[llvm] [RFC][SPIR-V] Add intrinsics to convert to/from ap.float (PR #164252)

[Dmitry Sidorov via llvm-commits]

================
@@ -21406,6 +21406,144 @@ environment <floatenv>` *except* for the rounding mode.
 This intrinsic is not supported on all targets. Some targets may not support
 all rounding modes.
 
+'``llvm.convert.to.arbitrary.fp``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+      declare <iNxM> @llvm.convert.to.arbitrary.fp.<iNxM>.<fNxM>(
+          <fNxM> <value>, metadata <interpretation>,
+          metadata <rounding mode>, i1 <saturation>)
+
+Overview:
+"""""""""
+
+The ``llvm.convert.to.arbitrary.fp`` intrinsic converts a native LLVM
+floating-point value to an arbitrary FP format, returning the result as an integer
+containing the arbitrary FP bits. This intrinsic is overloaded on both its return
+type and first argument.
+
+Arguments:
+""""""""""
+
+``value``
+  The native LLVM floating-point value to convert (e.g., ``half``, ``float``, ``double``).
+
+``interpretation``
+  A metadata string describing the target arbitrary FP format. Supported format names include:
+
+  - FP8 formats: ``"Float8E5M2"``, ``"Float8E5M2FNUZ"``, ``"Float8E4M3"``,
+    ``"Float8E4M3FN"``, ``"Float8E4M3FNUZ"``, ``"Float8E4M3B11FNUZ"``, ``"Float8E3M4"``,
+    ``"Float8E8M0FNU"``
+  - FP6 formats: ``"Float6E3M2FN"``, ``"Float6E2M3FN"``
+  - FP4 formats: ``"Float4E2M1FN"``
+
+``rounding mode``
+  A metadata string specifying the rounding mode. The permitted strings match those
+  accepted by :ref:`llvm.fptrunc.round <int_fptrunc_round>` (for example,
+  ``"round.tonearest"`` or ``"round.towardzero"``).
+
+``saturation``
+  A compile-time constant boolean value (``i1``). When ``true``, values outside the
+  representable range of the target format are clamped to the minimum or maximum normal value.
+  When ``false``, no saturation is applied. This parameter must be an immediate constant.
----------------
MrSidims wrote:

> Does this flag flip between saturating to +huge/-huge and +inf/-inf

Exactly, I've changed the description for intrinsics, hope it address this and other questions.

https://github.com/llvm/llvm-project/pull/164252