Adding visitors to regurgitate expression types or reset them.

src/ast-expression-visitor.cc

+// Copyright 2015 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "src/v8.h"
+
+#include "src/ast-expression-visitor.h"
+
+#include "src/ast.h"
+#include "src/codegen.h"
+#include "src/scopes.h"
+
+namespace v8 {
+namespace internal {
+
+
+#define RECURSE(call)               \
+  do {                              \
+    DCHECK(!HasStackOverflow());    \
+    call;                           \
+    if (HasStackOverflow()) return; \
+  } while (false)
+
+
+AstExpressionVisitor::AstExpressionVisitor(CompilationInfo* info)
+    : compilation_info_(info), depth_(0) {
+  InitializeAstVisitor(info->isolate(), info->zone());
+}
+
+
+void AstExpressionVisitor::Run() {
+  RECURSE(VisitFunctionLiteral(compilation_info_->literal()));
+}
+
+
+bool AstExpressionVisitor::VisitDeeperExpression(Expression* expression) {
+  if (HasStackOverflow()) return true;
+  ++depth_;
+  Visit(expression);
+  --depth_;
+  return false;
+}
+
+
+void AstExpressionVisitor::VisitVariableDeclaration(VariableDeclaration* decl) {
+}
+
+
+void AstExpressionVisitor::VisitFunctionDeclaration(FunctionDeclaration* decl) {
+  RECURSE(Visit(decl->fun()));
+}
+
+
+void AstExpressionVisitor::VisitImportDeclaration(ImportDeclaration* decl) {}
+
+
+void AstExpressionVisitor::VisitExportDeclaration(ExportDeclaration* decl) {}
+
+
+void AstExpressionVisitor::VisitStatements(ZoneList<Statement*>* stmts) {
+  for (int i = 0; i < stmts->length(); ++i) {
+    Statement* stmt = stmts->at(i);
+    RECURSE(Visit(stmt));

[bradn, 2015/08/22 01:19:12]

So Visit has baked in a short-circuit:

#define DEFINE_AST_VISITOR_SUBCLASS_MEMBERS()               \
 public:                                                    \
  void Visit(AstNode* node) final {                         \
    if (!CheckStackOverflow()) node->Accept(this);          \
  }                                                         \

So in terms of the suggestion you made by chat, wrapping this in VisitStmt or
somesuch, won't reduce the depth. Also, the macro has the advantage that in a
loop like this (or anywhere else where more than one visit call happens in
sequence), that you immediately exit the current function, instead of trying
each and backing out after each guard. Putting it in a function prevents the
return from skipping the rest of the function.

I could do for RECURSE what I did in this version for VisitDeeperExpression,
return a bool indicating if a short-circuit return should happen, but I'm not
sure that's more readable than the macro.

WDYT?
I'll try to catch you at some point to talk it over.

I do wonder if in general there might be some more coherent way to handle the
stack checks. It seems a shame to need to semi-reliably put in what amounts to
non-zero cost exception handling.
I would be interested in chatting about what the constraints really are here in
terms of using page faults etc.

In terms of specifically the AST visitor, would it be worthwhile to restructure
it to use a non-c-stack recursive pattern? I.e. Visit doesn't actually call
Accept directly, but instead pushes pending Visits onto a heap stack in the
visitor and an outer iterative loop dispatches the visits in the same order they
currently happen?

