allocate x64 block structures in the code buffer for better data locality

src/jit/backend/x64/x64_backend.cc

@@ -32,7 +32,8 @@ const int x64_num_registers = sizeof(x64_registers) / sizeof(Register);
 }
 }
 
-X64Backend::X64Backend(Memory &memory) : Backend(memory), emitter_(memory) {}
+X64Backend::X64Backend(Memory &memory)
+    : Backend(memory), emitter_(memory, 1024 * 1024 * 8) {}
 
 X64Backend::~X64Backend() {}
 
@@ -45,13 +46,32 @@ int X64Backend::num_registers() const {
 void X64Backend::Reset() { emitter_.Reset(); }
 
 RuntimeBlock *X64Backend::AssembleBlock(ir::IRBuilder &builder) {
-  X64Fn fn;
-
-  if (!emitter_.Emit(builder, &fn)) {
+  // allocate block structure at start of code buffer, making for nice data
+  // locality
+  X64Block *block = emitter_.getCurr<X64Block *>();
+  try {
+    emitter_.setSize(emitter_.getSize() + sizeof(X64Block));
+  } catch (const Xbyak::Error &) {
     return nullptr;
   }
 
-  return new X64Block(builder.guest_cycles(), fn);
+  // try to generate the x64 code. if the code buffer overflows let the backend
+  // know so it can reset the cache and try again
+  X64Fn fn;
+  try {
+    fn = emitter_.Emit(builder);
+  } catch (const Xbyak::Error &e) {
+    if (e == Xbyak::ERR_CODE_IS_TOO_BIG) {
+      return nullptr;
+    }
+    LOG_FATAL("X64 codegen failure, %s", e.what());
+  }
+
+  // initialize block structure
+  new (block) X64Block(builder.guest_cycles(), fn);
+
+  return block;
 }
 
-void X64Backend::FreeBlock(RuntimeBlock *block) { delete block; }
+void X64Backend::FreeBlock(RuntimeBlock *block) { /*delete block;*/
+}

src/jit/backend/x64/x64_emitter.h

@@ -27,16 +27,16 @@ enum {
 
 typedef uint32_t (*X64Fn)(void *guest_ctx, hw::Memory *memory);
 
-class X64Emitter {
+class X64Emitter : public Xbyak::CodeGenerator {
  public:
-  X64Emitter(hw::Memory &memory);
+  X64Emitter(hw::Memory &memory, size_t max_size);
   ~X64Emitter();
 
   Xbyak::Label &epilog_label() { return *epilog_label_; }
 
   void Reset();
 
-  bool Emit(ir::IRBuilder &builder, X64Fn *fn);
+  X64Fn Emit(ir::IRBuilder &builder);
 
   // helpers for the emitter callbacks
   const Xbyak::Operand &GetOperand(const ir::Value *v, int size = -1);
@@ -58,12 +58,7 @@ class X64Emitter {
   void EmitBody(ir::IRBuilder &builder);
   void EmitEpilog(ir::IRBuilder &builder, int stack_size);
 
-  int AlignLocals(ir::IRBuilder &builder);
-  int PushModifiedRegisters(ir::IRBuilder &builder);
-  void PopModifiedRegisters();
-
   hw::Memory &memory_;
-  Xbyak::CodeGenerator c_;
   Arena arena_;
   Xbyak::Label *epilog_label_;
   int modified_marker_;