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Add a dominator analysis.

This commit is contained in:
whitequark 2015-07-18 20:48:52 +03:00
parent 224a93fde3
commit 603d49dffa
3 changed files with 59 additions and 0 deletions

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@ -0,0 +1 @@
from .domination import DominatorTree

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@ -0,0 +1,48 @@
"""
:class:`DominatorTree` computes the dominance relation over
control flow graphs.
See http://www.cs.colostate.edu/~mstrout/CS553/slides/lecture04.pdf.
"""
from functools import reduce, cmp_to_key
# Key Idea
# If a node dominates all
# predecessors of node n, then it
# also dominates node n
class DominatorTree:
def __init__(self, func):
entry = func.get_entry()
self.dominated_by = { entry: {entry} }
for block in func.basic_blocks:
if block != entry:
self.dominated_by[block] = set(func.basic_blocks)
predecessors = {block: block.predecessors() for block in func.basic_blocks}
while True:
changed = False
for block in func.basic_blocks:
if block == entry:
continue
if not any(predecessors[block]):
# Unreachable blocks are dominated by everything
continue
new_dominated_by = {block}.union(
reduce(lambda a, b: a.intersection(b),
(self.dominated_by[pred] for pred in predecessors[block])))
if new_dominated_by != self.dominated_by[block]:
self.dominated_by[block] = new_dominated_by
changed = True
if not changed:
break
def in_domination_order(self):
blocks = list(self.dominated_by.keys())
blocks.sort(key=cmp_to_key(lambda a, b: a in self.dominated_by[b]))
return blocks

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@ -335,6 +335,9 @@ class BasicBlock(NamedValue):
return "\n".join(lines)
def __repr__(self):
return "<BasicBlock '{}'>".format(self.name)
class Argument(NamedValue):
"""
A function argument.
@ -383,6 +386,13 @@ class Function:
basic_block._detach()
self.basic_blocks.remove(basic_block)
def get_entry(self):
assert any(self.basic_blocks)
return self.basic_blocks[0]
def instructions(self):
for basic_block in self.basic_blocks:
yield from iter(basic_block.instructions)
def __str__(self):
printer = types.TypePrinter()