# (C) Copyright 2015-2019 Sei Lisa. All rights reserved.
#
# This file is part of LSL PyOptimizer.
#
# LSL PyOptimizer is free software: you can redistribute it and/or
# modify it under the terms of the GNU General Public License as
# published by the Free Software Foundation, either version 3 of the
# License, or (at your option) any later version.
#
# LSL PyOptimizer is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with LSL PyOptimizer. If not, see .
# Dead Code Removal optimization
from lslopt import lslfuncs
from lslopt.lslcommon import nr
class deadcode(object):
def MarkReferences(self, node):
"""Marks each node it passes through as executed (X), and each variable
as read (R) (with count) and/or written (W) (with node where it is, or
False if written more than once) as appropriate. Traces execution to
determine if any part of the code is never executed.
"""
# The 'X' key, when present, indicates whether a node is executed.
# Its value means whether this instruction will proceed to the next
# (True: it will; False: it won't).
if hasattr(node, 'X'):
return node.X # branch already analyzed
nt = node.nt
child = node.ch
# Control flow statements
if nt == 'STSW':
node.X = False # Executed but path-breaking.
sym = self.symtab[0][node.name]
if not hasattr(self.tree[sym['Loc']], 'X'):
self.MarkReferences(self.tree[sym['Loc']])
return False
if nt == 'JUMP':
node.X = False # Executed but path-breaking.
sym = self.symtab[node.scope][node.name]
if 'R' in sym:
sym['R'] += 1
else:
sym['R'] = 1
return False
if nt == 'RETURN':
node.X = False # Executed but path-breaking.
if child:
self.MarkReferences(child[0])
return False
if nt == 'IF':
# "When you get to a fork in the road, take it."
node.X = None # provisional value, refined later
self.MarkReferences(child[0])
condnode = child[0]
if condnode.nt == 'CONST':
if lslfuncs.cond(condnode.value):
# TRUE - 'then' branch always executed.
node.X = self.MarkReferences(child[1])
return node.X
elif len(child) == 3:
# FALSE - 'else' branch always executed.
node.X = self.MarkReferences(child[2])
return node.X
# else fall through
else:
cont = self.MarkReferences(child[1])
if len(child) == 3:
if not cont:
cont = self.MarkReferences(child[2])
node.X = cont
return cont
self.MarkReferences(child[2])
node.X = True
return True
if nt == 'WHILE':
node.X = None # provisional value, refined later
self.MarkReferences(child[0])
if child[0].nt == 'CONST':
if lslfuncs.cond(child[0].value):
# Infinite loop - unless it returns, it stops
# execution. But it is executed itself.
self.MarkReferences(child[1])
node.X = False
return node.X
# else the inside isn't executed at all, so don't mark it
else:
self.MarkReferences(child[1])
node.X = True
return True
if nt == 'DO':
node.X = None # provisional value, refined later
if not self.MarkReferences(child[0]):
node.X = False
return False
self.MarkReferences(child[1])
# It proceeds to the next statement unless it's an infinite loop
node.X = not (child[1].nt == 'CONST' and lslfuncs.cond(child[1].value))
return node.X
if nt == 'FOR':
node.X = None # provisional value, refined later
self.MarkReferences(child[0])
self.MarkReferences(child[1])
if child[1].nt == 'CONST':
if lslfuncs.cond(child[1].value):
# Infinite loop - unless it returns, it stops
# execution. But it is executed itself.
node.X = False
self.MarkReferences(child[3])
self.MarkReferences(child[2]) # this can't stop execution
return node.X
# else the body and the iterator aren't executed at all, so
# don't mark them
node.X = True
else:
node.X = True
self.MarkReferences(child[3])
self.MarkReferences(child[2])
# Mark the EXPRLIST as always executed, but not the subexpressions.
# That forces the EXPRLIST (which is a syntactic requirement) to be
# kept, while still simplifying the contents properly.
child[2].X = True
return True
if nt == '{}':
# Go through each statement in turn. If one stops execution,
# continue reading until either we find a used label (and resume
# execution) or reach the end (and return False). Otherwise return
# True.
continues = True
node.X = None # provisional
for stmt in child:
if continues or stmt.nt == '@':
continues = self.MarkReferences(stmt)
node.X = continues
return continues
if nt == 'FNCALL':
node.X = None # provisional
sym = self.symtab[0][node.name]
fdef = self.tree[sym['Loc']] if 'Loc' in sym else None
for idx in xrange(len(child)-1, -1, -1):
