feature: implemented the table.clone() builtin Lua API.

This change only support shallow clone. e.g

  local tab_clone = require "table.clone"
  local x = {x=12, y={5, 6, 7}}
  local y = tab_clone(x)
  ... use y ...

Deep clone will be supported by adding 'true' as the 2nd argument to table.clone

We observe 7% over-all speedup in the edgelang-fan compiler's compiling
speed whose Lua is generated by the fanlang compiler.

Signed-off-by: Yichun Zhang (agentzh) <agentzh@gmail.com>

Author: Shuxin Yang

src/lib_table.c

@@ -169,6 +169,17 @@ LJLIB_CF(table_concat)		LJLIB_REC(.)
   return 1;
 }
 
+LJLIB_NOREG LJLIB_CF(table_clone) LJLIB_REC(.)
+{
+  GCtab *src = lj_lib_checktab(L, 1);
+  GCtab *dup = lj_tab_dup(L, src);
+
+  settabV(L, L->base, dup);
+  L->top = L->base+1;
+
+  return 1;
+}
+
 /* ------------------------------------------------------------------------ */
 
 static void set2(lua_State *L, int i, int j)
@@ -304,6 +315,11 @@ static int luaopen_table_new(lua_State *L)
   return lj_lib_postreg(L, lj_cf_table_new, FF_table_new, "new");
 }
 
+static int luaopen_table_clone(lua_State *L)
+{
+  return lj_lib_postreg(L, lj_cf_table_clone, FF_table_clone, "clone");
+}
+
 static int luaopen_table_clear(lua_State *L)
 {
   return lj_lib_postreg(L, lj_cf_table_clear, FF_table_clear, "clear");
@@ -321,6 +337,7 @@ LUALIB_API int luaopen_table(lua_State *L)
   lua_setfield(L, -2, "unpack");
 #endif
   lj_lib_prereg(L, LUA_TABLIBNAME ".new", luaopen_table_new, tabV(L->top-1));
+  lj_lib_prereg(L, LUA_TABLIBNAME ".clone", luaopen_table_clone, tabV(L->top-1));
   lj_lib_prereg(L, LUA_TABLIBNAME ".clear", luaopen_table_clear, tabV(L->top-1));
   return 1;
 }

src/lj_ffrecord.c

@@ -1105,6 +1105,13 @@ static void LJ_FASTCALL recff_table_clear(jit_State *J, RecordFFData *rd)
   }  /* else: Interpreter will throw. */
 }
 
+static void LJ_FASTCALL recff_table_clone(jit_State *J, RecordFFData *rd)
+{
+  TRef src = J->base[0];
+  J->base[0] = lj_ir_call(J, IRCALL_lj_tab_clone, src);
+  UNUSED(rd);
+}
+
 /* -- I/O library fast functions ------------------------------------------ */
 
 /* Get FILE* for I/O function. Any I/O error aborts recording, so there's

src/lj_ircall.h

@@ -167,6 +167,7 @@ typedef struct CCallInfo {
   _(ANY,	lj_tab_clear,		1,  FS, NIL, 0) \
   _(ANY,	lj_tab_newkey,		3,   S, PGC, CCI_L) \
   _(ANY,	lj_tab_len,		1,  FL, INT, 0) \
+  _(ANY,	lj_tab_clone,		2,  FS, TAB, CCI_L) \
   _(ANY,	lj_gc_step_jit,		2,  FS, NIL, CCI_L) \
   _(ANY,	lj_gc_barrieruv,	2,  FS, NIL, 0) \
   _(ANY,	lj_mem_newgco,		2,  FS, PGC, CCI_L) \

src/lj_tab.c

@@ -686,3 +686,8 @@ MSize LJ_FASTCALL lj_tab_len(GCtab *t)
   return unbound_search(t, j);
 }
 
+
+GCtab * LJ_FASTCALL lj_tab_clone(lua_State *L, const GCtab *src)
+{
+  return lj_tab_dup(L, src);
+}

src/lj_tab.h

@@ -70,4 +70,6 @@ LJ_FUNC TValue *lj_tab_set(lua_State *L, GCtab *t, cTValue *key);
 LJ_FUNCA int lj_tab_next(lua_State *L, GCtab *t, TValue *key);
 LJ_FUNCA MSize LJ_FASTCALL lj_tab_len(GCtab *t);
 
+LJ_FUNCA GCtab * LJ_FASTCALL lj_tab_clone(lua_State *L, const GCtab *src);
+
 #endif