re PR middle-end/81088 (UBSAN: false positive as a result of reassosiation)

2017-06-14  Richard Biener  <rguenther@suse.de>

	PR middle-end/81088
	* fold-const.c (split_tree): Drop TREE_OVERFLOW flag from
	literal constants.
	(fold_binary_loc): When associating do not treat pre-existing
	TREE_OVERFLOW on literal constants as a reason to allow
	TREE_OVERFLOW on associated literal constants.

	* c-c++-common/ubsan/pr81088.c: New testcase.

From-SVN: r249192

gcc/ChangeLog

+2017-06-14  Richard Biener  <rguenther@suse.de>
+
+	PR middle-end/81088
+	* fold-const.c (split_tree): Drop TREE_OVERFLOW flag from
+	literal constants.
+	(fold_binary_loc): When associating do not treat pre-existing
+	TREE_OVERFLOW on literal constants as a reason to allow
+	TREE_OVERFLOW on associated literal constants.
+
 2017-06-14  Eric Botcazou  <ebotcazou@adacore.com>
 
 	* config/sparc/sparc.h (MASK_ISA): Add MASK_LEON and MASK_LEON3.

gcc/fold-const.c

@@ -880,6 +880,13 @@ split_tree (location_t loc, tree in, tree type, enum tree_code code,
 	}
     }
 
+  if (*litp
+      && TREE_OVERFLOW_P (*litp))
+    *litp = drop_tree_overflow (*litp);
+  if (*minus_litp
+      && TREE_OVERFLOW_P (*minus_litp))
+    *minus_litp = drop_tree_overflow (*minus_litp);
+
   return var;
 }
 
@@ -9703,11 +9710,6 @@ fold_binary_loc (location_t loc,
 		       + (lit0 != 0) + (lit1 != 0)
 		       + (minus_lit0 != 0) + (minus_lit1 != 0))))
 	    {
-	      bool any_overflows = false;
-	      if (lit0) any_overflows |= TREE_OVERFLOW (lit0);
-	      if (lit1) any_overflows |= TREE_OVERFLOW (lit1);
-	      if (minus_lit0) any_overflows |= TREE_OVERFLOW (minus_lit0);
-	      if (minus_lit1) any_overflows |= TREE_OVERFLOW (minus_lit1);
 	      var0 = associate_trees (loc, var0, var1, code, atype);
 	      con0 = associate_trees (loc, con0, con1, code, atype);
 	      lit0 = associate_trees (loc, lit0, lit1, code, atype);
@@ -9738,9 +9740,8 @@ fold_binary_loc (location_t loc,
 		}
 
 	      /* Don't introduce overflows through reassociation.  */
-	      if (!any_overflows
-		  && ((lit0 && TREE_OVERFLOW_P (lit0))
-		      || (minus_lit0 && TREE_OVERFLOW_P (minus_lit0))))
+	      if ((lit0 && TREE_OVERFLOW_P (lit0))
+		  || (minus_lit0 && TREE_OVERFLOW_P (minus_lit0)))
 		return NULL_TREE;
 
 	      if (minus_lit0)

gcc/testsuite/ChangeLog

+2017-06-14  Richard Biener  <rguenther@suse.de>
+
+	PR middle-end/81088
+	* c-c++-common/ubsan/pr81088.c: New testcase.
+
 2017-06-14  Eric Botcazou  <ebotcazou@adacore.com>
 
 	* gcc.target/sparc/overflow-4.c: Add -mno-vis3.

gcc/testsuite/c-c++-common/ubsan/pr81088.c

+/* { dg-do run } */
+/* { dg-options "-fsanitize=undefined -fsanitize-undefined-trap-on-error" } */
+
+short s = 2;
+short y = 1;
+int i;
+int main()
+{
+  i = -(s + (int)(~(unsigned)(0 / y))) + 0x7fffffff;
+  return 0;
+}