PR tree-optimization/89720 - Spurious -Warray-bounds warning on a range with max < min

gcc/ChangeLog:

	PR tree-optimization/89720
	* tree-vrp.c (vrp_prop::check_mem_ref): Treat range with max < min
	more conservatively, the same as anti-range.

gcc/testsuite/ChangeLog:

	PR tree-optimization/89720
	* gcc.dg/Warray-bounds-42.c: New test.

From-SVN: r269785

gcc/ChangeLog

+2019-03-18  Martin Sebor  <msebor@redhat.com>
+
+	PR tree-optimization/89720
+	* tree-vrp.c (vrp_prop::check_mem_ref): Treat range with max < min
+	more conservatively, the same as anti-range.
+
 2019-03-18  Richard Biener  <rguenther@suse.de>
 
 	PR middle-end/88945

gcc/testsuite/ChangeLog

+2019-03-18  Martin Sebor  <msebor@redhat.com>
+
+	PR tree-optimization/89720
+	* gcc.dg/Warray-bounds-42.c: New test.
+
 2019-03-19  H.J. Lu  <hongjiu.lu@intel.com>
 
 	PR c++/89630

gcc/testsuite/gcc.dg/Warray-bounds-42.c

+/* PR tree-optimization/89720 - Spurious -Warray-bounds warning on a range
+   with max < min
+   { dg-do compile }
+   { dg-options "-O2 -Wall" } */
+
+void f (char*, int);
+
+#if __SIZEOF_POINTER__ == 8
+
+void g (__INT64_TYPE__ i)
+{
+  char a[65536] = "";
+  char *p = a + (i & (__INT64_TYPE__)0xffffffff3fffffffLL);
+  f (p, *(p - 6));            /* { dg-bogus "\\\[-Warray-bounds" } */
+}
+
+#elif __SIZEOF_POINTER__ == 4
+
+void h (__INT32_TYPE__ i)
+{
+  char a[65536] = "";
+  char *p = a + (i & (__INT32_TYPE__)0x8fffffffLL);
+  f (p, *(p - 6));            /* { dg-bogus "\\\[-Warray-bounds" } */
+}
+
+#endif

gcc/tree-vrp.c

@@ -4546,9 +4546,9 @@ vrp_prop::check_mem_ref (location_t location, tree ref,
   const value_range *vr = NULL;
 
   /* Determine the offsets and increment OFFRANGE for the bounds of each.
-     The loop computes the the range of the final offset for expressions
-     such as (A + i0 + ... + iN)[CSTOFF] where i0 through iN are SSA_NAMEs
-     in some range.  */
+     The loop computes the range of the final offset for expressions such
+     as (A + i0 + ... + iN)[CSTOFF] where i0 through iN are SSA_NAMEs in
+     some range.  */
   while (TREE_CODE (arg) == SSA_NAME)
     {
       gimple *def = SSA_NAME_DEF_STMT (arg);
@@ -4583,8 +4583,6 @@ vrp_prop::check_mem_ref (location_t location, tree ref,
 
       if (vr->kind () == VR_RANGE)
 	{
-	  if (tree_int_cst_lt (vr->min (), vr->max ()))
-	    {
 	  offset_int min
 	    = wi::to_offset (fold_convert (ptrdiff_type_node, vr->min ()));
 	  offset_int max
@@ -4596,13 +4594,10 @@ vrp_prop::check_mem_ref (location_t location, tree ref,
 	    }
 	  else
 	    {
-		  offrange[0] += max;
-		  offrange[1] += min;
-		}
-	    }
-	  else
-	    {
-	      /* Conservatively add [-MAXOBJSIZE -1, MAXOBJSIZE]
+	      /* When MIN >= MAX, the offset is effectively in a union
+		 of two ranges: [-MAXOBJSIZE -1, MAX] and [MIN, MAXOBJSIZE].
+		 Since there is no way to represent such a range across
+		 additions, conservatively add [-MAXOBJSIZE -1, MAXOBJSIZE]
 		 to OFFRANGE.  */
 	      offrange[0] += arrbounds[0];
 	      offrange[1] += arrbounds[1];