Remove Scope::scope_uses_this_ flag

Use of the "this" variable is now tracked using scopes, like any other variable.

R=arv@chromium.org
LOG=N
BUG=

Review URL: https://codereview.chromium.org/1129823002

Cr-Commit-Position: refs/heads/master@{#28268}

src/compiler.cc

@@ -215,8 +215,7 @@ bool CompilationInfo::is_simple_parameter_list() {
 
 
 bool CompilationInfo::MayUseThis() const {
-  return scope()->uses_this() || scope()->inner_uses_this() ||
-         scope()->calls_sloppy_eval();
+  return scope()->has_this_declaration() && scope()->receiver()->is_used();
 }
 
 

src/compiler/ast-graph-builder.cc

@@ -2661,9 +2661,7 @@ Node* AstGraphBuilder::BuildPatchReceiverToGlobalProxy(Node* receiver) {
   // object). Otherwise there is nothing left to do here.
   if (is_strict(language_mode()) || info()->is_native()) return receiver;
 
-  // There is no need to perform patching if the receiver is never used. Note
-  // that scope predicates are purely syntactical, a call to eval might still
-  // inspect the receiver value.
+  // There is no need to perform patching if the receiver will never be used.
   if (!info()->MayUseThis()) return receiver;
 
   IfBuilder receiver_check(this);

src/preparser.h

@@ -2220,7 +2220,6 @@ ParserBase<Traits>::ParsePrimaryExpression(ExpressionClassifier* classifier,
           break;
         }
       }
-      scope_->RecordThisUsage();
       result = this->ThisExpression(scope_, factory(), beg_pos);
       break;
     }
@@ -3246,7 +3245,6 @@ ParserBase<Traits>::ParseStrongInitializationExpression(
   Consume(Token::THIS);
   int pos = position();
   function_state_->set_this_location(scanner()->location());
-  scope_->RecordThisUsage();
   ExpressionT this_expr = this->ThisExpression(scope_, factory(), pos);
 
   ExpressionT left = this->EmptyExpression();

src/scopes.cc

@@ -165,7 +165,6 @@ void Scope::SetDefaults(ScopeType scope_type, Scope* outer_scope,
   scope_calls_eval_ = false;
   scope_uses_arguments_ = false;
   scope_uses_super_property_ = false;
-  scope_uses_this_ = false;
   asm_module_ = false;
   asm_function_ = outer_scope != NULL && outer_scope->asm_module_;
   // Inherit the language mode from the parent scope.
@@ -173,7 +172,6 @@ void Scope::SetDefaults(ScopeType scope_type, Scope* outer_scope,
   outer_scope_calls_sloppy_eval_ = false;
   inner_scope_calls_eval_ = false;
   inner_scope_uses_arguments_ = false;
-  inner_scope_uses_this_ = false;
   inner_scope_uses_super_property_ = false;
   force_eager_compilation_ = false;
   force_context_allocation_ = (outer_scope != NULL && !is_function_scope())
@@ -371,7 +369,6 @@ Scope* Scope::FinalizeBlockScope() {
   // Propagate usage flags to outer scope.
   if (uses_arguments()) outer_scope_->RecordArgumentsUsage();
   if (uses_super_property()) outer_scope_->RecordSuperPropertyUsage();
-  if (uses_this()) outer_scope_->RecordThisUsage();
   if (scope_calls_eval_) outer_scope_->RecordEvalCall();
 
   return NULL;
@@ -921,13 +918,11 @@ void Scope::Print(int n) {
   if (scope_uses_arguments_) Indent(n1, "// scope uses 'arguments'\n");
   if (scope_uses_super_property_)
     Indent(n1, "// scope uses 'super' property\n");
-  if (scope_uses_this_) Indent(n1, "// scope uses 'this'\n");
   if (inner_scope_uses_arguments_) {
     Indent(n1, "// inner scope uses 'arguments'\n");
   }
   if (inner_scope_uses_super_property_)
     Indent(n1, "// inner scope uses 'super' property\n");
-  if (inner_scope_uses_this_) Indent(n1, "// inner scope uses 'this'\n");
   if (outer_scope_calls_sloppy_eval_) {
     Indent(n1, "// outer scope calls 'eval' in sloppy context\n");
   }
@@ -1283,9 +1278,6 @@ void Scope::PropagateScopeInfo(bool outer_scope_calls_sloppy_eval ) {
           inner->inner_scope_uses_super_property_) {
         inner_scope_uses_super_property_ = true;
       }
-      if (inner->scope_uses_this_ || inner->inner_scope_uses_this_) {
-        inner_scope_uses_this_ = true;
-      }
     }
     if (inner->force_eager_compilation_) {
       force_eager_compilation_ = true;

src/scopes.h

@@ -218,9 +218,6 @@ class Scope: public ZoneObject {
   // Inform the scope that the corresponding code uses "super".
   void RecordSuperPropertyUsage() { scope_uses_super_property_ = true; }
 
