[AST] Update the comments of the various Expr::Ignore* + Related cleanups

The description of what the various Expr::Ignore* do has drifted from the
actual implementation.

Inspection reveals that IgnoreParenImpCasts() is not equivalent to doing
IgnoreParens() + IgnoreImpCasts() until reaching a fixed point, but
IgnoreParenCasts() is equivalent to doing IgnoreParens() + IgnoreCasts()
until reaching a fixed point. There is also a fair amount of duplication
in the various Expr::Ignore* functions which increase the chance of further
future inconsistencies. In preparation for the next patch which will factor
out the implementation of the various Expr::Ignore*, do the following cleanups:

Remove Stmt::IgnoreImplicit, in favor of Expr::IgnoreImplicit. IgnoreImplicit
is the only function among all of the Expr::Ignore* which is available in Stmt.
There are only a few users of Stmt::IgnoreImplicit. They can just use instead
Expr::IgnoreImplicit like they have to do for the other Ignore*.

Move Expr::IgnoreImpCasts() from Expr.h to Expr.cpp. This made no difference
in the run-time with my usual benchmark (-fsyntax-only on all of Boost).

While we are at it, make IgnoreParenNoopCasts take a const reference to the
ASTContext for const correctness.

Update the comments to match what the Expr::Ignore* are actually doing.
I am not sure that listing exactly what each Expr::Ignore* do is optimal,
but it certainly looks better than the current state which is in my opinion
between misleading and just plain wrong.

The whole patch is NFC (if you count removing Stmt::IgnoreImplicit as NFC).

Differential Revision: https://reviews.llvm.org/D57266

Reviewed By: aaron.ballman

llvm-svn: 353006

Author: riccibruno

clang/include/clang/AST/Expr.h

@@ -746,67 +746,110 @@ class Expr : public Stmt {
   /// member expression.
   static QualType findBoundMemberType(const Expr *expr);
 
-  /// IgnoreImpCasts - Skip past any implicit casts which might
-  /// surround this expression.  Only skips ImplicitCastExprs.
+  /// Skip past any implicit casts which might surround this expression until
+  /// reaching a fixed point. Skips:
+  /// * ImplicitCastExpr
+  /// * FullExpr
   Expr *IgnoreImpCasts() LLVM_READONLY;
-
-  /// IgnoreImplicit - Skip past any implicit AST nodes which might
-  /// surround this expression.
-  Expr *IgnoreImplicit() LLVM_READONLY {
-    return cast<Expr>(Stmt::IgnoreImplicit());
-  }
-
-  const Expr *IgnoreImplicit() const LLVM_READONLY {
-    return const_cast<Expr*>(this)->IgnoreImplicit();
+  const Expr *IgnoreImpCasts() const {
+    return const_cast<Expr *>(this)->IgnoreImpCasts();
   }
 
-  /// IgnoreParens - Ignore parentheses.  If this Expr is a ParenExpr, return
-  ///  its subexpression.  If that subexpression is also a ParenExpr,
-  ///  then this method recursively returns its subexpression, and so forth.
-  ///  Otherwise, the method returns the current Expr.
-  Expr *IgnoreParens() LLVM_READONLY;
-
-  /// IgnoreParenCasts - Ignore parentheses and casts.  Strip off any ParenExpr
-  /// or CastExprs, returning their operand.
-  Expr *IgnoreParenCasts() LLVM_READONLY;
-
-  /// Ignore casts.  Strip off any CastExprs, returning their operand.
+  /// Skip past any casts which might surround this expression until reaching
+  /// a fixed point. Skips:
+  /// * CastExpr
+  /// * FullExpr
+  /// * MaterializeTemporaryExpr
+  /// * SubstNonTypeTemplateParmExpr
   Expr *IgnoreCasts() LLVM_READONLY;
-
-  /// IgnoreParenImpCasts - Ignore parentheses and implicit casts.  Strip off
-  /// any ParenExpr or ImplicitCastExprs, returning their operand.
+  const Expr *IgnoreCasts() const {
+    return const_cast<Expr *>(this)->IgnoreCasts();
+  }
+
+  /// Skip past any implicit AST nodes which might surround this expression
+  /// until reaching a fixed point. Skips:
+  /// * What IgnoreImpCasts() skips
+  /// * MaterializeTemporaryExpr
+  /// * CXXBindTemporaryExpr
+  Expr *IgnoreImplicit() LLVM_READONLY;
+  const Expr *IgnoreImplicit() const {
+    return const_cast<Expr *>(this)->IgnoreImplicit();
+  }
+
+  /// Skip past any parentheses which might surround this expression until
+  /// reaching a fixed point. Skips:
+  /// * ParenExpr
+  /// * UnaryOperator if `UO_Extension`
+  /// * GenericSelectionExpr if `!isResultDependent()`
+  /// * ChooseExpr if `!isConditionDependent()`
+  /// * ConstantExpr
+  Expr *IgnoreParens() LLVM_READONLY;
+  const Expr *IgnoreParens() const {
+    return const_cast<Expr *>(this)->IgnoreParens();
+  }
+
+  /// Skip past any parentheses and implicit casts which might surround this
+  /// expression until reaching a fixed point.
+  /// FIXME: IgnoreParenImpCasts really ought to be equivalent to
+  /// IgnoreParens() + IgnoreImpCasts() until reaching a fixed point. However
+  /// this is currently not the case. Instead IgnoreParenImpCasts() skips:
+  /// * What IgnoreParens() skips
+  /// * ImplicitCastExpr
+  /// * MaterializeTemporaryExpr
+  /// * SubstNonTypeTemplateParmExpr
   Expr *IgnoreParenImpCasts() LLVM_READONLY;
-
-  /// IgnoreConversionOperator - Ignore conversion operator. If this Expr is a
-  /// call to a conversion operator, return the argument.
-  Expr *IgnoreConversionOperator() LLVM_READONLY;
-
-  const Expr *IgnoreConversionOperator() const LLVM_READONLY {
-    return const_cast<Expr*>(this)->IgnoreConversionOperator();
+  const Expr *IgnoreParenImpCasts() const {
+    return const_cast<Expr *>(this)->IgnoreParenImpCasts();
   }
 
