--[[--------------------------------------------------------------------
optparser.lua: does parser-based optimizations
This file is part of LuaSrcDiet.
Copyright (c) 2008 Kein-Hong Man <khman@users.sf.net>
The COPYRIGHT file describes the conditions
under which this software may be distributed.
See the ChangeLog for more information.
----------------------------------------------------------------------]]
--[[--------------------------------------------------------------------
-- NOTES:
-- * For more parser-based optimization ideas, see the TODO items or
-- look at technotes.txt.
-- * The processing load is quite significant, but since this is an
-- off-line text processor, I believe we can wait a few seconds.
-- * TODO: might process "local a,a,a" wrongly... need tests!
-- * TODO: remove position handling if overlapped locals (rem < 0)
-- needs more study, to check behaviour
-- * TODO: there are probably better ways to do allocation, e.g. by
-- choosing better methods to sort and pick locals...
-- * TODO: we don't need 53*63 two-letter identifiers; we can make
-- do with significantly less depending on how many that are really
-- needed and improve entropy; e.g. 13 needed -> choose 4*4 instead
----------------------------------------------------------------------]]
local base = _G
local string = require "string"
local table = require "table"
module "optparser"
----------------------------------------------------------------------
-- Letter frequencies for reducing symbol entropy (fixed version)
-- * Might help a wee bit when the output file is compressed
-- * See Wikipedia: http://en.wikipedia.org/wiki/Letter_frequencies
-- * We use letter frequencies according to a Linotype keyboard, plus
-- the underscore, and both lower case and upper case letters.
-- * The arrangement below (LC, underscore, %d, UC) is arbitrary.
-- * This is certainly not optimal, but is quick-and-dirty and the
-- process has no significant overhead
----------------------------------------------------------------------
local LETTERS = "etaoinshrdlucmfwypvbgkqjxz_ETAOINSHRDLUCMFWYPVBGKQJXZ"
local ALPHANUM = "etaoinshrdlucmfwypvbgkqjxz_0123456789ETAOINSHRDLUCMFWYPVBGKQJXZ"
-- names or identifiers that must be skipped
-- * the first two lines are for keywords
local SKIP_NAME = {}
for v in string.gmatch([[
and break do else elseif end false for function if in
local nil not or repeat return then true until while
self]], "%S+") do
SKIP_NAME[v] = true
end
------------------------------------------------------------------------
-- variables and data structures
------------------------------------------------------------------------
local toklist, seminfolist, -- token lists
globalinfo, localinfo, -- variable information tables
globaluniq, localuniq, -- unique name tables
var_new, -- index of new variable names
varlist -- list of output variables
----------------------------------------------------------------------
-- preprocess information table to get lists of unique names
----------------------------------------------------------------------
local function preprocess(infotable)
local uniqtable = {}
for i = 1, #infotable do -- enumerate info table
local obj = infotable[i]
local name = obj.name
--------------------------------------------------------------------
if not uniqtable[name] then -- not found, start an entry
uniqtable[name] = {
decl = 0, token = 0, size = 0,
}
end
--------------------------------------------------------------------
local uniq = uniqtable[name] -- count declarations, tokens, size
uniq.decl = uniq.decl + 1
local xref = obj.xref
local xcount = #xref
uniq.token = uniq.token + xcount
uniq.size = uniq.size + xcount * #name
--------------------------------------------------------------------
if obj.decl then -- if local table, create first,last pairs
obj.id = i
obj.xcount = xcount
if xcount > 1 then -- if ==1, means local never accessed
obj.first = xref[2]
obj.last = xref[xcount]
end
--------------------------------------------------------------------
else -- if global table, add a back ref
uniq.id = i
end
--------------------------------------------------------------------
end--for
return uniqtable
end
----------------------------------------------------------------------
-- calculate actual symbol frequencies, in order to reduce entropy
-- * this may help further reduce the size of compressed sources
-- * note that since parsing optimizations is put before lexing
-- optimizations, the frequency table is not exact!
