Refactor transOCLBuiltinFromExtInst

Removed extra variables, simplified code, removed dead code related to
"read_image" handling: it is not present in OpenCL.std extended instruction
set and therefore we can't encounter it in `transOCLBuiltinFromExtInst`
function.

Author: AlexeySachkov

llvm-spirv/lib/SPIRV/SPIRVReader.cpp

@@ -4090,18 +4090,14 @@ Instruction *SPIRVToLLVM::transOCLBuiltinFromExtInst(SPIRVExtInst *BC,
   assert(BB && "Invalid BB");
   std::string MangledName;
   SPIRVWord EntryPoint = BC->getExtOp();
-  bool IsVarArg = false;
-  bool IsPrintf = false;
   std::string UnmangledName;
-  auto BArgs = BC->getArguments();
+  std::vector<SPIRVWord> BArgs = BC->getArguments();
 
   assert(BM->getBuiltinSet(BC->getExtSetId()) == SPIRVEIS_OpenCL &&
          "Not OpenCL extended instruction");
-  if (EntryPoint == OpenCLLIB::Printf)
-    IsPrintf = true;
-  else {
-    UnmangledName = OCLExtOpMap::map(static_cast<OCLExtOpKind>(EntryPoint));
-  }
+
+  bool IsPrintf = (EntryPoint == OpenCLLIB::Printf);
+  UnmangledName = OCLExtOpMap::map(static_cast<OCLExtOpKind>(EntryPoint));
 
   SPIRVDBG(spvdbgs() << "[transOCLBuiltinFromExtInst] OrigUnmangledName: "
                      << UnmangledName << '\n');
@@ -4111,21 +4107,16 @@ Instruction *SPIRVToLLVM::transOCLBuiltinFromExtInst(SPIRVExtInst *BC,
 
   if (IsPrintf) {
     MangledName = "printf";
-    IsVarArg = true;
     ArgTypes.resize(1);
-  } else if (UnmangledName.find("read_image") == 0) {
-    auto ModifiedArgTypes = ArgTypes;
-    ModifiedArgTypes[1] = getOrCreateOpaquePtrType(M, "opencl.sampler_t");
-    mangleOpenClBuiltin(UnmangledName, ModifiedArgTypes, MangledName);
   } else {
     mangleOpenClBuiltin(UnmangledName, ArgTypes, MangledName);
   }
   SPIRVDBG(spvdbgs() << "[transOCLBuiltinFromExtInst] ModifiedUnmangledName: "
                      << UnmangledName << " MangledName: " << MangledName
                      << '\n');
 
-  FunctionType *FT =
-      FunctionType::get(transType(BC->getType()), ArgTypes, IsVarArg);
+  FunctionType *FT = FunctionType::get(transType(BC->getType()), ArgTypes,
+                                       /* IsVarArg */ IsPrintf);
   Function *F = M->getFunction(MangledName);
   if (!F) {
     F = Function::Create(FT, GlobalValue::ExternalLinkage, MangledName, M);