[PATCH] D137954: Enable roundeven.

[Matt Arsenault via Phabricator via llvm-commits]

arsenm added inline comments.


================
Comment at: llvm/lib/Target/AMDGPU/AMDGPUISelLowering.cpp:1195
+  case ISD::FROUNDEVEN:
+    return LowerFROUND(Op, DAG);
   case ISD::FROUND: return LowerFROUND(Op, DAG);
----------------
Leonc wrote:
> arsenm wrote:
> > I'm perpetually confused by the variety of rounding functions.
> > 
> > llvm.rint => round to nearest integer, in current rounding mode (which is assumed to be round nearest even), which is implied by being non-constrained
> > llvm.nearbyint => same as llvm.rint, except no FP exceptions. FP exceptions aren't supported with non-constrained intrinsics, so this distinction is pointless
> > 
> > llvm.round -> round, away from 0
> > llvm.roundeven -> round halfway nearest 0
> > 
> > 
> > so I think this isn't the same as round, but is supposed to be the same as llvm.rint (which we have 3 different names for)
> I thought `llvm.roundeven` is supposed to always round to nearest even regardless of the rounding mode. Does our implementation of `llvm.rint` ignore the rounding mode?
Yes. This is all legacy cruft from when people were imaging possible solutions to supporting strictfp in the distant future without an actual design in mind. The non-strict, regular floating point intrinsics all assume RTE rounding with no fp exceptions.

This cruft is bothering me; as a follow up, can you prepare a patch to deprecate the old intrinsics and auto-upgrade them so we're left with one?


Repository:
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  https://reviews.llvm.org/D137954/new/

https://reviews.llvm.org/D137954