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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 ast's are equal-ish (does not compare position)
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
local opts = {}
--Optimization 1
--Folds things with an operator when 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.
opts[2] = function(ast)
if ast.tag == "Call" and ast.pos == 160 then
print("Ast:")
printtable(ast)
print("ast[1][1]")
printtable(ast[1][1])
print("ast[2]")
printtable(ast[2])
local dcr = deepcompare(ast[1][1],ast[2])
print("Deepcompare:",dcr)
--error("stopping")
end
if ast.tag == "Call" and deepcompare(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]
print("After correcting for invoke, ast is")
printtable(ast)
--error("Call that should be invoke detected")
return true
end
end
return opts
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