[PATCH] Fix UB in round_up_loc (PR c/67338)

[Jakub Jelinek]

Hi!

divisor is unsigned int parameter, if it is 0x80000000, we invoke UB.
val is wide_int, so (int) -divisor achieves the same result without UB.

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

2017-03-20  Jakub Jelinek  <ja...@redhat.com>

        PR c/67338
        * fold-const.c (round_up_loc): Negate divisor in unsigned type to
        avoid UB.

        * gcc.dg/pr67338.c: New test.

--- gcc/fold-const.c.jj 2017-03-16 17:18:25.000000000 +0100
+++ gcc/fold-const.c    2017-03-20 07:53:53.680953740 +0100
@@ -14250,7 +14250,7 @@ round_up_loc (location_t loc, tree value
 
          overflow_p = TREE_OVERFLOW (value);
          val += divisor - 1;
-         val &= - (int) divisor;
+         val &= (int) -divisor;
          if (val == 0)
            overflow_p = true;
 
--- gcc/testsuite/gcc.dg/pr67338.c.jj   2017-03-20 09:09:05.489002468 +0100
+++ gcc/testsuite/gcc.dg/pr67338.c      2017-03-20 09:08:54.000000000 +0100
@@ -0,0 +1,4 @@
+/* PR c/67338 */
+/* { dg-do compile { target *-*-linux* *-*-gnu* } } */
+
+struct S { __attribute__((aligned (1 << 28))) double a; };

        Jakub