def basic_block(statements: List[Statement]) -> BasicBlock:
done_label = TempManager.new_label()
statement_lists = []
block_start_index = 0
for index, statement in enumerate(statements):
if isinstance(statement, Label):
# If the label is supposed to be the beginning of a new block, we do not end the
# previous block since it was already ended by a jump.
# If not, then we end the previous block and start the new one with the current label.
if block_start_index < index:
statement_lists.append(statements[block_start_index:index])
block_start_index = index
elif isinstance(statement, Jump) or isinstance(statement,
ConditionalJump):
statement_lists.append(statements[block_start_index:index + 1])
block_start_index = index + 1
last_block = statements[block_start_index:len(statements)] + [
Jump(Name(done_label), [done_label])
]
statement_lists.append(last_block)
for index, statement_list in enumerate(statement_lists):
if not isinstance(statement_list[0], Label):
statement_lists[index] = [Label(TempManager.new_label())
] + statement_list
for index, statement_list in enumerate(statement_lists[:-1]):
if not isinstance(statement_list[-1], Jump) and not isinstance(
statement_list[-1], ConditionalJump):
next_block_label = statement_lists[index + 1][0]
statement_lists[index] = statement_list + [
Jump(Name(next_block_label.label), [next_block_label.label])
]
return BasicBlock(done_label, statement_lists)
def for_expression(
variable: TranslatedExpression,
lo: TranslatedExpression,
hi: TranslatedExpression,
body: TranslatedExpression,
break_label: TempLabel,
) -> TranslatedExpression:
test_label = TempManager.new_label()
body_label = TempManager.new_label()
limit = TempManager.new_temp()
variable_expression = convert_to_expression(variable)
sequence = Sequence([
Move(variable_expression, convert_to_expression(lo)),
Move(Temporary(limit), convert_to_expression(hi)),
Label(test_label),
ConditionalJump(
RelationalOperator.le,
variable_expression,
Temporary(limit),
body_label,
break_label,
),
Label(body_label),
convert_to_statement(body),
Move(
variable_expression,
BinaryOperation(BinaryOperator.plus, variable_expression,
Constant(1)),
),
Jump(Name(test_label), [test_label]),
Label(break_label),
])
return NoResult(sequence)
def if_expression(
test: TranslatedExpression,
then: TranslatedExpression,
else_do: Optional[TranslatedExpression],
) -> TranslatedExpression:
test_condition = convert_to_condition(test)
then_expression = convert_to_expression(then)
else_expression = (convert_to_expression(else_do)
if else_do is not None else Constant(0))
true_label = TempManager.new_label()
false_label = TempManager.new_label()
join_label = TempManager.new_label()
result = TempManager.new_temp()
patch_true_labels(test_condition.trues, true_label)
patch_false_labels(test_condition.trues, false_label)
sequence = Sequence([
test_condition.statement,
Label(true_label),
Move(Temporary(result), then_expression),
Jump(Name(join_label), [join_label]),
Label(false_label),
Move(Temporary(result), else_expression),
Label(join_label),
])
return Expression(EvaluateSequence(sequence, Temporary(result)))
def convert_to_expression(exp: TranslatedExpression) -> tree.Expression:
if isinstance(exp, Expression):
return exp.expression
if isinstance(exp, NoResult):
return EvaluateSequence(exp.statement, Constant(0))
if isinstance(exp, Conditional):
temporary_value = TempManager.new_temp()
true = TempManager.new_label()
false = TempManager.new_label()
patch_true_labels(exp.condition.trues, true)
patch_false_labels(exp.condition.falses, false)
return EvaluateSequence(
Move(Temporary(temporary_value), Constant(1)),
EvaluateSequence(
exp.condition.statement,
EvaluateSequence(
Label(false),
EvaluateSequence(
Move(Temporary(temporary_value), Constant(0)),
