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Change idom() method to get_a_dom(), update uses, and documentation.

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This commit is contained in:
Jon Riehl 2013-05-08 18:23:55 -05:00
commit 8787af154e
1 changed files with 20 additions and 10 deletions
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30
llpython/control_flow.py
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@ -101,15 +101,25 @@ class ControlFlowGraph (object):
if hasattr(self, 'reaching_definitions'):
del self.reaching_definitions
def idom (self, block):
'''Compute the immediate dominator (idom) of the given block
key. Returns None if the block has no in edges.
def get_a_dom (self, block):
'''Find an immediate predecessor of the given block such that
the predecessor is either the only entry point, or the
precessor is not in its own dominance set (a non-loop
predecessor). Returns None if the given block has no
predecessor.
Note that in the case where there are multiple immediate
dominators (a join after a non-loop branch), this returns one
of the predecessors, but is not guaranteed to reliably select
one over the others (depends on the ordering of the set type
iterator).'''
Note that in the case where there are multiple dominators (a
join after a non-loop branch), this returns one of the
predecessors, but is not guaranteed to reliably select one
over the others (depends on the ordering of the set type
iterator).
Note: Previously, this method's documentation erroneously
identified the return value as being the immediate dominator
of the input block. Instead, it attempts to find a "nearby"
dominator. Normally, the immediate dominator of a join is the
least upperbound of the closed immediate dominance
relationship over its two entrants.'''
preds = self.blocks_in[block]
npreds = len(preds)
if npreds == 0:
@ -143,7 +153,7 @@ class ControlFlowGraph (object):
ret_val = {}
for pred in preds:
ret_val[pred] = self.block_writes_to_writer_map(pred)
crnt = self.idom(pred)
crnt = self.get_a_dom(pred)
while crnt != None:
crnt_writer_map = self.block_writes_to_writer_map(crnt)
# This order of update favors the first definitions
@ -151,7 +161,7 @@ class ControlFlowGraph (object):
# visits blocks in reverse execution order.
crnt_writer_map.update(ret_val[pred])
ret_val[pred] = crnt_writer_map
crnt = self.idom(crnt)
crnt = self.get_a_dom(crnt)
if not has_memoized:
self.reaching_definitions = {}
self.reaching_definitions[block] = ret_val