[clang] [Clang] Implement P2718R0 "Lifetime extension in range-based for loops" (PR #76361)

via cfe-commits cfe-commits at lists.llvm.org
Mon Dec 25 07:59:15 PST 2023


llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: None (yronglin)

<details>
<summary>Changes</summary>

 Implement P2718R0 "Lifetime extension in range-based for loops" (https://wg21.link/P2718R0)

Differential Revision: https://reviews.llvm.org/D153701

---

Patch is 43.09 KiB, truncated to 20.00 KiB below, full version: https://github.com/llvm/llvm-project/pull/76361.diff


10 Files Affected:

- (modified) clang/include/clang/Parse/Parser.h (+1-1) 
- (modified) clang/include/clang/Sema/Sema.h (+33-1) 
- (modified) clang/lib/Parse/ParseDecl.cpp (+19) 
- (modified) clang/lib/Parse/ParseStmt.cpp (+1-1) 
- (modified) clang/lib/Sema/SemaExpr.cpp (+18-4) 
- (modified) clang/lib/Sema/SemaExprCXX.cpp (+26-20) 
- (modified) clang/lib/Sema/SemaInit.cpp (+4) 
- (modified) clang/lib/Sema/SemaStmt.cpp (+9-1) 
- (added) clang/test/AST/ast-dump-for-range-lifetime.cpp (+355) 
- (modified) clang/test/CXX/special/class.temporary/p6.cpp (+234) 


``````````diff
diff --git a/clang/include/clang/Parse/Parser.h b/clang/include/clang/Parse/Parser.h
index 2dbe090bd0932f..a467ff6157962c 100644
--- a/clang/include/clang/Parse/Parser.h
+++ b/clang/include/clang/Parse/Parser.h
@@ -2377,7 +2377,7 @@ class Parser : public CodeCompletionHandler {
   struct ForRangeInit {
     SourceLocation ColonLoc;
     ExprResult RangeExpr;
-
+    SmallVector<MaterializeTemporaryExpr *, 8> LifetimeExtendTemps;
     bool ParsedForRangeDecl() { return !ColonLoc.isInvalid(); }
   };
   struct ForRangeInfo : ForRangeInit {
diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
index 5e3b57ea33220b..250194f90d503c 100644
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -1338,6 +1338,12 @@ class Sema final {
     /// context not already known to be immediately invoked.
     llvm::SmallPtrSet<DeclRefExpr *, 4> ReferenceToConsteval;
 
+    /// P2718R0 - Lifetime extension in range-based for loops.
+    /// MaterializeTemporaryExprs in for-range-init expression which need to
+    /// extend lifetime. Add MaterializeTemporaryExpr* if the value of
+    /// IsInLifetimeExtendingContext is true.
+    SmallVector<MaterializeTemporaryExpr *, 8> ForRangeLifetimeExtendTemps;
+
     /// \brief Describes whether we are in an expression constext which we have
     /// to handle differently.
     enum ExpressionKind {
@@ -1357,6 +1363,19 @@ class Sema final {
     // VLAs).
     bool InConditionallyConstantEvaluateContext = false;
 
+    /// Whether we are currently in a context in which temporaries must be
+    /// lifetime-extended (Eg. in a for-range initializer).
+    bool IsInLifetimeExtendingContext = false;
+
+    /// Whether we should materialize temporaries in discarded expressions.
+    ///
+    /// [C++23][class.temporary]/p2.6 when a prvalue that has type other than cv
+    /// void appears as a discarded-value expression ([expr.context]).
+    ///
+    /// We do not materialize temporaries by default in order to avoid creating
+    /// unnecessary temporary objects.
+    bool MaterializePRValueInDiscardedExpression = 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
@@ -5215,7 +5234,8 @@ class Sema final {
                                   Stmt *LoopVar,
                                   SourceLocation ColonLoc, Expr *Collection,
                                   SourceLocation RParenLoc,
-                                  BuildForRangeKind Kind);