-- * yes, this will miss --keep block comments too...
----------------------------------------------------------------------
local function recalc_for_entropy(option)
local byte = string.byte
local char = string.char
-- table of token classes to accept in calculating symbol frequency
local ACCEPT = {
TK_KEYWORD = true, TK_NAME = true, TK_NUMBER = true,
TK_STRING = true, TK_LSTRING = true,
}
if not option["opt-comments"] then
ACCEPT.TK_COMMENT = true
ACCEPT.TK_LCOMMENT = true
end
--------------------------------------------------------------------
-- create a new table and remove any original locals by filtering
--------------------------------------------------------------------
local filtered = {}
for i = 1, #toklist do
filtered[i] = seminfolist[i]
end
for i = 1, #localinfo do -- enumerate local info table
local obj = localinfo[i]
local xref = obj.xref
for j = 1, obj.xcount do
local p = xref[j]
filtered[p] = "" -- remove locals
end
end
--------------------------------------------------------------------
local freq = {} -- reset symbol frequency table
for i = 0, 255 do freq[i] = 0 end
for i = 1, #toklist do -- gather symbol frequency
local tok, info = toklist[i], filtered[i]
if ACCEPT[tok] then
for j = 1, #info do
local c = byte(info, j)
freq[c] = freq[c] + 1
end
end--if
end--for
--------------------------------------------------------------------
-- function to re-sort symbols according to actual frequencies
--------------------------------------------------------------------
local function resort(symbols)
local symlist = {}
for i = 1, #symbols do -- prepare table to sort
local c = byte(symbols, i)
symlist[i] = { c = c, freq = freq[c], }
end
table.sort(symlist, -- sort selected symbols
function(v1, v2)
return v1.freq > v2.freq
end
)
local charlist = {} -- reconstitute the string
for i = 1, #symlist do
charlist[i] = char(symlist[i].c)
end
return table.concat(charlist)
end
--------------------------------------------------------------------
LETTERS = resort(LETTERS) -- change letter arrangement
ALPHANUM = resort(ALPHANUM)
end
----------------------------------------------------------------------
-- returns a string containing a new local variable name to use, and
-- a flag indicating whether it collides with a global variable
-- * trapping keywords and other names like 'self' is done elsewhere
----------------------------------------------------------------------
local function new_var_name()
local var
local cletters, calphanum = #LETTERS, #ALPHANUM
local v = var_new
if v < cletters then -- single char
v = v + 1
var = string.sub(LETTERS, v, v)
else -- longer names
local range, sz = cletters, 1 -- calculate # chars fit
repeat
v = v - range
range = range * calphanum
sz = sz + 1
until range > v
local n = v % cletters -- left side cycles faster
v = (v - n) / cletters -- do first char first
n = n + 1
var = string.sub(LETTERS, n, n)
while sz > 1 do
local m = v % calphanum
v = (v - m) / calphanum
m = m + 1
var = var..string.sub(ALPHANUM, m, m)
sz = sz - 1
end
end
var_new = var_new + 1
return var, globaluniq[var] ~= nil
end
----------------------------------------------------------------------
-- calculate and print some statistics
-- * probably better in main source, put here for now
----------------------------------------------------------------------
local function stats_summary(globaluniq, localuniq, afteruniq, option)
local print = print or base.print
local fmt = string.format
local opt_details = option.DETAILS
local uniq_g , uniq_li, uniq_lo, uniq_ti, uniq_to, -- stats needed
decl_g, decl_li, decl_lo, decl_ti, decl_to,
token_g, token_li, token_lo, token_ti, token_to,
size_g, size_li, size_lo, size_ti, size_to
= 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0
local function avg(c, l) -- safe average function
if c == 0 then return 0 end
return l / c
end
--------------------------------------------------------------------
-- collect statistics (note: globals do not have declarations!)
