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Re: c-family PATCH to improve -Wsign-compare (PR c/81417)
On Tue, Jul 25, 2017 at 08:50:24AM -0600, Martin Sebor wrote:
> How hard would it be to also suppress the warning for benign
> comparisons like C++ manages to do? E.g., C warns on this
> code even though there's no problem with it:
>
> int foo (unsigned int b)
> {
> const int a = 1;
> return (a < b);
> }
The C++ FE can fold const int to it's initial value, but C's fold cannot.
But there's decl_constant_value which is able to do it, so this might
be just about
--- a/gcc/c/c-typeck.c
+++ b/gcc/c/c-typeck.c
@@ -11783,9 +11783,15 @@ build_binary_op (location_t location, enum tree_code code,
}
if (warn_sign_compare)
- warn_for_sign_compare (location, orig_op0_folded,
- orig_op1_folded, op0, op1,
- result_type, resultcode);
+ {
+ if (VAR_P (orig_op0_folded))
+ orig_op0_folded = decl_constant_value (orig_op0_folded);
+ if (VAR_P (orig_op1_folded))
+ orig_op1_folded = decl_constant_value (orig_op1_folded);
+ warn_for_sign_compare (location, orig_op0_folded,
+ orig_op1_folded, op0, op1,
+ result_type, resultcode);
+ }
if (!in_late_binary_op && !int_operands)
{
if (!op0_maybe_const || TREE_CODE (op0) != INTEGER_CST)
Marek