tree-ssa-sccvn.c (visit_phi): Compare invariant addresses as base and offset.

2018-08-01  Richard Biener  <rguenther@suse.de>

	* tree-ssa-sccvn.c (visit_phi): Compare invariant addresses
	as base and offset.

	* gcc.dg/tree-ssa/ssa-fre-68.c: New testcase.

From-SVN: r263206

gcc/ChangeLog

+2018-08-01  Richard Biener  <rguenther@suse.de>
+
+	* tree-ssa-sccvn.c (visit_phi): Compare invariant addresses
+	as base and offset.
+
 2018-08-01  Martin Liska  <mliska@suse.cz>
 
 	* value-prof.c (gimple_divmod_fixed_value_transform): Unify

gcc/testsuite/ChangeLog

+2018-08-01  Richard Biener  <rguenther@suse.de>
+
+	* gcc.dg/tree-ssa/ssa-fre-68.c: New testcase.
+
 2018-08-01  Uros Bizjak  <ubizjak@gmail.com>
 
 	* gcc.dg/plugin/poly-int-07_plugin.c (dg-options): Use -O0.

gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-68.c

+/* { dg-do compile } */
+/* { dg-options "-O -fdump-tree-fre1" } */
+
+struct S { char a[3]; char b[5]; } s = { "abc", "defg" };
+
+__SIZE_TYPE__
+foo (struct S s, int a, int b)
+{
+  char *p = (char *) &s.a[0];
+  if (a)
+    p = (char *) &s.a;
+  else if (b)
+    p = (char *) &s;
+  return __builtin_strlen (p);
+}
+
+__SIZE_TYPE__
+bar (int a, int b)
+{
+  char *p = (char *) &s.a[0];
+  if (a)
+    p = (char *) &s.a;
+  else if (b)
+    p = (char *) &s;
+  return __builtin_strlen (p);
+}
+
+/* { dg-final { scan-tree-dump-times "strlen \\\(&s" 2 "fre1" } } */

gcc/tree-ssa-sccvn.c

@@ -3941,6 +3941,8 @@ static bool
 visit_phi (gimple *phi)
 {
   tree result, sameval = VN_TOP, seen_undef = NULL_TREE;
+  tree sameval_base = NULL_TREE;
+  poly_int64 soff, doff;
   unsigned n_executable = 0;
   bool allsame = true;
   edge_iterator ei;
@@ -3971,6 +3973,23 @@ visit_phi (gimple *phi)
 	  sameval = def;
 	else if (!expressions_equal_p (def, sameval))
 	  {
+	    /* We know we're arriving only with invariant addresses here,
+	       try harder comparing them.  We can do some caching here
+	       which we cannot do in expressions_equal_p.  */
+	    if (TREE_CODE (def) == ADDR_EXPR
+		&& TREE_CODE (sameval) == ADDR_EXPR
+		&& sameval_base != (void *)-1)
+	      {
+		if (!sameval_base)
+		  sameval_base = get_addr_base_and_unit_offset
+				   (TREE_OPERAND (sameval, 0), &soff);
+		if (!sameval_base)
+		  sameval_base = (tree)(void *)-1;
+		else if ((get_addr_base_and_unit_offset
+			    (TREE_OPERAND (def, 0), &doff) == sameval_base)
+			 && known_eq (soff, doff))
+		  continue;
+	      }
 	    allsame = false;
 	    break;
 	  }