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Eliminate ExpToLValAction and DeleteTmpAction (#636)

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We will eventually need the ability to materialize temporaries eventually, but we don't really seem to need it yet, and when we do, I think we should do it in a way that gives uniform treatment to temporaries and local variables.
This commit is contained in:
Geoff Romer
2021-07-12 14:04:32 -07:00
committed by GitHub
parent 4b69c204bb
commit c396672a59
3 changed files with 18 additions and 99 deletions
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executable_semantics/interpreter/interpreter.cpp
+17 -57
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@@ -26,8 +26,7 @@ State* state = nullptr;
auto PatternMatch(const Value* pat, const Value* val, Env,
std::list<std::string>*, int) -> std::optional<Env>;
auto Step() -> void;
auto GetMember(Address a, const std::string& f, int line_num) -> Address;
auto GetMember(const Value* v, const std::string& f, int line_num) -> Address;
//
// Auxiliary Functions
//
@@ -642,16 +641,15 @@ void StepLvalue() {
if (act->pos == 0) {
// { {e.f :: C, E, F} :: S, H}
// -> { e :: [].f :: C, E, F} :: S, H}
frame->todo.Push(
Action::MakeLValAction(exp->GetFieldAccessExpression().aggregate));
frame->todo.Push(Action::MakeExpressionAction(
exp->GetFieldAccessExpression().aggregate));
act->pos++;
} else {
// { v :: [].f :: C, E, F} :: S, H}
// -> { { &v.f :: C, E, F} :: S, H }
const Value* str = act->results[0];
Address a =
GetMember(ValToPtr(str, exp->line_num),
exp->GetFieldAccessExpression().field, exp->line_num);
Address a = GetMember(str, exp->GetFieldAccessExpression().field,
exp->line_num);
frame->todo.Pop(1);
frame->todo.Push(Action::MakeValAction(Value::MakePointerValue(a)));
}
@@ -718,9 +716,10 @@ void StepLvalue() {
case ExpressionKind::AutoTypeLiteral:
case ExpressionKind::ContinuationTypeLiteral:
case ExpressionKind::BindingExpression: {
frame->todo.Pop();
frame->todo.Push(Action::MakeExpToLValAction());
frame->todo.Push(Action::MakeExpressionAction(exp));
std::cerr << "Can't treat expression as lvalue: ";
PrintExp(exp);
std::cerr << std::endl;
exit(-1);
}
}
}
@@ -820,18 +819,18 @@ void StepExp() {
if (act->pos == 0) {
// { { e.f :: C, E, F} :: S, H}
// -> { { e :: [].f :: C, E, F} :: S, H}
frame->todo.Push(
Action::MakeLValAction(exp->GetFieldAccessExpression().aggregate));
frame->todo.Push(Action::MakeExpressionAction(
exp->GetFieldAccessExpression().aggregate));
act->pos++;
} else {
// { { v :: [].f :: C, E, F} :: S, H}
// -> { { v_f :: C, E, F} : S, H}
auto a =
GetMember(ValToPtr(act->results[0], exp->line_num),
exp->GetFieldAccessExpression().field, exp->line_num);
const Value* element = state->heap.Read(a, exp->line_num);
Address element =
GetMember(act->results[0], exp->GetFieldAccessExpression().field,
exp->line_num);
frame->todo.Pop(1);
frame->todo.Push(Action::MakeValAction(element));
frame->todo.Push(
Action::MakeValAction(state->heap.Read(element, exp->line_num)));
}
break;
}
@@ -1300,8 +1299,7 @@ void StepStmt() {
}
}
auto GetMember(Address a, const std::string& f, int line_num) -> Address {
const Value* v = state->heap.Read(a, line_num);
auto GetMember(const Value* v, const std::string& f, int line_num) -> Address {
switch (v->tag()) {
case ValKind::StructValue: {
auto a = FindTupleField(f, v->GetStructValue().inits);
@@ -1342,31 +1340,6 @@ auto GetMember(Address a, const std::string& f, int line_num) -> Address {
}
}
void InsertDelete(Action* del, Stack<Action*>& todo) {
if (!todo.IsEmpty()) {
switch (todo.Top()->tag()) {
case ActionKind::StatementAction: {
// This places the delete before the enclosing statement.
// Not sure if that is OK. Conceptually it should go after
// but that is tricky for some statements, like 'return'. -Jeremy
todo.Push(del);
break;
}
case ActionKind::LValAction:
case ActionKind::ExpressionAction:
case ActionKind::ValAction:
case ActionKind::ExpToLValAction:
case ActionKind::DeleteTmpAction:
auto top = todo.Pop();
InsertDelete(del, todo);
todo.Push(top);
break;
}
} else {
todo.Push(del);
}
}
// State transition.
void Step() {
Frame* frame = state->stack.Top();
@@ -1378,19 +1351,6 @@ void Step() {
Action* act = frame->todo.Top();
switch (act->tag()) {
case ActionKind::DeleteTmpAction:
state->heap.Deallocate(act->GetDeleteTmpAction().delete_tmp);
frame->todo.Pop(1);
frame->todo.Push(Action::MakeValAction(act->results[0]));
break;
case ActionKind::ExpToLValAction: {
Address a = state->heap.AllocateValue(act->results[0]);
auto del = Action::MakeDeleteTmpAction(a);
frame->todo.Pop(1);
InsertDelete(del, frame->todo);
frame->todo.Push(Action::MakeValAction(Value::MakePointerValue(a)));
break;
}
case ActionKind::ValAction: {
Action* val_act = frame->todo.Pop();
Action* act = frame->todo.Top();