[PATCH] Fix -fsanitize=undefined vs. x + y < x (PR sanitizer/87837)

[Jakub Jelinek]

Hi!

I wish I had a better fix, but I don't, trying to sanitize signed integer
arithmetics in the FEs already before any folding there is complicated by
that arithmetics being created just in way too many spots.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2018-11-05  Jakub Jelinek  <ja...@redhat.com>

        PR sanitizer/87837
        * match.pd (X + Y < X): Don't optimize if TYPE_OVERFLOW_SANITIZED.

        * c-c++-common/ubsan/pr87837.c: New test.

--- gcc/match.pd.jj     2018-10-31 10:33:07.438686055 +0100
+++ gcc/match.pd        2018-11-01 10:26:44.251883633 +0100
@@ -1572,6 +1572,7 @@ (define_operator_list COND_TERNARY
   (op:c (plus:c@2 @0 @1) @1)
   (if (ANY_INTEGRAL_TYPE_P (TREE_TYPE (@0))
        && TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (@0))
+       && !TYPE_OVERFLOW_SANITIZED (TREE_TYPE (@0))
        && (CONSTANT_CLASS_P (@0) || single_use (@2)))
    (op @0 { build_zero_cst (TREE_TYPE (@0)); }))))
 /* For equality, this is also true with wrapping overflow.  */
--- gcc/testsuite/c-c++-common/ubsan/pr87837.c.jj       2018-11-01 
10:37:35.159186004 +0100
+++ gcc/testsuite/c-c++-common/ubsan/pr87837.c  2018-11-01 10:39:56.162868607 
+0100
@@ -0,0 +1,18 @@
+/* PR sanitizer/87837 */
+/* { dg-do run } */
+/* { dg-options "-fsanitize=signed-integer-overflow -Wno-unused-variable" } */
+
+int
+foo (int n)
+{
+  return n + __INT_MAX__ < n;
+}
+
+int
+main ()
+{
+  volatile int a = foo (1);
+  return 0;
+}
+
+/* { dg-output "signed integer overflow: 1 \\+ 2147483647 cannot be 
represented in type 'int'" } */

        Jakub