[llvm] [RFC][SPIR-V] Add llvm.arbitrary.fp.convert intrinsic (PR #164252)

[Dmitry Sidorov via llvm-commits]

================
@@ -21406,6 +21406,69 @@ environment <floatenv>` *except* for the rounding mode.
 This intrinsic is not supported on all targets. Some targets may not support
 all rounding modes.
 
+'``llvm.arbitrary.fp.convert``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+      declare <type> @llvm.arbitrary.fp.convert(
+          <type> <value>, metadata <result interpretation>,
+          metadata <input interpretation>, metadata <rounding mode>,
+          i32 <saturation>)
+
+Overview:
+"""""""""
+
+The ``llvm.arbitrary.fp.convert`` intrinsic performs conversions
+between values whose interpretation differs from their representation
+in LLVM IR. The intrinsic is overloaded on both its return type and first
+argument. Metadata operands describe how the raw bits should be interpreted
+before and after the conversion.
+
+Arguments:
+""""""""""
+
+``value``
+  The value to convert. Its interpretation is described by ``input
+  interpretation``.
+
+``result interpretation``
+  A metadata string that describes the type of the result. The string
+  can be ``"none"`` (no conversion needed), ``"signed"`` or ``"unsigned"`` (for
----------------
MrSidims wrote:

This was an attempt to create an omnipotent intrinsic to allow conversions to/from, lets say i4 and i8 (as they described in OCP spec). But I see, that having such intrinsic lead to lots of inconveniences, so I've decided to:
a. remove int conversions - they can be handled in a different way;
b. split the intrinsic into 2.

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