group x64 blocks together under the same symbol for profiling

src/jit/backend/x64/x64_backend.cc

@@ -46,13 +46,20 @@ const Register x64_registers[] = {
     {"xmm10", ir::VALUE_FLOAT_MASK}, {"xmm11", ir::VALUE_FLOAT_MASK}};
 
 const int x64_num_registers = sizeof(x64_registers) / sizeof(Register);
+
+// this will break down if running two instances of the x64 backend, but it's
+// extremely useful when profiling to group JITd blocks of code with an actual
+// symbol name
+static const size_t x64_codegen_size = 1024 * 1024 * 8;
+static uint8_t x64_codegen[x64_codegen_size];
+
 }
 }
 }
 }
 
 X64Backend::X64Backend(Memory &memory)
-    : Backend(memory), emitter_(1024 * 1024 * 8) {}
+    : Backend(memory), emitter_(x64_codegen, x64_codegen_size) {}
 
 X64Backend::~X64Backend() {}
 

src/jit/backend/x64/x64_emitter.cc

@@ -116,8 +116,8 @@ static X64Emit x64_emitters[NUM_OPCODES];
   } x64_##op##_init;                                    \
   void op(X64Emitter &e, const Instr *instr)
 
-X64Emitter::X64Emitter(size_t max_size)
-    : CodeGenerator(max_size),
+X64Emitter::X64Emitter(void *buffer, size_t buffer_size)
+    : CodeGenerator(buffer_size, buffer),
       arena_(1024),
       source_map_(nullptr),
       memory_(nullptr),

src/jit/backend/x64/x64_emitter.h

@@ -35,7 +35,7 @@ enum {
 
 class X64Emitter : public Xbyak::CodeGenerator {
  public:
-  X64Emitter(size_t max_size);
+  X64Emitter(void *buffer, size_t buffer_size);
   ~X64Emitter();
 
   Xbyak::Label &epilog_label() { return *epilog_label_; }