[Bug target/83497] [8 Regression] CPU2000 172.mgrid starts failing with r254730

[pthaugen at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83497

Pat Haugen <pthaugen at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|WAITING                     |RESOLVED
         Resolution|---                         |INVALID

--- Comment #5 from Pat Haugen <pthaugen at gcc dot gnu.org> ---
I have confirmed that this is indeed just a precision difference due to a
different mix and order of instructions for the computation in the RESID loop,
valid reassociation with -ffast-math. The difference is then compounded as the
benchmark iterates over the values.

The specdiff command for mgrid specifies an absolute tolerance of "-a 1e-12"
and uses the absolute difference when seeing if two values are within the
specified tolerance. In this case they were not.