# Each element is a "write" on the callee's parameter.
# E.g. f(integer a, integer b) { f(2,3); } means 2, 3 are
# writes to a and b.
# This has been eliminated, as it causes more trouble than
# it fixes.
self.MarkReferences(child[idx])
if fdef is not None:
psym = self.symtab[fdef.pscope][fdef.pnames[idx]]
#if 'W' in psym:
# psym['W'] = False
#else:
# psym['W'] = child[idx]
psym['W'] = False
if 'Loc' in sym:
if not hasattr(self.tree[sym['Loc']], 'X'):
self.MarkReferences(self.tree[sym['Loc']])
node.X = self.tree[sym['Loc']].X
else:
node.X = 'stop' not in sym
# Note that JUMP analysis is incomplete. To do it correctly, we
# should follow the jump right to its destination, in order to know
# if that branch leads to a RETURN or completely stops the event.
# With our code structure, following the JUMP is unfeasible.
# For that reason, we can't track whether a branch ends in RETURN
# or in something more powerful like a script reset, in order to
# propagate it through the function definition to the caller.
#
# In practice, this means that the caller can't distinguish this:
# fn() { return; }
# from this:
# fn() { llResetScript(); }
# and therefore, invocations of the function that are followed by
# code can't know whether that code is dead or not.
#
# What does that have to do with jumps? Well, imagine this:
# fn(integer x) { if (x) jump x1; else jump x2;
# @x1; return; @x2; llResetScript(); }
# What of the branches of if() is taken, depends on where the jumps
# lead to. Assuming the last one always is wrong, because it would
# mark in the caller code that may execute, as dead, e.g. here:
# fn2() { fn(); x = 1; }
return node.X
if nt == 'DECL':
sym = self.symtab[node.scope][node.name]
if child is not None:
sym['W'] = child[0]
else:
sym['W'] = nr(nt='CONST', t=node.t,
value=self.DefaultValues[node.t])
node.X = True
if child is not None:
if hasattr(child[0], 'orig'):
orig = child[0].orig
self.MarkReferences(orig)
child[0].X = orig.X
if orig.nt == 'LIST':
# Add fake writes to variables used in list elements in
# 'orig', so they don't get deleted (Issue #3)
for subnode in orig.ch:
if subnode.nt == 'IDENT':
# can only happen in globals
assert subnode.scope == 0
sym = self.symtab[0][subnode.name]
sym['W'] = False
self.tree[sym['Loc']].X = True
elif subnode.nt in ('VECTOR', 'ROTATION'):
for sub2node in subnode.ch:
if sub2node.nt == 'IDENT':
# can only happen in globals
assert sub2node.scope == 0
sym = self.symtab[0][sub2node.name]
sym['W'] = False
self.tree[sym['Loc']].X = True
else:
self.MarkReferences(child[0])
return True
# ---- Starting here, all node types return through the bottom
# (except '=').
node.X = None # provisional
if nt in self.assign_ops or nt in ('--V', '++V', 'V++', 'V--'):
ident = node.ch[0]
if ident.nt == 'FLD':
ident = ident.ch[0]
assert ident.nt == 'IDENT'
sym = self.symtab[ident.scope][ident.name]
if ident.scope == 0:
# Mark the global first.
self.MarkReferences(self.tree[sym['Loc']])
# In any case, this is at least the second write, so mark it as such
# (SSA would be a plus for this to be optimal)
sym['W'] = False
if nt == '=':
# Prevent the first node from being mistaken as a read, by
# recursing only on the RHS node.
self.MarkReferences(child[1])
node.X = True
return True
elif nt == 'FLD':
# Mark this variable as referenced by a Field (recursing will mark
# the ident as read later)
self.symtab[child[0].scope][child[0].name]['Fld'] = True
elif nt == 'IDENT':
sym = self.symtab[node.scope][node.name]
# Mark global if it's one.
if 'W' not in sym and node.scope == 0:
self.MarkReferences(self.tree[sym['Loc']])
# Increase read counter
if 'R' in sym:
sym['R'] += 1
else:
sym['R'] = 1
node.X = True
if child is not None:
for subnode in child:
self.MarkReferences(subnode)
return True
def OKtoRemoveSymbol(self, curnode):
"""If the given node's name must be simplified, that is, replaced or
deleted (deleted if declaration, replaced if identifier), it returns
the symbol table entry. Otherwise it returns False.
