On Tue, Oct 1, 2019 at 10:56 AM Alexandre Oliva <[email protected]> wrote:
>
> Optimizing gcc.dg/torture/pr41094.c, the compiler computes the
> constant value and short-circuits the whole thing. At -O0, however,
> on 32-bit x86, the call to pow() remains, and the program compares the
> returned value in a stack register, with excess precision, with the
> exact return value expected from pow(). If libm's pow() returns a
> slightly off result, the compare fails. If the value in the register
> is stored in a separate variable, so it gets rounded to double
> precision, and then compared, the compare passes.
>
> It's not clear that the test was meant to detect libm's reliance on
> rounding off the excess precision, but I guess it wasn't, so I propose
> this slight change that enables it to pass regardless of the slight
> inaccuracy of the C library in use.
>
> Regstrapped on x86_64-linux-gnu, and tested on the affected target.
> Ok to install?
OK.
Richard.
>
> for gcc/testsuite/ChangeLog
>
> * gcc.dg/torture/pr41094.c: Introduce intermediate variable.
> ---
> gcc/testsuite/gcc.dg/torture/pr41094.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/gcc/testsuite/gcc.dg/torture/pr41094.c
> b/gcc/testsuite/gcc.dg/torture/pr41094.c
> index 2a4e9616cbfad..9219a1741a37f 100644
> --- a/gcc/testsuite/gcc.dg/torture/pr41094.c
> +++ b/gcc/testsuite/gcc.dg/torture/pr41094.c
> @@ -13,7 +13,8 @@ double foo(void)
>
> int main()
> {
> - if (foo() != 2.0)
> + double r = foo ();
> + if (r != 2.0)
> abort ();
> return 0;
> }
>
> --
> Alexandre Oliva, freedom fighter he/him https://FSFLA.org/blogs/lxo
> Be the change, be Free! FSF VP & FSF Latin America board member
> GNU Toolchain Engineer Free Software Evangelist
> Hay que enGNUrecerse, pero sin perder la terGNUra jamás - Che GNUevara