-  const Expr *IgnoreParenImpCasts() const LLVM_READONLY {
-    return const_cast<Expr*>(this)->IgnoreParenImpCasts();
+  /// Skip past any parentheses and casts which might surround this expression
+  /// until reaching a fixed point. Skips:
+  /// * What IgnoreParens() skips
+  /// * What IgnoreCasts() skips
+  Expr *IgnoreParenCasts() LLVM_READONLY;
+  const Expr *IgnoreParenCasts() const {
+    return const_cast<Expr *>(this)->IgnoreParenCasts();
   }
 
-  /// Ignore parentheses and lvalue casts.  Strip off any ParenExpr and
-  /// CastExprs that represent lvalue casts, returning their operand.
+  /// Skip conversion operators. If this Expr is a call to a conversion
+  /// operator, return the argument.
+  Expr *IgnoreConversionOperator() LLVM_READONLY;
+  const Expr *IgnoreConversionOperator() const {
+    return const_cast<Expr *>(this)->IgnoreConversionOperator();
+  }
+
+  /// Skip past any parentheses and lvalue casts which might surround this
+  /// expression until reaching a fixed point. Skips:
+  /// * What IgnoreParens() skips
+  /// * What IgnoreCasts() skips, except that only lvalue-to-rvalue
+  ///   casts are skipped
+  /// FIXME: This is intended purely as a temporary workaround for code
+  /// that hasn't yet been rewritten to do the right thing about those
+  /// casts, and may disappear along with the last internal use.
   Expr *IgnoreParenLValueCasts() LLVM_READONLY;
-
-  const Expr *IgnoreParenLValueCasts() const LLVM_READONLY {
-    return const_cast<Expr*>(this)->IgnoreParenLValueCasts();
-  }
-
-  /// IgnoreParenNoopCasts - Ignore parentheses and casts that do not change the
-  /// value (including ptr->int casts of the same size).  Strip off any
-  /// ParenExpr or CastExprs, returning their operand.
-  Expr *IgnoreParenNoopCasts(ASTContext &Ctx) LLVM_READONLY;
-
-  /// Ignore parentheses and derived-to-base casts.
+  const Expr *IgnoreParenLValueCasts() const {
+    return const_cast<Expr *>(this)->IgnoreParenLValueCasts();
+  }
+
+  /// Skip past any parenthese and casts which do not change the value
+  /// (including ptr->int casts of the same size) until reaching a fixed point.
+  /// Skips:
+  /// * What IgnoreParens() skips
+  /// * CastExpr which do not change the value
+  /// * SubstNonTypeTemplateParmExpr
+  Expr *IgnoreParenNoopCasts(const ASTContext &Ctx) LLVM_READONLY;
+  const Expr *IgnoreParenNoopCasts(const ASTContext &Ctx) const {
+    return const_cast<Expr *>(this)->IgnoreParenNoopCasts(Ctx);
+  }
+
+  /// Skip past any parentheses and derived-to-base casts until reaching a
+  /// fixed point. Skips:
+  /// * What IgnoreParens() skips
+  /// * CastExpr which represent a derived-to-base cast (CK_DerivedToBase,
+  ///   CK_UncheckedDerivedToBase and CK_NoOp)
   Expr *ignoreParenBaseCasts() LLVM_READONLY;
-
-  const Expr *ignoreParenBaseCasts() const LLVM_READONLY {
-    return const_cast<Expr*>(this)->ignoreParenBaseCasts();
+  const Expr *ignoreParenBaseCasts() const {
+    return const_cast<Expr *>(this)->ignoreParenBaseCasts();
   }
 
