Add some C++-specific comments in the parsing methods of if/switch/while/for.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@56060 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Parse/ParseStmt.cpp

@@ -434,6 +434,12 @@ Parser::StmtResult Parser::ParseIfStatement() {
 
   // C99 6.8.4p3 - In C99, the if statement is a block.  This is not
   // the case for C90.
+  //
+  // C++ 6.4p3:
+  // A name introduced by a declaration in a condition is in scope from its
+  // point of declaration until the end of the substatements controlled by the
+  // condition.
+  //
   if (C99orCXX)
     EnterScope(Scope::DeclScope | Scope::ControlScope);
 
@@ -457,6 +463,21 @@ Parser::StmtResult Parser::ParseIfStatement() {
   // C99 6.8.4p3 - In C99, the body of the if statement is a scope, even if
   // there is no compound stmt.  C90 does not have this clause.  We only do this
   // if the body isn't a compound statement to avoid push/pop in common cases.
+  //
+  // C++ 6.4p1:
+  // The substatement in a selection-statement (each substatement, in the else
+  // form of the if statement) implicitly defines a local scope.
+  //
+  // For C++ we create a scope for the condition and a new scope for
+  // substatements because:
+  // -When the 'then' scope exits, we want the condition declaration to still be
+  //    active for the 'else' scope too.
+  // -Sema will detect name clashes by considering declarations of a
+  //    'ControlScope' as part of its direct subscope.
+  // -If we wanted the condition and substatement to be in the same scope, we
+  //    would have to notify ParseStatement not to create a new scope. It's
+  //    simpler to let it create a new scope.
+  //
   bool NeedsInnerScope = C99orCXX && Tok.isNot(tok::l_brace);
   if (NeedsInnerScope) EnterScope(Scope::DeclScope);
 
@@ -479,6 +500,11 @@ Parser::StmtResult Parser::ParseIfStatement() {
     // there is no compound stmt.  C90 does not have this clause.  We only do
     // this if the body isn't a compound statement to avoid push/pop in common
     // cases.
+    //
+    // C++ 6.4p1:
+    // The substatement in a selection-statement (each substatement, in the else
+    // form of the if statement) implicitly defines a local scope.
+    //
     NeedsInnerScope = C99orCXX && Tok.isNot(tok::l_brace);
     if (NeedsInnerScope) EnterScope(Scope::DeclScope);
     
@@ -532,6 +558,12 @@ Parser::StmtResult Parser::ParseSwitchStatement() {
 
   // C99 6.8.4p3 - In C99, the switch statement is a block.  This is
   // not the case for C90.  Start the switch scope.
+  //
+  // C++ 6.4p3:
+  // A name introduced by a declaration in a condition is in scope from its
+  // point of declaration until the end of the substatements controlled by the
+  // condition.
+  //
   if (C99orCXX)
     EnterScope(Scope::BreakScope | Scope::DeclScope | Scope::ControlScope);
   else
@@ -557,6 +589,14 @@ Parser::StmtResult Parser::ParseSwitchStatement() {
   // C99 6.8.4p3 - In C99, the body of the switch statement is a scope, even if
   // there is no compound stmt.  C90 does not have this clause.  We only do this
   // if the body isn't a compound statement to avoid push/pop in common cases.
+  //
+  // C++ 6.4p1:
+  // The substatement in a selection-statement (each substatement, in the else
+  // form of the if statement) implicitly defines a local scope.
+  //
+  // See comments in ParseIfStatement for why we create a scope for the
+  // condition and a new scope for substatement in C++.
+  //
   bool NeedsInnerScope = C99orCXX && Tok.isNot(tok::l_brace);
   if (NeedsInnerScope) EnterScope(Scope::DeclScope);
   
@@ -595,6 +635,12 @@ Parser::StmtResult Parser::ParseWhileStatement() {
 
   // C99 6.8.5p5 - In C99, the while statement is a block.  This is not
   // the case for C90.  Start the loop scope.
+  //
+  // C++ 6.4p3:
+  // A name introduced by a declaration in a condition is in scope from its
+  // point of declaration until the end of the substatements controlled by the
+  // condition.
+  //
   if (C99orCXX)
     EnterScope(Scope::BreakScope | Scope::ContinueScope |
                Scope::DeclScope  | Scope::ControlScope);
@@ -614,6 +660,14 @@ Parser::StmtResult Parser::ParseWhileStatement() {
   // C99 6.8.5p5 - In C99, the body of the if statement is a scope, even if
   // there is no compound stmt.  C90 does not have this clause.  We only do this
   // if the body isn't a compound statement to avoid push/pop in common cases.
+  //
+  // C++ 6.5p2:
+  // The substatement in an iteration-statement implicitly defines a local scope
+  // which is entered and exited each time through the loop.
+  //
+  // See comments in ParseIfStatement for why we create a scope for the
+  // condition and a new scope for substatement in C++.
+  //
   bool NeedsInnerScope = C99orCXX && Tok.isNot(tok::l_brace);
   if (NeedsInnerScope) EnterScope(Scope::DeclScope);
   
@@ -710,6 +764,15 @@ Parser::StmtResult Parser::ParseForStatement() {
 
   // C99 6.8.5p5 - In C99, the for statement is a block.  This is not
   // the case for C90.  Start the loop scope.
+  //
+  // C++ 6.4p3:
+  // A name introduced by a declaration in a condition is in scope from its
+  // point of declaration until the end of the substatements controlled by the
+  // condition.
+  // C++ 6.5.3p1:
+  // Names declared in the for-init-statement are in the same declarative-region
+  // as those declared in the condition.
+  //
   if (C99orCXX)
     EnterScope(Scope::BreakScope | Scope::ContinueScope |
                Scope::DeclScope  | Scope::ControlScope);
@@ -808,6 +871,14 @@ Parser::StmtResult Parser::ParseForStatement() {
   // C99 6.8.5p5 - In C99, the body of the if statement is a scope, even if
   // there is no compound stmt.  C90 does not have this clause.  We only do this
   // if the body isn't a compound statement to avoid push/pop in common cases.
+  //
+  // C++ 6.5p2:
+  // The substatement in an iteration-statement implicitly defines a local scope
+  // which is entered and exited each time through the loop.
+  //
+  // See comments in ParseIfStatement for why we create a scope for
+  // for-init-statement/condition and a new scope for substatement in C++.
+  //
   bool NeedsInnerScope = C99orCXX && Tok.isNot(tok::l_brace);
   if (NeedsInnerScope) EnterScope(Scope::DeclScope);