-  // Inform the scope that the corresponding code uses "this".
-  void RecordThisUsage() { scope_uses_this_ = true; }
-
   // Set the language mode flag (unless disabled by a global flag).
   void SetLanguageMode(LanguageMode language_mode) {
     language_mode_ = language_mode;
@@ -324,10 +321,6 @@ class Scope: public ZoneObject {
   bool inner_uses_super_property() const {
     return inner_scope_uses_super_property_;
   }
-  // Does this scope access "this".
-  bool uses_this() const { return scope_uses_this_; }
-  // Does any inner scope access "this".
-  bool inner_uses_this() const { return inner_scope_uses_this_; }
 
   const Scope* NearestOuterEvalScope() const {
     if (is_eval_scope()) return this;
@@ -592,8 +585,6 @@ class Scope: public ZoneObject {
   bool scope_uses_arguments_;
   // This scope uses "super" property ('super.foo').
   bool scope_uses_super_property_;
-  // This scope uses "this".
-  bool scope_uses_this_;
   // This scope contains an "use asm" annotation.
   bool asm_module_;
   // This scope's outer context is an asm module.
@@ -609,7 +600,6 @@ class Scope: public ZoneObject {
   bool inner_scope_calls_eval_;
   bool inner_scope_uses_arguments_;
   bool inner_scope_uses_super_property_;
-  bool inner_scope_uses_this_;
   bool force_eager_compilation_;
   bool force_context_allocation_;
 

test/cctest/test-parsing.cc

@@ -962,7 +962,6 @@ TEST(ScopeUsesArgumentsSuperThis) {
     THIS = 1 << 2,
     INNER_ARGUMENTS = 1 << 3,
     INNER_SUPER_PROPERTY = 1 << 4,
-    INNER_THIS = 1 << 5
   };
 
   static const struct {
@@ -977,7 +976,7 @@ TEST(ScopeUsesArgumentsSuperThis) {
     {"return this + arguments[0]", ARGUMENTS | THIS},
     {"return this + arguments[0] + super.x",
      ARGUMENTS | SUPER_PROPERTY | THIS},
-    {"return x => this + x", INNER_THIS},
+    {"return x => this + x", THIS},
     {"return x => super.f() + x", INNER_SUPER_PROPERTY},
     {"this.foo = 42;", THIS},
     {"this.foo();", THIS},
@@ -991,9 +990,7 @@ TEST(ScopeUsesArgumentsSuperThis) {
     {"while (true) { while (true) { while (true) return this } }", THIS},
     {"while (true) { while (true) { while (true) return super.f() } }",
      SUPER_PROPERTY},
-    {"if (1) { return () => { while (true) new this() } }", INNER_THIS},
-    // Note that propagation of the inner_uses_this() value does not
-    // cross boundaries of normal functions onto parent scopes.
+    {"if (1) { return () => { while (true) new this() } }", THIS},
     {"return function (x) { return this + x }", NONE},
     {"return { m(x) { return super.m() + x } }", NONE},
     {"var x = function () { this.foo = 42 };", NONE},
@@ -1004,10 +1001,10 @@ TEST(ScopeUsesArgumentsSuperThis) {
     {"return { m(x) { return () => super.m() } }", NONE},
     // Flags must be correctly set when using block scoping.
     {"\"use strict\"; while (true) { let x; this, arguments; }",
-     INNER_ARGUMENTS | INNER_THIS},
+     INNER_ARGUMENTS | THIS},
     {"\"use strict\"; while (true) { let x; this, super.f(), arguments; }",
-     INNER_ARGUMENTS | INNER_SUPER_PROPERTY | INNER_THIS},
-    {"\"use strict\"; if (foo()) { let x; this.f() }", INNER_THIS},
+     INNER_ARGUMENTS | INNER_SUPER_PROPERTY | THIS},
+    {"\"use strict\"; if (foo()) { let x; this.f() }", THIS},
     {"\"use strict\"; if (foo()) { let x; super.f() }",
      INNER_SUPER_PROPERTY},
     {"\"use strict\"; if (1) {"
@@ -1071,13 +1068,15 @@ TEST(ScopeUsesArgumentsSuperThis) {
                scope->uses_arguments());
       CHECK_EQ((source_data[i].expected & SUPER_PROPERTY) != 0,
                scope->uses_super_property());
-      CHECK_EQ((source_data[i].expected & THIS) != 0, scope->uses_this());
+      if ((source_data[i].expected & THIS) != 0) {
+        // Currently the is_used() flag is conservative; all variables in a
+        // script scope are marked as used.
+        CHECK(scope->LookupThis()->is_used());
+      }
       CHECK_EQ((source_data[i].expected & INNER_ARGUMENTS) != 0,
                scope->inner_uses_arguments());
       CHECK_EQ((source_data[i].expected & INNER_SUPER_PROPERTY) != 0,
                scope->inner_uses_super_property());
-      CHECK_EQ((source_data[i].expected & INNER_THIS) != 0,
-               scope->inner_uses_this());
     }
   }
 }