[clang] [Clang] [Sema] Ensure noexcept(typeid(E)) checks if E throws when needed (PR #95846)

[Mital Ashok via cfe-commits]

https://github.com/MitalAshok created https://github.com/llvm/llvm-project/pull/95846

3ad31e12ccfc7db25f3cbedc4ee966e7099ac78f changed it so that not all potentially-evaluated `typeid`s were marked as potentially-throwing, but I forgot to check the subexpression if the null check of the `typeid` didn't potentially-throw. This adds that check.

>From 89da8b3bcc678430fe4225c723e87914f2c378cd Mon Sep 17 00:00:00 2001
From: Mital Ashok <mital at mitalashok.co.uk>
Date: Mon, 17 Jun 2024 21:48:57 +0100
Subject: [PATCH] [Clang] [Sema] Ensure noexcept(typeid(E)) checks if E throws
 when needed

---
 clang/lib/Sema/SemaExceptionSpec.cpp           |  9 +++++++--
 .../test/SemaCXX/cxx0x-noexcept-expression.cpp | 18 ++++++++++++++++++
 2 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/clang/lib/Sema/SemaExceptionSpec.cpp b/clang/lib/Sema/SemaExceptionSpec.cpp
index 67e0c7c63909e..ef1128cedf994 100644
--- a/clang/lib/Sema/SemaExceptionSpec.cpp
+++ b/clang/lib/Sema/SemaExceptionSpec.cpp
@@ -1111,13 +1111,18 @@ static CanThrowResult canDynamicCastThrow(const CXXDynamicCastExpr *DC) {
 }
 
 static CanThrowResult canTypeidThrow(Sema &S, const CXXTypeidExpr *DC) {
-  if (DC->isTypeOperand())
+  // Operand is not evaluated, cannot possibly throw
+  if (!DC->isPotentiallyEvaluated())
     return CT_Cannot;
 
   if (DC->isValueDependent())
     return CT_Dependent;
 
-  return DC->hasNullCheck() ? CT_Can : CT_Cannot;
+  // Can throw std::bad_typeid if a nullptr is dereferenced
+  if (DC->hasNullCheck())
+    return CT_Can;
+
+  return S.canThrow(DC->getExprOperand());
 }
 
 CanThrowResult Sema::canThrow(const Stmt *S) {
diff --git a/clang/test/SemaCXX/cxx0x-noexcept-expression.cpp b/clang/test/SemaCXX/cxx0x-noexcept-expression.cpp
index c2b2244c117a0..1e86a31fffcbf 100644
--- a/clang/test/SemaCXX/cxx0x-noexcept-expression.cpp
+++ b/clang/test/SemaCXX/cxx0x-noexcept-expression.cpp
@@ -1,6 +1,10 @@
 // RUN: %clang_cc1 -fsyntax-only -verify -std=c++2a %s -fexceptions -fcxx-exceptions -Wno-unevaluated-expression
 // RUN: %clang_cc1 -fsyntax-only -verify -std=c++2a %s -fexceptions -fcxx-exceptions -Wno-unevaluated-expression -fexperimental-new-constant-interpreter
 
+namespace std {
+struct type_info;
+}
+
 void f(); // expected-note {{possible target for call}}
 void f(int); // expected-note {{possible target for call}}
 
@@ -97,3 +101,17 @@ void j() noexcept(0);
 void k() noexcept(1);
 void l() noexcept(2); // expected-error {{noexcept specifier argument evaluates to 2, which cannot be narrowed to type 'bool'}}
 } // namespace P1401
+
+template<bool NoexceptConstructor, bool NoexceptDestructor>
+struct Polymorphic {
+  Polymorphic() noexcept(NoexceptConstructor) {}
+  virtual ~Polymorphic() noexcept(NoexceptDestructor) {}
+};
+
+static_assert(noexcept(typeid(Polymorphic<false, false>{})));  // Not evaluated (not glvalue)
+static_assert(noexcept(typeid((Polymorphic<true, true>&&) Polymorphic<true, true>{})));
+static_assert(!noexcept(typeid((Polymorphic<false, true>&&) Polymorphic<false, true>{})));
+static_assert(!noexcept(typeid((Polymorphic<true, false>&&) Polymorphic<true, false>{})));
+static_assert(!noexcept(typeid(*&(const Polymorphic<true, true>&) Polymorphic<true, true>{})));
+static_assert(!noexcept(typeid(*&(const Polymorphic<false, true>&) Polymorphic<false, true>{})));
+static_assert(!noexcept(typeid(*&(const Polymorphic<true, false>&) Polymorphic<true, false>{})));