Use a local variable to save/restore the context on entry/exit, instead of

runtime/vm/code_generator_x64.cc

 // 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.
 
 #include "vm/globals.h"  // Needed here to get TARGET_ARCH_X64.
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/code_generator.h"
 
 #include "lib/error.h"
@@ skipping 594 matching lines @@
                       0,
                       kStackOverflowRuntimeEntry);
   __ Bind(&no_stack_overflow);
 }
 
 
 void CodeGenerator::GenerateReturnEpilog(ReturnNode* node) {
   // Unchain the context(s) up to context level 0.
   intptr_t current_context_level = context_level();
   ASSERT(current_context_level >= 0);
-  if (!parsed_function_.function().IsClosureFunction()) {
-    if (current_context_level > 0) {
-      // CTX on entry was saved on the stack, but not linked as context parent.
-      __ popq(CTX);
-    }
+  if (parsed_function_.saved_context_var() != NULL) {
+    // CTX on entry was saved, but not linked as context parent.
+    GenerateLoadVariable(CTX, *parsed_function_.saved_context_var());
   } else {
     while (current_context_level-- > 0) {
       __ movq(CTX, FieldAddress(CTX, Context::parent_offset()));
     }
   }
 #ifdef DEBUG
   // Check that the entry stack size matches the exit stack size.
   __ movq(R10, RBP);
   __ subq(R10, RSP);
   ASSERT(locals_space_size() >= 0);
@@ skipping 177 matching lines @@
     // The loop local scope declares variables that are captured.
     // Allocate and chain a new context.
     __ movq(R10, Immediate(num_context_variables));
     const ExternalLabel label("alloc_context",
                               StubCode::AllocateContextEntryPoint());
     GenerateCall(node_sequence->token_index(), &label, PcDescriptors::kOther);
 
     // If this node_sequence is the body of the function being compiled, and if
     // this function is not a closure, do not link the current context as the
     // parent of the newly allocated context, as it is not accessible. Instead,
-    // save it on the stack and restore it on exit.
+    // save it in a pre-allocated variable and restore it on exit.
     if ((node_sequence == parsed_function_.node_sequence()) &&
-         !parsed_function_.function().IsClosureFunction()) {
-      __ pushq(CTX);
+        (parsed_function_.saved_context_var() != NULL)) {
+      GenerateStoreVariable(
+          *parsed_function_.saved_context_var(), CTX, kNoRegister);
       const Immediate raw_null =
           Immediate(reinterpret_cast<intptr_t>(Object::null()));
       __ movq(CTX, raw_null);
     }
 
     // Chain the new context in RAX to its parent in CTX.
     __ StoreIntoObject(RAX,
                        FieldAddress(RAX, Context::parent_offset()),
                        CTX);
     // Set new context as current context.
@@ skipping 30 matching lines @@
   // code checking the type of the actual arguments.
   if (FLAG_enable_type_checks &&
       (node_sequence == parsed_function_.node_sequence())) {
     GenerateArgumentTypeChecks();
   }
   for (int i = 0; i < node_sequence->length(); i++) {
     AstNode* child_node = node_sequence->NodeAt(i);
     state()->set_root_node(child_node);
     child_node->Visit(this);
   }
-  if (num_context_variables > 0) {
-    // Unchain the previously allocated context.
-    if ((node_sequence == parsed_function_.node_sequence()) &&
-         !parsed_function_.function().IsClosureFunction()) {
-      __ popq(CTX);
-    } else {
-      __ movq(CTX, FieldAddress(CTX, Context::parent_offset()));
-    }
+
+  // Unchain the previously allocated context.
+  if ((node_sequence == parsed_function_.node_sequence()) &&
+      (parsed_function_.saved_context_var() != NULL)) {
+    ASSERT(num_context_variables > 0);
+    GenerateLoadVariable(CTX, *parsed_function_.saved_context_var());
+  } else if (num_context_variables > 0) {
+    __ movq(CTX, FieldAddress(CTX, Context::parent_offset()));
   }
+
   // If this node sequence is labeled, a break out of the sequence will have
   // taken care of unchaining the context.
   if (node_sequence->label() != NULL) {
     __ Bind(node_sequence->label()->break_label());
-    if ((num_context_variables > 0) &&
-        (node_sequence == parsed_function_.node_sequence()) &&
-         !parsed_function_.function().IsClosureFunction()) {
-      __ popq(CTX);
+
+    // The context saved on entry must be restored.
+    if ((node_sequence == parsed_function_.node_sequence()) &&
+        (parsed_function_.saved_context_var() != NULL)) {
+      GenerateLoadVariable(CTX, *parsed_function_.saved_context_var());
     }
   }
   set_context_level(previous_context_level);
 }
 
 
 void CodeGenerator::VisitArgumentListNode(ArgumentListNode* arguments) {
   for (int i = 0; i < arguments->length(); i++) {
     AstNode* argument = arguments->NodeAt(i);
     argument->Visit(this);
@@ skipping 1641 matching lines @@
   // and ':stacktrace_var' can never be captured variables.
   // Restore CTX from local variable ':saved_context'.
   GenerateLoadVariable(CTX, node->context_var());
 
   // Restore RSP from RBP as we are coming from a throw and the code for
   // popping arguments has not been run.
   ASSERT(locals_space_size() >= 0);
   __ movq(RSP, RBP);
   __ subq(RSP, Immediate(locals_space_size()));
 
-  if ((context_level() > 0) &&
-      !parsed_function_.function().IsClosureFunction()) {
-    // CTX was saved on entry.
-    __ subq(RSP, Immediate(kWordSize));
-  }
-
   // The JumpToExceptionHandler trampoline code sets up
   // - the exception object in RAX (kExceptionObjectReg)
   // - the stacktrace object in register RDX (kStackTraceObjectReg)
   // We now setup the exception object and the trace object
   // so that the handler code has access to these objects.
   GenerateStoreVariable(node->exception_var(),
                         kExceptionObjectReg,
                         kNoRegister);
   GenerateStoreVariable(node->stacktrace_var(),
                         kStackTraceObjectReg,
@@ skipping 130 matching lines @@
   const Error& error = Error::Handle(
       Parser::FormatError(script, token_index, "Error", format, args));
   va_end(args);
   Isolate::Current()->long_jump_base()->Jump(1, error);
   UNREACHABLE();
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64