EvaluateSequence(Label(true),
Temporary(temporary_value)),
),
),
),
)
def convert_to_statement(exp: TranslatedExpression) -> tree.Statement:
if isinstance(exp, Expression):
return StatementExpression(exp.expression)
if isinstance(exp, NoResult):
return exp.statement
if isinstance(exp, Conditional):
true = TempManager.new_label()
false = TempManager.new_label()
patch_true_labels(exp.condition.trues, true)
patch_false_labels(exp.condition.falses, false)
return Sequence([exp.condition.statement, Label(true), Label(false)])
def while_expression(test: TranslatedExpression, body: TranslatedExpression,
break_label: TempLabel) -> TranslatedExpression:
test_label = TempManager.new_label()
body_label = TempManager.new_label()
sequence = Sequence([
Label(test_label),
ConditionalJump(
RelationalOperator.ne,
convert_to_expression(test),
Constant(0),
body_label,
break_label,
),
Label(body_label),
convert_to_statement(body),
Jump(Name(test_label), [test_label]),
Label(break_label),
])
return NoResult(sequence)
def string_expression(string: str) -> TranslatedExpression:
string_label = TempManager.new_label()
FragmentManager.add_fragment(StringFragment(string_label, string))
return Expression(Name(string_label))
def translate_declaration(
value_env: SymbolTable[EnvironmentEntry],
type_env: SymbolTable[Type],
declaration: ast.Declaration,
level: RealLevel,
break_label: Optional[TempLabel],
) -> TranslatedExpression:
if isinstance(declaration, ast.FunctionDecBlock):
# Function declaration block: Check that all function names are unique. Then, evaluate each
# function header and add it to the value environment. Then, for each function, push its
# parameters to the value environment and make sure the function body returns the same type
# as the declared one.
if not check_name_uniqueness(declaration.function_dec_list):
raise SemanticError(
"All names in the function declaration block must be unique",
declaration.position,
)
function_entries = []
for function_dec in declaration.function_dec_list:
formals = []
for parameter in function_dec.params:
param_type = type_env.find(parameter.type)
if param_type is None:
raise SemanticError(
f"Undefined argument type {parameter.type} for parameter {parameter.name}"
+ f"in function {function_dec.name}",
parameter.position,
)
formals.append(param_type)
if function_dec.return_type is None:
return_type = VoidType()
else:
return_type = type_env.find(function_dec.return_type)
if return_type is None:
raise SemanticError(
f"Undefined return type {function_dec.return_type}" +
f" for function {function_dec.name}",
function_dec.position,
)
function_label = TempManager.new_label()
function_level = RealLevel(level, function_label,
function_dec.param_escapes)
function_entry = FunctionEntry(function_level, function_label,
formals, return_type)
function_entries.append(function_entry)
value_env.add(function_dec.name, function_entry)
for function_dec, function_entry in zip(declaration.function_dec_list,
function_entries):
value_env.begin_scope()
# We ignore the static link since we need the accesses of the REAL function formals.
formal_accesses = function_entry.level.formals()[1:]
for param, formal_type, formal_access in zip(
function_dec.params, function_entry.formals,
formal_accesses):
value_env.add(param.name,
VariableEntry(formal_access, formal_type))
trans_exp = translate_expression(
value_env,
type_env,
function_entry.level,
function_dec.body,
break_label,
)
if not are_types_equal(trans_exp.type, function_entry.result):
raise SemanticError(
f"Function {function_dec.name} returns a value of a type" +
" different than its declared type",
function_dec.position,
)
IRT.proc_entry_exit(function_entry.level, trans_exp.expression)
value_env.end_scope()
return no_op_expression()
elif isinstance(declaration, ast.VariableDec):
