DBC: Another allocation fast path

runtime/vm/simulator_dbc.cc

 // Copyright (c) 2016, 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.
 
 #include <setjmp.h>  // NOLINT
 #include <stdlib.h>
 
 #include "vm/globals.h"
 #if defined(TARGET_ARCH_DBC)
 
@@ skipping 2279 matching lines @@
       Exit(thread, FP, SP + 3, pc);
       NativeArguments args(thread, 1, SP + 1, SP + 2);
       INVOKE_RUNTIME(DRT_InitStaticField, args);
     }
     DISPATCH();
   }
 
   // TODO(vegorov) allocation bytecodes can benefit from the new-space
   // allocation fast-path that does not transition into the runtime system.
   {
+    BYTECODE(AllocateUninitializedContext, A_D);
+    const uint16_t num_context_variables = rD;
+    const intptr_t instance_size = Context::InstanceSize(num_context_variables);
+    const uword start =
+        thread->heap()->new_space()->TryAllocate(instance_size);
+    if (LIKELY(start != 0)) {
+      uword tags = 0;
+      tags = RawObject::ClassIdTag::update(kContextCid, tags);
+      tags = RawObject::SizeTag::update(instance_size, tags);
+      *reinterpret_cast<uword*>(start + Array::tags_offset()) = tags;
+      *reinterpret_cast<uword*>(start + Context::num_variables_offset()) =
+          num_context_variables;
+      FP[rA] = reinterpret_cast<RawObject*>(start + kHeapObjectTag);
+      pc += 2;
+    }
+    DISPATCH();
+  }
+
+  {
     BYTECODE(AllocateContext, A_D);
     const uint16_t num_context_variables = rD;
     {
       *++SP = 0;
       SP[1] = Smi::New(num_context_variables);
       Exit(thread, FP, SP + 2, pc);
       NativeArguments args(thread, 1, SP + 1, SP);
       INVOKE_RUNTIME(DRT_AllocateContext, args);
     }
     DISPATCH();
@@ skipping 35 matching lines @@
     SP[2] = LOAD_CONSTANT(rD);  // Class object.
     SP[3] = null_value;  // Type arguments.
     Exit(thread, FP, SP + 4, pc);
     NativeArguments args(thread, 2, SP + 2, SP + 1);
     INVOKE_RUNTIME(DRT_AllocateObject, args);
     SP++;  // Result is in SP[1].
     DISPATCH();
   }
 
   {
+    BYTECODE(AllocateTOpt, A_D);
+    const uword tags = Smi::Value(RAW_CAST(Smi, LOAD_CONSTANT(rD)));
+    const intptr_t instance_size = RawObject::SizeTag::decode(tags);
+    const uword start = thread->heap()->new_space()->TryAllocate(instance_size);
+    if (LIKELY(start != 0)) {
+      RawObject* type_args = SP[0];
+      const intptr_t type_args_offset = Bytecode::DecodeD(*pc);
+      *reinterpret_cast<uword*>(start + Instance::tags_offset()) = tags;
+      *reinterpret_cast<RawObject**>(start + type_args_offset) = type_args;
+      for (intptr_t current_offset = sizeof(RawInstance);
+           current_offset < instance_size;
+           current_offset += kWordSize) {
+        *reinterpret_cast<RawObject**>(start + current_offset) = null_value;
+      }
+      FP[rA] = reinterpret_cast<RawObject*>(start + kHeapObjectTag);
+      SP -= 1;  // Consume the type arguments on the stack.
+      pc += 4;
+    }
+    DISPATCH();
+  }
+
+  {
     BYTECODE(AllocateT, 0);
     SP[1] = SP[-0];  // Class object.
     SP[2] = SP[-1];  // Type arguments
     Exit(thread, FP, SP + 3, pc);
     NativeArguments args(thread, 2, SP + 1, SP - 1);
     INVOKE_RUNTIME(DRT_AllocateObject, args);
     SP -= 1;  // Result is in SP - 1.
     DISPATCH();
   }
 
@@ skipping 921 matching lines @@
   pc_ = pc;
   special_[kExceptionSpecialIndex] = raw_exception;
   special_[kStacktraceSpecialIndex] = raw_stacktrace;
   buf->Longjmp();
   UNREACHABLE();
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_DBC