def _extract_loop_lifting_candidates(cfg, blocks):
"""
Returns a list of loops that are candidate for loop lifting
"""
# check well-formed-ness of the loop
def same_exit_point(loop):
"all exits must point to the same location"
outedges = set()
for k in loop.exits:
succs = set(x for x, _ in cfg.successors(k))
if not succs:
# If the exit point has no successor, it contains an return
# statement, which is not handled by the looplifting code.
# Thus, this loop is not a candidate.
return False
outedges |= succs
return len(outedges) == 1
def one_entry(loop):
"there is one entry"
return len(loop.entries) == 1
def cannot_yield(loop):
"cannot have yield inside the loop"
insiders = set(loop.body) | set(loop.entries) | set(loop.exits)
for blk in map(blocks.__getitem__, insiders):
for inst in blk.body:
if isinstance(inst, ir.Assign):
if isinstance(inst.value, ir.Yield):
return False
return True
return [loop for loop in find_top_level_loops(cfg)
if same_exit_point(loop) and one_entry(loop) and cannot_yield(loop)]
def _extract_loop_lifting_candidates(cfg, blocks):
"""
Returns a list of loops that are candidate for loop lifting
"""
# check well-formed-ness of the loop
def same_exit_point(loop):
"all exits must point to the same location"
outedges = set()
for k in loop.exits:
succs = set(x for x, _ in cfg.successors(k))
if not succs:
# If the exit point has no successor, it contains an return
# statement, which is not handled by the looplifting code.
# Thus, this loop is not a candidate.
return False
outedges |= succs
return len(outedges) == 1
def one_entry(loop):
"there is one entry"
return len(loop.entries) == 1
def cannot_yield(loop):
"cannot have yield inside the loop"
insiders = set(loop.body) | set(loop.entries) | set(loop.exits)
for blk in map(blocks.__getitem__, insiders):
for inst in blk.body:
if isinstance(inst, ir.Assign):
if isinstance(inst.value, ir.Yield):
return False
return True
return [loop for loop in find_top_level_loops(cfg)
if same_exit_point(loop) and one_entry(loop) and cannot_yield(loop)]
def _extract_loop_lifting_candidates(cfg, blocks):
"""
Returns a list of loops that are candidate for loop lifting
"""
# check well-formed-ness of the loop
def same_exit_point(loop):
"all exits must point to the same location"
outedges = set()
for k in loop.exits:
succs = set(x for x, _ in cfg.successors(k))
if not succs:
# If the exit point has no successor, it contains an return
# statement, which is not handled by the looplifting code.
# Thus, this loop is not a candidate.
_logger.debug("return-statement in loop.")
return False
outedges |= succs
ok = len(outedges) == 1
_logger.debug("same_exit_point=%s", ok)
return ok
def one_entry(loop):
"there is one entry"
ok = len(loop.entries) == 1
_logger.debug("one_entry=%s", ok)
return ok
def cannot_yield(loop):
"cannot have yield inside the loop"
insiders = set(loop.body) | set(loop.entries) | set(loop.exits)
for blk in map(blocks.__getitem__, insiders):
for inst in blk.body:
if isinstance(inst, ir.Assign):
if isinstance(inst.value, ir.Yield):
_logger.debug("has yield")
return False
_logger.debug("no yield")
return True
_logger.info('finding looplift candidates')
# the check for cfg.entry_point in the loop.entries is to prevent a bad
# rewrite where a prelude for a lifted loop would get written into block -1
# if a loop entry were in block 0
candidates = []
for loop in find_top_level_loops(cfg):
_logger.debug("top-level loop: %s", loop)
if (same_exit_point(loop) and one_entry(loop) and cannot_yield(loop)
and cfg.entry_point() not in loop.entries):
candidates.append(loop)
_logger.debug("add candidate: %s", loop)
return candidates
