Implement loop variable assignment analysis.

src/compiler/ast-graph-builder.cc

Index: src/compiler/ast-graph-builder.cc
diff --git a/src/compiler/ast-graph-builder.cc b/src/compiler/ast-graph-builder.cc
index b97260111ea45ffb0ea1683b4347183bb90be733..a4deb5324918ea9d2fcbfa350f1ea10601438a3d 100644
--- a/src/compiler/ast-graph-builder.cc
+++ b/src/compiler/ast-graph-builder.cc
@@ -5,10 +5,11 @@
 #include "src/compiler/ast-graph-builder.h"
 
 #include "src/compiler.h"
+#include "src/compiler/ast-loop-assignment-analyzer.h"
 #include "src/compiler/control-builders.h"
 #include "src/compiler/machine-operator.h"
-#include "src/compiler/node-properties.h"
 #include "src/compiler/node-properties-inl.h"
+#include "src/compiler/node-properties.h"
 #include "src/full-codegen.h"
 #include "src/parser.h"
 #include "src/scopes.h"
@@ -24,7 +25,8 @@ AstGraphBuilder::AstGraphBuilder(Zone* local_zone, CompilationInfo* info,
       jsgraph_(jsgraph),
       globals_(0, info->zone()),
       breakable_(NULL),
-      execution_context_(NULL) {
+      execution_context_(NULL),
+      loop_assignment_analysis_(NULL) {
   InitializeAstVisitor(info->zone());
 }
 
@@ -59,6 +61,12 @@ bool AstGraphBuilder::CreateGraph() {
   int parameter_count = info()->num_parameters();
   graph()->SetStart(graph()->NewNode(common()->Start(parameter_count)));
 
+  if (FLAG_loop_assignment_analysis) {
+    // TODO(turbofan): use a temporary zone for the loop assignment analysis.
+    AstLoopAssignmentAnalyzer analyzer(zone(), info());
+    loop_assignment_analysis_ = analyzer.Analyze();
+  }
+
   // Initialize the top-level environment.
   Environment env(this, scope, graph()->start());
   set_environment(&env);
@@ -579,9 +587,16 @@ void AstGraphBuilder::VisitSwitchStatement(SwitchStatement* stmt) {
 }
 
 
+BitVector* AstGraphBuilder::GetVariablesAssignedInLoop(
+    IterationStatement* stmt) {
+  if (loop_assignment_analysis_ == NULL) return NULL;

[danno, 2014/10/28 14:23:29]

This seems a bit weird. Why is it OK to call this at all when
loop_assignment_analysis_ == NULL?

[titzer, 2014/10/28 17:16:03]

It's so that there's one place where we make the decision about whether to
perform the analysis (i.e. in CreateGraph()), and later we just check if there
is an analysis result available.

+  return loop_assignment_analysis_->GetVariablesAssignedInLoop(stmt);
+}
+
+
 void AstGraphBuilder::VisitDoWhileStatement(DoWhileStatement* stmt) {
   LoopBuilder while_loop(this);
-  while_loop.BeginLoop();
+  while_loop.BeginLoop(GetVariablesAssignedInLoop(stmt));
   VisitIterationBody(stmt, &while_loop, 0);
   while_loop.EndBody();
   VisitForTest(stmt->cond());
@@ -593,7 +608,7 @@ void AstGraphBuilder::VisitDoWhileStatement(DoWhileStatement* stmt) {
 
 void AstGraphBuilder::VisitWhileStatement(WhileStatement* stmt) {
   LoopBuilder while_loop(this);
-  while_loop.BeginLoop();
+  while_loop.BeginLoop(GetVariablesAssignedInLoop(stmt));
   VisitForTest(stmt->cond());
   Node* condition = environment()->Pop();
   while_loop.BreakUnless(condition);
@@ -606,7 +621,7 @@ void AstGraphBuilder::VisitWhileStatement(WhileStatement* stmt) {
 void AstGraphBuilder::VisitForStatement(ForStatement* stmt) {
   LoopBuilder for_loop(this);
   VisitIfNotNull(stmt->init());
-  for_loop.BeginLoop();
+  for_loop.BeginLoop(GetVariablesAssignedInLoop(stmt));
   if (stmt->cond() != NULL) {
     VisitForTest(stmt->cond());
     Node* condition = environment()->Pop();
@@ -682,7 +697,7 @@ void AstGraphBuilder::VisitForInStatement(ForInStatement* stmt) {
         environment()->Push(jsgraph()->ZeroConstant());
         // PrepareForBailoutForId(stmt->BodyId(), NO_REGISTERS);
         LoopBuilder for_loop(this);
-        for_loop.BeginLoop();
+        for_loop.BeginLoop(GetVariablesAssignedInLoop(stmt));
         // Check loop termination condition.
         Node* index = environment()->Peek(0);
         Node* exit_cond =