Ping:
https://gcc.gnu.org/ml/gcc-patches/2019-02/msg00363.html
On Wed, 2019-02-06 at 21:23 -0500, David Malcolm wrote:
> PR c++/88680 reports excess warnings from -Wtype-limits after the C++
> FE's use of location wrappers was extended in r267272 for cases such
> as:
>
> const unsigned n = 8;
> static_assert (n >= 0 && n % 2 == 0, "");
>
> t.C:3:18: warning: comparison of unsigned expression >= 0 is always
> true
> [-Wtype-limits]
> 3 | static_assert (n >= 0 && n % 2 == 0, "");
> | ~~^~~~
>
> The root cause is that the location wrapper around "n" breaks the
> suppression of the warning for the "if OP0 is a constant that is >=
> 0"
> case.
>
> This patch fixes it by calling fold_for_warn on OP0, extracting the
> constant.
>
> Successfully bootstrapped & regrtested on x86_64-pc-linux-gnu.
>
> OK for trunk?
>
> gcc/c-family/ChangeLog:
> PR c++/88680
> * c-common.c (shorten_compare): Call fold_for_warn on op0 when
> implementing -Wtype-limits.
>
> gcc/testsuite/ChangeLog:
> PR c++/88680
> * g++.dg/wrappers/pr88680.C: New test.
> ---
> gcc/c-family/c-common.c | 2 +-
> gcc/testsuite/g++.dg/wrappers/pr88680.C | 47
> +++++++++++++++++++++++++++++++++
> 2 files changed, 48 insertions(+), 1 deletion(-)
> create mode 100644 gcc/testsuite/g++.dg/wrappers/pr88680.C
>
> diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c
> index d3b5879..5813e0a 100644
> --- a/gcc/c-family/c-common.c
> +++ b/gcc/c-family/c-common.c
> @@ -3114,7 +3114,7 @@ shorten_compare (location_t loc, tree *op0_ptr,
> tree *op1_ptr,
> /* Here we must do the comparison on the nominal type
> using the args exactly as we received them. */
> type = *restype_ptr;
> - primop0 = op0;
> + primop0 = fold_for_warn (op0);
> primop1 = op1;
>
> if (!real1 && !real2 && integer_zerop (primop1)
> diff --git a/gcc/testsuite/g++.dg/wrappers/pr88680.C
> b/gcc/testsuite/g++.dg/wrappers/pr88680.C
> new file mode 100644
> index 0000000..86945db
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/wrappers/pr88680.C
> @@ -0,0 +1,47 @@
> +// { dg-do compile { target c++11 } }
> +// { dg-options "-Wtype-limits" }
> +
> +const unsigned N = 8;
> +const unsigned P = 0;
> +
> +enum { FOO, BAR };
> +
> +static_assert (N >= 0 && N % 2 == 0, "");
> +static_assert (FOO >= 0, "");
> +static_assert (FOO >= FOO, "");
> +static_assert (FOO >= P, "");
> +static_assert (BAR >= P, "");
> +static_assert (N >= FOO, "");
> +
> +void test(unsigned n)
> +{
> + if (N >= 0 && N % 2 == 0, "")
> + return;
> + if (FOO >= 0, "")
> + return;
> + if (FOO >= FOO, "")
> + return;
> + if (FOO >= P, "")
> + return;
> + if (BAR >= P)
> + return;
> + if (N >= FOO, "")
> + return;
> + if (n >= 0) // { dg-warning ">= 0 is always true" }
> + return;
> + if (n < 0) // { dg-warning "< 0 is always false" }
> + return;
> + if (n >= FOO)
> + return;
> + if (n < FOO)
> + return;
> + if (N >= 0)
> + return;
> + if (N < 0)
> + return;
> + if (N >= FOO)
> + return;
> + if (N < FOO)
> + return;
> +
> +}