+                                  BuildForRangeKind Kind,
+                                  ArrayRef<MaterializeTemporaryExpr *> LifetimeExtendTemps = {});
   StmtResult BuildCXXForRangeStmt(SourceLocation ForLoc,
                                   SourceLocation CoawaitLoc,
                                   Stmt *InitStmt,
@@ -9956,6 +9976,18 @@ class Sema final {
     return currentEvaluationContext().isImmediateFunctionContext();
   }
 
+  bool isInLifetimeExtendingContext() const {
+    assert(!ExprEvalContexts.empty() &&
+           "Must be in an expression evaluation context");
+    return ExprEvalContexts.back().IsInLifetimeExtendingContext;
+  }
+
+  bool ShouldMaterializePRValueInDiscardedExpression() const {
+    assert(!ExprEvalContexts.empty() &&
+           "Must be in an expression evaluation context");
+    return ExprEvalContexts.back().MaterializePRValueInDiscardedExpression;
+  }
+
   bool isCheckingDefaultArgumentOrInitializer() const {
     const ExpressionEvaluationContextRecord &Ctx = currentEvaluationContext();
     return (Ctx.Context ==
diff --git a/clang/lib/Parse/ParseDecl.cpp b/clang/lib/Parse/ParseDecl.cpp
index ed006f9d67de45..8b809aa9c3df26 100644
--- a/clang/lib/Parse/ParseDecl.cpp
+++ b/clang/lib/Parse/ParseDecl.cpp
@@ -2312,12 +2312,31 @@ Parser::DeclGroupPtrTy Parser::ParseDeclGroup(ParsingDeclSpec &DS,
     bool IsForRangeLoop = false;
     if (TryConsumeToken(tok::colon, FRI->ColonLoc)) {
       IsForRangeLoop = true;
+      EnterExpressionEvaluationContext ForRangeInitContext(
+          Actions, Sema::ExpressionEvaluationContext::PotentiallyEvaluated,
+          /*LambdaContextDecl=*/nullptr,
+          Sema::ExpressionEvaluationContextRecord::EK_Other,
+          getLangOpts().CPlusPlus23);
+
+      // P2718R0 - Lifetime extension in range-based for loops.
+      if (getLangOpts().CPlusPlus23) {
+        auto &LastRecord = Actions.ExprEvalContexts.back();
+        LastRecord.IsInLifetimeExtendingContext = true;
+
+        // Materialize non-`cv void` prvalue temporaries in discarded
+        // expressions. These materialized temporaries may be lifetime-extented.
+        LastRecord.MaterializePRValueInDiscardedExpression = true;
+      }
+
       if (getLangOpts().OpenMP)
         Actions.startOpenMPCXXRangeFor();
       if (Tok.is(tok::l_brace))
         FRI->RangeExpr = ParseBraceInitializer();
       else
         FRI->RangeExpr = ParseExpression();
+      if (getLangOpts().CPlusPlus23)
+        FRI->LifetimeExtendTemps = std::move(
+            Actions.ExprEvalContexts.back().ForRangeLifetimeExtendTemps);
     }
 
     Decl *ThisDecl = Actions.ActOnDeclarator(getCurScope(), D);
diff --git a/clang/lib/Parse/ParseStmt.cpp b/clang/lib/Parse/ParseStmt.cpp
index d0ff33bd1379ab..de883eb99765c9 100644
--- a/clang/lib/Parse/ParseStmt.cpp
+++ b/clang/lib/Parse/ParseStmt.cpp
@@ -2288,7 +2288,7 @@ StmtResult Parser::ParseForStatement(SourceLocation *TrailingElseLoc) {
     ForRangeStmt = Actions.ActOnCXXForRangeStmt(
         getCurScope(), ForLoc, CoawaitLoc, FirstPart.get(),
         ForRangeInfo.LoopVar.get(), ForRangeInfo.ColonLoc, CorrectedRange.get(),
-        T.getCloseLocation(), Sema::BFRK_Build);
+        T.getCloseLocation(), Sema::BFRK_Build, ForRangeInfo.LifetimeExtendTemps);
 
   // Similarly, we need to do the semantic analysis for a for-range
   // statement immediately in order to close over temporaries correctly.
