[cfe-dev] [llvm-dev] RFC: change -fp-contract=off to actually disable FMAs

Tim Northover via cfe-dev cfe-dev at lists.llvm.org
Wed Jul 10 13:36:15 PDT 2019

On Wed, 10 Jul 2019 at 21:09, Scott Manley via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> Numerically identical, sure. But, there are other reasons to disable FMAD fusion -- namely for performance comparisons.

That's not typically something we'd expose to the end user in any way.
Clang as a compiler should be selecting what it thinks is the fastest
sequence to do some particular job; if it's wrong then that's a bug,
not something to add a command-line flag for.

I suspect that's behind the documentation discrepancy you've noticed.
For many people working on LLVM they're the same thing: as long as
behaviour isn't changed for the end user (in valid programs), anything



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