[interpreter] Add ConditionalControlFlowBuilder

This refactors logic for handling IfStatement and Conditional nodes (including
block-coverage related slot and counter creation) into a new control-flow
builder.

Bug: v8:6000
Change-Id: Ib5b1724bdf8571fb55d310be79cc60dcf5473b81
Reviewed-on: https://chromium-review.googlesource.com/579509
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46818}

src/interpreter/bytecode-generator.cc

@@ -1201,48 +1201,36 @@ void BytecodeGenerator::VisitEmptyStatement(EmptyStatement* stmt) {
 }
 
 void BytecodeGenerator::VisitIfStatement(IfStatement* stmt) {
+  ConditionalControlFlowBuilder conditional_builder(
+      builder(), block_coverage_builder_, stmt);
   builder()->SetStatementPosition(stmt);
 
-  int then_slot =
-      AllocateBlockCoverageSlotIfEnabled(stmt, SourceRangeKind::kThen);
-  int else_slot =
-      AllocateBlockCoverageSlotIfEnabled(stmt, SourceRangeKind::kElse);
-
   if (stmt->condition()->ToBooleanIsTrue()) {
     // Generate then block unconditionally as always true.
-    BuildIncrementBlockCoverageCounterIfEnabled(then_slot);
+    conditional_builder.Then();
     Visit(stmt->then_statement());
   } else if (stmt->condition()->ToBooleanIsFalse()) {
     // Generate else block unconditionally if it exists.
     if (stmt->HasElseStatement()) {
-      BuildIncrementBlockCoverageCounterIfEnabled(else_slot);
+      conditional_builder.Else();
       Visit(stmt->else_statement());
     }
   } else {
     // TODO(oth): If then statement is BreakStatement or
     // ContinueStatement we can reduce number of generated
     // jump/jump_ifs here. See BasicLoops test.
-    BytecodeLabel end_label;
-    BytecodeLabels then_labels(zone()), else_labels(zone());
-    VisitForTest(stmt->condition(), &then_labels, &else_labels,
-                 TestFallthrough::kThen);
+    VisitForTest(stmt->condition(), conditional_builder.then_labels(),
+                 conditional_builder.else_labels(), TestFallthrough::kThen);
 
-    then_labels.Bind(builder());
-    BuildIncrementBlockCoverageCounterIfEnabled(then_slot);
+    conditional_builder.Then();
     Visit(stmt->then_statement());
 
     if (stmt->HasElseStatement()) {
-      builder()->Jump(&end_label);
-      else_labels.Bind(builder());
-      BuildIncrementBlockCoverageCounterIfEnabled(else_slot);
+      conditional_builder.JumpToEnd();
+      conditional_builder.Else();
       Visit(stmt->else_statement());
-    } else {
-      else_labels.Bind(builder());
     }
-    builder()->Bind(&end_label);
   }
-  BuildIncrementBlockCoverageCounterIfEnabled(stmt,
-                                              SourceRangeKind::kContinuation);
 }
 
 void BytecodeGenerator::VisitSloppyBlockFunctionStatement(
@@ -1819,35 +1807,27 @@ void BytecodeGenerator::VisitDoExpression(DoExpression* expr) {
 }
 
 void BytecodeGenerator::VisitConditional(Conditional* expr) {
-  int then_slot =
-      AllocateBlockCoverageSlotIfEnabled(expr, SourceRangeKind::kThen);
-  int else_slot =
-      AllocateBlockCoverageSlotIfEnabled(expr, SourceRangeKind::kElse);
+  ConditionalControlFlowBuilder conditional_builder(
+      builder(), block_coverage_builder_, expr);
 
   if (expr->condition()->ToBooleanIsTrue()) {
     // Generate then block unconditionally as always true.
+    conditional_builder.Then();
     VisitForAccumulatorValue(expr->then_expression());
-    BuildIncrementBlockCoverageCounterIfEnabled(then_slot);
   } else if (expr->condition()->ToBooleanIsFalse()) {
     // Generate else block unconditionally if it exists.
+    conditional_builder.Else();
     VisitForAccumulatorValue(expr->else_expression());
-    BuildIncrementBlockCoverageCounterIfEnabled(else_slot);
   } else {
-    BytecodeLabel end_label;
-    BytecodeLabels then_labels(zone()), else_labels(zone());
+    VisitForTest(expr->condition(), conditional_builder.then_labels(),
+                 conditional_builder.else_labels(), TestFallthrough::kThen);
 