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 960f513d1111b2..45f6f50e6f7385 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -6256,7 +6256,7 @@ ExprResult Sema::BuildCXXDefaultArgExpr(SourceLocation CallLoc,
   assert(Param->hasDefaultArg() && "can't build nonexistent default arg");
 
   bool NestedDefaultChecking = isCheckingDefaultArgumentOrInitializer();
-
+  bool IsInLifetimeExtendingContext = isInLifetimeExtendingContext();
   std::optional<ExpressionEvaluationContextRecord::InitializationContext>
       InitializationContext =
           OutermostDeclarationWithDelayedImmediateInvocations();
@@ -6289,9 +6289,19 @@ ExprResult Sema::BuildCXXDefaultArgExpr(SourceLocation CallLoc,
     ImmediateCallVisitor V(getASTContext());
     if (!NestedDefaultChecking)
       V.TraverseDecl(Param);
-    if (V.HasImmediateCalls) {
-      ExprEvalContexts.back().DelayedDefaultInitializationContext = {
-          CallLoc, Param, CurContext};
+
+    // Rewrite the call argument that was created from the corresponding
+    // parameter's default argument.
+    if (V.HasImmediateCalls || IsInLifetimeExtendingContext) {
+      if (V.HasImmediateCalls)
+        ExprEvalContexts.back().DelayedDefaultInitializationContext = {
+            CallLoc, Param, CurContext};
+      // Pass down lifetime extendning flag, and collect temporaries in
+      // CreateMaterializeTemporaryExpr when we rewrite the call argument.
+      auto &LastRecord = ExprEvalContexts.back();
+      auto &PrevRecord = ExprEvalContexts[ExprEvalContexts.size() - 2];
+      LastRecord.IsInLifetimeExtendingContext = IsInLifetimeExtendingContext;
+
       EnsureImmediateInvocationInDefaultArgs Immediate(*this);
       ExprResult Res;
       runWithSufficientStackSpace(CallLoc, [&] {
@@ -6305,6 +6315,10 @@ ExprResult Sema::BuildCXXDefaultArgExpr(SourceLocation CallLoc,
       if (Res.isInvalid())
         return ExprError();
       Init = Res.get();
+
+      // Collect MaterializeTemporaryExprs in the rewrited CXXDefaultArgExpr.
+      PrevRecord.ForRangeLifetimeExtendTemps.append(
+          LastRecord.ForRangeLifetimeExtendTemps);
     }
   }
 
diff --git a/clang/lib/Sema/SemaExprCXX.cpp b/clang/lib/Sema/SemaExprCXX.cpp
index 4ae04358d5df7c..3590582fb5912e 100644
--- a/clang/lib/Sema/SemaExprCXX.cpp
+++ b/clang/lib/Sema/SemaExprCXX.cpp
@@ -8209,21 +8209,6 @@ ExprResult Sema::IgnoredValueConversions(Expr *E) {
     E = result.get();
   }
 
-  // C99 6.3.2.1:
-  //   [Except in specific positions,] an lvalue that does not have
-  //   array type is converted to the value stored in the
-  //   designated object (and is no longer an lvalue).
-  if (E->isPRValue()) {
-    // In C, function designators (i.e. expressions of function type)
-    // are r-values, but we still want to do function-to-pointer decay
-    // on them.  This is both technically correct and convenient for
-    // some clients.
-    if (!getLangOpts().CPlusPlus && E->getType()->isFunctionType())
-      return DefaultFunctionArrayConversion(E);
-
-    return E;
-  }
-
   if (getLangOpts().CPlusPlus) {
     // The C++11 standard defines the notion of a discarded-value expression;
     // normally, we don't need to do anything to handle it, but if it is a
@@ -8244,11 +8229,32 @@ ExprResult Sema::IgnoredValueConversions(Expr *E) {
     //   If the expression is a prvalue after this optional conversion, the
     //   temporary materialization conversion is applied.
     //
-    // 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.
-    // FIXME: We don't emit lifetime markers for the temporaries due to this.
