[Clang] Preserve CXXParenListInitExpr in TreeTransform. #138518

cor3ntin · 2025-05-05T12:36:09Z

We were converting a CXXParenListInitExpr to a ParenListExpr in TreeTransform.

However, ParenListExpr is typeless, so Clang could not rebuild the correct initialization sequence in some contexts.

We were converting a CXXParenListInitExpr to a ParenListExpr in Treetransform. However, ParenListExpr is typeless so clang could not rebuild the correct initialization sequence in some contexts. Fixes 72880

llvmbot · 2025-05-05T12:36:43Z

@llvm/pr-subscribers-clang

Author: cor3ntin (cor3ntin)

Changes

We were converting a CXXParenListInitExpr to a ParenListExpr in TreeTransform.

However, ParenListExpr is typeless, so Clang could not rebuild the correct initialization sequence in some contexts.

#Fixes 72880

Full diff: https://github.com/llvm/llvm-project/pull/138518.diff

6 Files Affected:

(modified) clang/docs/ReleaseNotes.rst (+1)
(modified) clang/include/clang/AST/ExprCXX.h (+2-2)
(modified) clang/include/clang/Sema/Sema.h (+5)
(modified) clang/lib/Sema/SemaExpr.cpp (+9)
(modified) clang/lib/Sema/TreeTransform.h (+28-4)
(modified) clang/test/SemaCXX/paren-list-agg-init.cpp (+32-5)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 4bd9d904e1ea9..55a46fb6f947e 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -642,6 +642,7 @@ Bug Fixes to C++ Support
   (#GH136432), (#GH137014), (#GH138018)
 - Fixed an assertion when trying to constant-fold various builtins when the argument
   referred to a reference to an incomplete type. (#GH129397)
+- Fixed a crash when a cast involved a parenthesized aggregate initialization in dependent context. (#GH72880)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/include/clang/AST/ExprCXX.h b/clang/include/clang/AST/ExprCXX.h
index 844f6dd90ae1d..04d08b022c562 100644
--- a/clang/include/clang/AST/ExprCXX.h
+++ b/clang/include/clang/AST/ExprCXX.h
@@ -5124,8 +5124,8 @@ class CXXParenListInitExpr final
 
   void updateDependence() { setDependence(computeDependence(this)); }
 
-  ArrayRef<Expr *> getInitExprs() {
-    return ArrayRef(getTrailingObjects<Expr *>(), NumExprs);
+  MutableArrayRef<Expr *> getInitExprs() {
+    return MutableArrayRef(getTrailingObjects<Expr *>(), NumExprs);
   }
 
   const ArrayRef<Expr *> getInitExprs() const {
diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
index 19343eb0af092..741951cb9ea0e 100644
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -7167,6 +7167,11 @@ class Sema final : public SemaBase {
   ExprResult ActOnParenExpr(SourceLocation L, SourceLocation R, Expr *E);
   ExprResult ActOnParenListExpr(SourceLocation L, SourceLocation R,
                                 MultiExprArg Val);
+  ExprResult ActOnCXXParenListInitExpr(ArrayRef<Expr *> Args, QualType T,
+                                       unsigned NumUserSpecifiedExprs,
+                                       SourceLocation InitLoc,
+                                       SourceLocation LParenLoc,
+                                       SourceLocation RParenLoc);
 
   /// ActOnStringLiteral - The specified tokens were lexed as pasted string
   /// fragments (e.g. "foo" "bar" L"baz").  The result string has to handle
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index d72d97addfac2..787b07c4080ea 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -7985,6 +7985,15 @@ ExprResult Sema::ActOnParenListExpr(SourceLocation L,
   return ParenListExpr::Create(Context, L, Val, R);
 }
 
+ExprResult Sema::ActOnCXXParenListInitExpr(ArrayRef<Expr *> Args, QualType T,
+                                           unsigned NumUserSpecifiedExprs,
+                                           SourceLocation InitLoc,
+                                           SourceLocation LParenLoc,
+                                           SourceLocation RParenLoc) {
+  return CXXParenListInitExpr::Create(Context, Args, T, NumUserSpecifiedExprs,
+                                      InitLoc, LParenLoc, RParenLoc);
+}
+
 bool Sema::DiagnoseConditionalForNull(const Expr *LHSExpr, const Expr *RHSExpr,
                                       SourceLocation QuestionLoc) {
   const Expr *NullExpr = LHSExpr;
diff --git a/clang/lib/Sema/TreeTransform.h b/clang/lib/Sema/TreeTransform.h
index aed00e0ff06cd..a3120f61f0d9c 100644
--- a/clang/lib/Sema/TreeTransform.h
+++ b/clang/lib/Sema/TreeTransform.h
@@ -3099,6 +3099,15 @@ class TreeTransform {
     return getSema().ActOnParenListExpr(LParenLoc, RParenLoc, SubExprs);
   }
 
