[Bug middle-end/79818] [7 Regression] wrong code with -fwrapv and -Os/-O1/-O2/-O3

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79818

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P1
             Status|NEW                         |ASSIGNED
          Component|c                           |middle-end

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Hum, not sure how it escaped my review, but

/* Transform comparisons of the form X +- C1 CMP C2 to X CMP C2 -+ C1.  */
(for cmp (eq ne)
 (for op (plus minus)
      rop (minus plus)
  (simplify
   (cmp (op@3 @0 INTEGER_CST@1) INTEGER_CST@2)
   (if (!TREE_OVERFLOW (@1) && !TREE_OVERFLOW (@2)
        && !TYPE_OVERFLOW_SANITIZED (TREE_TYPE (@0))
        && !TYPE_OVERFLOW_TRAPS (TREE_TYPE (@0))
        && !TYPE_SATURATING (TREE_TYPE (@0)))
    (with { tree res = int_const_binop (rop, @2, @1); }
     (if (TREE_OVERFLOW (res))
      { constant_boolean_node (cmp == NE_EXPR, type); }

is quite different from

  /* Transform comparisons of the form X +- C1 CMP C2 to X CMP C2 -+ C1.  */
  if ((TREE_CODE (arg0) == PLUS_EXPR || TREE_CODE (arg0) == MINUS_EXPR)
      && (equality_code
          || (ANY_INTEGRAL_TYPE_P (TREE_TYPE (arg0))
              && TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (arg0))))
      && TREE_CODE (TREE_OPERAND (arg0, 1)) == INTEGER_CST
      && !TREE_OVERFLOW (TREE_OPERAND (arg0, 1))
      && TREE_CODE (arg1) == INTEGER_CST
      && !TREE_OVERFLOW (arg1))
...
      /* If the constant operation overflowed this can be
         simplified as a comparison against INT_MAX/INT_MIN.  */
      if (TREE_OVERFLOW (new_const)
          && !TYPE_OVERFLOW_WRAPS (TREE_TYPE (arg0)))

I belive it has to be && TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (arg0)),
otherwise we'd fold for -fno-strict-overflow.

Testing the following.

Index: gcc/match.pd
===================================================================
--- gcc/match.pd        (revision 245837)
+++ gcc/match.pd        (working copy)
@@ -3688,7 +3688,8 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
        && !TYPE_OVERFLOW_TRAPS (TREE_TYPE (@0))
        && !TYPE_SATURATING (TREE_TYPE (@0)))
     (with { tree res = int_const_binop (rop, @2, @1); }
-     (if (TREE_OVERFLOW (res))
+     (if (TREE_OVERFLOW (res)
+         && TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (@0)))
       { constant_boolean_node (cmp == NE_EXPR, type); }
       (if (single_use (@3))
        (cmp @0 { res; }))))))))