"""
# 'W':False means written more than once, i.e. not only in the
# declaration. Variables written more than once can't be
# simplified by this code.
# If not written more than once:
# For expressions:
# - Remove expressions read only once, replacing the value, but only
# if the readers are not fields of vectors or rotations, and if
# they are side-effect free.
# For constants:
# - Remove lists, vectors and rotations read only once.
# - Floats are removed if their value has no decimals or if
# used no more than N times (for some N).
# - Strings, keys and integers are just removed.
sym = self.symtab[curnode.scope][curnode.name]
if 'R' not in sym:
return sym # if not used, it can be removed
# Event parameters do not have 'W' in sym.
if 'W' not in sym:
return False
if sym['W'] is not False:
node = sym['W']
nt = node.nt
# This screws up swaps. See
# unit_tests/regression.suite/aggressive-local-removal.lsl
# It can't be done without a reliable CFG-based method (SSA or
# the like).
# while nt == 'IDENT':
# # Follow the chain of identifiers all the way to the original
# if self.symtab[node.scope][node.name].get('W', False) is False:
# return sym
# sym = self.symtab[node.scope][node.name]
# node = sym['W']
# nt = node.nt
if nt == 'CONST':
tcurnode = curnode.t
if tcurnode in ('integer', 'string', 'key'):
return sym
if tcurnode == 'float':
if sym['R'] <= 3 or type(node.value) == int:
return sym
elif tcurnode == 'vector' \
or tcurnode == 'list' and len(node.value) <= 3:
if sym['R'] <= 1:
return sym
elif tcurnode == 'rotation' \
or tcurnode == 'list' and len(node.value) <= 4:
if sym['R'] <= 1:
return sym
return False
# To replace expressions, they MUST be side-effect free, or they
# will be executed at a different time.
# Also, we can't safely replace expressions unless shrinknames is
# active. shrinknames assigns a different identifier to each
# variable, which avoids conflicts. Consider this scenario:
# integer i=2;
# default{state_entry(){integer j=i+1; integer i=4; llSleep(i+j);}}
# Replacing j with i+1 in llOwnerSay will produce wrong code because
# the name i is redefined after j is assigned. shrinknames prevents
# that.
# FIXME: shrinknames and SEF are not enough guarantee. This needs
# analyzing a control flow graph.
#if not self.shrinknames or not node.SEF:
if True or not self.shrinknames or not node.SEF:
return False
if nt not in ('VECTOR', 'ROTATION'):
# If it's an expression and the reference is to a field, we
# can't simplify. Consider e.g.:
# vector v = llGetVel(); llOwnerSay((string)v.z);
# However, if it's a field coming from a Vector or Rotation
# expression, we can embed the corresponding component, e.g.
# vector v = ; llOwnerSay((string)v.y);
# can be replaced with: llOwnerSay((string)((float)(i+2)));
if 'Fld' in sym:
return False
if sym['R'] == 1:
return sym
return False
def CleanNode(self, curnode):
"""Recursively checks if the children are used, deleting those that are
not.
"""
if curnode.ch is None or (curnode.nt == 'DECL'
and curnode.scope == 0):
return
# NOTE: Should not depend on 'Loc', since the nodes that are the
# destination of 'Loc' are renumbered as we delete stuff from globals.
index = int(curnode.nt in self.assign_ops) # don't recurse into lvalues
while index < len(curnode.ch):
node = curnode.ch[index]
if not hasattr(node, 'X'):
if curnode.ch[index].nt == 'JUMP':
# Decrease label reference count
scope = curnode.ch[index].scope
name = curnode.ch[index].name
assert self.symtab[scope][name]['ref'] > 0
self.symtab[scope][name]['ref'] -= 1
del curnode.ch[index]
continue
nt = node.nt
if nt == 'DECL':
if self.OKtoRemoveSymbol(node):
if not node.ch or node.ch[0].SEF:
del curnode.ch[index]
continue
node = curnode.ch[index] = nr(nt='EXPR', t=node.t,
ch=[self.Cast(node.ch[0], node.t)])
elif nt == 'FLD':
sym = self.OKtoRemoveSymbol(node.ch[0])
if sym:
value = sym['W']
