[Clang] Refactor implementation of "Lifetime extension in range-based for loops" (#87930)

This PR remove `InMaterializeTemporaryObjectContext` , because it's
redundant, materialize non-cv void prvalue temporaries in discarded
expressions can only appear under lifetime-extension context.

Signed-off-by: yronglin <[email protected]>

Author: yronglin

clang/include/clang/Sema/Sema.h

@@ -5099,34 +5099,6 @@ class Sema final : public SemaBase {
     /// example, in a for-range initializer).
     bool InLifetimeExtendingContext = false;
 
-    /// Whether we are currently in a context in which all temporaries must be
-    /// materialized.
-    ///
-    /// [class.temporary]/p2:
-    /// The materialization of a temporary object is generally delayed as long
-    /// as possible in order to avoid creating unnecessary temporary objects.
-    ///
-    /// Temporary objects are materialized:
-    ///   (2.1) when binding a reference to a prvalue ([dcl.init.ref],
-    ///   [expr.type.conv], [expr.dynamic.cast], [expr.static.cast],
-    ///   [expr.const.cast], [expr.cast]),
-    ///
-    ///   (2.2) when performing member access on a class prvalue ([expr.ref],
-    ///   [expr.mptr.oper]),
-    ///
-    ///   (2.3) when performing an array-to-pointer conversion or subscripting
-    ///   on an array prvalue ([conv.array], [expr.sub]),
-    ///
-    ///   (2.4) when initializing an object of type
-    ///   std​::​initializer_list<T> from a braced-init-list
-    ///   ([dcl.init.list]),
-    ///
-    ///   (2.5) for certain unevaluated operands ([expr.typeid], [expr.sizeof])
-    ///
-    ///   (2.6) when a prvalue that has type other than cv void appears as a
-    ///   discarded-value expression ([expr.context]).
-    bool InMaterializeTemporaryObjectContext = false;
-
     // When evaluating immediate functions in the initializer of a default
     // argument or default member initializer, this is the declaration whose
     // default initializer is being evaluated and the location of the call
@@ -6398,19 +6370,6 @@ class Sema final : public SemaBase {
     }
   }
 
-  /// keepInMaterializeTemporaryObjectContext - Pull down
-  /// InMaterializeTemporaryObjectContext flag from previous context.
-  void keepInMaterializeTemporaryObjectContext() {
-    if (ExprEvalContexts.size() > 2 &&
-        ExprEvalContexts[ExprEvalContexts.size() - 2]
-            .InMaterializeTemporaryObjectContext) {
-      auto &LastRecord = ExprEvalContexts.back();
-      auto &PrevRecord = ExprEvalContexts[ExprEvalContexts.size() - 2];
-      LastRecord.InMaterializeTemporaryObjectContext =
-          PrevRecord.InMaterializeTemporaryObjectContext;
-    }
-  }
-
   DefaultedComparisonKind getDefaultedComparisonKind(const FunctionDecl *FD) {
     return getDefaultedFunctionKind(FD).asComparison();
   }
@@ -6554,12 +6513,6 @@ class Sema final : public SemaBase {
   /// used in initializer of the field.
   llvm::MapVector<FieldDecl *, DeleteLocs> DeleteExprs;
 
-  bool isInMaterializeTemporaryObjectContext() const {
-    assert(!ExprEvalContexts.empty() &&
-           "Must be in an expression evaluation context");
-    return ExprEvalContexts.back().InMaterializeTemporaryObjectContext;
-  }
-
   ParsedType getInheritingConstructorName(CXXScopeSpec &SS,
                                           SourceLocation NameLoc,
                                           const IdentifierInfo &Name);

clang/lib/Parse/ParseDecl.cpp

@@ -2380,10 +2380,6 @@ Parser::DeclGroupPtrTy Parser::ParseDeclGroup(ParsingDeclSpec &DS,
       if (getLangOpts().CPlusPlus23) {
         auto &LastRecord = Actions.ExprEvalContexts.back();
         LastRecord.InLifetimeExtendingContext = true;
-
-        // Materialize non-`cv void` prvalue temporaries in discarded
-        // expressions. These materialized temporaries may be lifetime-extented.
-        LastRecord.InMaterializeTemporaryObjectContext = true;
       }
 
