[llvm] LangRef: rint, nearbyint: mention that default rounding mode is assumed (PR #77191)

[Andy Kaylor via llvm-commits]

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@@ -15751,7 +15751,9 @@ Semantics:
 """"""""""
 
 This function returns the same values as the libm ``rint`` functions
-would, and handles error conditions in the same way.
+would, and handles error conditions in the same way. The rounding mode
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andykaylor wrote:

Is there a version of the C standard that specifies that rint *will* raise the inexact exception if the result isn't exact? The version I looked at (a draft version of C11), says it "may" raise the inexact exception.

Either way, I think this is irrelevant for the LLVM intrinsic since "The default LLVM floating-point environment assumes that traps are disabled and status flags are not observable."

https://github.com/llvm/llvm-project/pull/77191