-    VisitForTest(expr->condition(), &then_labels, &else_labels,
-                 TestFallthrough::kThen);
-
-    then_labels.Bind(builder());
-    BuildIncrementBlockCoverageCounterIfEnabled(then_slot);
+    conditional_builder.Then();
     VisitForAccumulatorValue(expr->then_expression());
-    builder()->Jump(&end_label);
+    conditional_builder.JumpToEnd();
 
-    else_labels.Bind(builder());
-    BuildIncrementBlockCoverageCounterIfEnabled(else_slot);
+    conditional_builder.Else();
     VisitForAccumulatorValue(expr->else_expression());
-    builder()->Bind(&end_label);
   }
 }
 

src/interpreter/control-flow-builders.cc

@@ -160,6 +160,41 @@ void TryFinallyBuilder::EndFinally() {
   // Nothing to be done here.
 }
 
+ConditionalControlFlowBuilder::~ConditionalControlFlowBuilder() {
+  if (!else_labels_.is_bound()) else_labels_.Bind(builder());
+  end_labels_.Bind(builder());
+
+  DCHECK(end_labels_.empty() || end_labels_.is_bound());
+  DCHECK(then_labels_.empty() || then_labels_.is_bound());
+  DCHECK(else_labels_.empty() || else_labels_.is_bound());
+
+  // IfStatement requires a continuation counter, Conditional does not (as it
+  // can only contain expressions).
+  if (block_coverage_builder_ != nullptr && node_->IsIfStatement()) {
+    block_coverage_builder_->IncrementBlockCounter(
+        node_, SourceRangeKind::kContinuation);
+  }
+}
+
+void ConditionalControlFlowBuilder::JumpToEnd() {
+  DCHECK(end_labels_.empty());  // May only be called once.
+  builder()->Jump(end_labels_.New());
+}
+
+void ConditionalControlFlowBuilder::Then() {
+  then_labels()->Bind(builder());
+  if (block_coverage_builder_ != nullptr) {
+    block_coverage_builder_->IncrementBlockCounter(block_coverage_then_slot_);
+  }
+}
+
+void ConditionalControlFlowBuilder::Else() {
+  else_labels()->Bind(builder());
+  if (block_coverage_builder_ != nullptr) {
+    block_coverage_builder_->IncrementBlockCounter(block_coverage_else_slot_);
+  }
+}
+
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8

src/interpreter/control-flow-builders.h

@@ -231,6 +231,49 @@ class V8_EXPORT_PRIVATE TryFinallyBuilder final : public ControlFlowBuilder {
   BytecodeLabels finalization_sites_;
 };
 
+class V8_EXPORT_PRIVATE ConditionalControlFlowBuilder final
+    : public ControlFlowBuilder {
+ public:
+  ConditionalControlFlowBuilder(BytecodeArrayBuilder* builder,
+                                BlockCoverageBuilder* block_coverage_builder,
+                                AstNode* node)
+      : ControlFlowBuilder(builder),
+        end_labels_(builder->zone()),
+        then_labels_(builder->zone()),
+        else_labels_(builder->zone()),
+        node_(node),
+        block_coverage_builder_(block_coverage_builder) {
+    DCHECK(node->IsIfStatement() || node->IsConditional());
+    if (block_coverage_builder != nullptr) {
+      block_coverage_then_slot_ =
+          block_coverage_builder->AllocateBlockCoverageSlot(
+              node, SourceRangeKind::kThen);
+      block_coverage_else_slot_ =
+          block_coverage_builder->AllocateBlockCoverageSlot(
+              node, SourceRangeKind::kElse);
+    }
+  }
+  ~ConditionalControlFlowBuilder();
+
+  BytecodeLabels* then_labels() { return &then_labels_; }
+  BytecodeLabels* else_labels() { return &else_labels_; }
+
+  void Then();
+  void Else();
+
+  void JumpToEnd();
+
+ private:
+  BytecodeLabels end_labels_;
+  BytecodeLabels then_labels_;
+  BytecodeLabels else_labels_;
+
+  AstNode* node_;
+  int block_coverage_then_slot_;
+  int block_coverage_else_slot_;
+  BlockCoverageBuilder* block_coverage_builder_;
+};
+
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8