-    // FIXME: Do any other AST consumers care about this?
+    // We do not materialize temporaries by default in order to avoid creating
+    // 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 (ShouldMaterializePRValueInDiscardedExpression() && getLangOpts().CPlusPlus17 &&
+        E->isPRValue() && !E->getType()->isVoidType()) {
+      ExprResult Res = TemporaryMaterializationConversion(E);
+      if (Res.isInvalid())
+        return E;
+      E = Res.get();
+    }
+    return E;
+  }
+
+  // C99 6.3.2.1:
+  //   [Except in specific positions,] an lvalue that does not have
+  //   array type is converted to the value stored in the
+  //   designated object (and is no longer an lvalue).
+  if (E->isPRValue()) {
+    // In C, function designators (i.e. expressions of function type)
+    // are r-values, but we still want to do function-to-pointer decay
+    // on them.  This is both technically correct and convenient for
+    // some clients.
+    if (!getLangOpts().CPlusPlus && E->getType()->isFunctionType())
+      return DefaultFunctionArrayConversion(E);
+
     return E;
   }
 
diff --git a/clang/lib/Sema/SemaInit.cpp b/clang/lib/Sema/SemaInit.cpp
index 61d244f3bb9798..42e4d1eacce78d 100644
--- a/clang/lib/Sema/SemaInit.cpp
+++ b/clang/lib/Sema/SemaInit.cpp
@@ -8469,6 +8469,10 @@ Sema::CreateMaterializeTemporaryExpr(QualType T, Expr *Temporary,
   // are done in both CreateMaterializeTemporaryExpr and MaybeBindToTemporary,
   // but there may be a chance to merge them.
   Cleanup.setExprNeedsCleanups(false);
+  if (isInLifetimeExtendingContext()) {
+    auto &Record = ExprEvalContexts.back();
+    Record.ForRangeLifetimeExtendTemps.push_back(MTE);
+  }
   return MTE;
 }
 
diff --git a/clang/lib/Sema/SemaStmt.cpp b/clang/lib/Sema/SemaStmt.cpp
index f0b03db690843a..759453f319e2b5 100644
--- a/clang/lib/Sema/SemaStmt.cpp
+++ b/clang/lib/Sema/SemaStmt.cpp
@@ -2487,7 +2487,8 @@ StmtResult Sema::ActOnCXXForRangeStmt(Scope *S, SourceLocation ForLoc,
                                       SourceLocation CoawaitLoc, Stmt *InitStmt,
                                       Stmt *First, SourceLocation ColonLoc,
                                       Expr *Range, SourceLocation RParenLoc,
-                                      BuildForRangeKind Kind) {
+                                      BuildForRangeKind Kind,
+                                      ArrayRef<MaterializeTemporaryExpr *> LifetimeExtendTemps) {
   // FIXME: recover in order to allow the body to be parsed.
   if (!First)
     return StmtError();
@@ -2539,6 +2540,12 @@ StmtResult Sema::ActOnCXXForRangeStmt(Scope *S, SourceLocation ForLoc,
     return StmtError();
   }
 
+  if (getLangOpts().CPlusPlus23) {
+    auto Entity = InitializedEntity::InitializeVariable(RangeVar);
+    for (auto *MTE : LifetimeExtendTemps)
+      MTE->setExtendingDecl(RangeVar, Entity.allocateManglingNumber());
+  }
+
   // Claim the type doesn't contain auto: we've already done the checking.
   DeclGroupPtrTy RangeGroup =
       BuildDeclaratorGroup(MutableArrayRef<Decl *>((Decl **)&RangeVar, 1));
@@ -2783,6 +2790,7 @@ StmtResult Sema::BuildCXXForRangeStmt(SourceLocation ForLoc,
       LoopVar->setType(SubstAutoTypeDependent(LoopVar->getType()));
     }
   } else if (!BeginDeclStmt.get()) {
+
     SourceLocation RangeLoc = RangeVar->getLocation();
 
     const QualType RangeVarNonRefType = RangeVarType.getNonReferenceType();
diff --git a/clang/test/AST/ast-dump-for-range-lifetime.cpp b/clang/test/AST/ast-dump-for-range-lifetime.cpp
new file mode 100644
