Simplify AST by extending LetNode and replace CommaNode.

runtime/vm/flow_graph_builder.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/flow_graph_builder.h"
 
 #include "lib/invocation_mirror.h"
 #include "vm/ast_printer.h"
 #include "vm/code_descriptors.h"
 #include "vm/dart_entry.h"
@@ skipping 1859 matching lines @@
     Append(for_value);
     Value* temp_val = for_value.value();
     node->TempAt(i)->set_index(GetCurrentTempLocalIndex());
     Do(new PushTempInstr(temp_val));
     AllocateTempIndex();
   }
 }
 
 
 void EffectGraphVisitor::VisitLetNode(LetNode* node) {
-  BuildLetTempExpressions(node);
   intptr_t num_temps = node->num_temps();
+  if (num_temps > 0) {
+    BuildLetTempExpressions(node);
+    // TODO(fschneider): Generate better code for effect context by visiting the
+    // body for effect. Currently, the value of the body expression is
+    // materialized and then dropped. This also requires changing DropTempsInstr
+    // to have zero or one inputs.
 
-  // TODO(fschneider): Generate better code for effect context by visiting the
-  // body for effect. Currently, the value of the body expression is
-  // materialized and then dropped. This also requires changing DropTempsInstr
-  // to have zero or one inputs.
-  ValueGraphVisitor for_value(owner(), temp_index());
-  node->body()->Visit(&for_value);
-  Append(for_value);
-  Value* result_value = for_value.value();
-  DeallocateTempIndex(num_temps);
-  Do(new DropTempsInstr(num_temps, result_value));
+    // Visit body.
+    for (intptr_t i = 0; i < node->nodes().length() - 1; ++i) {
+      EffectGraphVisitor for_effect(owner(), temp_index());
+      node->nodes()[i]->Visit(&for_effect);
+      Append(for_effect);
+    }
+    // Visit the last body expression for value.
+    ValueGraphVisitor for_value(owner(), temp_index());
+    node->nodes()[node->nodes().length() - 1]->Visit(&for_value);

[Kevin Millikin (Google), 2013/06/06 12:18:33]

node->nodes()->Last()

[Florian Schneider, 2013/06/06 12:33:39]

Done.

+    Append(for_value);
+    Value* result_value = for_value.value();
+    DeallocateTempIndex(num_temps);
+    Do(new DropTempsInstr(num_temps, result_value));
+  } else {
+    ASSERT(num_temps == 0);
+    for (intptr_t i = 0; i < node->nodes().length(); ++i) {
+      EffectGraphVisitor for_effect(owner(), temp_index());
+      node->nodes()[i]->Visit(&for_effect);
+      Append(for_effect);
+    }
+  }
 }
 
 
 void ValueGraphVisitor::VisitLetNode(LetNode* node) {
   BuildLetTempExpressions(node);
 
+  // Visit body.
+  for (intptr_t i = 0; i < node->nodes().length() - 1; ++i) {
+    EffectGraphVisitor for_effect(owner(), temp_index());
+    node->nodes()[i]->Visit(&for_effect);
+    Append(for_effect);
+  }
+  // Visit the last body expression for value.
   ValueGraphVisitor for_value(owner(), temp_index());
-  node->body()->Visit(&for_value);
+  node->nodes()[node->nodes().length() - 1]->Visit(&for_value);

[Kevin Millikin (Google), 2013/06/06 12:18:33]

Also here.

[Florian Schneider, 2013/06/06 12:33:39]

Done.

   Append(for_value);
   Value* result_value = for_value.value();
+
   intptr_t num_temps = node->num_temps();
   if (num_temps > 0) {
     DeallocateTempIndex(num_temps);
     ReturnDefinition(new DropTempsInstr(num_temps, result_value));
   } else {
     ReturnValue(result_value);
   }
 }
 
 
@@ skipping 1295 matching lines @@
   AddInstruction(
       new CatchEntryInstr(node->exception_var(), node->stacktrace_var()));
   BuildLoadContext(node->context_var());
 
   EffectGraphVisitor for_catch(owner(), temp_index());
   node->VisitChildren(&for_catch);
   Append(for_catch);
 }
 
 
-void EffectGraphVisitor::VisitCommaNode(CommaNode* node) {
-  EffectGraphVisitor for_effect_first(owner(), temp_index());
-  node->first()->Visit(&for_effect_first);
-  Append(for_effect_first);
-
-  EffectGraphVisitor for_effect_second(owner(), temp_index());
-  node->second()->Visit(&for_effect_second);
-  Append(for_effect_second);
-}
-
-
-void ValueGraphVisitor::VisitCommaNode(CommaNode* node) {
-  EffectGraphVisitor for_effect(owner(), temp_index());
-  node->first()->Visit(&for_effect);
-  Append(for_effect);
-
-  ValueGraphVisitor for_value(owner(), temp_index());
-  node->second()->Visit(&for_value);
-  Append(for_value);
-  ReturnValue(for_value.value());
-}
-
-
 void EffectGraphVisitor::VisitTryCatchNode(TryCatchNode* node) {
   InlineBailout("EffectGraphVisitor::VisitTryCatchNode (exception)");
   intptr_t old_try_index = owner()->try_index();
   intptr_t try_index = owner()->AllocateTryIndex();
   owner()->set_try_index(try_index);
 
   // Preserve CTX into local variable '%saved_context'.
   BuildStoreContext(node->context_var());
 
   EffectGraphVisitor for_try_block(owner(), temp_index());
@@ skipping 238 matching lines @@
   intptr_t len = OS::SNPrint(NULL, 0, kFormat, function_name, reason) + 1;
   char* chars = Isolate::Current()->current_zone()->Alloc<char>(len);
   OS::SNPrint(chars, len, kFormat, function_name, reason);
   const Error& error = Error::Handle(
       LanguageError::New(String::Handle(String::New(chars))));
   Isolate::Current()->long_jump_base()->Jump(1, error);
 }
 
 
 }  // namespace dart