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

[Eli Friedman 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.
+
+Semantics:
+""""""""""
+
+The intrinsic converts the native LLVM floating-point value to the arbitrary FP
+format specified by ``interpretation``, applying the requested rounding mode and
+saturation behavior. The result is returned as an integer (e.g., ``i8`` for FP8,
+``i6`` for FP6) containing the encoded arbitrary FP bits. When saturation is enabled,
+values that exceed the representable range are clamped to the minimum or maximum
+normal value of the target format.
+
+Example:
+""""""""
+
+::
+
+      ; Convert half to FP8 E4M3 format
+      %fp8bits = call i8 @llvm.convert.to.arbitrary.fp.i8.f16(
+          half %value, metadata !"Float8E4M3",
+          metadata !"round.tonearest", i1 false)
+
+      ; Convert vector of float to FP8 E5M2 with saturation
+      %vec_fp8 = call <4 x i8> @llvm.convert.to.arbitrary.fp.v4i8.v4f32(
+          <4 x float> %values, metadata !"Float8E5M2",
+          metadata !"round.towardzero", i1 true)
+
+'``llvm.convert.from.arbitrary.fp``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+      declare <fNxM> @llvm.convert.from.arbitrary.fp.<fNxM>.<iNxM>(
+          <iNxM> <value>, metadata <interpretation>,
+          metadata <rounding mode>, i1 <saturation>)
----------------
efriedma-quic wrote:

Please fix the documentation to state more clearly what happens when "saturation" is false, for destination formats that have infinity, and formats that don't have infinity, since the spec has specific requirements.

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