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--[[
Optimizatoins for abstract syntax trees
]]
local msg = io.write
--A debugging function, a replacement for glua PrintTable
local function printtable(tbl, tabset)
tabset = tabset or 0
for k,v in pairs(tbl) do
for i = 0,tabset do msg("\t") end
msg(k .. ":")
if type(v) == "table" then
msg("\n")
printtable(v, tabset + 1)
else
msg(tostring(v) .. "\n")
end
end
end
--A function to see if two tables are equal-ish
local function deepcompare(tbl1, tbl2)
if type(tbl1) ~= type(tbl2) then return false end
for k,v in pairs(tbl1) do
print("Checking ", k, " from tbl1")
if k == "pos" then goto cont end
if type(v) == "table" then
print("It is a table! going deeper")
if not deepcompare(v,tbl2[k]) then
return false
end
else
print("Checking ", v , " against ", tbl2[k])
if v ~= tbl2[k] then
return false
end
end
::cont::
end
return true
end
--Makes sure 2 things are refrenceing the same index
local function indexcompare(tbl1,tbl2)
if type(tbl1) ~= "table" or type(tbl2) ~= "table" then return false end
--print("indexcompare is checking ",tbl1,tbl2)
--printtable(tbl1)
--print("is the same as")
--printtable(tbl2)
if tbl1.tag == "Id" and tbl2.tag == "Id" then
return tbl1[1] == tbl2[1]
elseif tbl1.tag == "Index" and tbl2.tag == "Index" then
return indexcompare(tbl1[1],tbl2[1]) and indexcompare(tbl1[2],tbl2[2])
elseif tbl1.tag == "String" and tbl2.tag == "String" then
return tbl1[1] == tbl2[1]
else
return false
end
end
local opts = {}
--Optimization 1
--Folds things with an operator when we have numbers on both sides, and the fold results in a smaller string
local foldables = {
["add"] = function(a,b) return a + b end,
["mul"] = function(a,b) return a * b end,
["mod"] = function(a,b) return a % b end,
["sub"] = function(a,b) return a - b end,
--["div"] = function(a,b) return a / b end,-- division has the chance to give us really long strings!
}
opts[1] = function(ast)
if ast.tag ~= "Op" then return false end
local opname = ast[1]
local func = foldables[opname]
if ast[3] ~= nil and func ~= nil and ast[2].tag == "Number" and ast[3].tag == "Number" then
ast.tag = "Number"
ast[1] = func(ast[2][1],ast[3][1])
for i = 2,#ast do
ast[i] = nil
end
return true
end
return false
end
--Optimization 2
--Find places where we can replace calls with invokes.
--Lua provides syntax sugar where
-- table.method(table,arg1,arg2,...)
--is the same as
-- table:method(arg1,arg2,...)
opts[2] = function(ast)
--[[for debugging
if ast.tag == "Call" then
--print("Ast:")
--printtable(ast)
--print("ast[1][1]")
--printtable(ast[1][1])
--print("ast[2]")
--printtable(ast[2])
--local dcr = indexcompare(ast[1][1],ast[2])
--print("indexcompare:",dcr)
--error("stopping")
end
]]
--The ands are to make sure we short circut before indexing a nil
if ast.tag == "Call" and ast[1][1] and ast[2] and indexcompare(ast[1][1][1], ast[2][1]) then
--print("Before correcting for invoke, ast is")
--printtable(ast)
for i = 2,#ast[2] do
ast[i] = ast[i + 1]
end
ast.tag = "Invoke"
ast[2] = ast[1][2]
ast[1] = ast[1][1]
return true
end
return false
end
--Find places where we have multiple variables declared, but not initalized
--and turn it into a 1-liner
--so local a local b local c
--becomes
--local a,b,c
--TODO: This can be done faster and in 1 pass with a little extra complexity
opts[3] = function(ast)
if ast.tag == "Block" then
for i = 1,#ast do
if ast[i].tag == "Local" and next(ast[i][2]) == nil then
local cursor = ast[i]
local r
i = i + 1
while ast[i].tag == "Local" and next(ast[i][2]) == nil do
table.insert(cursor[1],ast[i][1][1])
table.remove(ast,i)
i = i + 1
r = true
end
if r then return true end
end
end
return false
end
return false
end
return opts
|
