[clang][Interp] Implement __builtin_addressof (#77303)

We don't need to do anything here, since the input is already a Pointer.
The only complexity is that we pre-classify the parameters as PT_Ptr,
but they might end up being of a different pointer type, e.g. PT_FnPtr.

clang/lib/AST/Interp/Interp.cpp

@@ -134,6 +134,18 @@ void cleanupAfterFunctionCall(InterpState &S, CodePtr OpPC) {
   if (CurFunc->isUnevaluatedBuiltin())
     return;
 
+  // Some builtin functions require us to only look at the call site, since
+  // the classified parameter types do not match.
+  if (CurFunc->isBuiltin()) {
+    const auto *CE =
+        cast<CallExpr>(S.Current->Caller->getExpr(S.Current->getRetPC()));
+    for (int32_t I = CE->getNumArgs() - 1; I >= 0; --I) {
+      const Expr *A = CE->getArg(I);
+      popArg(S, A);
+    }
+    return;
+  }
+
   if (S.Current->Caller && CurFunc->isVariadic()) {
     // CallExpr we're look for is at the return PC of the current function, i.e.
     // in the caller.

clang/lib/AST/Interp/InterpBuiltin.cpp

@@ -164,6 +164,8 @@ static bool retPrimValue(InterpState &S, CodePtr OpPC, APValue &Result,
   case X:                                                                      \
     return Ret<X>(S, OpPC, Result);
   switch (*T) {
+    RET_CASE(PT_Ptr);
+    RET_CASE(PT_FnPtr);
     RET_CASE(PT_Float);
     RET_CASE(PT_Bool);
     RET_CASE(PT_Sint8);
@@ -613,15 +615,34 @@ static bool interp__builtin_ffs(InterpState &S, CodePtr OpPC,
   return true;
 }
 
+static bool interp__builtin_addressof(InterpState &S, CodePtr OpPC,
+                                      const InterpFrame *Frame,
+                                      const Function *Func,
+                                      const CallExpr *Call) {
+  PrimType PtrT =
+      S.getContext().classify(Call->getArg(0)->getType()).value_or(PT_Ptr);
+
+  if (PtrT == PT_FnPtr) {
+    const FunctionPointer &Arg = S.Stk.peek<FunctionPointer>();
+    S.Stk.push<FunctionPointer>(Arg);
+  } else if (PtrT == PT_Ptr) {
+    const Pointer &Arg = S.Stk.peek<Pointer>();
+    S.Stk.push<Pointer>(Arg);
+  } else {
+    assert(false && "Unsupported pointer type passed to __builtin_addressof()");
+  }
+  return true;
+}
+
 bool InterpretBuiltin(InterpState &S, CodePtr OpPC, const Function *F,
                       const CallExpr *Call) {
   InterpFrame *Frame = S.Current;
   APValue Dummy;
 
-  QualType ReturnType = Call->getCallReturnType(S.getCtx());
-  std::optional<PrimType> ReturnT = S.getContext().classify(ReturnType);
+  std::optional<PrimType> ReturnT = S.getContext().classify(Call->getType());
+
   // If classify failed, we assume void.
-  assert(ReturnT || ReturnType->isVoidType());
+  assert(ReturnT || Call->getType()->isVoidType());
 
   switch (F->getBuiltinID()) {
   case Builtin::BI__builtin_is_constant_evaluated:
@@ -820,6 +841,12 @@ bool InterpretBuiltin(InterpState &S, CodePtr OpPC, const Function *F,
     if (!interp__builtin_ffs(S, OpPC, Frame, F, Call))
       return false;
     break;
+  case Builtin::BIaddressof:
+  case Builtin::BI__addressof:
+  case Builtin::BI__builtin_addressof:
+    if (!interp__builtin_addressof(S, OpPC, Frame, F, Call))
+      return false;
+    break;
 
   default:
     return false;

clang/test/AST/Interp/functions.cpp

@@ -389,3 +389,27 @@ namespace Packs {
   static_assert(foo<int, char>() == 2, "");
   static_assert(foo<>() == 0, "");
 }
+
+namespace AddressOf {
+  struct S {} s;
+  static_assert(__builtin_addressof(s) == &s, "");
+
+  struct T { constexpr T *operator&() const { return nullptr; } int n; } t;
+  constexpr T *pt = __builtin_addressof(t);
+  static_assert(&pt->n == &t.n, "");
+
+  struct U { int n : 5; } u;
+  int *pbf = __builtin_addressof(u.n); // expected-error {{address of bit-field requested}} \
+                                       // ref-error {{address of bit-field requested}}
+
+  S *ptmp = __builtin_addressof(S{}); // expected-error {{taking the address of a temporary}} \
+                                      // expected-warning {{temporary whose address is used as value of local variable 'ptmp' will be destroyed at the end of the full-expression}} \
+                                      // ref-error {{taking the address of a temporary}} \
+                                      // ref-warning {{temporary whose address is used as value of local variable 'ptmp' will be destroyed at the end of the full-expression}}
+
+  constexpr int foo() {return 1;}
+  static_assert(__builtin_addressof(foo) == foo, "");
+
+  constexpr _Complex float F = {3, 4};
+  static_assert(__builtin_addressof(F) == &F, "");
+}