llvm dev - Apr 2021 - RFC: Create new intrinsic llvm.arith.fence to control FP optimization at expression level

Intel would like to contribute a new intrinsic llvm.arith.fence to control
floating point optimization at the expression level.

The purpose is to provide fine control, at the expression level, over floating
point optimization when -ffast-math (-ffp-model=fast) is enabled. We are also
proposing a new clang builtin that provides access to this intrinsic, as well as
a new clang command line option -fprotect-parens that will be implemented using
this intrinsic.

The RFC and preliminary llvm patch is here, https://reviews.llvm.org/D99675,
looking for comments!  Thank you.  I'll post a clang patch later this week.