# Mark as executed, so it isn't optimized out.
value.X = True
fieldidx = 'xyzs'.index(node.fld)
if value.nt == 'CONST':
value = value.value[fieldidx]
value = nr(nt='CONST', X=True, SEF=True,
t=self.PythonType2LSL[type(value)], value=value)
value = self.Cast(value, 'float')
SEF = True
else: # assumed VECTOR or ROTATION per OKtoRemoveSymbol
SEF = value.SEF
value = self.Cast(value.ch[fieldidx], 'float')
# Replace it
node = curnode.ch[index] = value
node.SEF = SEF
elif nt == 'IDENT':
sym = self.OKtoRemoveSymbol(node)
if sym:
# Mark as executed, so it isn't optimized out.
# Make shallow copy.
# TODO: Should the copy be a deep copy?
assert sym.get('W', False) is not False
new = sym['W'].copy()
if hasattr(new, 'orig'):
del new.orig
new.X = True
# this part makes no sense?
#new.SEF = sym['W'].SEF
if new.t != node.t:
new = self.Cast(new, node.t)
curnode.ch[index] = node = new
# Delete orig if present, as we've eliminated the original
#if hasattr(sym['W'], 'orig'):
# del sym['W'].orig
elif nt in self.assign_ops:
ident = node.ch[0]
if ident.nt == 'FLD':
ident = ident.ch[0]
sym = self.OKtoRemoveSymbol(ident)
if sym:
node = curnode.ch[index] = self.Cast(node.ch[1], node.t)
elif nt in ('IF', 'WHILE', 'DO', 'FOR'):
# If the mandatory statement is to be removed, replace it
# with a ; to prevent leaving the statement empty.
child = node.ch
idx = 3 if nt == 'FOR' else 0 if nt == 'DO' else 1
if not hasattr(child[idx], 'X'):
child[idx] = nr(nt=';', t=None, X=True, SEF=True)
if nt == 'DO' and not hasattr(child[1],'X'):
# Mandatory condition but not executed - replace
child[1] = nr(nt='CONST', X=True, SEF=True, t='integer',
value=0)
self.CleanNode(node)
index += 1
def RemoveDeadCode(self):
"""Simple reference-based dead code removal. It also performs a
simplified form of constant propagation, taking advantage of the fact
that it analyzes the code flow.
"""
# TODO: Converting to SSA first would facilitate DCR.
# The SSA should be followed by constant and expression propagation,
# then constant folding and then dead code removal.
# Start at state default and mark everything referenced from there.
# At the end, unreferenced globals and states will be removed.
# We assume all events in a state are executed.
#
# This may not be the case, e.g. a target()/no_target() without
# llTarget, sensor()/no_sensor() without llSensor(), listen() without
# llListen, timer without llSetTimerEvent, etc. but we're not that
# sophisticated (yet).
# TODO: Inlining of functions that are a single 'return' line.
if lslfuncs.lslcommon.IsCalc:
# Do nothing if in calculator mode (there's no default event
# and it crashes without this)
return
statedef = self.tree[self.symtab[0]['default']['Loc']]
assert statedef.nt == 'STDEF' and statedef.name == 'default'
self.MarkReferences(statedef)
# Track removal of global lines, to reasign locations later.
LocMap = range(len(self.tree))
GlobalDeletions = []
# Perform the removal
idx = 0
while idx < len(self.tree):
# Globals are special.
# We need to track the locations too.
node = self.tree[idx]
delete = False
if not hasattr(node, 'X'):
delete = True
elif node.nt == 'DECL':
delete = self.OKtoRemoveSymbol(node)
if delete:
# Mark the symbol for later deletion from symbol table.
# We can't remove it here because there may be more references
# that we will remove in CleanNode later, that hold the
# original value.
if node.nt == 'DECL' or node.nt == 'STDEF':
GlobalDeletions.append(node.name)
del self.tree[idx]
del LocMap[idx]
else:
idx += 1
self.CleanNode(node)
# Remove the globals now.
for name in GlobalDeletions:
del self.symtab[0][name]
del GlobalDeletions
# Reassign locations
for name in self.symtab[0]:
if name != -1:
sym = self.symtab[0][name]
if 'Loc' in sym:
try:
sym['Loc'] = LocMap.index(sym['Loc'])
except ValueError:
# Subtree deleted - delete the Loc
del sym['Loc']