--------------------------------------------------------------------
for name, uniq in base.pairs(globaluniq) do
uniq_g = uniq_g + 1
token_g = token_g + uniq.token
size_g = size_g + uniq.size
end
for name, uniq in base.pairs(localuniq) do
uniq_li = uniq_li + 1
decl_li = decl_li + uniq.decl
token_li = token_li + uniq.token
size_li = size_li + uniq.size
end
for name, uniq in base.pairs(afteruniq) do
uniq_lo = uniq_lo + 1
decl_lo = decl_lo + uniq.decl
token_lo = token_lo + uniq.token
size_lo = size_lo + uniq.size
end
uniq_ti = uniq_g + uniq_li
decl_ti = decl_g + decl_li
token_ti = token_g + token_li
size_ti = size_g + size_li
uniq_to = uniq_g + uniq_lo
decl_to = decl_g + decl_lo
token_to = token_g + token_lo
size_to = size_g + size_lo
--------------------------------------------------------------------
-- detailed stats: global list
--------------------------------------------------------------------
if opt_details then
local sorted = {} -- sort table of unique global names by size
for name, uniq in base.pairs(globaluniq) do
uniq.name = name
sorted[#sorted + 1] = uniq
end
table.sort(sorted,
function(v1, v2)
return v1.size > v2.size
end
)
local tabf1, tabf2 = "%8s%8s%10s %s", "%8d%8d%10.2f %s"
local hl = string.rep("-", 44)
print("*** global variable list (sorted by size) ***\n"..hl)
print(fmt(tabf1, "Token", "Input", "Input", "Global"))
print(fmt(tabf1, "Count", "Bytes", "Average", "Name"))
print(hl)
for i = 1, #sorted do
local uniq = sorted[i]
print(fmt(tabf2, uniq.token, uniq.size, avg(uniq.token, uniq.size), uniq.name))
end
print(hl)
print(fmt(tabf2, token_g, size_g, avg(token_g, size_g), "TOTAL"))
print(hl.."\n")
--------------------------------------------------------------------
-- detailed stats: local list
--------------------------------------------------------------------
local tabf1, tabf2 = "%8s%8s%8s%10s%8s%10s %s", "%8d%8d%8d%10.2f%8d%10.2f %s"
local hl = string.rep("-", 70)
print("*** local variable list (sorted by allocation order) ***\n"..hl)
print(fmt(tabf1, "Decl.", "Token", "Input", "Input", "Output", "Output", "Global"))
print(fmt(tabf1, "Count", "Count", "Bytes", "Average", "Bytes", "Average", "Name"))
print(hl)
for i = 1, #varlist do -- iterate according to order assigned
local name = varlist[i]
local uniq = afteruniq[name]
local old_t, old_s = 0, 0
for j = 1, #localinfo do -- find corresponding old names and calculate
local obj = localinfo[j]
if obj.name == name then
old_t = old_t + obj.xcount
old_s = old_s + obj.xcount * #obj.oldname
end
end
print(fmt(tabf2, uniq.decl, uniq.token, old_s, avg(old_t, old_s),
uniq.size, avg(uniq.token, uniq.size), name))
end
print(hl)
print(fmt(tabf2, decl_lo, token_lo, size_li, avg(token_li, size_li),
size_lo, avg(token_lo, size_lo), "TOTAL"))
print(hl.."\n")
end--if opt_details
--------------------------------------------------------------------
-- display output
--------------------------------------------------------------------
local tabf1, tabf2 = "%-16s%8s%8s%8s%8s%10s", "%-16s%8d%8d%8d%8d%10.2f"
local hl = string.rep("-", 58)
print("*** local variable optimization summary ***\n"..hl)
print(fmt(tabf1, "Variable", "Unique", "Decl.", "Token", "Size", "Average"))
print(fmt(tabf1, "Types", "Names", "Count", "Count", "Bytes", "Bytes"))
print(hl)
print(fmt(tabf2, "Global", uniq_g, decl_g, token_g, size_g, avg(token_g, size_g)))
print(hl)
print(fmt(tabf2, "Local (in)", uniq_li, decl_li, token_li, size_li, avg(token_li, size_li)))
print(fmt(tabf2, "TOTAL (in)", uniq_ti, decl_ti, token_ti, size_ti, avg(token_ti, size_ti)))
print(hl)
print(fmt(tabf2, "Local (out)", uniq_lo, decl_lo, token_lo, size_lo, avg(token_lo, size_lo)))