   /// Determine whether this expression is a default function argument.
@@ -825,24 +868,6 @@ class Expr : public Stmt {
   /// Whether this expression is an implicit reference to 'this' in C++.
   bool isImplicitCXXThis() const;
 
-  const Expr *IgnoreImpCasts() const LLVM_READONLY {
-    return const_cast<Expr*>(this)->IgnoreImpCasts();
-  }
-  const Expr *IgnoreParens() const LLVM_READONLY {
-    return const_cast<Expr*>(this)->IgnoreParens();
-  }
-  const Expr *IgnoreParenCasts() const LLVM_READONLY {
-    return const_cast<Expr*>(this)->IgnoreParenCasts();
-  }
-  /// Strip off casts, but keep parentheses.
-  const Expr *IgnoreCasts() const LLVM_READONLY {
-    return const_cast<Expr*>(this)->IgnoreCasts();
-  }
-
-  const Expr *IgnoreParenNoopCasts(ASTContext &Ctx) const LLVM_READONLY {
-    return const_cast<Expr*>(this)->IgnoreParenNoopCasts(Ctx);
-  }
-
   static bool hasAnyTypeDependentArguments(ArrayRef<Expr *> Exprs);
 
   /// For an expression of class type or pointer to class type,
@@ -3167,18 +3192,6 @@ class ImplicitCastExpr final
   friend class CastExpr;
 };
 
-inline Expr *Expr::IgnoreImpCasts() {
-  Expr *e = this;
-  while (true)
-    if (ImplicitCastExpr *ice = dyn_cast<ImplicitCastExpr>(e))
-      e = ice->getSubExpr();
-    else if (FullExpr *fe = dyn_cast<FullExpr>(e))
-      e = fe->getSubExpr();
-    else
-      break;
-  return e;
-}
-
 /// ExplicitCastExpr - An explicit cast written in the source
 /// code.
 ///

clang/include/clang/AST/Stmt.h

@@ -1072,13 +1072,6 @@ class alignas(void *) Stmt {
   ///   works on systems with GraphViz (Mac OS X) or dot+gv installed.
   void viewAST() const;
 
-  /// Skip past any implicit AST nodes which might surround this
-  /// statement, such as ExprWithCleanups or ImplicitCastExpr nodes.
-  Stmt *IgnoreImplicit();
-  const Stmt *IgnoreImplicit() const {
-    return const_cast<Stmt *>(this)->IgnoreImplicit();
-  }
-
   /// Skip no-op (attributed, compound) container stmts and skip captured
   /// stmt at the top, if \a IgnoreCaptured is true.
   Stmt *IgnoreContainers(bool IgnoreCaptured = false);

clang/lib/ARCMigrate/TransRetainReleaseDealloc.cpp

@@ -269,8 +269,8 @@ class RetainReleaseDeallocRemover :
 
     if (prevChildS != childE) {
       prevStmt = *prevChildS;
-      if (prevStmt)
-        prevStmt = prevStmt->IgnoreImplicit();
+      if (auto *E = dyn_cast_or_null<Expr>(prevStmt))
+        prevStmt = E->IgnoreImplicit();
     }
 
     if (currChildS == childE)
@@ -280,8 +280,8 @@ class RetainReleaseDeallocRemover :
       return std::make_pair(prevStmt, nextStmt);
 
     nextStmt = *currChildS;
-    if (nextStmt)
-      nextStmt = nextStmt->IgnoreImplicit();
+    if (auto *E = dyn_cast_or_null<Expr>(nextStmt))
+      nextStmt = E->IgnoreImplicit();
 
     return std::make_pair(prevStmt, nextStmt);
   }

clang/lib/ARCMigrate/TransformActions.cpp

@@ -313,7 +313,9 @@ void TransformActionsImpl::removeStmt(Stmt *S) {
   assert(IsInTransaction && "Actions only allowed during a transaction");
   ActionData data;
   data.Kind = Act_RemoveStmt;
-  data.S = S->IgnoreImplicit(); // important for uniquing
+  if (auto *E = dyn_cast<Expr>(S))
+    S = E->IgnoreImplicit(); // important for uniquing
+  data.S = S;
   CachedActions.push_back(data);
 }
 

clang/lib/ARCMigrate/Transforms.cpp

@@ -286,10 +286,11 @@ class RemovablesCollector : public RecursiveASTVisitor<RemovablesCollector> {
   void mark(Stmt *S) {
     if (!S) return;
 
-    while (LabelStmt *Label = dyn_cast<LabelStmt>(S))
+    while (auto *Label = dyn_cast<LabelStmt>(S))
       S = Label->getSubStmt();
-    S = S->IgnoreImplicit();
-    if (Expr *E = dyn_cast<Expr>(S))
+    if (auto *E = dyn_cast<Expr>(S))
+      S = E->IgnoreImplicit();
+    if (auto *E = dyn_cast<Expr>(S))
       Removables.insert(E);
   }
 };