Disable Lua 5.2 features by default. See -DLUAJIT_ENABLE_LUA52COMPAT.

src/Makefile

@@ -62,6 +62,11 @@ CCWARN= -Wall
 # Note that most of these are NOT suitable for benchmarking or release mode!
 XCFLAGS=
 #
+# Enable some upwards-compatible features from Lua 5.2 that are unlikely
+# to break existing code (e.g. __pairs). Note that this does not provide
+# full compatibility with Lua 5.2 at this time.
+#XCFLAGS+= -DLUAJIT_ENABLE_LUA52COMPAT
+#
 # Disable the use of CMOV and FCOMI*/FUCOMI* instructions in the interpreter.
 # This is only necessary if you intend to run the code on REALLY ANCIENT CPUs
 # (before Pentium Pro, or on the VIA C3). This generally slows down the

src/buildvm_ppc.dasc

@@ -1098,11 +1098,16 @@ static void build_subroutines(BuildCtx *ctx)
   |  checktab TAB:CARG1
   |   lwz PC, FRAME_PC(BASE)
   |  checkfail ->fff_fallback
-  |  lwz TAB:TMP2, TAB:CARG1->metatable
+#ifdef LUAJIT_ENABLE_LUA52COMPAT
+  |   lwz TAB:TMP2, TAB:CARG1->metatable
   |  evldd CFUNC:TMP0, CFUNC:RB->upvalue[0]
-  |  cmplwi TAB:TMP2, 0
+  |   cmplwi TAB:TMP2, 0
   |  la RA, -8(BASE)
-  |  bne ->fff_fallback
+  |   bne ->fff_fallback
+#else
+  |  evldd CFUNC:TMP0, CFUNC:RB->upvalue[0]
+  |  la RA, -8(BASE)
+#endif
   |   evstdd TAB:CARG1, 0(BASE)
   |   evstdd TISNIL, 8(BASE)
   |  li RD, (3+1)*8
@@ -1153,11 +1158,16 @@ static void build_subroutines(BuildCtx *ctx)
   |  checktab TAB:CARG1
   |   lwz PC, FRAME_PC(BASE)
   |  checkfail ->fff_fallback
-  |  lwz TAB:TMP2, TAB:CARG1->metatable
+#ifdef LUAJIT_ENABLE_LUA52COMPAT
+  |   lwz TAB:TMP2, TAB:CARG1->metatable
   |  evldd CFUNC:TMP0, CFUNC:RB->upvalue[0]
-  |  cmplwi TAB:TMP2, 0
+  |   cmplwi TAB:TMP2, 0
   |  la RA, -8(BASE)
-  |  bne ->fff_fallback
+  |   bne ->fff_fallback
+#else
+  |  evldd CFUNC:TMP0, CFUNC:RB->upvalue[0]
+  |  la RA, -8(BASE)
+#endif
   |    evsplati TMP1, 0
   |   evstdd TAB:CARG1, 0(BASE)
   |    evstdd TMP1, 8(BASE)

src/buildvm_x86.dasc

@@ -1511,7 +1511,9 @@ static void build_subroutines(BuildCtx *ctx, int cmov, int sse)
   |.ffunc_1 pairs
   |  mov TAB:RB, [BASE]
   |  cmp dword [BASE+4], LJ_TTAB;  jne ->fff_fallback
+#ifdef LUAJIT_ENABLE_LUA52COMPAT
   |  cmp dword TAB:RB->metatable, 0; jne ->fff_fallback
+#endif
   |  mov CFUNC:RB, [BASE-8]
   |  mov CFUNC:RD, CFUNC:RB->upvalue[0]
   |  mov PC, [BASE-4]
@@ -1575,7 +1577,9 @@ static void build_subroutines(BuildCtx *ctx, int cmov, int sse)
   |.ffunc_1 ipairs
   |  mov TAB:RB, [BASE]
   |  cmp dword [BASE+4], LJ_TTAB;  jne ->fff_fallback
+#ifdef LUAJIT_ENABLE_LUA52COMPAT
   |  cmp dword TAB:RB->metatable, 0; jne ->fff_fallback
+#endif
   |  mov CFUNC:RB, [BASE-8]
   |  mov CFUNC:RD, CFUNC:RB->upvalue[0]
   |  mov PC, [BASE-4]

src/lib_base.c

@@ -249,6 +249,7 @@ LJLIB_ASM(next)
   return FFH_UNREACHABLE;
 }
 
+#ifdef LUAJIT_ENABLE_LUA52COMPAT
 static int ffh_pairs(lua_State *L, MMS mm)
 {
   TValue *o = lj_lib_checkany(L, 1);
@@ -264,6 +265,9 @@ static int ffh_pairs(lua_State *L, MMS mm)
     return FFH_RES(3);
   }
 }
+#else
+#define ffh_pairs(L, mm)	(lj_lib_checktab(L, 1), FFH_UNREACHABLE)
+#endif
 
 LJLIB_PUSH(lastcl)
 LJLIB_ASM(pairs)

src/lj_obj.h

@@ -410,6 +410,12 @@ enum {
 #define setvmstate(g, st)	((g)->vmstate = ~LJ_VMST_##st)
 
 /* Metamethods. */
+#ifdef LUAJIT_ENABLE_LUA52COMPAT
+#define MMDEF_52(_) _(pairs) _(ipairs)
+#else
+#define MMDEF_52(_)
+#endif
+
 #define MMDEF(_) \
   _(index) _(newindex) _(gc) _(mode) _(eq) \
   /* Only the above (fast) metamethods are negative cached (max. 8). */ \
@@ -417,7 +423,7 @@ enum {
   /* The following must be in ORDER ARITH. */ \
   _(add) _(sub) _(mul) _(div) _(mod) _(pow) _(unm) \
   /* The following are used in the standard libraries. */ \
-  _(metatable) _(tostring) _(pairs) _(ipairs)
+  _(metatable) _(tostring) MMDEF_52(_)
 
 typedef enum {
 #define MMENUM(name)	MM_##name,

src/lj_record.c

@@ -1426,7 +1426,10 @@ static void LJ_FASTCALL recff_ipairs_aux(jit_State *J, RecordFFData *rd)
 
 static void LJ_FASTCALL recff_ipairs(jit_State *J, RecordFFData *rd)
 {
-  if (!recff_metacall(J, rd, MM_ipairs)) {
+#ifdef LUAJIT_ENABLE_LUA52COMPAT
+  if (!recff_metacall(J, rd, MM_ipairs))
+#endif
+  {
     TRef tab = J->base[0];
     if (tref_istab(tab)) {
       J->base[0] = lj_ir_kfunc(J, funcV(&J->fn->c.upvalue[0]));