[PATCH] D72841: Add support for pragma float_control, to control precision and exception behavior at the source level

[Steve Canon via Phabricator via cfe-commits]

scanon added a comment.

> Prior to this change contract was never generated in the case of in-statement contraction only, instead clang was emitting llvm.fmuladd to inform the backend that only those were eligible for contraction. From a correctness perspective I think this was perfectly fine.
> 
> Currently I don't see any logic to generate "blocking intrinsics" (I guess to define a region around the instructions emitted for the given statement). Until such mechanism is in place, I think that generating the contract fast-math flag also for in-statement contraction is wrong because it breaks the original program semantic.

This is exactly right. If we are going to have new in-statement optimizations, then we probably do need to add some blocking intrinsic (which would be elidable given suitable fast-math flags); the system of generating fmuladd works well for FMA contraction, but doesn't really generalize to other optimizations of this sort.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D72841/new/

https://reviews.llvm.org/D72841