[Clang] call HandleImmediateInvocation before checking for immediate escacalating expressions (reland) (#124708)

HandleImmediateInvocation can call MarkExpressionAsImmediateEscalating 
and should always be called before
CheckImmediateEscalatingFunctionDefinition.
    
However, we were not doing that in `ActFunctionBody`.

Fixes #119046

Author: cor3ntin

clang/docs/ReleaseNotes.rst

@@ -1036,6 +1036,7 @@ Bug Fixes to C++ Support
 - Fix type of expression when calling a template which returns an ``__array_rank`` querying a type depending on a
   template parameter. Now, such expression can be used with ``static_assert`` and ``constexpr``. (#GH123498)
 - Correctly determine the implicit constexprness of lambdas in dependent contexts. (#GH97958) (#GH114234)
+- Fix that some dependent immediate expressions did not cause immediate escalation (#GH119046)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^

clang/lib/Sema/SemaDecl.cpp

@@ -16019,7 +16019,6 @@ Decl *Sema::ActOnFinishFunctionBody(Decl *dcl, Stmt *Body,
       if (!FD->isDeletedAsWritten())
         FD->setBody(Body);
       FD->setWillHaveBody(false);
-      CheckImmediateEscalatingFunctionDefinition(FD, FSI);
 
       if (getLangOpts().CPlusPlus14) {
         if (!FD->isInvalidDecl() && Body && !FD->isDependentContext() &&
@@ -16397,6 +16396,9 @@ Decl *Sema::ActOnFinishFunctionBody(Decl *dcl, Stmt *Body,
     // the declaration context below. Otherwise, we're unable to transform
     // 'this' expressions when transforming immediate context functions.
 
+  if (FD)
+    CheckImmediateEscalatingFunctionDefinition(FD, getCurFunction());
+
   if (!IsInstantiation)
     PopDeclContext();
 

clang/test/CodeGenCXX/gh119046.cpp

@@ -0,0 +1,32 @@
+// RUN: %clang_cc1 -std=c++2a -triple x86_64-elf-gnu %s -emit-llvm -o - | FileCheck %s
+
+struct S {
+    consteval void operator()() {}
+};
+
+template <class Fn>
+constexpr void dispatch(Fn fn) {
+    fn();
+}
+
+template <class Visitor>
+struct value_visitor {
+    constexpr void operator()() { visitor(); }
+    Visitor&& visitor;
+};
+
+template <class Visitor>
+constexpr auto make_dispatch() {
+    return dispatch<value_visitor<S>>;
+}
+
+template <class Visitor>
+constexpr void visit(Visitor&&) {
+    make_dispatch<Visitor>();
+}
+
+void f() { visit(S{}); }
+
+// CHECK: define {{.*}} @_Z1fv
+// CHECK-NOT: define {{.*}} @_Z5visitI1SEvOT_
+// CHECK-NOT: define {{.*}} @_Z13make_dispatchI1SEDav

clang/test/SemaCXX/cxx2b-consteval-propagate.cpp

@@ -560,3 +560,19 @@ void foo() {
     S s;
 }
 } // namespace GH118000
+
+namespace GH119046 {
+
+template <typename Cls> constexpr auto tfn(int) {
+  return (unsigned long long)(&Cls::sfn);
+  //expected-note@-1 {{'tfn<GH119046::S>' is an immediate function because its body evaluates the address of a consteval function 'sfn'}}
+};
+struct S { static consteval void sfn() {} };
+
+int f() {
+  int a = 0; // expected-note{{declared here}}
+  return tfn<S>(a);
+  //expected-error@-1 {{call to immediate function 'GH119046::tfn<GH119046::S>' is not a constant expression}}
+  //expected-note@-2 {{read of non-const variable 'a' is not allowed in a constant expression}}
+}
+}