[Bug c/89126] missing -Wtype-limits for int variables

[Bug c/89126] missing -Wtype-limits for int variables

[linkw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89126

Kewen Lin <linkw at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 CC|                            |linkw at gcc dot gnu.org

--- Comment #4 from Kewen Lin <linkw at gcc dot gnu.org> ---
(In reply to Martin Sebor from comment #3)

> Eventually, after the function returns the inequality expression without a
> warning, c_parser_condition() calls c_fully_fold() on it which folds it into
> a constant, without a warning.

Happened to notice this PR when trying to answer the question [1].  The part
doing the folding is from match.pd.

/* Non-equality compare simplifications from fold_binary  */
(for cmp (lt gt le ge)
 /* Comparisons with the highest or lowest possible integer of
    the specified precision will have known values.  */
 (simplify
  (cmp (convert?@2 @0) uniform_integer_cst_p@1)
...
     (if (wi::to_wide (cst) == max)
      (switch
       (if (cmp == GT_EXPR)
        { constant_boolean_node (false, type); })
       (if (cmp == GE_EXPR)
        (eq @2 @1))
       (if (cmp == LE_EXPR)
        { constant_boolean_node (true, type); })

I noticed there are some warning support in match.pd like
fold_overflow_warning. Not sure whether we can add the similar supports there. 
Probably hard to get LOC?

[1] https://gcc.gnu.org/pipermail/gcc-help/2021-January/139755.html