsi_end_p (gsi) && stmt_ends_bb_p (gsi_stmt (gsi)))
+  if (cast_stmt)
     {
-      gsi_insert_before (&gsi, new_stmt, GSI_SAME_STMT);
-      if (cast_stmt)
-	{
-	  gsi_insert_before (&gsi, cast_stmt, GSI_SAME_STMT);
-	  gimple_set_location (cast_stmt, loc);
-	}
+      gimple_set_location (cast_stmt, loc);
+      gsi_insert_on_edge (e, cast_stmt);
     }
-  else
-    {
-      if (cast_stmt)
-	{
-	  gsi_insert_after (&gsi, cast_stmt, GSI_NEW_STMT);
-	  gimple_set_location (cast_stmt, loc);
-	}
-      gsi_insert_after (&gsi, new_stmt, GSI_NEW_STMT);
-    }
 
   gimple_set_location (new_stmt, loc);
+  gsi_insert_on_edge (e, new_stmt);
 
   if (dump_file && (dump_flags & TDF_DETAILS))
     {
       if (cast_stmt)
 	{
-	  fprintf (dump_file, "Inserting cast in block %d: ",
-		   insert_bb->index);
+	  fprintf (dump_file, "Inserting cast on edge %d->%d: ",
+		   e->src->index, e->dest->index);
 	  print_gimple_stmt (dump_file, cast_stmt, 0);
 	}
-      fprintf (dump_file, "Inserting in block %d: ", insert_bb->index);
+      fprintf (dump_file, "Inserting on edge %d->%d: ", e->src->index,
+	       e->dest->index);
       print_gimple_stmt (dump_file, new_stmt, 0);
     }
 
@@ -3770,6 +3754,10 @@ analyze_candidates_and_replace (void)
 	  free (incr_vec);
 	}
     }
+
+  /* For conditional candidates, we may have uncommitted insertions
+     on edges to clean up.  */
+  gsi_commit_edge_inserts ();
 }
 
 namespace {
Index: gcc/testsuite/g++.dg/torture/pr81354.C
===================================================================
--- gcc/testsuite/g++.dg/torture/pr81354.C	(nonexistent)
+++ gcc/testsuite/g++.dg/torture/pr81354.C	(working copy)
@@ -0,0 +1,24 @@
+// PR81354 reported this test as crashing in a limited range of revisions.
+// { dg-do compile }
+
+struct T { double a; double b; };
+
+void foo(T Ad[], int As[2])
+{
+  int j;
+  int i;
+  int Bs[2] = {0,0};
+  T Bd[16];
+
+  for (j = 0; j < 4; j++) {
+    for (i = 0; i + 1 <= j + 1; i++) {
+      Ad[i + As[0] * j] = Bd[i + Bs[0] * j];
+    }
+
+    i = j + 1;  // <- comment out this line and it does not crash
+    for (; i + 1 < 5; i++) {
+      Ad[i + As[0] * j].a = 0.0;
+      Ad[i + As[0] * j].b = 0.0;
+    }
+  }
+}