index 00000000000000..dec2e29184526e
--- /dev/null
+++ b/clang/test/AST/ast-dump-for-range-lifetime.cpp
@@ -0,0 +1,355 @@
+// RUN: %clang_cc1 -std=c++23 -triple x86_64-linux-gnu -fcxx-exceptions -ast-dump %s \
+// RUN: | FileCheck -strict-whitespace %s
+
+namespace P2718R0 {
+
+// Test basic
+struct A {
+  int a[3] = {1, 2, 3};
+  A() {}
+  ~A() {}
+  const int *begin() const { return a; }
+  const int *end() const { return a + 3; }
+  A& r() { return *this; }
+  A g() { return A(); }
+};
+
+A g() { return A(); }
+const A &f1(const A &t) { return t; }
+
+void test1() {
+  [[maybe_unused]] int sum = 0;
+  // CHECK: FunctionDecl {{.*}} test1 'void ()'
+  // CHECK:      |   `-CXXForRangeStmt {{.*}}
+  // CHECK-NEXT: |     |-<<<NULL>>>
+  // CHECK-NEXT: |     |-DeclStmt {{.*}}
+  // CHECK-NEXT: |     | `-VarDecl {{.*}} implicit used __range1 'const A &' cinit
+  // CHECK-NEXT: |     |   `-ExprWithCleanups {{.*}} 'const A':'const P2718R0::A' lvalue
+  // CHECK-NEXT: |     |     `-CallExpr {{.*}} 'const A':'const P2718R0::A' lvalue
+  // CHECK-NEXT: |     |       |-ImplicitCastExpr {{.*}} 'const A &(*)(const A &)' <FunctionToPointerDecay>
+  // CHECK-NEXT: |     |       | `-DeclRefExpr {{.*}} 'const A &(const A &)' lvalue Function {{.*}} 'f1' 'const A &(const A &)'
+  // CHECK-NEXT: |     |       `-MaterializeTemporaryExpr {{.*}} 'const A':'const P2718R0::A' lvalue extended by Var {{.*}} '__range1' 'const A &'
+  // CHECK-NEXT: |     |         `-ImplicitCastExpr {{.*}} 'const A':'const P2718R0::A' <NoOp>
+  // CHECK-NEXT: |     |           `-CXXBindTemporaryExpr {{.*}} 'A':'P2718R0::A' (CXXTemporary {{.*}})
+  // CHECK-NEXT: |     |             `-CallExpr {{.*}} 'A':'P2718R0::A'
+  // CHECK-NEXT: |     |               `-ImplicitCastExpr {{.*}} 'A (*)()' <FunctionToPointerDecay>
+  // CHECK-NEXT: |     |                 `-DeclRefExpr {{.*}} 'A ()' lvalue Function {{.*}} 'g' 'A ()'
+  for (auto e : f1(g()))
+    sum += e;
+}
+
+struct B : A {};
+int (&f(const A *))[3];
+const A *g(const A &);
+void bar(int) {}
+
+void test2() {
+  // CHECK: FunctionDecl {{.*}} test2 'void ()'
+  // CHECK:      |   `-CXXForRangeStmt {{.*}}
+  // CHECK-NEXT: |     |-<<<NULL>>>
+  // CHECK-NEXT: |     |-DeclStmt {{.*}}
+  // CHECK-NEXT: |     | `-VarDecl {{.*}} implicit used __range1 'int (&)[3]' cinit
+  // CHECK-NEXT: |     |   `-ExprWithCleanups {{.*}} 'int[3]' lvalue
+  // CHECK-NEXT: |     |     `-CallExpr {{.*}} 'int[3]' lvalue
+  // CHECK-NEXT: |     |       |-ImplicitCastExpr {{.*}} 'int (&(*)(const A *))[3]' <FunctionToPointerDecay>
+  // CHECK-NEXT: |     |       | `-DeclRefExpr {{.*}} 'int (&(const A *))[3]' lvalue Function {{.*}} 'f' 'int (&(const A *))[3]'
+  // CHECK-NEXT: |     |       `-CallExpr {{.*}} 'const A *'
+  // CHECK-NEXT: |     |         |-ImplicitCastExpr {{.*}} 'const A *(*)(const A &)' <FunctionToPointerDecay>
+  // CHECK-NEXT: |     |         | `-DeclRefExpr {{.*}} 'const A *(const A &)' lvalue Function {{.*}} 'g' 'const A *(const A &)'
+  // CHECK-NEXT: |     |         `-ImplicitCastExpr {{.*}} 'const A':'const P2718R0::A' lvalue <DerivedToBase (A)>
+  // CHECK-NEXT: |     |           `-MaterializeTemporaryExpr {{.*}} 'const B':'const P2718R0::B' lvalue extended by Var {{.*}} '__range1' 'int (&)[3]'
+  // CHECK-NEXT: |     |             `-ImplicitCastExpr {{.*}} 'const B':'const P2718R0::B' <NoOp>
+  // CHECK-NEXT: |     |               `-CXXBindTemporaryExpr {{.*}} 'B':'P2718R0::B' (CXXTemporary {{.*}})
+  // CHECK-NEXT: |     |                 `-CXXTemporaryObjectExpr {{.*}} 'B':'P2718R0::B' 'void () noexcept(false)' zeroing
