def while_loop(ast, i, o):
'''Reachability for a while loop.
L: while (true) S
In[S] = In[L]
Out[L] = No
L: while (false) S
In[S] = No
Out[L] = In[L]
L: while (E) S
In[S] = In[L]
Out[L] = In[L]'''
# Make sure that the while expression is a Boolean.
if ast.expression.expr_type != ast_type.ASTType.ASTBoolean:
raise reachability.ReachabilityError('While expression is not a boolean.')
# The first two cases, where the expression has been resolved to True or
# False.
if ast.expression.const_value is not None:
if ast.expression.const_value:
# Though it doesn't affect our return value, check the children
# statements for reachability.
if ast.statement:
reachability.check_block_or_statement(ast.statement, in_value=o)
return o, NO
else:
# This while loop is unreachable.
return NO, o
# The last case, where our expression is not a constant.
if ast.statement is not None:
reachability.check_block_or_statement(ast.statement, in_value=o)
return o, o
def if_statement(ast, i, o):
'''Reachability for an IF statement.
L: if (E) S_1 else S_2
In[S_1] = In[L]
In[S_2] = In[L]
Out[L] = Out[S_1] or Out[S_2]'''
if ast.if_statement is not None:
if_in, if_out = reachability.check_block_or_statement(
ast.if_statement, in_value=o)
if ast.else_statement is not None:
else_in, else_out = reachability.check_block_or_statement(
ast.else_statement, in_value=o)
# The out value is the OR between the if and else out values.
new_out = (MAYBE if if_out == MAYBE or else_out == MAYBE else NO)
return o, new_out
# If statement with no else:
# Out[L] = Out[S_1] OR In[L] = In[L] = o
return o, o
def for_loop(ast, i, o):
'''Reachability for a for loop.
L: for (S_1; false; S_2) S_3
In[S] = No
Out[L] = In[L]
L: for (S_1; true; S_2) S_3
In[S] = In[L]
Out[L] = No
L: for (S_1; E; S_2) S_3
In[S] = In[L]
Out[L] = In[L]'''
has_expr = (ast.expression is not None)
# Make sure the for expression is a Boolean if it exists.
if has_expr and ast.expression.expr_type != ast_type.ASTType.ASTBoolean:
raise reachability.ReachabilityError('For expression is not a boolean.')
# The first two cases, where the condition expression is a constant.
if has_expr and ast.expression.const_value is not None:
if ast.expression.const_value:
# Check all children statements for reachability.
if ast.init:
reachability.check_block_or_statement(ast.init, in_value=o)
if ast.update:
reachability.check_block_or_statement(ast.update, in_value=o)
if ast.statement:
reachability.check_block_or_statement(ast.statement, in_value=o)
return o, NO
else:
# The for loop is unreachable.
return NO, o
# Our expression is not a constant.
# Check all children statements for reachability.
if ast.init:
reachability.check_block_or_statement(ast.init, in_value=o)
if ast.update:
reachability.check_block_or_statement(ast.update, in_value=o)
if ast.statement:
reachability.check_block_or_statement(ast.statement, in_value=o)
# If there is no expression, the for loop runs forever.
if not has_expr:
return o, NO
return o, o
