[PATCH] D74729: [FPEnv] Intrinsic for setting rounding mode

[Matt Arsenault via Phabricator via llvm-commits]

arsenm added inline comments.


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Comment at: llvm/docs/LangRef.rst:18146-18150
+    0  - toward zero
+    1  - to nearest, ties to even
+    2  - toward positive infinity
+    3  - toward negative infinity
+    4  - to nearest, ties away from zero
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sepavloff wrote:
> RKSimon wrote:
> > arsenm wrote:
> > > I'm wondering if this should be more opaque, and broader for the entire FP environment (not just the rounding mode). For AMDGPU we have a number of additional bits in the FP environment. We also have the denormal mode, enabling FP exceptions, and a few more exotic target specific FP mode bits.
> > @arsenm Would these extra bits be exclusive modes or would you need this to support target specific mode combos?
> > I'm wondering if this should be more opaque, and broader for the entire FP environment (not just the rounding mode). 
> 
> C library defined function `fesetmode`, which sets all control modes, not just rounding. It make sense to introduce intrinsic for it, which would serve these purposes.
We have the rounding mode controls as presented here, however they are broken down by FP type. We can separately set the rounding mode for f32 and f64/f16, so there are two different settings. We also have the denormal mode, for inputs and outputs, also broken down by type in the same way. The denormal handling and per-type handling I think deserve consideration here

We have 2 additional target specific FP bits nothing else would need to really think about, but it would be nice if you could set the exact mode you want in a single intrinsic call. I'm less interested in these though


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https://reviews.llvm.org/D74729