+  ExprResult RebuildCXXParenListInitExpr(ArrayRef<Expr *> Args, QualType T,
+                                         unsigned NumUserSpecifiedExprs,
+                                         SourceLocation InitLoc,
+                                         SourceLocation LParenLoc,
+                                         SourceLocation RParenLoc) {
+    return getSema().ActOnCXXParenListInitExpr(Args, T, NumUserSpecifiedExprs,
+                                               InitLoc, LParenLoc, RParenLoc);
+  }
+
   /// Build a new address-of-label expression.
   ///
   /// By default, performs semantic analysis, using the name of the label
@@ -3315,6 +3324,11 @@ class TreeTransform {
       return getSema().BuildCXXTypeConstructExpr(
           TInfo, LParenLoc, MultiExprArg(PLE->getExprs(), PLE->getNumExprs()),
           RParenLoc, ListInitialization);
+
+    if (auto *PLE = dyn_cast<CXXParenListInitExpr>(Sub))
+      return getSema().BuildCXXTypeConstructExpr(
+          TInfo, LParenLoc, PLE->getInitExprs(), RParenLoc, ListInitialization);
+
     return getSema().BuildCXXTypeConstructExpr(TInfo, LParenLoc,
                                                MultiExprArg(&Sub, 1), RParenLoc,
                                                ListInitialization);
@@ -16487,12 +16501,22 @@ ExprResult
 TreeTransform<Derived>::TransformCXXParenListInitExpr(CXXParenListInitExpr *E) {
   SmallVector<Expr *, 4> TransformedInits;
   ArrayRef<Expr *> InitExprs = E->getInitExprs();
-  if (TransformExprs(InitExprs.data(), InitExprs.size(), true,
-                     TransformedInits))
+
+  QualType T = getDerived().TransformType(E->getType());
+
+  bool ArgChanged = false;
+  ;
+
+  if (getDerived().TransformExprs(InitExprs.data(), InitExprs.size(), true,
+                                  TransformedInits, &ArgChanged))
     return ExprError();
 
-  return getDerived().RebuildParenListExpr(E->getBeginLoc(), TransformedInits,
-                                           E->getEndLoc());
+  if (!ArgChanged && T == E->getType())
+    return E;
+
+  return getDerived().RebuildCXXParenListInitExpr(
+      TransformedInits, T, E->getUserSpecifiedInitExprs().size(),
+      E->getInitLoc(), E->getBeginLoc(), E->getEndLoc());
 }
 
 template<typename Derived>
diff --git a/clang/test/SemaCXX/paren-list-agg-init.cpp b/clang/test/SemaCXX/paren-list-agg-init.cpp
index b2d0f2564bb59..ba7dffdc1af9f 100644
--- a/clang/test/SemaCXX/paren-list-agg-init.cpp
+++ b/clang/test/SemaCXX/paren-list-agg-init.cpp
@@ -83,7 +83,7 @@ template <typename T, char CH>
 void bar() {
   T t = 0;
   A a(CH, 1.1); // OK; C++ paren list constructors are supported in semantic tree transformations.
-  // beforecxx20-warning@-1 2{{aggregate initialization of type 'A' from a parenthesized list of values is a C++20 extension}}
+  // beforecxx20-warning@-1 {{aggregate initialization of type 'A' from a parenthesized list of values is a C++20 extension}}
 }
 
 template <class T, class... Args>
@@ -157,9 +157,6 @@ void foo(int n) { // expected-note {{declared here}}
   constexpr F f2(1, 1); // OK: f2.b is initialized by a constant expression.
   // beforecxx20-warning@-1 {{aggregate initialization of type 'const F' from a parenthesized list of values is a C++20 extension}}
 
