[PATCH] D27028: Add intrinsics for constrained floating point operations

[Steve Canon via Phabricator via llvm-commits]

scanon added inline comments.


================
Comment at: docs/LangRef.rst:12147
+
+'``llvm.experimental.constrained.fsub``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
----------------
DavidKreitzer wrote:
> This question might be beyond the scope of this initial change set, but here goes.
> 
> FP negation is currently handled using fsub -0, X. Is that sufficient in a constrained context? If we allow X to be a signaling NaN, -0-X should raise Invalid while -X should not, at least according to IEEE-754.
> 
Probably more importantly, -X has a defined signbit (the negation of whatever the signbit of X was), but -0-X does not [assuming the obvious binding of -X to the IEEE 754 negate operation and -0-X to the subtract operation].


Repository:
  rL LLVM

https://reviews.llvm.org/D27028