print(fmt(tabf2, "TOTAL (out)", uniq_to, decl_to, token_to, size_to, avg(token_to, size_to)))
print(hl.."\n")
end
----------------------------------------------------------------------
-- main entry point
-- * does only local variable optimization for now
----------------------------------------------------------------------
function optimize(option, _toklist, _seminfolist, _globalinfo, _localinfo)
-- set tables
toklist, seminfolist, globalinfo, localinfo
= _toklist, _seminfolist, _globalinfo, _localinfo
var_new = 0 -- reset variable name allocator
varlist = {}
------------------------------------------------------------------
-- preprocess global/local tables, handle entropy reduction
------------------------------------------------------------------
globaluniq = preprocess(globalinfo)
localuniq = preprocess(localinfo)
if option["opt-entropy"] then -- for entropy improvement
recalc_for_entropy(option)
end
------------------------------------------------------------------
-- build initial declared object table, then sort according to
-- token count, this might help assign more tokens to more common
-- variable names such as 'e' thus possibly reducing entropy
-- * an object knows its localinfo index via its 'id' field
-- * special handling for "self" special local (parameter) here
------------------------------------------------------------------
local object = {}
for i = 1, #localinfo do
object[i] = localinfo[i]
end
table.sort(object, -- sort largest first
function(v1, v2)
return v1.xcount > v2.xcount
end
)
------------------------------------------------------------------
-- the special "self" function parameters must be preserved
-- * the allocator below will never use "self", so it is safe to
-- keep those implicit declarations as-is
------------------------------------------------------------------
local temp, j, gotself = {}, 1, false
for i = 1, #object do
local obj = object[i]
if not obj.isself then
temp[j] = obj
j = j + 1
else
gotself = true
end
end
object = temp
------------------------------------------------------------------
-- a simple first-come first-served heuristic name allocator,
-- note that this is in no way optimal...
-- * each object is a local variable declaration plus existence
-- * the aim is to assign short names to as many tokens as possible,
-- so the following tries to maximize name reuse
-- * note that we preserve sort order
------------------------------------------------------------------
local nobject = #object
while nobject > 0 do
local varname, gcollide
repeat
varname, gcollide = new_var_name() -- collect a variable name
until not SKIP_NAME[varname] -- skip all special names
varlist[#varlist + 1] = varname -- keep a list
local oleft = nobject
------------------------------------------------------------------
-- if variable name collides with an existing global, the name
-- cannot be used by a local when the name is accessed as a global
-- during which the local is alive (between 'act' to 'rem'), so
-- we drop objects that collides with the corresponding global
------------------------------------------------------------------
if gcollide then
-- find the xref table of the global
local gref = globalinfo[globaluniq[varname].id].xref
local ngref = #gref
-- enumerate for all current objects; all are valid at this point
for i = 1, nobject do
local obj = object[i]
local act, rem = obj.act, obj.rem -- 'live' range of local
-- if rem < 0, it is a -id to a local that had the same name
-- so follow rem to extend it; does this make sense?
while rem < 0 do
rem = localinfo[-rem].rem
end
local drop
for j = 1, ngref do
local p = gref[j]
if p >= act and p <= rem then drop = true end -- in range?
