[petsc-dev] Building PETSc on LLNL Lassen

[Jed Brown]

<jacob.fai at gmail.com> writes:

> According to https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html :
>
> -ffp-contract=style
>
>     -ffp-contract=off disables floating-point expression contraction. -ffp-contract=fast enables floating-point expression contraction such as forming of fused multiply-add operations if the target has native support for them. -ffp-contract=on enables floating-point expression contraction if allowed by the language standard. This is currently not implemented and treated equal to -ffp-contract=off.
>
>     The default is -ffp-contract=fast.
>
> We don't need to turn it on, although maybe the default is -ffp-contract only after certain versions of gcc.

It's off with -std=c11 and -std=c99. Doesn't seem to care about -std=c++1* versus -std=gnu++1*.

https://godbolt.org/z/jqMsEG

It's always off by default with Clang (and with Rust, which is a longer story).