+    if (stmt->IsJump()) break;
+  }
+}
+
+
+void AstExpressionVisitor::VisitBlock(Block* stmt) {
+  RECURSE(VisitStatements(stmt->statements()));
+}
+
+
+void AstExpressionVisitor::VisitExpressionStatement(ExpressionStatement* stmt) {
+  RECURSE(Visit(stmt->expression()));
+}
+
+
+void AstExpressionVisitor::VisitEmptyParentheses(EmptyParentheses* expr) {
+  UNREACHABLE();
+}
+
+
+void AstExpressionVisitor::VisitEmptyStatement(EmptyStatement* stmt) {}
+
+
+void AstExpressionVisitor::VisitIfStatement(IfStatement* stmt) {
+  RECURSE(Visit(stmt->condition()));
+  RECURSE(Visit(stmt->then_statement()));
+  RECURSE(Visit(stmt->else_statement()));
+}
+
+
+void AstExpressionVisitor::VisitContinueStatement(ContinueStatement* stmt) {}
+
+
+void AstExpressionVisitor::VisitBreakStatement(BreakStatement* stmt) {}
+
+
+void AstExpressionVisitor::VisitReturnStatement(ReturnStatement* stmt) {
+  RECURSE(Visit(stmt->expression()));
+}
+
+
+void AstExpressionVisitor::VisitWithStatement(WithStatement* stmt) {
+  RECURSE(stmt->expression());
+  RECURSE(stmt->statement());
+}
+
+
+void AstExpressionVisitor::VisitSwitchStatement(SwitchStatement* stmt) {
+  RECURSE(Visit(stmt->tag()));
+
+  ZoneList<CaseClause*>* clauses = stmt->cases();
+
+  for (int i = 0; i < clauses->length(); ++i) {
+    CaseClause* clause = clauses->at(i);
+    Expression* label = clause->label();
+    RECURSE(Visit(label));
+    ZoneList<Statement*>* stmts = clause->statements();
+    RECURSE(VisitStatements(stmts));
+  }
+}
+
+
+void AstExpressionVisitor::VisitCaseClause(CaseClause* clause) {
+  UNREACHABLE();
+}
+
+
+void AstExpressionVisitor::VisitDoWhileStatement(DoWhileStatement* stmt) {
+  RECURSE(Visit(stmt->body()));
+  RECURSE(Visit(stmt->cond()));
+}
+
+
+void AstExpressionVisitor::VisitWhileStatement(WhileStatement* stmt) {
+  RECURSE(Visit(stmt->cond()));
+  RECURSE(Visit(stmt->body()));
+}
+
+
+void AstExpressionVisitor::VisitForStatement(ForStatement* stmt) {
+  RECURSE(Visit(stmt->init()));
+  RECURSE(Visit(stmt->cond()));
+  RECURSE(Visit(stmt->next()));
+  RECURSE(Visit(stmt->body()));
+}
+
+
+void AstExpressionVisitor::VisitForInStatement(ForInStatement* stmt) {
+  RECURSE(Visit(stmt->enumerable()));
+  RECURSE(Visit(stmt->body()));
+}
+
+
+void AstExpressionVisitor::VisitForOfStatement(ForOfStatement* stmt) {
+  RECURSE(Visit(stmt->iterable()));
+  RECURSE(Visit(stmt->body()));
+}
+
+
+void AstExpressionVisitor::VisitTryCatchStatement(TryCatchStatement* stmt) {
+  RECURSE(Visit(stmt->try_block()));
+  RECURSE(Visit(stmt->catch_block()));
+}
+
+
+void AstExpressionVisitor::VisitTryFinallyStatement(TryFinallyStatement* stmt) {
+  RECURSE(Visit(stmt->try_block()));
+  RECURSE(Visit(stmt->finally_block()));
+}
+
+
+void AstExpressionVisitor::VisitDebuggerStatement(DebuggerStatement* stmt) {}
+
+
+void AstExpressionVisitor::VisitFunctionLiteral(FunctionLiteral* expr) {
+  Scope* scope = expr->scope();
+  VisitExpression(expr);
+  ++depth_;
+  VisitDeclarations(scope->declarations());
+  VisitStatements(expr->body());
+  --depth_;
+}
+
+
+void AstExpressionVisitor::VisitNativeFunctionLiteral(
+    NativeFunctionLiteral* expr) {}
+
+
+void AstExpressionVisitor::VisitConditional(Conditional* expr) {
+  RECURSE(Visit(expr->condition()));
+  RECURSE(Visit(expr->then_expression()));
+  RECURSE(Visit(expr->else_expression()));
+}
+
+
+void AstExpressionVisitor::VisitVariableProxy(VariableProxy* expr) {
+  VisitExpression(expr);
+}
+
+
+void AstExpressionVisitor::VisitLiteral(Literal* expr) {
+  VisitExpression(expr);
+}
+
+
+void AstExpressionVisitor::VisitRegExpLiteral(RegExpLiteral* expr) {
