[RISCV] Add RISCVInstPrinter and basic MC assembler tests

With the addition of RISCVInstPrinter, it is now possible to test the basic 
operation of the RISCV MC layer.

Differential Revision: https://reviews.llvm.org/D23564

llvm-svn: 310917
diff --git a/llvm/lib/Target/RISCV/InstPrinter/RISCVInstPrinter.cpp b/llvm/lib/Target/RISCV/InstPrinter/RISCVInstPrinter.cpp
new file mode 100644
index 0000000..23f3352c0
--- /dev/null
+++ b/llvm/lib/Target/RISCV/InstPrinter/RISCVInstPrinter.cpp
@@ -0,0 +1,55 @@
+//===-- RISCVInstPrinter.cpp - Convert RISCV MCInst to asm syntax ---------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This class prints an RISCV MCInst to a .s file.
+//
+//===----------------------------------------------------------------------===//
+
+#include "RISCVInstPrinter.h"
+#include "llvm/MC/MCAsmInfo.h"
+#include "llvm/MC/MCExpr.h"
+#include "llvm/MC/MCInst.h"
+#include "llvm/MC/MCSymbol.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/FormattedStream.h"
+using namespace llvm;
+
+#define DEBUG_TYPE "asm-printer"
+
+// Include the auto-generated portion of the assembly writer.
+#include "RISCVGenAsmWriter.inc"
+
+void RISCVInstPrinter::printInst(const MCInst *MI, raw_ostream &O,
+                                 StringRef Annot, const MCSubtargetInfo &STI) {
+  printInstruction(MI, O);
+  printAnnotation(O, Annot);
+}
+
+void RISCVInstPrinter::printRegName(raw_ostream &O, unsigned RegNo) const {
+  O << getRegisterName(RegNo);
+}
+
+void RISCVInstPrinter::printOperand(const MCInst *MI, unsigned OpNo,
+                                  raw_ostream &O, const char *Modifier) {
+  assert((Modifier == 0 || Modifier[0] == 0) && "No modifiers supported");
+  const MCOperand &MO = MI->getOperand(OpNo);
+
+  if (MO.isReg()) {
+    printRegName(O, MO.getReg());
+    return;
+  }
+
+  if (MO.isImm()) {
+    O << MO.getImm();
+    return;
+  }
+
+  assert(MO.isExpr() && "Unknown operand kind in printOperand");
+  MO.getExpr()->print(O, &MAI);
+}