class Find_LICM_Candidates(SyntaxVisitor):
def __init__(self):
SyntaxVisitor.__init__(self)
self.mutable_types = None
self.volatile_vars = ScopedSet()
self.depends_on = {}
self.safe_to_move = set([])
self.curr_block_id = None
self.block_contains_return = set([])
self.may_alias = None
def visit_fn(self, fn):
self.volatile_vars.push(fn.arg_names)
self.may_alias = may_alias(fn)
SyntaxVisitor.visit_fn(self, fn)
return self.safe_to_move
def mark_safe_assignments(self, block, volatile_set):
for stmt in block:
klass = stmt.__class__
if klass is Assign and \
stmt.lhs.__class__ is Var:
name = stmt.lhs.name
dependencies = self.depends_on.get(name, set([]))
volatile = name in volatile_set or \
any(d in volatile_set for d in dependencies)
if not volatile:
self.safe_to_move.add(name)
# just in case there are Returns in nested control flow
# we should probably avoid changing the performance characteristics
# by pulling out statements which will never run
elif klass is If:
if id(stmt.true) in self.block_contains_return or \
id(stmt.false) in self.block_contains_return:
break
elif klass is While:
if id(stmt.body) in self.block_contains_return:
break
elif klass is Return:
break
def mark_curr_block_returns(self):
self.block_contains_return.add(self.curr_block_id)
def does_block_return(self, block):
return id(block) in self.block_contains_return
def visit_Return(self, stmt):
self.mark_curr_block_returns()
def visit_block(self, stmts):
self.curr_block_id = id(stmts)
SyntaxVisitor.visit_block(self, stmts)
def visit_merge(self, merge, both_branches = True):
pass
def visit_ForLoop(self, stmt):
self.volatile_vars.push(stmt.merge.keys())
self.volatile_vars.add(stmt.var.name)
SyntaxVisitor.visit_ForLoop(self, stmt)
if self.does_block_return(stmt.body):
self.block_contains_return()
volatile_in_scope = self.volatile_vars.pop()
self.mark_safe_assignments(stmt.body, volatile_in_scope)
def visit_While(self, stmt):
self.volatile_vars.push(stmt.merge.keys())
SyntaxVisitor.visit_While(self, stmt)
if self.does_block_return(stmt.body):
self.block_contains_return()
volatile_in_scope = self.volatile_vars.pop()
self.mark_safe_assignments(stmt.body, volatile_in_scope)
def visit_Var(self, expr):
self.volatile_vars.add(expr.name)
def visit_If(self, stmt):
self.volatile_vars.push(stmt.merge.keys())
self.visit_expr(stmt.cond)
SyntaxVisitor.visit_If(self, stmt)
if self.does_block_return(stmt.true) or self.does_block_return(stmt.false):
self.mark_curr_block_returns()
volatile_in_scope = self.volatile_vars.pop()
self.mark_safe_assignments(stmt.true, volatile_in_scope)
self.mark_safe_assignments(stmt.false, volatile_in_scope)
def is_mutable_alloc(self, expr):
c = expr.__class__
return c is Alloc or \
c is AllocArray or \
c is Array or \
c is ArrayView or \
c is Slice or \
(c is Struct and not isinstance(expr.type, ImmutableT))
def visit_Assign(self, stmt):
lhs_names = collect_binding_names(stmt.lhs)
rhs_names = collect_var_names(stmt.rhs)
for x in lhs_names:
dependencies = self.depends_on.get(x, set([]))
dependencies.update(rhs_names)
self.depends_on[x] = dependencies
if any(x in self.volatile_vars for x in rhs_names):
self.volatile_vars.update(lhs_names)
elif self.is_mutable_alloc(stmt.rhs):
if len(lhs_names) == 1 and \
len(self.may_alias.get(lhs_names[0], [])) <= 1:
pass
else:
self.volatile_vars.update(lhs_names)
# mark any array writes as volatile
if stmt.lhs.__class__ is Index:
assert stmt.lhs.value.__class__ is Var, \
"Expected LHS array to be variable but instead got %s" % stmt
self.volatile_vars.add(stmt.lhs.value.name)