2 files changed, 14 insertions, 4 deletions
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 14ee02c..58694e5 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -2407,6 +2407,9 @@ void CompilerInvocationBase::GenerateDiagnosticArgs(
     // This option is automatically generated from UndefPrefixes.
     if (Warning == "undef-prefix")
       continue;
+    // This option is automatically generated from CheckConstexprFunctionBodies.
+    if (Warning == "invalid-constexpr" || Warning == "no-invalid-constexpr")
+      continue;
     Consumer(StringRef("-W") + Warning);
   }
 
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 631fd4e..3c28da1 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -2469,11 +2469,18 @@ static bool CheckConstexprFunctionBody(Sema &SemaRef, const FunctionDecl *Dcl,
   //     base class sub-objects shall be a constexpr constructor.
   //
   // Note that this rule is distinct from the "requirements for a constexpr
-  // function", so is not checked in CheckValid mode.
+  // function", so is not checked in CheckValid mode. Because the check for
+  // constexpr potential is expensive, skip the check if the diagnostic is
+  // disabled, the function is declared in a system header, or we're in C++23
+  // or later mode (see https://wg21.link/P2448).
+  bool SkipCheck =
+      !SemaRef.getLangOpts().CheckConstexprFunctionBodies ||
+      SemaRef.getSourceManager().isInSystemHeader(Dcl->getLocation()) ||
+      SemaRef.getDiagnostics().isIgnored(
+          diag::ext_constexpr_function_never_constant_expr, Dcl->getLocation());
   SmallVector<PartialDiagnosticAt, 8> Diags;
-  if (Kind == Sema::CheckConstexprKind::Diagnose &&
-      !Expr::isPotentialConstantExpr(Dcl, Diags) &&
-      !SemaRef.getLangOpts().CPlusPlus23) {
+  if (Kind == Sema::CheckConstexprKind::Diagnose && !SkipCheck &&
+      !Expr::isPotentialConstantExpr(Dcl, Diags)) {
     SemaRef.Diag(Dcl->getLocation(),
                  diag::ext_constexpr_function_never_constant_expr)
         << isa<CXXConstructorDecl>(Dcl) << Dcl->isConsteval()