[ARM] [MC] Refactor the constant pool classes

ARMTargetStreamer implements ConstantPool and AssmeblerConstantPools
to keep track of assembler-generated constant pools that are used for
ldr-pseudo.

When implementing ldr-pseudo for AArch64, these two classes can be reused.
So this patch factors them out from ARM target to the general MC lib.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211198 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/MC/ConstantPools.h

@@ -0,0 +1,80 @@
+//===- ConstantPool.h - Keep track of assembler-generated  ------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file declares the ConstantPool and AssemblerConstantPools classes.
+//
+//===----------------------------------------------------------------------===//
+
+
+#ifndef LLVM_MC_CONSTANTPOOL_H
+#define LLVM_MC_CONSTANTPOOL_H
+
+#include "llvm/ADT/SmallVector.h"
+namespace llvm {
+class MCContext;
+class MCExpr;
+class MCSection;
+class MCStreamer;
+class MCSymbol;
+// A class to keep track of assembler-generated constant pools that are use to
+// implement the ldr-pseudo.
+class ConstantPool {
+  typedef SmallVector<std::pair<MCSymbol *, const MCExpr *>, 4> EntryVecTy;
+  EntryVecTy Entries;
+
+public:
+  // Initialize a new empty constant pool
+  ConstantPool() {}
+
+  // Add a new entry to the constant pool in the next slot.
+  // \param Value is the new entry to put in the constant pool.
+  //
+  // \returns a MCExpr that references the newly inserted value
+  const MCExpr *addEntry(const MCExpr *Value, MCContext &Context);
+
+  // Emit the contents of the constant pool using the provided streamer.
+  void emitEntries(MCStreamer &Streamer);
+
+  // Return true if the constant pool is empty
+  bool empty();
+};
+
+class AssemblerConstantPools {
+  // Map type used to keep track of per-Section constant pools used by the
+  // ldr-pseudo opcode. The map associates a section to its constant pool. The
+  // constant pool is a vector of (label, value) pairs. When the ldr
+  // pseudo is parsed we insert a new (label, value) pair into the constant pool
+  // for the current section and add MCSymbolRefExpr to the new label as
+  // an opcode to the ldr. After we have parsed all the user input we
+  // output the (label, value) pairs in each constant pool at the end of the
+  // section.
+  //
+  // We use the MapVector for the map type to ensure stable iteration of
+  // the sections at the end of the parse. We need to iterate over the
+  // sections in a stable order to ensure that we have print the
+  // constant pools in a deterministic order when printing an assembly
+  // file.
+  typedef MapVector<const MCSection *, ConstantPool> ConstantPoolMapTy;
+  ConstantPoolMapTy ConstantPools;
+
+public:
+  AssemblerConstantPools() {}
+  ~AssemblerConstantPools() {}
+
+  void emitAll(MCStreamer &Streamer);
+  void emitForCurrentSection(MCStreamer &Streamer);
+  const MCExpr *addEntry(MCStreamer &Streamer, const MCExpr *Expr);
+
+private:
+  ConstantPool *getConstantPool(const MCSection *Section);
+  ConstantPool &getOrCreateConstantPool(const MCSection *Section);
+};
+} // end namespace llvm
+
+#endif