Perf: Add ad-hoc benchmarking function wrapper.

Expose native timer functions to Lua.

scripts/tundra/boot.lua

@@ -1,6 +1,7 @@
 module(..., package.seeall)
 
 -- Use "strict" when developing to flag accesses to nil global variables
+-- This has very low perf impact (<0.1%), so always leave it on.
 require "strict"
 
 local os        = require "os"
@@ -9,6 +10,7 @@ local util      = require "tundra.util"
 local depgraph  = require "tundra.depgraph"
 local unitgen   = require "tundra.unitgen"
 local buildfile = require "tundra.buildfile"
+local native    = require "tundra.native"
 
 -- This trio is so useful we want them everywhere without imports.
 function _G.printf(msg, ...)
@@ -27,6 +29,22 @@ function _G.croak(msg, ...)
   os.exit(1)
 end
 
+-- Expose benchmarking function for those times everything sucks
+--
+-- Wrap a function so that it prints execution times.
+--
+-- Usage:
+--   foo = bench("foo", foo) -- benchmark function foo
+function _G.bench(name, fn) 
+  return function (...)
+    local t1 = native.get_timer()
+    local result = { fn(...) }
+    local t2 = native.get_timer()
+    printf("%s: %ss", name, native.timerdiff(t1, t2))
+    return unpack(result)
+  end
+end
+
 local environment = require "tundra.environment"
 local nodegen     = require "tundra.nodegen"
 local decl        = require "tundra.decl"

src/LuaInterface.cpp

@@ -470,6 +470,23 @@ static int LuaWin32RegisterQuery(lua_State *L)
 }
 #endif
 
+static int LuaTime(lua_State* L)
+{
+  lua_pushinteger(L, TimerGet());
+  return 1;
+}
+
+static int LuaTimeDiff(lua_State* L)
+{
+  lua_Integer a = luaL_checkinteger(L, 1);
+  lua_Integer b = luaL_checkinteger(L, 2);
+  double d = t2::TimerDiffSeconds(a, b);
+  char buffer[64];
+  snprintf(buffer, sizeof buffer, "%.5f", d);
+  lua_pushstring(L, buffer);
+  return 1;
+}
+
 static const luaL_Reg s_LuaFunctions[] = {
   { "exit",             LuaTundraExit },
   { "list_directory",   LuaListDirectory },
@@ -482,6 +499,8 @@ static const luaL_Reg s_LuaFunctions[] = {
   { "djb2_hash_path",   LuaDjb2HashPath },
   { "getcwd",           LuaGetCwd },
   { "mkdir",            LuaMkdir },
+  { "get_timer",        LuaTime },
+  { "timerdiff",        LuaTimeDiff },
 #ifdef _WIN32
   { "reg_query",        LuaWin32RegisterQuery },
 #endif