Workaround for prefetch_cache_control failing due to unknown type size on opaque pointers

Currently `handleCacheControlINTELForPrefetch` requires type size to perform call conversion correctly,
but on opaque pointers such size is not available and we cannot just extract it anyhow.

We're waiting for "OpUntypedPrefetch" extension which will support opaque pointers in such cases.

Meanwhile as of today I'm adding skip of the whole prefetch conversion when opaque pointer type is involved
and we're waiting for update about the status of "OpUntypedPrefetch"

Author: bokrzesi

IGC/AdaptorOCL/preprocess_spvir/HandleSPIRVDecorations/HandleSpirvDecorationMetadata.cpp

@@ -326,6 +326,14 @@ void HandleSpirvDecorationMetadata::handleCacheControlINTELForPrefetch(llvm::Cal
   // explicit element size as arg.
   PointerType *PTy = dyn_cast<PointerType>(I.getArgOperand(0)->getType());
   IGC_ASSERT(PTy);
+
+  // As of today there's no "OpUntypedPrefetch" which as previous comments mentions,
+  // is needed to implement this prefetch correctly on opaque pointers.
+  // It will of course result in performance penalty and needs to be changed once
+  // "OpUntypedPrefetch" is ready.
+  if (IGCLLVM::isOpaquePointerTy(PTy))
+    return;
+
   args.push_back(ConstantInt::get(Type::getInt32Ty(I.getContext()),
                                   IGCLLVM::getNonOpaquePtrEltTy(PTy)->getPrimitiveSizeInBits() / 8));