Add special bytecodes for builtins.

BC_ISTYPE, BC_ISNUM: fast type checks/coercions.
BC_TGETR, BC_TSETR: fast rawgeti/rawseti, no type checks for table/key.

src/host/genlibbc.lua

@@ -6,6 +6,15 @@
 -- Released under the MIT license. See Copyright Notice in luajit.h
 ----------------------------------------------------------------------------
 
+local ffi = require("ffi")
+local bit = require("bit")
+local vmdef = require("jit.vmdef")
+local bcnames = vmdef.bcnames
+
+local format = string.format
+
+local isbe = (string.byte(string.dump(function() end), 5) % 2 == 1)
+
 local function usage(arg)
   io.stderr:write("Usage: ", arg and arg[0] or "genlibbc",
 		  " [-o buildvm_libbc.h] lib_*.c\n")
@@ -36,15 +45,100 @@ local function read_files(names)
   return src
 end
 
+local function transform_lua(code)
+  local fixup = {}
+  local n = -30000
+  code = string.gsub(code, "CHECK_(%w*)%((.-)%)", function(tp, var)
+    n = n + 1
+    fixup[n] = { "CHECK", tp }
+    return format("%s=%d", var, n)
+  end)
+  code = string.gsub(code, "PAIRS%((.-)%)", function(var)
+    fixup.PAIRS = true
+    return format("nil, %s, 0", var)
+  end)
+  return "return "..code, fixup
+end
+
+local function read_uleb128(p)
+  local v = p[0]; p = p + 1
+  if v >= 128 then
+    local sh = 7; v = v - 128
+    repeat
+      local r = p[0]
+      v = v + bit.lshift(bit.band(r, 128), sh)
+      sh = sh + 7
+      p = p + 1
+    until r < 128
+  end
+  return p, v
+end
+
+-- ORDER LJ_T
+local name2itype = {
+  str = 5, func = 9, tab = 12, int = 14, num = 15
+}
+
+local BC = {}
+for i=0,#bcnames/6-1 do
+  BC[string.gsub(string.sub(bcnames, i*6+1, i*6+6), " ", "")] = i
+end
+local xop, xra = isbe and 3 or 0, isbe and 2 or 1
+local xrc, xrb = isbe and 1 or 2, isbe and 0 or 3
+
+local function fixup_dump(dump, fixup)
+  local buf = ffi.new("uint8_t[?]", #dump+1, dump)
+  local p = buf+5
+  local n, sizebc
+  p, n = read_uleb128(p)
+  local start = p
+  p = p + 4
+  p = read_uleb128(p)
+  p = read_uleb128(p)
+  p, sizebc = read_uleb128(p)
+  local rawtab = {}
+  for i=0,sizebc-1 do
+    local op = p[xop]
+    if op == BC.KSHORT then
+      local rd = p[xrc] + 256*p[xrb]
+      rd = bit.arshift(bit.lshift(rd, 16), 16)
+      local f = fixup[rd]
+      if f then
+	if f[1] == "CHECK" then
+	  local tp = f[2]
+	  if tp == "tab" then rawtab[p[xra]] = true end
+	  p[xop] = tp == "num" and BC.ISNUM or BC.ISTYPE
+	  p[xrb] = 0
+	  p[xrc] = name2itype[tp]
+	else
+	  error("unhandled fixup type: "..f[1])
+	end
+      end
+    elseif op == BC.TGETV then
+      if rawtab[p[xrb]] then
+	p[xop] = BC.TGETR
+      end
+    elseif op == BC.TSETV then
+      if rawtab[p[xrb]] then
+	p[xop] = BC.TSETR
+      end
+    elseif op == BC.ITERC then
+      if fixup.PAIRS then
+	p[xop] = BC.ITERN
+      end
+    end
+    p = p + 4
+  end
+  return ffi.string(start, n)
+end
+
 local function find_defs(src)
   local defs = {}
   for name, code in string.gmatch(src, "LJLIB_LUA%(([^)]*)%)%s*/%*(.-)%*/") do
     local env = {}
-    local func = assert(load("return "..code, "", nil, env))()
-    local d = string.dump(func, true)
-    local ofs = 6
-    while string.byte(d, ofs) > 127 do ofs = ofs + 1 end
-    defs[name] = string.sub(d, ofs+1, -2)
+    local tcode, fixup = transform_lua(code)
+    local func = assert(load(tcode, "", nil, env))()
+    defs[name] = fixup_dump(string.dump(func, true), fixup)
     defs[#defs+1] = name
   end
   return defs
@@ -54,9 +148,7 @@ local function gen_header(defs)
   local t = {}
   local function w(x) t[#t+1] = x end
   w("/* This is a generated file. DO NOT EDIT! */\n\n")
-  w("static const int libbc_endian = ")
-  w(string.byte(string.dump(function() end), 5) % 2)
-  w(";\n\n")
+  w("static const int libbc_endian = ") w(isbe and 1 or 0) w(";\n\n")
   local s = ""
   for _,name in ipairs(defs) do
     s = s .. defs[name]