# Variable declaration: Translate the expression, make sure its type matches the declared
# type and that a variable initialized to nil has a type declaration of a record type.
trans_exp = translate_expression(value_env, type_env, level,
declaration.exp, break_label)
if isinstance(trans_exp.type, NilType) and declaration.type is None:
raise SemanticError(
f"Must declare the type of variable {declaration.name} when initializing it to nil",
declaration.position,
)
variable_type = trans_exp.type
if declaration.type is not None:
declared_type = type_env.find(declaration.type)
if declared_type is None:
raise SemanticError(
f"Undefined type {declaration.type} in variable declaration"
+ f" for {declaration.name}",
declaration.position,
)
if isinstance(trans_exp.type, NilType) and not isinstance(
declared_type, RecordType):
raise SemanticError(
f"Variable {declaration.name} must be of a record type when initialized to nil",
declaration.position,
)
if not are_types_equal(declared_type, trans_exp.type):
raise SemanticError(
f"Initial value for variable {declaration.name} is not of its"
+ f" declared type {declaration.type}",
declaration.position,
)
variable_type = declared_type
variable_access = level.alloc_local(declaration.escape)
value_env.add(declaration.name,
VariableEntry(variable_access, variable_type))
return IRT.assignment_expression(
IRT.simple_variable(variable_access, level), trans_exp.expression)
elif isinstance(declaration, ast.TypeDecBlock):
# Type declaration block: Check that all type names are unique. Then, follow these steps:
# - Add a dummy reference to the type environment for every type declaration, so as to be
# able to recognize undefined types in the following step.
# - Translate each type and add it to the type environment. In this step, references to
# types in the same block are stored as a name reference and not as a pointer to the real
# referenced type.
# - For each definition that is a type alias (the name we give to those that just name
# another type instead of creating a record or array), keep moving forward in the type
# aliases chain until you find a record or array type. Then make all involved type aliases
# point to that record or array type. If you only find type aliases, you are inside a loop,
# so return an error once you detect it.
# - Go through all types again and, now that all type aliases are eliminated and point
# at the right type definition, eliminate any name type references left by replacing them
# with a pointer to the right type.
# This implementation is not optimized at all, but It Just Works(TM) and we found it easier
# to follow than the one in the book.
if not check_name_uniqueness(declaration.type_dec_list):
raise SemanticError(
"All names in the type declaration block must be unique",
declaration.position,
)
for type_dec in declaration.type_dec_list:
type_env.add(type_dec.name, NameType(type_dec.name))
for type_dec in declaration.type_dec_list:
type_env.add(type_dec.name, translate_type(type_env,
type_dec.type))
for type_dec in declaration.type_dec_list:
if simplify_type_aliases(type_dec.name, type_env, set()) is None:
raise SemanticError(
f"Cyclic type definition found involving type {type_dec.name}",
type_dec.position,
)
for type_dec in declaration.type_dec_list:
type_definition = type_env.find(type_dec.name)
eliminate_name_types(type_definition, type_env)
return no_op_expression()
else:
raise SemanticError("Unknown declaration kind", declaration.position)
def translate_expression(
value_env: SymbolTable[EnvironmentEntry],
type_env: SymbolTable[Type],
level: RealLevel,
expression: ast.Expression,
break_label: Optional[TempLabel],
) -> TypedExpression:
if isinstance(expression, ast.VarExp):
# Variable name: Translate the variable and return that value.
return translate_variable(value_env, type_env, level, expression.var)
if isinstance(expression, ast.NilExp):
# Nil constant: Return nil type.
return TypedExpression(IRT.nil_expression(), NilType())
if isinstance(expression, ast.IntExp):
# Integer constant: Return integer type.
return TypedExpression(IRT.integer_expression(expression.int),
IntType())
if isinstance(expression, ast.StringExp):
# String constant: Return string type.
return TypedExpression(IRT.string_expression(expression.string),
StringType())
if isinstance(expression, ast.CallExp):
