def eliminate_dead_code(block):
"""
Dead code elimination:
TODO: example...
The algorithm used is as follows:
- Traverse through the statements in reverse order.
- If the statement definition is dead, remove it. A variable is dead if it
is not used in the rest of the block, and is not in the `out' set of the
block.
"""
changed = False
for n, s in enumerate(block):
for reg in s.get_def():
if is_reg_dead_after(reg, block, n):
# Statement is redefined later, so this statement is useless
if block.verbose:
s.stype = 'comment'
s.options['block'] = False
s.set_message(' dead register %s' % reg)
s.name = ' Dead:\t%s\t%s' % (s.name, ','.join(map(str, s)))
else:
s.remove = True
changed = True
if not block.verbose:
block.apply_filter(lambda s: not hasattr(s, 'remove'))
return changed
def find_free_reg(block, start):
"""Find a temporary register that is free in a given list of statements."""
for i in xrange(8, 16):
tmp = '$%d' % i
if is_reg_dead_after(tmp, block, start):
return tmp
raise Exception('No temporary register is available.')