Lazily generate local var descriptors.

runtime/vm/flow_graph_compiler.cc

 // Copyright (c) 2013, 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_XXX.
 
 #include "vm/flow_graph_compiler.h"
 
 #include "vm/bit_vector.h"
 #include "vm/cha.h"
@@ skipping 13 matching lines @@
 #include "vm/stack_frame.h"
 #include "vm/stub_code.h"
 #include "vm/symbols.h"
 
 namespace dart {
 
 DEFINE_FLAG(bool, always_megamorphic_calls, false,
     "Instance call always as megamorphic.");
 DEFINE_FLAG(bool, trace_inlining_intervals, false,
     "Inlining interval diagnostics");
+DEFINE_FLAG(bool, eager_info_computation, false,
+    "TRANSITIONAL: Eagerly compute local var descriptors.");
 DEFINE_FLAG(bool, enable_simd_inline, true,
     "Enable inlining of SIMD related method calls.");
 DEFINE_FLAG(int, min_optimization_counter_threshold, 5000,
     "The minimum invocation count for a function.");
 DEFINE_FLAG(int, optimization_counter_scale, 2000,
     "The scale of invocation count, by size of the function.");
 DEFINE_FLAG(bool, source_lines, false, "Emit source line as assembly comment.");
 DEFINE_FLAG(bool, use_megamorphic_stub, true, "Out of line megamorphic lookup");
 
 DECLARE_FLAG(bool, code_comments);
@@ skipping 875 matching lines @@
 
 void FlowGraphCompiler::FinalizeVarDescriptors(const Code& code) {
   if (code.is_optimized()) {
     // Optimized code does not need variable descriptors. They are
     // only stored in the unoptimized version.
     code.set_var_descriptors(Object::empty_var_descriptors());
     return;
   }
   LocalVarDescriptors& var_descs = LocalVarDescriptors::Handle();
   if (parsed_function().node_sequence() == NULL) {
+    // TODO(srdjan): Implement lazy local var descriptors if Irregexp functions.
     ASSERT(flow_graph().IsIrregexpFunction());
     var_descs = LocalVarDescriptors::New(1);
     RawLocalVarDescriptors::VarInfo info;
     info.set_kind(RawLocalVarDescriptors::kSavedCurrentContext);
     info.scope_id = 0;
     info.begin_pos = 0;
     info.end_pos = 0;
     info.set_index(parsed_function().current_context_var()->index());
     var_descs.SetVar(0, Symbols::CurrentContextVar(), &info);
   } else {
-    var_descs =
-        parsed_function_.node_sequence()->scope()->GetVarDescriptors(
-            parsed_function_.function());
+    if (FLAG_eager_info_computation) {
+      var_descs =
+          parsed_function_.node_sequence()->scope()->GetVarDescriptors(
+              parsed_function_.function());
+    }
   }
   code.set_var_descriptors(var_descs);
 }
 
 
 void FlowGraphCompiler::FinalizeStaticCallTargetsTable(const Code& code) {
   ASSERT(code.static_calls_target_table() == Array::null());
   code.set_static_calls_target_table(
       Array::Handle(Array::MakeArray(static_calls_target_table_)));
 }
@@ skipping 769 matching lines @@
 
 
 void FlowGraphCompiler::FrameStateClear() {
   ASSERT(!is_optimizing());
   frame_state_.TruncateTo(0);
 }
 #endif
 
 
 }  // namespace dart