[Clang] Correctly handle allocation in template arguments

[cor3ntin]

Summary

Fixes #62462

[tbaeder]

clang/lib/AST/ExprConstant.cpp

15356–15367

Makes more sense, I think?

[cor3ntin]

Address @tbaeder feedback

[shafik]

clang/lib/AST/ExprConstant.cpp

15357–15366

Can you add a comment explaining why this is necessary, I don't see it myself. Maybe a quote from the standard if it is applicable as well.

Also the description of the PR should be more descriptive even if it is mostly a copy past of your comment from the bug report.

[cor3ntin]

Update commit message and add comment referencing the standard.

[Fznamznon]

clang/docs/ReleaseNotes.rst

419

Not an expert in this, but I assume _ after link is needed.

[cor3ntin]

Fix release notes

[cor3ntin]

Formatting.

[erichkeane]

I think this looks right, and you've satisfied all the other reviewers. LGTM.

clang/docs/ReleaseNotes.rst

- Fix a stack overflow issue when evaluating ``consteval`` default arguments.
   (`#60082` <https://github.com/llvm/llvm-project/issues/60082>`_)
 - Fix the assertion hit when generating code for global variable initializer of
   _BitInt(1) type.
   (`#62207 <https://github.com/llvm/llvm-project/issues/62207>`_)
 - Fix lambdas and other anonymous function names not respecting ``-fdebug-prefix-map``
   (`#62192 <https://github.com/llvm/llvm-project/issues/62192>`_)
 - Fix crash when attempting to pass a non-pointer type as first argument of
   ``__builtin_assume_aligned``.
-  (`#62305 <https://github.com/llvm/llvm-project/issues/62305>`_) 
+  (`#62305 <https://github.com/llvm/llvm-project/issues/62305>`_)
 
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 Bug Fixes to Attribute Support
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 - Fixed a bug where attribute annotations on type specifiers (enums, classes,
   structs, unions, and scoped enums) were not properly ignored, resulting in
- Fix bug in the computation of the ``__has_unique_object_representations``
   (`#61336 <https://github.com/llvm/llvm-project/issues/61336>`_)
 - Fix default member initializers sometimes being ignored when performing
   parenthesized aggregate initialization of templated types.
   (`#62266 <https://github.com/llvm/llvm-project/issues/62266>`_)
 - Fix overly aggressive lifetime checks for parenthesized aggregate
   initialization.
   (`#61567 <https://github.com/llvm/llvm-project/issues/61567>`_)
 - Fix a crash when expanding a pack as the index of a subscript expression.
+- Fix handling of constexpr dynamic memory allocations in template
+  arguments. (`#62462 <https://github.com/llvm/llvm-project/issues/62462>`_)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^
 
 Miscellaneous Bug Fixes
 ^^^^^^^^^^^^^^^^^^^^^^^
 
 Miscellaneous Clang Crashes Fixed

clang/lib/AST/ExprConstant.cpp

bool Expr::EvaluateAsConstantExpr(EvalResult &Result, const ASTContext &Ctx,
   // represent the result of the evaluation. CheckConstantExpression ensures
   // this doesn't escape.
   MaterializeTemporaryExpr BaseMTE(T, const_cast<Expr*>(this), true);
   APValue::LValueBase Base(&BaseMTE);
 
   Info.setEvaluatingDecl(Base, Result.Val);
   LValue LVal;
   LVal.set(Base);
 
-  if (!::EvaluateInPlace(Result.Val, Info, LVal, this) || Result.HasSideEffects)
+  {
+    // C++23 [intro.execution]/p5
+    // A full-expression is [...] a constant-expression
+    // So we need to make sure temporary objects are destroyed after having
+    // evaluating the expression (per C++23 [class.temporary]/p4).
+    FullExpressionRAII Scope(Info);
+    if (!::EvaluateInPlace(Result.Val, Info, LVal, this) ||
+        Result.HasSideEffects || !Scope.destroy())
       return false;
+  }
 
   if (!Info.discardCleanups())
     llvm_unreachable("Unhandled cleanup; missing full expression marker?");
 
   if (!CheckConstantExpression(Info, getExprLoc(), getStorageType(Ctx, this),
                                Result.Val, Kind))
     return false;
   if (!CheckMemoryLeaks(Info))
     return false;

clang/test/SemaCXX/cxx2a-constexpr-dynalloc.cpp

constexpr bool h() {
     p->~A();
     std::construct_at<A>(p);
     p->~A();
     alloc.deallocate(p);
     return true;
   }
   static_assert(h());
 }
+
+namespace GH62462 {
+
+class string {
+public:
+  char *mem;
+  constexpr string() {
+    this->mem = new char(1);
+  }
+  constexpr ~string() {
+    delete this->mem;
+  }
+  constexpr unsigned size() const { return 4; }
+};
+
+
+template <unsigned N>
+void test() {};
+
+void f() {
+    test<string().size()>();
+}
+
+}