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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'): if hasattr(self, 'reaching_definitions'):
del self.reaching_definitions del self.reaching_definitions
def idom (self, block): def get_a_dom (self, block):
'''Compute the immediate dominator (idom) of the given block '''Find an immediate predecessor of the given block such that
key. Returns None if the block has no in edges. 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 Note that in the case where there are multiple dominators (a
dominators (a join after a non-loop branch), this returns one join after a non-loop branch), this returns one of the
of the predecessors, but is not guaranteed to reliably select predecessors, but is not guaranteed to reliably select one
one over the others (depends on the ordering of the set type over the others (depends on the ordering of the set type
iterator).''' 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] preds = self.blocks_in[block]
npreds = len(preds) npreds = len(preds)
if npreds == 0: if npreds == 0:
@ -143,7 +153,7 @@ class ControlFlowGraph (object):
ret_val = {} ret_val = {}
for pred in preds: for pred in preds:
ret_val[pred] = self.block_writes_to_writer_map(pred) ret_val[pred] = self.block_writes_to_writer_map(pred)
crnt = self.idom(pred) crnt = self.get_a_dom(pred)
while crnt != None: while crnt != None:
crnt_writer_map = self.block_writes_to_writer_map(crnt) crnt_writer_map = self.block_writes_to_writer_map(crnt)
# This order of update favors the first definitions # This order of update favors the first definitions
@ -151,7 +161,7 @@ class ControlFlowGraph (object):
# visits blocks in reverse execution order. # visits blocks in reverse execution order.
crnt_writer_map.update(ret_val[pred]) crnt_writer_map.update(ret_val[pred])
ret_val[pred] = crnt_writer_map ret_val[pred] = crnt_writer_map
crnt = self.idom(crnt) crnt = self.get_a_dom(crnt)
if not has_memoized: if not has_memoized:
self.reaching_definitions = {} self.reaching_definitions = {}
self.reaching_definitions[block] = ret_val self.reaching_definitions[block] = ret_val