# Function call: Look up the function name, check the types of the parameters and return
# its return value type.
func_value = value_env.find(expression.func)
if func_value is None:
raise SemanticError(f"Undefined function {expression.func}",
expression.position)
if not isinstance(func_value, FunctionEntry):
raise SemanticError(
f"Non-function value {expression.func} is not callable",
expression.position,
)
if len(expression.args) != len(func_value.formals):
raise SemanticError(
f"Wrong number of arguments in function call to {expression.func},"
+
f" {len(func_value.formals)} expected, but {len(expression.args)} given",
expression.position,
)
translated_arguments = []
for arg_position in range(len(expression.args)):
trans_exp = translate_expression(value_env, type_env, level,
expression.args[arg_position],
break_label)
translated_arguments.append(trans_exp.expression)
if not are_types_equal(func_value.formals[arg_position],
trans_exp.type):
raise SemanticError(
f"Wrong type for argument in position {arg_position}" +
f" in call to {expression.func}",
expression.position,
)
return TypedExpression(
IRT.call_expression(func_value.label, func_value.level, level,
translated_arguments),
func_value.result,
)
if isinstance(expression, ast.OpExp):
# Operation: If an arithmetic operation, check if both values are Integers.
# If an in/equality comparison, check if both values have the same type.
# If an order comparison, check if both values are either Integers or Strings.
left = translate_expression(value_env, type_env, level,
expression.left, break_label)
right = translate_expression(value_env, type_env, level,
expression.right, break_label)
if expression.oper in (
ast.Oper.plus,
ast.Oper.minus,
ast.Oper.times,
ast.Oper.divide,
):
if not isinstance(left.type, IntType):
raise SemanticError(
"Left arithmetic operand must be an Integer",
expression.left.position,
)
if not isinstance(right.type, IntType):
raise SemanticError(
"Right arithmetic operand must be an Integer",
expression.right.position,
)
intermediate_expression = IRT.arithmetic_operation_expression(
expression.oper, left.expression, right.expression)
elif expression.oper in (
ast.Oper.eq,
ast.Oper.neq,
ast.Oper.lt,
ast.Oper.le,
ast.Oper.gt,
ast.Oper.ge,
):
if not are_types_equal(left.type, right.type):
raise SemanticError(
"Values must be of the same type to test for equality or order",
expression.position,
)
if expression.oper in (
ast.Oper.lt,
ast.Oper.le,
ast.Oper.gt,
ast.Oper.ge,
) and not (are_types_equal(left.type, IntType())
or are_types_equal(left.type, StringType())):
raise SemanticError(
"Values must be Integers or Strings to compare their order",
expression.position,
)
if are_types_equal(left.type, StringType()):
intermediate_expression = IRT.string_conditional_operation_expression(
expression.oper, left.expression, right.expression)
else:
intermediate_expression = IRT.conditional_operation_expression(
expression.oper, left.expression, right.expression)
else:
raise SemanticError("Unknown operator", expression.position)
return TypedExpression(intermediate_expression, IntType())
if isinstance(expression, ast.RecordExp):
# Record creation: Check the type is a record type, that only and all its defined fields
# are declared and that all their associated expressions have the declared type.
trans_typ = type_env.find(expression.type)
if trans_typ is None:
raise SemanticError(
f"Undefined record type {expression.type}",
expression.position,
)
if not isinstance(trans_typ, RecordType):
raise SemanticError(
f"Trying to create a record of type {expression.type}, which is not a record type",
expression.position,
)
checked_fields = {}
for exp_field in expression.fields:
if exp_field.name in checked_fields:
raise SemanticError(
f"Repeated field assignment for field {exp_field.name} in record creation",
exp_field.position,
)
found_field = False
expected_field_type = None
for type_field in trans_typ.fields:
if type_field.name == exp_field.name:
found_field = True
expected_field_type = type_field.type
break
if not found_field:
raise SemanticError(
f"Unknown field {exp_field.name} in record creation",
exp_field.position,
)
trans_exp = translate_expression(value_env, type_env, level,
exp_field.exp, break_label)
checked_fields[exp_field.name] = trans_exp.expression
if not are_types_equal(expected_field_type, trans_exp.type):
raise SemanticError(
f"Assigning value of a wrong type to field {exp_field.name} in record creation",
exp_field.exp.position,
)
if len(checked_fields) < len(trans_typ.fields):
raise SemanticError(
"Missing field assignment in record creation",
expression.position,
)
ordered_field_expressions = [
checked_fields[field.name] for field in trans_typ.fields
]
return TypedExpression(
IRT.record_expression(ordered_field_expressions), trans_typ)
if isinstance(expression, ast.SeqExp):