+  VisitExpression(expr);
+}
+
+
+void AstExpressionVisitor::VisitObjectLiteral(ObjectLiteral* expr) {
+  VisitExpression(expr);
+  ZoneList<ObjectLiteralProperty*>* props = expr->properties();
+  for (int i = 0; i < props->length(); ++i) {
+    ObjectLiteralProperty* prop = props->at(i);
+    if (VisitDeeperExpression(prop->value())) return;
+  }
+}
+
+
+void AstExpressionVisitor::VisitArrayLiteral(ArrayLiteral* expr) {
+  VisitExpression(expr);
+  ZoneList<Expression*>* values = expr->values();
+  for (int i = 0; i < values->length(); ++i) {
+    Expression* value = values->at(i);
+    if (VisitDeeperExpression(value)) return;
+  }
+}
+
+
+void AstExpressionVisitor::VisitAssignment(Assignment* expr) {
+  VisitExpression(expr);
+  if (VisitDeeperExpression(expr->target())) return;
+  if (VisitDeeperExpression(expr->value())) return;
+}
+
+
+void AstExpressionVisitor::VisitYield(Yield* expr) {
+  RECURSE(Visit(expr->generator_object()));
+  RECURSE(Visit(expr->expression()));
+}
+
+
+void AstExpressionVisitor::VisitThrow(Throw* expr) {
+  RECURSE(Visit(expr->exception()));
+}
+
+
+void AstExpressionVisitor::VisitProperty(Property* expr) {
+  RECURSE(Visit(expr->obj()));
+  RECURSE(Visit(expr->key()));
+}
+
+
+void AstExpressionVisitor::VisitCall(Call* expr) {
+  VisitExpression(expr);
+  if (VisitDeeperExpression(expr->expression())) return;
+  ZoneList<Expression*>* args = expr->arguments();
+  for (int i = 0; i < args->length(); ++i) {
+    Expression* arg = args->at(i);
+    if (VisitDeeperExpression(arg)) return;
+  }
+}
+
+
+void AstExpressionVisitor::VisitCallNew(CallNew* expr) {
+  VisitExpression(expr);
+  if (VisitDeeperExpression(expr->expression())) return;
+  ZoneList<Expression*>* args = expr->arguments();
+  for (int i = 0; i < args->length(); ++i) {
+    Expression* arg = args->at(i);
+    if (VisitDeeperExpression(arg)) return;
+  }
+}
+
+
+void AstExpressionVisitor::VisitCallRuntime(CallRuntime* expr) {
+  VisitExpression(expr);
+  ZoneList<Expression*>* args = expr->arguments();
+  for (int i = 0; i < args->length(); ++i) {
+    Expression* arg = args->at(i);
+    if (VisitDeeperExpression(arg)) return;
+  }
+}
+
+
+void AstExpressionVisitor::VisitUnaryOperation(UnaryOperation* expr) {
+  VisitExpression(expr);
+  if (VisitDeeperExpression(expr->expression())) return;
+}
+
+
+void AstExpressionVisitor::VisitCountOperation(CountOperation* expr) {
+  VisitExpression(expr);
+  if (VisitDeeperExpression(expr->expression())) return;
+}
+
+
+void AstExpressionVisitor::VisitBinaryOperation(BinaryOperation* expr) {
+  VisitExpression(expr);
+  if (VisitDeeperExpression(expr->left())) return;
+  if (VisitDeeperExpression(expr->right())) return;
+}
+
+
+void AstExpressionVisitor::VisitCompareOperation(CompareOperation* expr) {
+  VisitExpression(expr);
+  if (VisitDeeperExpression(expr->left())) return;
+  if (VisitDeeperExpression(expr->right())) return;
+}
+
+
+void AstExpressionVisitor::VisitThisFunction(ThisFunction* expr) {
+  VisitExpression(expr);
+}
+
+
+void AstExpressionVisitor::VisitDeclarations(ZoneList<Declaration*>* decls) {
+  for (int i = 0; i < decls->length(); ++i) {
+    Declaration* decl = decls->at(i);
+    RECURSE(Visit(decl));
+  }
+}
+
+
+void AstExpressionVisitor::VisitClassLiteral(ClassLiteral* expr) {}
+
+
+void AstExpressionVisitor::VisitSpread(Spread* expr) {}
+
+
+void AstExpressionVisitor::VisitSuperPropertyReference(
+    SuperPropertyReference* expr) {}
+
+
+void AstExpressionVisitor::VisitSuperCallReference(SuperCallReference* expr) {}
+}
+
+
+}  // namespace v8::internal