def _handle_Load(self, expr_idx: int, expr: Load, stmt_idx: int,
stmt: Statement, block: Optional[Block]):
addr = self._handle_expr(0, expr.addr, stmt_idx, stmt, block)
if addr is not None and addr is not expr.addr:
new_expr = expr.copy()
new_expr.addr = addr
return new_expr
return None
def _unify_local_variables(self) -> bool:
"""
Find variables that are definitely equivalent and then eliminate unnecessary copies.
"""
simplified = False
prop = self._compute_propagation()
if not prop.equivalence:
return simplified
addr_and_idx_to_block: Dict[Tuple[int, int], Block] = {}
for block in self.func_graph.nodes():
addr_and_idx_to_block[(block.addr, block.idx)] = block
equivalences: Dict[Any, Set[Equivalence]] = defaultdict(set)
atom_by_loc = set()
for eq in prop.equivalence:
equivalences[eq.atom1].add(eq)
atom_by_loc.add((eq.codeloc, eq.atom1))
# sort keys to ensure a reproducible result
sorted_loc_and_atoms = sorted(atom_by_loc, key=lambda x: x[0])
for _, atom in sorted_loc_and_atoms:
eqs = equivalences[atom]
if len(eqs) > 1:
continue
eq = next(iter(eqs))
# Acceptable equivalence classes:
#
# stack variable == register
# register variable == register
# stack variable == Conv(register, M->N)
# global variable == register
#
# Equivalence is generally created at assignment sites. Therefore, eq.atom0 is the definition and
# eq.atom1 is the use.
the_def = None
if isinstance(eq.atom0, SimMemoryVariable
): # covers both Stack and Global variables
if isinstance(eq.atom1, Register):
# stack_var == register or global_var == register
to_replace = eq.atom1
to_replace_is_def = False
elif isinstance(eq.atom1, Convert) and isinstance(
eq.atom1.operand, Register):
# stack_var == Conv(register, M->N)
to_replace = eq.atom1.operand
to_replace_is_def = False
else:
continue
elif isinstance(eq.atom0, Register):
if isinstance(eq.atom1, Register):
# register == register
if self.project.arch.is_artificial_register(
eq.atom0.reg_offset, eq.atom0.size):
to_replace = eq.atom0
to_replace_is_def = True
else:
to_replace = eq.atom1
to_replace_is_def = False
else:
continue
else:
continue
# find the definition of this register
rd = self._compute_reaching_definitions()
if to_replace_is_def:
# find defs
defs = []
for def_ in rd.all_definitions:
if def_.codeloc == eq.codeloc:
if isinstance(to_replace, SimStackVariable):
if isinstance(def_.atom, atoms.MemoryLocation) \
and isinstance(def_.atom.addr, atoms.SpOffset):
if to_replace.offset == def_.atom.addr.offset:
defs.append(def_)
elif isinstance(to_replace, Register):
if isinstance(def_.atom, atoms.Register) \
and to_replace.reg_offset == def_.atom.reg_offset:
defs.append(def_)
if len(defs) != 1:
continue
the_def = defs[0]
else:
# find uses
defs = rd.all_uses.get_uses_by_location(eq.codeloc)
if len(defs) != 1:
# there are multiple defs for this register - we do not support replacing all of them
continue
for def_ in defs:
def_: Definition
if isinstance(
def_.atom, atoms.Register
) and def_.atom.reg_offset == to_replace.reg_offset:
# found it!
the_def = def_
break
if the_def is None:
continue
if isinstance(the_def.codeloc, ExternalCodeLocation):