+  for (auto e : f(g(B())))
+    bar(e);
+}
+
+// Test discard statement.
+struct LockGuard {
+    LockGuard() {}
+    ~LockGuard() {}
+};
+
+void test3() {
+  int v[] = {42, 17, 13};
+
+  // CHECK: FunctionDecl {{.*}} test3 'void ()'
+  // CHECK:      -CXXForRangeStmt {{.*}}
+  // CHECK-NEXT:  |-<<<NULL>>>
+  // CHECK-NEXT:  |-DeclStmt {{.*}}
+  // CHECK-NEXT:  | `-VarDecl {{.*}} implicit used __range1 'int (&)[3]' cinit
+  // CHECK-NEXT:  |   `-ExprWithCleanups {{.*}} 'int[3]' lvalue
+  // CHECK-NEXT:  |     `-BinaryOperator {{.*}} 'int[3]' lvalue ','
+  // CHECK-NEXT:  |       |-CXXStaticCastExpr {{.*}} 'void' static_cast<void> <ToVoid>
+  // CHECK-NEXT:  |       | `-MaterializeTemporaryExpr {{.*}} 'LockGuard':'P2718R0::LockGuard' xvalue extended by Var {{.*}} '__range1' 'int (&)[3]'
+  // CHECK-NEXT:  |       |   `-CXXBindTemporaryExpr {{.*}} 'LockGuard':'P2718R0::LockGuard' (CXXTemporary {{.*}})
+  // CHECK-NEXT:  |       |     `-CXXTemporaryObjectExpr {{.*}} 'LockGuard':'P2718R0::LockGuard' 'void ()'
+  // CHECK-NEXT:  |       `-DeclRefExpr {{.*}} 'int[3]' lvalue Var {{.*}} 'v' 'int[3]'
+  for ([[maybe_unused]] int x : static_cast<void>(LockGuard()), v)
+    LockGuard guard;
+
+  // CHECK:      -CXXForRangeStmt {{.*}}
+  // CHECK-NEXT:  |-<<<NULL>>>
+  // CHECK-NEXT:  |-DeclStmt {{.*}}
+  // CHECK-NEXT:  | `-VarDecl {{.*}} implicit used __range1 'int (&)[3]' cinit
+  // CHECK-NEXT:  |   `-ExprWithCleanups {{.*}} 'int[3]' lvalue
+  // CHECK-NEXT:  |     `-BinaryOperator {{.*}} 'int[3]' lvalue ','
+  // CHECK-NEXT:  |       |-CStyleCastExpr {{.*}} 'void' <ToVoid>
+  // CHECK-NEXT:  |       | `-MaterializeTemporaryExpr {{.*}} 'LockGuard':'P2718R0::LockGuard' xvalue extended by Var {{.*}} '__range1' 'int (&)[3]'
+  // CHECK-NEXT:  |       |   `-CXXBindTemporaryExpr {{.*}} 'LockGuard':'P2718R0::LockGuard' (CXXTemporary {{.*}})
+  // CHECK-NEXT:  |       |     `-CXXTemporaryObjectExpr {{.*}} 'LockGuard':'P2718R0::LockGuard' 'void ()'
+  // CHECK-NEXT:  |       `-DeclRefExpr {{.*}} 'int[3]' lvalue Var {{.*}} 'v' 'int[3]'
+  for ([[maybe_unused]] int x : (void)LockGuard(), v)
+    LockGuard guard;
+
+  // CHECK:      -CXXForRangeStmt {{.*}}
+  // CHECK-NEXT:  |-<<<NULL>>>
+  // CHECK-NEXT:  |-DeclStmt {{.*}}
+  // CHECK-NEXT:  | `-VarDecl {{.*}} implicit used __range1 'int (&)[3]' cinit
+  // CHECK-NEXT:  |   `-ExprWithCleanups {{.*}} 'int[3]' lvalue
+  // CHECK-NEXT:  |     `-BinaryOperator {{.*}} 'int[3]' lvalue ','
+  // CHECK-NEXT:  |       |-MaterializeTemporaryExpr {{.*}} 'LockGuard':'P2718R0::LockGuard' xvalue extended by Var {{.*}} '__range1' 'int (&)[3]'
+  // CHECK-NEXT:  |       | `-CXXBindTemporaryExpr {{.*}} 'LockGuard':'P2718R0::LockGuard' (CXXTemporary {{.*}})
+  // CHECK-NEXT:  |       |   `-CXXTemporaryObjectExpr {{.*}} 'LockGuard':'P2718R0::LockGuard' 'void ()'
+  // CHECK-NEXT:  |       `-DeclRefExpr {{.*}} 'int[3]' lvalue Var {{.*}} 'v' 'int[3]'
+  for ([[maybe_unused]] int x : LockGuard(), v)
+    LockGuard guard;
+}
+
+// Test default arg
+int (&default_arg_fn(const A & = A()))[3];
+void test4() {
+
+  // CHECK: FunctionDecl {{.*}} test4 'void ()'
+  // FIXME: Should dump CXXDefaultArgExpr->getExpr() if CXXDefaultArgExpr has been rewrited?
+  for (auto e : default_arg_fn()) 
+    bar(e);
+}
+
+struct DefaultA {
+  DefaultA() {}
+  ~DefaultA() {}
+};
...
[truncated]

``````````

</details>


https://github.com/llvm/llvm-project/pull/76361


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