[clang][bytecode] Start implementing __builtin_{,dynamic}_object_size (#136478)

Author: tbaederr

clang/lib/AST/ByteCode/Descriptor.h

@@ -265,7 +265,7 @@ struct Descriptor final {
   bool isUnknownSizeArray() const { return Size == UnknownSizeMark; }
 
   /// Checks if the descriptor is of a primitive.
-  bool isPrimitive() const { return !IsArray && !ElemRecord && !IsDummy; }
+  bool isPrimitive() const { return !IsArray && !ElemRecord && PrimT; }
 
   /// Checks if the descriptor is of an array.
   bool isArray() const { return IsArray; }

clang/lib/AST/ByteCode/InterpBuiltin.cpp

@@ -2179,6 +2179,52 @@ static bool interp__builtin_memchr(InterpState &S, CodePtr OpPC,
   return true;
 }
 
+static unsigned computeFullDescSize(const ASTContext &ASTCtx,
+                                    const Descriptor *Desc) {
+
+  if (Desc->isPrimitive())
+    return ASTCtx.getTypeSizeInChars(Desc->getType()).getQuantity();
+
+  if (Desc->isArray())
+    return ASTCtx.getTypeSizeInChars(Desc->getElemQualType()).getQuantity() *
+           Desc->getNumElems();
+
+  if (Desc->isRecord())
+    return ASTCtx.getTypeSizeInChars(Desc->getType()).getQuantity();
+
+  llvm_unreachable("Unhandled descriptor type");
+  return 0;
+}
+
+static bool interp__builtin_object_size(InterpState &S, CodePtr OpPC,
+                                        const InterpFrame *Frame,
+                                        const Function *Func,
+                                        const CallExpr *Call) {
+  PrimType KindT = *S.getContext().classify(Call->getArg(1));
+  [[maybe_unused]] unsigned Kind = peekToAPSInt(S.Stk, KindT).getZExtValue();
+
+  assert(Kind <= 3 && "unexpected kind");
+
+  const Pointer &Ptr =
+      S.Stk.peek<Pointer>(align(primSize(KindT)) + align(primSize(PT_Ptr)));
+
+  if (Ptr.isZero())
+    return false;
+
+  const Descriptor *DeclDesc = Ptr.getDeclDesc();
+  if (!DeclDesc)
+    return false;
+
+  const ASTContext &ASTCtx = S.getASTContext();
+
+  unsigned ByteOffset = 0;
+  unsigned FullSize = computeFullDescSize(ASTCtx, DeclDesc);
+
+  pushInteger(S, FullSize - ByteOffset, Call->getType());
+
+  return true;
+}
+
 bool InterpretBuiltin(InterpState &S, CodePtr OpPC, const Function *F,
                       const CallExpr *Call, uint32_t BuiltinID) {
   if (!S.getASTContext().BuiltinInfo.isConstantEvaluated(BuiltinID))
@@ -2681,6 +2727,12 @@ bool InterpretBuiltin(InterpState &S, CodePtr OpPC, const Function *F,
       return false;
     break;
 
+  case Builtin::BI__builtin_object_size:
+  case Builtin::BI__builtin_dynamic_object_size:
+    if (!interp__builtin_object_size(S, OpPC, Frame, F, Call))
+      return false;
+    break;
+
   default:
     S.FFDiag(S.Current->getLocation(OpPC),
              diag::note_invalid_subexpr_in_const_expr)

clang/test/AST/ByteCode/builtin-object-size.cpp

@@ -0,0 +1,14 @@
+// RUN: %clang_cc1 -fexperimental-new-constant-interpreter -verify=both,expected %s
+// RUN: %clang_cc1                                         -verify=both,ref      %s
+
+// both-no-diagnostics
+
+int a;
+static_assert(__builtin_object_size(&a, 0) == sizeof(int), "");
+float f;
+static_assert(__builtin_object_size(&f, 0) == sizeof(float), "");
+int arr[2];
+static_assert(__builtin_object_size(&arr, 0) == (sizeof(int)*2), "");
+
+float arrf[2];
+static_assert(__builtin_object_size(&arrf, 0) == (sizeof(float)*2), "");