Start adding an integrated assembler.

src/assembler.h

Index: src/assembler.h
diff --git a/src/assembler.h b/src/assembler.h
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+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+//
+// Modified by the Subzero authors.
+//
+//===- subzero/src/assembler.h - Integrated assembler -----------*- C++ -*-===//
+//
+//                        The Subzero Code Generator
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file declares the Assembler base class.  Instructions are assembled
+// by architecture-specific assemblers that derive from this base class.
+// This base class manages buffers and fixups for emitting code, etc.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef SUBZERO_SRC_ASSEMBLER_H
+#define SUBZERO_SRC_ASSEMBLER_H
+
+#include "IceDefs.h"
+
+#include "llvm/Support/Allocator.h"
+
+namespace Ice {
+
+// Forward declarations.
+class Assembler;
+class AssemblerFixup;
+class AssemblerBuffer;
+class MemoryRegion;
+
+// TODO(jvoung): Do we care if uword was uintptr_t or not?
+
+// Assembler fixups are positions in generated code that hold relocation
+// information that needs to be processed before finalizing the code
+// into executable memory.
+class AssemblerFixup {
+public:
+  virtual void Process(const MemoryRegion &region, intptr_t position) = 0;
+
+  // It would be ideal if the destructor method could be made private,
+  // but the g++ compiler complains when this is subclassed.
+  virtual ~AssemblerFixup() { llvm_unreachable("~AssemblerFixup used"); }
+
+private:
+  AssemblerFixup *previous_;
+  intptr_t position_;
+
+  AssemblerFixup *previous() const { return previous_; }
+  void set_previous(AssemblerFixup *previous) { previous_ = previous; }
+
+  intptr_t position() const { return position_; }
+  void set_position(intptr_t position) { position_ = position; }
+
+  friend class AssemblerBuffer;
+};
+
+// Assembler buffers are used to emit binary code. They grow on demand.
+class AssemblerBuffer {
+public:
+  AssemblerBuffer(Assembler &);
+  ~AssemblerBuffer();
+
+  // Basic support for emitting, loading, and storing.
+  template <typename T> void Emit(T value) {
+    assert(HasEnsuredCapacity());
+    *reinterpret_cast<T *>(cursor_) = value;
+    cursor_ += sizeof(T);
+  }
+
+  template <typename T> T Load(intptr_t position) const {
+    assert(position >= 0 &&
+           position <= (Size() - static_cast<intptr_t>(sizeof(T))));
+    return *reinterpret_cast<T *>(contents_ + position);
+  }
+
+  template <typename T> void Store(intptr_t position, T value) {
+    assert(position >= 0 &&
+           position <= (Size() - static_cast<intptr_t>(sizeof(T))));
+    *reinterpret_cast<T *>(contents_ + position) = value;
+  }
+
+  // Emit a fixup at the current location.
+  void EmitFixup(AssemblerFixup *fixup) {
+    fixup->set_previous(fixup_);
+    fixup->set_position(Size());
+    fixup_ = fixup;
+  }
+
+  // Get the size of the emitted code.
+  intptr_t Size() const { return cursor_ - contents_; }
+  uintptr_t contents() const { return contents_; }
+
+  // Copy the assembled instructions into the specified memory block
+  // and apply all fixups.
+  void FinalizeInstructions(const MemoryRegion &region);
+
+// To emit an instruction to the assembler buffer, the EnsureCapacity helper
+// must be used to guarantee that the underlying data area is big enough to
+// hold the emitted instruction. Usage:
+//
+//     AssemblerBuffer buffer;
+//     AssemblerBuffer::EnsureCapacity ensured(&buffer);
+//     ... emit bytes for single instruction ...
+
+#if defined(DEBUG)
+  class EnsureCapacity {
+  public:
+    explicit EnsureCapacity(AssemblerBuffer *buffer);
+    ~EnsureCapacity();
+
+  private:
+    AssemblerBuffer *buffer_;
+    intptr_t gap_;
+
+    intptr_t ComputeGap() { return buffer_->Capacity() - buffer_->Size(); }
+  };
+
+  bool has_ensured_capacity_;
+  bool HasEnsuredCapacity() const { return has_ensured_capacity_; }
+#else
+  class EnsureCapacity {
+  public:
+    explicit EnsureCapacity(AssemblerBuffer *buffer) {
+      if (buffer->cursor() >= buffer->limit())
+        buffer->ExtendCapacity();
+    }
+  };
+
+  // When building the C++ tests, assertion code is enabled. To allow
+  // asserting that the user of the assembler buffer has ensured the
+  // capacity needed for emitting, we add a dummy method in non-debug mode.
+  bool HasEnsuredCapacity() const { return true; }
+#endif
+
+  // Returns the position in the instruction stream.
+  intptr_t GetPosition() const { return cursor_ - contents_; }
+
+private:
+  // The limit is set to kMinimumGap bytes before the end of the data area.
+  // This leaves enough space for the longest possible instruction and allows
+  // for a single, fast space check per instruction.
+  static const intptr_t kMinimumGap = 32;
+
+  uintptr_t contents_;
+  uintptr_t cursor_;
+  uintptr_t limit_;
+  Assembler &assembler_;
+  AssemblerFixup *fixup_;
+#if defined(DEBUG)
+  bool fixups_processed_;
+#endif
+
+  uintptr_t cursor() const { return cursor_; }
+  uintptr_t limit() const { return limit_; }
+  intptr_t Capacity() const {
+    assert(limit_ >= contents_);
+    return (limit_ - contents_) + kMinimumGap;
+  }
+
+  // Process the fixup chain.
+  void ProcessFixups(const MemoryRegion &region);
+
+  // Compute the limit based on the data area and the capacity. See
+  // description of kMinimumGap for the reasoning behind the value.
+  static uintptr_t ComputeLimit(uintptr_t data, intptr_t capacity) {
+    return data + capacity - kMinimumGap;
+  }
+
+  void ExtendCapacity();
+
+  friend class AssemblerFixup;
+};
+
+class Assembler {
+public:
+  Assembler() {}
+  ~Assembler() {}
+
+  // Allocate a chunk of bytes using the per-Assembler allocator.
+  uintptr_t AllocateBytes(size_t bytes) {
+    // re: Alignment -- We just need to be able to write bytes to this,
+    // so there's not a real requirement (e.g., not related to NaCl bundle
+    // alignment). When code is finalized and copied out to the .o file's
+    // text section, then we will care about alignment.
+    const size_t Alignment = 16;
+    return reinterpret_cast<uintptr_t>(Allocator.Allocate(bytes, Alignment));
+  }
+
+  // Allocate data of type T using the per-Assembler allocator.
+  template <typename T> T *Allocate() { return Allocator.Allocate<T>(); }
+
+private:
+  llvm::BumpPtrAllocator Allocator;
+
+  Assembler(const Assembler &) LLVM_DELETED_FUNCTION;
+  Assembler &operator=(const Assembler &) LLVM_DELETED_FUNCTION;
+};
+
+} // end of namespace Ice
+
+#endif // SUBZERO_SRC_ASSEMBLER_H_