-  bar<int, 'a'>();
-  // beforecxx20-note@-1 {{in instantiation of function template specialization 'bar<int, 'a'>' requested here}}
-
   G<char> g('b', 'b');
   // beforecxx20-warning@-1 {{aggregate initialization of type 'G<char>' from a parenthesized list of values is a C++20 extension}}
 
@@ -354,7 +351,7 @@ using Td = int[]; Td d(42,43);
 // beforecxx20-warning@-1 {{aggregate initialization of type 'int[2]' from a parenthesized list of values is a C++20 extension}}
 template<typename T, int Sz> using ThroughAlias = T[Sz];
 ThroughAlias<int, 1> e(42);
-// beforecxx20-warning@-1 {{aggregate initialization of type 'ThroughAlias<int, 1>' (aka 'int[1]') from a parenthesized list of values is a C++20 extension}} 
+// beforecxx20-warning@-1 {{aggregate initialization of type 'ThroughAlias<int, 1>' (aka 'int[1]') from a parenthesized list of values is a C++20 extension}}
 
 }
 
@@ -376,3 +373,33 @@ static_assert(S(1, 2) == S(3, 4));
 // beforecxx20-warning@-1 2{{C++20 extension}}
 
 }
+
+namespace GH72880 {
+struct Base {};
+struct Derived : Base {
+    int count = 42;
+};
+
+template <typename T>
+struct BaseTpl {};
+template <typename T>
+struct DerivedTpl : BaseTpl<T> {
+    int count = 43;
+};
+template <typename T> struct S {
+  void f() {
+      Derived a = static_cast<Derived>(Base());
+      // beforecxx20-warning@-1 {{C++20 extension}}
+      DerivedTpl b = static_cast<DerivedTpl<T>>(BaseTpl<T>());
+      // beforecxx20-warning@-1 {{C++20 extension}}
+      static_assert(static_cast<Derived>(Base()).count == 42);
+      // beforecxx20-warning@-1 {{C++20 extension}}
+      static_assert(static_cast<DerivedTpl<T>>(BaseTpl<T>()).count == 43);
+      // beforecxx20-warning@-1 {{C++20 extension}}
+  }
+};
+
+void test() {
+    S<int>{}.f(); // beforecxx20-note {{requested here}}
+}
+}

erichkeane

Please change the commit message to do Fixes # instead of the reverse, so this actually closes the bug :)

erichkeane · 2025-05-05T13:51:07Z

clang/lib/Sema/TreeTransform.h

+  QualType T = getDerived().TransformType(E->getType());
+
+  bool ArgChanged = false;
+  ;


extra semicolon for no reason?

zyn0217 · 2025-05-05T14:13:36Z

clang/lib/Sema/TreeTransform.h

+  if (!ArgChanged && T == E->getType())
+    return E;


Do we want to handle AlwaysRebuild?

We were converting a CXXParenListInitExpr to a ParenListExpr in TreeTransform. However, ParenListExpr is typeless, so Clang could not rebuild the correct initialization sequence in some contexts. Fixes llvm#72880

[Clang] Preserve CXXParenListInitExpr in TreeTransform.

22af52c

We were converting a CXXParenListInitExpr to a ParenListExpr in Treetransform. However, ParenListExpr is typeless so clang could not rebuild the correct initialization sequence in some contexts. Fixes 72880

cor3ntin requested review from erichkeane and AaronBallman May 5, 2025 12:36

llvmbot added clang Clang issues not falling into any other category clang:frontend Language frontend issues, e.g. anything involving "Sema" labels May 5, 2025

erichkeane approved these changes May 5, 2025

View reviewed changes

zyn0217 approved these changes May 5, 2025

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address feedback

df48cd1

cor3ntin merged commit 13926e1 into llvm:main May 5, 2025
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cor3ntin deleted the gh72880 branch May 5, 2025 16:46

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[Clang] Preserve CXXParenListInitExpr in TreeTransform. #138518

[Clang] Preserve CXXParenListInitExpr in TreeTransform. #138518

cor3ntin commented May 5, 2025 •

edited

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llvmbot commented May 5, 2025

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erichkeane May 5, 2025

zyn0217 May 5, 2025

[Clang] Preserve CXXParenListInitExpr in TreeTransform. #138518

[Clang] Preserve CXXParenListInitExpr in TreeTransform. #138518

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cor3ntin commented May 5, 2025 •

edited

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