[clang] [llvm] [NVPTX] Add conversion intrinsics from/to fp8 types (e4m3, e5m2) (PR #102969)

[Artem Belevich via cfe-commits]

================
@@ -722,6 +722,37 @@ let hasSideEffects = false in {
 
   defm CVT_f16x2 : CVT_FROM_FLOAT_V2_SM80<"f16x2", Int32Regs>;
   defm CVT_bf16x2 : CVT_FROM_FLOAT_V2_SM80<"bf16x2", Int32Regs>;
+
+  // FP8 conversions.
+  multiclass CVT_TO_F8X2<string F8Name> {
+    def _f32 :
+      NVPTXInst<(outs Int16Regs:$dst),
+                (ins Float32Regs:$src1, Float32Regs:$src2, CvtMode:$mode),
+                !strconcat("cvt${mode:base}.satfinite${mode:relu}.",
+                F8Name, "x2.f32 \t$dst, $src1, $src2;"), []>,
+      Requires<[hasPTX<81>, hasSM<89>]>;
+    def _f16x2 :
+      NVPTXInst<(outs Int16Regs:$dst),
+                (ins Int32Regs:$src, CvtMode:$mode),
+                !strconcat("cvt${mode:base}.satfinite${mode:relu}.",
+                F8Name, "x2.f16x2 \t$dst, $src;"), []>,
+      Requires<[hasPTX<81>, hasSM<89>]>;
+  }
+
+  defm CVT_e4m3x2 : CVT_TO_F8X2<"e4m3">;
+  defm CVT_e5m2x2 : CVT_TO_F8X2<"e5m2">;
+
+  multiclass CVT_FROM_F8X2<string F8Name> {
+    def x2 :
+      NVPTXInst<(outs Int32Regs:$dst),
----------------
Artem-B wrote:

It would be useful to add a comment that the output i32 is actually <2 x f16> as `x2` does not give enough of a hint. Or, perhaps rename it to `_f16x2`

https://github.com/llvm/llvm-project/pull/102969