[llvm] [NFC] [Docs] Document IIT encoding flow for intrinsic type signatures (PR #185453)

[Durgadoss R via llvm-commits]

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@@ -349,6 +349,9 @@ DecodeIITType(unsigned &NextElt, ArrayRef<unsigned char> Infos,
         IITDescriptor::get(IITDescriptor::Pointer, Infos[NextElt++]));
     return;
   case IIT_ARG: {
+    // IIT_ARG is the primary token for overloaded intrinsics, each "any"-typed
+    // parameter or return type is encoded as IIT_ARG + ArgInfo.
+    // ArgInfo byte: bits[4:0] = argument index, bits[7:5] = argument kind.
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durga4github wrote:

Thanks specifically for this!

https://github.com/llvm/llvm-project/pull/185453