Encoding fixes

Author: cassiebeckley

llvm/lib/Target/SPIRV/MCTargetDesc/SPIRVMCCodeEmitter.cpp

@@ -114,7 +114,9 @@ void SPIRVMCCodeEmitter::encodeUnknownType(const MCInst &MI,
   // Encode the first 32 SPIR-V bytes with the number of args and the opcode.
   const uint64_t OpCode = MI.getOperand(1).getImm();
   const uint32_t NumWords = MI.getNumOperands();
-  const uint32_t FirstWord = (NumWords << 16) | OpCode;
+  const uint32_t FirstWord = (0xFF & NumWords) << 16 | (0xFF & OpCode);
+
+  // encoding: <opcode+len> <result type> [<operand0> <operand1> ...]
   support::endian::write(CB, FirstWord, llvm::endianness::little);
 
   emitOperand(MI.getOperand(0), CB);