# Sequence of expressions: Evaluate each of them and return the type of the last one.
if len(expression.seq) == 0:
return translate_expression(
value_env,
type_env,
level,
ast.EmptyExp(expression.position),
break_label,
)
translated_expressions = []
last_expression_type = VoidType()
for seq_expression in expression.seq:
trans_exp = translate_expression(value_env, type_env, level,
seq_expression, break_label)
translated_expressions.append(trans_exp.expression)
last_expression_type = trans_exp.type
return TypedExpression(IRT.sequence_expression(translated_expressions),
last_expression_type)
if isinstance(expression, ast.AssignExp):
# Assignment: Look up the l-value, make sure it's not a loop variable and that the
# expression and l-value types match.
if isinstance(expression.var, ast.SimpleVar):
var_entry = value_env.find(expression.var.sym)
if var_entry is None:
raise SemanticError(
f"Trying to assign a value to undefined variable {expression.var.sym}",
expression.var.position,
)
if isinstance(var_entry,
VariableEntry) and not var_entry.is_editable:
raise SemanticError(
f"For loop variable {expression.var.sym} is not assignable",
expression.var.position,
)
trans_var = translate_variable(value_env, type_env, level,
expression.var)
trans_exp = translate_expression(value_env, type_env, level,
expression.exp, break_label)
if not are_types_equal(trans_var.type, trans_exp.type):
raise SemanticError(
"Trying to assign a value to a variable of a different type",
expression.position,
)
return TypedExpression(
IRT.assignment_expression(trans_var.expression,
trans_exp.expression),
VoidType(),
)
if isinstance(expression, ast.IfExp):
# If: Check the conditional expression returns an Integer type.
# If it only has a then branch, then check it produces no value and return no value.
# If it also has an else branch. make sure both produce the same type and return it.
trans_test = translate_expression(value_env, type_env, level,
expression.test, break_label)
if not isinstance(trans_test.type, IntType):
raise SemanticError(
"The condition of an If expression must be an Integer",
expression.test.position,
)
trans_then = translate_expression(value_env, type_env, level,
expression.then_do, break_label)
if expression.else_do is None:
if not isinstance(trans_then.type, VoidType):
raise SemanticError(
"Then branch of an If expression must produce no value" +
" when there is no Else branch",
expression.then_do.position,
)
return TypedExpression(
IRT.if_expression(trans_test.expression, trans_then.expression,
None),
VoidType(),
)
trans_else = translate_expression(value_env, type_env, level,
expression.else_do, break_label)
if not are_types_equal(trans_then.type, trans_else.type):
raise SemanticError(
"Then and Else branches of an If expression must return values of the same type",
expression.position,
)
# Special check in case one of the branches returns NilType and the other a RecordType.
# In that case, we should return the RecordType since it's the most generic one.
if isinstance(trans_then.type, NilType):
returned_type = trans_else.type
else:
returned_type = trans_then.type
return TypedExpression(
IRT.if_expression(trans_test.expression, trans_then.expression,
trans_else.expression),
returned_type,
)
if isinstance(expression, ast.WhileExp):
# While: Check that the condition is an Integer and that the body produces no value.
trans_test = translate_expression(value_env, type_env, level,
expression.test, break_label)
if not isinstance(trans_test.type, IntType):
raise SemanticError(
"The condition of a While expression must be an Integer",
expression.position,
)
value_env.begin_scope(True)
type_env.begin_scope(True)
new_break_label = TempManager.new_label()
trans_body = translate_expression(value_env, type_env, level,
expression.body, new_break_label)
if not isinstance(trans_body.type, VoidType):
raise SemanticError("While body must produce no value",
expression.body.position)
value_env.end_scope()
type_env.end_scope()
return TypedExpression(
IRT.while_expression(trans_test.expression, trans_body.expression,
new_break_label),
VoidType(),
)
if isinstance(expression, ast.BreakExp):