end
if drop then
obj.skip = true
oleft = oleft - 1
end
end--for
end--if gcollide
------------------------------------------------------------------
-- now the first unassigned local (since it's sorted) will be the
-- one with the most tokens to rename, so we set this one and then
-- eliminate all others that collides, then any locals that left
-- can then reuse the same variable name; this is repeated until
-- all local declaration that can use this name is assigned
-- * the criteria for local-local reuse/collision is:
-- A is the local with a name already assigned
-- B is the unassigned local under consideration
-- => anytime A is accessed, it cannot be when B is 'live'
-- => to speed up things, we have first/last accesses noted
------------------------------------------------------------------
while oleft > 0 do
local i = 1
while object[i].skip do -- scan for first object
i = i + 1
end
------------------------------------------------------------------
-- first object is free for assignment of the variable name
-- [first,last] gives the access range for collision checking
------------------------------------------------------------------
oleft = oleft - 1
local obja = object[i]
i = i + 1
obja.newname = varname
obja.skip = true
obja.done = true
local first, last = obja.first, obja.last
local xref = obja.xref
------------------------------------------------------------------
-- then, scan all the rest and drop those colliding
-- if A was never accessed then it'll never collide with anything
-- otherwise trivial skip if:
-- * B was activated after A's last access (last < act)
-- * B was removed before A's first access (first > rem)
-- if not, see detailed skip below...
------------------------------------------------------------------
if first and oleft > 0 then -- must have at least 1 access
local scanleft = oleft
while scanleft > 0 do
while object[i].skip do -- next valid object
i = i + 1
end
scanleft = scanleft - 1
local objb = object[i]
i = i + 1
local act, rem = objb.act, objb.rem -- live range of B
-- if rem < 0, extend range of rem thru' following local
while rem < 0 do
rem = localinfo[-rem].rem
end
--------------------------------------------------------
if not(last < act or first > rem) then -- possible collision
--------------------------------------------------------
-- B is activated later than A or at the same statement,
-- this means for no collision, A cannot be accessed when B
-- is alive, since B overrides A (or is a peer)
--------------------------------------------------------
if act >= obja.act then
for j = 1, obja.xcount do -- ... then check every access
local p = xref[j]
if p >= act and p <= rem then -- A accessed when B live!
oleft = oleft - 1
objb.skip = true
break
end
end--for
--------------------------------------------------------
-- A is activated later than B, this means for no collision,
-- A's access is okay since it overrides B, but B's last
-- access need to be earlier than A's activation time
--------------------------------------------------------
else
if objb.last and objb.last >= obja.act then
oleft = oleft - 1
objb.skip = true
end
end
end
--------------------------------------------------------
if oleft == 0 then break end
end
end--if first
------------------------------------------------------------------
end--while
------------------------------------------------------------------
-- after assigning all possible locals to one variable name, the
-- unassigned locals/objects have the skip field reset and the table
-- is compacted, to hopefully reduce iteration time
------------------------------------------------------------------
local temp, j = {}, 1
for i = 1, nobject do
local obj = object[i]
if not obj.done then
obj.skip = false
temp[j] = obj
j = j + 1
end
end
object = temp -- new compacted object table
nobject = #object -- objects left to process
------------------------------------------------------------------
end--while
------------------------------------------------------------------
-- after assigning all locals with new variable names, we can
-- patch in the new names, and reprocess to get 'after' stats
------------------------------------------------------------------
for i = 1, #localinfo do -- enumerate all locals
local obj = localinfo[i]
local xref = obj.xref
if obj.newname then -- if got new name, patch it in
for j = 1, obj.xcount do
local p = xref[j] -- xrefs indexes the token list
seminfolist[p] = obj.newname
end
obj.name, obj.oldname -- adjust names
= obj.newname, obj.name
else
obj.oldname = obj.name -- for cases like 'self'
end
end
------------------------------------------------------------------
-- deal with statistics output
------------------------------------------------------------------
if gotself then -- add 'self' to end of list
varlist[#varlist + 1] = "self"
end
local afteruniq = preprocess(localinfo)
stats_summary(globaluniq, localuniq, afteruniq, option)
------------------------------------------------------------------
end