diff mbox series

Store float for pow result test

Message ID ory2y4kfng.fsf@lxoliva.fsfla.org
State New
Headers show
Series Store float for pow result test | expand

Commit Message

Alexandre Oliva Oct. 1, 2019, 8:56 a.m. UTC 
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?


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(-)

Comments

Richard Biener Oct. 1, 2019, 11:09 a.m. UTC | #1 
On Tue, Oct 1, 2019 at 10:56 AM Alexandre Oliva <oliva@adacore.com> 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
diff mbox series

Patch

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;
 }