# this is a function argument. we enter a slightly different logic and try to eliminate copies of this
# argument if
# (a) the on-stack copy of it has never been modified in this function
# (b) the function argument register has never been updated.
# TODO: we may loosen requirement (b) once we have real register versioning in AIL.
defs = [
def_ for def_ in rd.all_definitions
if def_.codeloc == eq.codeloc
]
all_uses_with_def = None
replace_with = None
remove_initial_assignment = None
if defs and len(defs) == 1:
stackvar_def = defs[0]
if isinstance(stackvar_def.atom, atoms.MemoryLocation) \
and isinstance(stackvar_def.atom.addr, SpOffset):
# found the stack variable
# Make sure there is no other write to this location
if any((def_ != stackvar_def
and def_.atom == stackvar_def.atom)
for def_ in rd.all_definitions
if isinstance(def_.atom, atoms.MemoryLocation)):
continue
# Make sure the register is never updated across this function
if any((def_ != the_def and def_.atom == the_def.atom)
for def_ in rd.all_definitions
if isinstance(def_.atom, atoms.Register)):
continue
# find all its uses
all_stackvar_uses: Set[Tuple[CodeLocation, Any]] = set(
rd.all_uses.get_uses_with_expr(stackvar_def))
all_uses_with_def = set()
should_abort = False
for use in all_stackvar_uses:
used_expr = use[1]
if used_expr is not None and used_expr.size != stackvar_def.size:
should_abort = True
break
all_uses_with_def.add((stackvar_def, use))
if should_abort:
continue
#to_replace = Load(None, StackBaseOffset(None, self.project.arch.bits, eq.atom0.offset),
# eq.atom0.size, endness=self.project.arch.memory_endness)
replace_with = eq.atom1
remove_initial_assignment = True
if all_uses_with_def is None:
continue
else:
if isinstance(eq.atom0, SimStackVariable):
# create the memory loading expression
new_idx = None if self._ail_manager is None else next(
self._ail_manager.atom_ctr)
replace_with = Load(
new_idx,
StackBaseOffset(None, self.project.arch.bits,
eq.atom0.offset),
eq.atom0.size,
endness=self.project.arch.memory_endness)
elif isinstance(eq.atom0, SimMemoryVariable) and isinstance(
eq.atom0.addr, int):
# create the memory loading expression
new_idx = None if self._ail_manager is None else next(
self._ail_manager.atom_ctr)
replace_with = Load(
new_idx,
Const(None, None, eq.atom0.addr,
self.project.arch.bits),
eq.atom0.size,
endness=self.project.arch.memory_endness)
elif isinstance(eq.atom0, Register):
if isinstance(eq.atom1, Register):
if self.project.arch.is_artificial_register(
eq.atom0.reg_offset, eq.atom0.size):
replace_with = eq.atom1
else:
replace_with = eq.atom0
else:
raise RuntimeError("Unsupported atom1 type %s." %
type(eq.atom1))
else:
raise RuntimeError("Unsupported atom0 type %s." %
type(eq.atom0))
to_replace_def = the_def
# find all uses of this definition
# we make a copy of the set since we may touch the set (uses) when replacing expressions
all_uses: Set[Tuple[CodeLocation, Any]] = set(
rd.all_uses.get_uses_with_expr(to_replace_def))
# make sure none of these uses are phi nodes (depends on more than one def)
all_uses_with_unique_def = set()
for use_and_expr in all_uses:
use_loc, used_expr = use_and_expr
defs_and_exprs = rd.all_uses.get_uses_by_location(
use_loc, exprs=True)
filtered_defs = {
def_
for def_, expr_ in defs_and_exprs if expr_ == used_expr
}
if len(filtered_defs) == 1:
all_uses_with_unique_def.add(use_and_expr)
else:
# optimization: break early
break
if len(all_uses) != len(all_uses_with_unique_def):
# only when all uses are determined by the same definition will we continue with the simplification
continue
all_uses_with_def = set((to_replace_def, use_and_expr)
for use_and_expr in all_uses)
remove_initial_assignment = False # expression folding will take care of it
if not all_uses_with_def:
# definitions without uses may simply be our data-flow analysis being incorrect. do not remove them.
continue
# TODO: We can only replace all these uses with the stack variable if the stack variable isn't
# TODO: re-assigned of a new value. Perform this check.
# replace all uses
all_uses_replaced = True
for def_, use_and_expr in all_uses_with_def:
u, used_expr = use_and_expr
if u == eq.codeloc:
# skip the very initial assignment location
continue
old_block = addr_and_idx_to_block.get(
(u.block_addr, u.block_idx), None)
if old_block is None:
continue
# if there is an updated block, use it
the_block = self.blocks.get(old_block, old_block)
stmt: Statement = the_block.statements[u.stmt_idx]
replace_with_copy = replace_with.copy()
if to_replace.size != replace_with_copy.size:
new_idx = None if self._ail_manager is None else next(
self._ail_manager.atom_ctr)
replace_with_copy = Convert(
new_idx,
replace_with_copy.bits,
to_replace.bits,
False,
replace_with_copy,
)
r, new_block = self._replace_expr_and_update_block(
the_block, u.stmt_idx, stmt, def_, u, used_expr,
replace_with_copy)
if r:
self.blocks[old_block] = new_block
else:
# failed to replace a use - we need to keep the initial assignment!
all_uses_replaced = False
simplified |= r
if all_uses_replaced and remove_initial_assignment:
# the initial statement can be removed
self._assignments_to_remove.add(eq.codeloc)
if simplified:
self._clear_cache()
return simplified