[clang][Interp] Make CXXTemporaryObjectExprs leave a value behind

[tbaeder]

Summary

visitLocalInitializer() pops the pointer from the stack again, but we
might be called in a situation where the caller would actually like to
use the value.

[shafik]

clang/lib/AST/Interp/ByteCodeExprGen.cpp

1022

Could you just pass DiscardResult to visitLocalInitializer

[tbaeder]

clang/lib/AST/Interp/ByteCodeExprGen.cpp

1022

Nope, the visitInitializer function(s) don't handle DiscardResult at all right now; they just initialize an already existing value.

[tbaeder]

Ping

[tbaeder]

Ping

[tbaeder]

Ping

[shafik]

LGTM

[tbaeder]

This was pushed as part of the initializer rework.

clang/lib/AST/Interp/ByteCodeExprGen.cpp

bool ByteCodeExprGen<Emitter>::VisitCXXBindTemporaryExpr(
     const CXXBindTemporaryExpr *E) {
 
   return this->visit(E->getSubExpr());
 }
 
 template <class Emitter>
 bool ByteCodeExprGen<Emitter>::VisitCXXTemporaryObjectExpr(
     const CXXTemporaryObjectExpr *E) {
-
   if (std::optional<unsigned> LocalIndex =
           allocateLocal(E, /*IsExtended=*/false)) {
-    return this->visitLocalInitializer(E, *LocalIndex);
+    if (!this->emitGetPtrLocal(*LocalIndex, E))
+      return false;
+
+    if (!this->visitInitializer(E))
+      return false;
+
+    if (DiscardResult)
+      return this->emitPopPtr(E);
+    return true;
   }
   return false;
 }
 
 template <class Emitter>
 bool ByteCodeExprGen<Emitter>::VisitCompoundLiteralExpr(
     const CompoundLiteralExpr *E) {
   std::optional<PrimType> T = classify(E->getType());

clang/test/AST/Interp/records.cpp

namespace MutableFields {
 
   /// FIXME: This should also be rejected in the new interpreter.
   constexpr Foo GlobalF;
   constexpr int foo2() { // ref-error {{never produces a constant expression}}
     return GlobalF.I; // ref-note {{read of mutable member 'I' is not allowed in a constant expression}}
   }
 }
 
+namespace TemporaryObjectExpr {
+  struct F {
+    int a;
+    constexpr F() : a(12) {}
+  };
+  constexpr int foo(F f) {
+    return 0;
+  }
+  /// FIXME: This should also work in C++14, but it needs suport for
+  ///   CXXConstructExpr. I think.
+#if __cplusplus > 201402L
+  static_assert(foo(F()) == 0, "");
+#endif
+
+}