[PATCH] D31276: Add #pragma clang fast_math

[Adam Nemet via Phabricator via cfe-commits]

anemet added a comment.

In https://reviews.llvm.org/D31276#708992, @hfinkel wrote:

> High-level comment ;)
>
>   #pragma clang fast_math contract_fast(on)
>   
>
> This seems a bit unfortunate because 'fast' appears twice? How are we planning on naming the other fast-math flags? Maybe we should just name it:


This is just pure laziness on my part, I was hoping that all these flags can be implemented with on/off but if you find it confusing that's a good indicator.

> 
> 
>   #pragma clang math constract_fast(on)
>    
> 
> or
> 
>   #pragma clang math contract(fast) // we could also accept off/on here for consistency and compatibility with the standard pragma
>    
> 
> or maybe fp_math or floating_point_math or floating_point or fp instead of math.
> 
> I think that I prefer this last form (because it does not repeat 'fast' and also makes our extension a pure superset of the standard pragma).
> 
> What do you want to name the other flags? I'd prefer if they're grammatically consistent. Maybe we should stick closely to the command-line options, and have:
> 
>   fp_contract(on/off/fast)
>   unsafe_optimizations(on/off)
>   finite_only(on/off)
>    
> 
> What do you think?

I really like #pragma clang fp or fp_math because contraction feels different from the other fast-math flags.  That said then we don't want to repeat fp in fp_contract.

We should probably have the full list to make sure it works though with all the FMFs.  Here is a straw-man proposal:

  UnsafeAlgebra          #pragma clang fp unsafe_optimizations(on/off)
  NoNaNs                     #pragma clang fp no_nans(on/off)
  NoInfs                        #pragma clang fp finite_only(on/off)
  NoSignedZeros         #pragma clang fp no_signed_zeros(on/off)
  AllowReciprocal        #pragma clang fp reciprocal_math
  AllowContract           #pragma clang fp contract(on/off/fast)

The negative ones feel a bit strange...   What do you think?


https://reviews.llvm.org/D31276