patch to goto optional semicolon changing opcodes
[
Date Prev][
Date Next][
Thread Prev][
Thread Next]
[
Date Index]
[
Thread Index]
- Subject: patch to goto optional semicolon changing opcodes
- From: Patrick Donnelly <batrick@...>
- Date: 2012年5月19日 00:34:15 -0400
Sorry about vague subject. I'll try to clarify:
I'm using luac to confirm that the code formatted by [1] does not
change the behavior of a program. I've noticed that the optional
semicolon that terminates a goto or break statement [inside an if
block (I don't know why)] will influence the bytecode generation. If
there is a semicolon, an extra unreachable JMP is added:
$ luac -l -p - <<< "for i = 1, 2 do if true then break end end"
main <stdin:0,0> (9 instructions at 0x24a20d0)
0+ params, 5 slots, 1 upvalue, 4 locals, 2 constants, 0 functions
1 [1] LOADK 0 -1 ; 1
2 [1] LOADK 1 -2 ; 2
3 [1] LOADK 2 -1 ; 1
4 [1] FORPREP 0 3 ; to 8
5 [1] LOADBOOL 4 1 0
6 [1] TEST 4 1
7 [1] JMP 0 1 ; to 9
8 [1] FORLOOP 0 -4 ; to 5
9 [1] RETURN 0 1
$ luac -l -p - <<< "for i = 1, 2 do if true then break; end end"
main <stdin:0,0> (10 instructions at 0xca50d0)
0+ params, 5 slots, 1 upvalue, 4 locals, 2 constants, 0 functions
1 [1] LOADK 0 -1 ; 1
2 [1] LOADK 1 -2 ; 2
3 [1] LOADK 2 -1 ; 1
4 [1] FORPREP 0 4 ; to 9
5 [1] LOADBOOL 4 1 0
6 [1] TEST 4 1
7 [1] JMP 0 2 ; to 10
8 [1] JMP 0 0 ; to 9
9 [1] FORLOOP 0 -5 ; to 5
10 [1] RETURN 0 1
The patch to fix this is simple, similar to removing the optional
semicolon for the return statement.
Index: lua-5.2.0/src/lparser.c
===================================================================
--- lua-5.2.0/src/lparser.c (revision 47)
+++ lua-5.2.0/src/lparser.c (working copy)
@@ -1191,6 +1191,7 @@
luaX_next(ls); /* skip break */
label = luaS_new(ls->L, "break");
}
+ testnext(ls, ';'); /* skip optional semicolon */
g = newlabelentry(ls, &ls->dyd->gt, label, line, pc);
findlabel(ls, g); /* close it if label already defined */
}
I don't really consider this a bug (obviously) but hopefully Lua 5.2.1
can include this.
[1] http://lua-users.org/lists/lua-l/2012-04/msg01082.html
--
- Patrick Donnelly