       if (getLangOpts().OpenMP)

clang/lib/Sema/SemaExpr.cpp

@@ -6314,7 +6314,6 @@ ExprResult Sema::BuildCXXDefaultArgExpr(SourceLocation CallLoc,
       // Pass down lifetime extending flag, and collect temporaries in
       // CreateMaterializeTemporaryExpr when we rewrite the call argument.
       keepInLifetimeExtendingContext();
-      keepInMaterializeTemporaryObjectContext();
       EnsureImmediateInvocationInDefaultArgs Immediate(*this);
       ExprResult Res;
       runWithSufficientStackSpace(CallLoc, [&] {
@@ -18679,9 +18678,9 @@ void Sema::PopExpressionEvaluationContext() {
   // Append the collected materialized temporaries into previous context before
   // exit if the previous also is a lifetime extending context.
   auto &PrevRecord = ExprEvalContexts[ExprEvalContexts.size() - 2];
-  if (getLangOpts().CPlusPlus23 && isInLifetimeExtendingContext() &&
-      PrevRecord.InLifetimeExtendingContext && !ExprEvalContexts.empty()) {
-    auto &PrevRecord = ExprEvalContexts[ExprEvalContexts.size() - 2];
+  if (getLangOpts().CPlusPlus23 && Rec.InLifetimeExtendingContext &&
+      PrevRecord.InLifetimeExtendingContext &&
+      !Rec.ForRangeLifetimeExtendTemps.empty()) {
     PrevRecord.ForRangeLifetimeExtendTemps.append(
         Rec.ForRangeLifetimeExtendTemps);
   }

clang/lib/Sema/SemaExprCXX.cpp

@@ -8429,7 +8429,7 @@ ExprResult Sema::IgnoredValueConversions(Expr *E) {
     // unnecessary temporary objects. If we skip this step, IR generation is
     // able to synthesize the storage for itself in the aggregate case, and
     // adding the extra node to the AST is just clutter.
-    if (isInMaterializeTemporaryObjectContext() && getLangOpts().CPlusPlus17 &&
+    if (isInLifetimeExtendingContext() && getLangOpts().CPlusPlus17 &&
         E->isPRValue() && !E->getType()->isVoidType()) {
       ExprResult Res = TemporaryMaterializationConversion(E);
       if (Res.isInvalid())

clang/lib/Sema/SemaTemplateInstantiateDecl.cpp

@@ -5483,7 +5483,6 @@ void Sema::InstantiateVariableInitializer(
         *this, Sema::ExpressionEvaluationContext::PotentiallyEvaluated, Var);
 
     keepInLifetimeExtendingContext();
-    keepInMaterializeTemporaryObjectContext();
     // Instantiate the initializer.
     ExprResult Init;
 

clang/lib/Sema/TreeTransform.h

@@ -4177,7 +4177,6 @@ ExprResult TreeTransform<Derived>::TransformInitializer(Expr *Init,
       getSema(), EnterExpressionEvaluationContext::InitList,
       Construct->isListInitialization());
 
-  getSema().keepInLifetimeExtendingContext();
   getSema().keepInLifetimeExtendingContext();
   SmallVector<Expr*, 8> NewArgs;
   bool ArgChanged = false;
@@ -8752,10 +8751,6 @@ TreeTransform<Derived>::TransformCXXForRangeStmt(CXXForRangeStmt *S) {
   if (getSema().getLangOpts().CPlusPlus23) {
     auto &LastRecord = getSema().ExprEvalContexts.back();
     LastRecord.InLifetimeExtendingContext = true;
-
-    // Materialize non-`cv void` prvalue temporaries in discarded
-    // expressions. These materialized temporaries may be lifetime-extented.
-    LastRecord.InMaterializeTemporaryObjectContext = true;
   }
   StmtResult Init =
       S->getInit() ? getDerived().TransformStmt(S->getInit()) : StmtResult();