On Wed, Jul 29, 2015 at 04:08:22PM +0200, Marek Polacek wrote:
> As discussed elsewhere, -Wtautological-compare shouldn't warn about
> floating-point types because of the way NaN behave.
>
> I've been meaning to commit this one as obvious, but I'm not sure
> whether I should also use HONOR_NANS or whether I can safely ignore
> that here.
>
> Bootstrapped/regtested on x86_64-linux, ok for trunk?
>
> 2015-07-29 Marek Polacek <pola...@redhat.com>
>
> * c-common.c (warn_tautological_cmp): Bail for float types.
>
> * c-c++-common/Wtautological-compare-3.c: New test.
>
> diff --git gcc/c-family/c-common.c gcc/c-family/c-common.c
> index caa801e..9456729 100644
> --- gcc/c-family/c-common.c
> +++ gcc/c-family/c-common.c
> @@ -1910,6 +1910,12 @@ warn_tautological_cmp (location_t loc, enum tree_code
> code, tree lhs, tree rhs)
> || (CONVERT_EXPR_P (rhs) || TREE_CODE (rhs) == NON_LVALUE_EXPR))
> return;
>
> + /* Don't warn if either LHS or RHS has an IEEE floating point-type.
Eh, make this "floating-point type".
> + It could be a NaN, and NaN never compares equal to anything, even
> + itself. */
> + if (FLOAT_TYPE_P (TREE_TYPE (lhs)) || FLOAT_TYPE_P (TREE_TYPE (rhs)))
> + return;
> +
> if (operand_equal_p (lhs, rhs, 0))
> {
> /* Don't warn about array references with constant indices;
> diff --git gcc/testsuite/c-c++-common/Wtautological-compare-3.c
> gcc/testsuite/c-c++-common/Wtautological-compare-3.c
> index e69de29..64807b0 100644
> --- gcc/testsuite/c-c++-common/Wtautological-compare-3.c
> +++ gcc/testsuite/c-c++-common/Wtautological-compare-3.c
> @@ -0,0 +1,20 @@
> +/* { dg-do compile } */
> +/* { dg-options "-Wtautological-compare" } */
> +/* Test we don't warn for floats. */
> +
> +struct S { double d; float f; };
> +
> +void
> +fn1 (int i, float f, double d, struct S *s, float *fp)
> +{
> + if (f == f);
> + if (f != f);
> + if (d == d);
> + if (d != d);
> + if (fp[i] == fp[i]);
> + if (fp[i] != fp[i]);
> + if (s->f == s->f);
> + if (s->f != s->f);
> + if (s->d == s->d);
> + if (s->d != s->d);
> +}
>
> Marek
Marek
