Generate some intrinsics using our IR.

runtime/vm/intermediate_language_x64.cc

Index: runtime/vm/intermediate_language_x64.cc
===================================================================
--- runtime/vm/intermediate_language_x64.cc	(revision 39909)
+++ runtime/vm/intermediate_language_x64.cc	(working copy)
@@ -83,6 +83,13 @@
 void ReturnInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
   Register result = locs()->in(0).reg();
   ASSERT(result == RAX);
+
+  if (compiler->intrinsic_mode()) {
+    // Intrinsics don't have a frame.
+    __ ret();
+    return;
+  }
+
 #if defined(DEBUG)
   __ Comment("Stack Check");
   Label done;
@@ -1523,7 +1530,6 @@
                  String::Handle(cls_.PrettyName()).ToCString());
     }
     __ Bind(entry_label());
-
     const Code& stub =
         Code::Handle(isolate, stub_code->GetAllocationStubForClass(cls_));
     const ExternalLabel label(stub.EntryPoint());
@@ -1546,22 +1552,30 @@
                        Instruction* instruction,
                        const Class& cls,
                        Register result) {
-    BoxAllocationSlowPath* slow_path =
-        new BoxAllocationSlowPath(instruction, cls, result);
-    compiler->AddSlowPathCode(slow_path);
+    if (compiler->intrinsic_mode()) {
+      __ TryAllocate(cls,
+                     compiler->intrinsic_slow_path_label(),
+                     Assembler::kFarJump,
+                     result,
+                     PP);
+    } else {
+      BoxAllocationSlowPath* slow_path =
+          new BoxAllocationSlowPath(instruction, cls, result);
+      compiler->AddSlowPathCode(slow_path);
 
-    __ TryAllocate(cls,
-                   slow_path->entry_label(),
-                   Assembler::kFarJump,
-                   result,
-                   PP);
-    __ Bind(slow_path->exit_label());
+      __ TryAllocate(cls,
+                     slow_path->entry_label(),
+                     Assembler::kFarJump,
+                     result,
+                     PP);
+      __ Bind(slow_path->exit_label());
+    }
   }
 
  private:
   Instruction* instruction_;
   const Class& cls_;
-  Register result_;
+  const Register result_;
 };