# Break: Make sure that the closest scope start is a While or a For loop.
if not value_env.is_closest_scope_a_loop():
raise SemanticError(
"Break expression must be inside a For or While loop",
expression.position,
)
return TypedExpression(IRT.break_expression(break_label), VoidType())
if isinstance(expression, ast.ForExp):
# For: Check that ends of the for variable iteration are Integers. Then add a non editable
# Integer variable to the value env and evaluate the body, making sure it produces no value.
trans_lo = translate_expression(value_env, type_env, level,
expression.lo, break_label)
if not isinstance(trans_lo.type, IntType):
raise SemanticError(
"Starting value for loop variable in a For expression must be an Integer",
expression.lo.position,
)
trans_hi = translate_expression(value_env, type_env, level,
expression.hi, break_label)
if not isinstance(trans_hi.type, IntType):
raise SemanticError(
"Ending value for loop variable in a For expression must be an Integer",
expression.hi.position,
)
value_env.begin_scope(True)
type_env.begin_scope(True)
new_break_label = TempManager.new_label()
loop_variable_access = level.alloc_local(expression.escape)
value_env.add(expression.var,
VariableEntry(loop_variable_access, IntType(), False))
trans_body = translate_expression(value_env, type_env, level,
expression.body, new_break_label)
if not isinstance(trans_body.type, VoidType):
raise SemanticError("For body must produce no value",
expression.body.position)
value_env.end_scope()
type_env.end_scope()
return TypedExpression(
IRT.for_expression(
IRT.simple_variable(loop_variable_access, level),
trans_lo.expression,
trans_hi.expression,
trans_body.expression,
new_break_label,
),
VoidType(),
)
if isinstance(expression, ast.LetExp):
# Let: Go through all declarations and then evaluate the body of the expression. The return
# type is the one of the last expression in the body (or Void if there are none)
value_env.begin_scope()
type_env.begin_scope()
translated_declarations = []
for declaration in expression.decs.declaration_list:
translated_declarations.append(
translate_declaration(value_env, type_env, declaration, level,
break_label))
trans_exp = translate_expression(value_env, type_env, level,
expression.body, break_label)
value_env.end_scope()
type_env.end_scope()
return TypedExpression(
IRT.let_expression(translated_declarations, trans_exp.expression),
trans_exp.type,
)
if isinstance(expression, ast.ArrayExp):
# Array creation: Check that the declared type is an array type, that the size is an Integer
# and that the initial value is of the type of the elements of the array.
trans_typ = type_env.find(expression.type)
if trans_typ is None:
raise SemanticError(
f"Undefined array type {expression.type}",
expression.position,
)
if not isinstance(trans_typ, ArrayType):
raise SemanticError(
f"Trying to create an array of type {expression.type}, which is not an array type",
expression.position,
)
trans_size = translate_expression(value_env, type_env, level,
expression.size, break_label)
if not isinstance(trans_size.type, IntType):
raise SemanticError("Array size must be an Integer",
expression.size.position)
trans_init = translate_expression(value_env, type_env, level,
expression.init, break_label)
if not are_types_equal(trans_typ.type, trans_init.type):
raise SemanticError(
"Array initial value must be of its declared type",
expression.init.position,
)
return TypedExpression(
IRT.array_expression(trans_size.expression, trans_init.expression),
trans_typ,
)
if isinstance(expression, ast.EmptyExp):
return TypedExpression(IRT.empty_expression(), VoidType())
raise SemanticError("Unknown expression kind", expression.position)
def add_new_false_label(statements: List[Statement]):
new_false_label = TempManager.new_label()
statements[-1].false = new_false_label
statements.append(Label(new_false_label))
statements.append(Jump(Name(new_false_label), [new_false_label]))