From 4758113043b6c362a0fdce77715c711332d909dc Mon Sep 17 00:00:00 2001
From: Roberto Ierusalimschy <roberto@inf.puc-rio.br>
Date: Tue, 19 Apr 2011 13:22:13 -0300
Subject: [PATCH] change in opcode OP_LOADNIL: B is used as a counter instead
 of a register. (Avoids an assignment to R(B), not present in any other
 instruction.)

---
 lcode.c    | 18 +++++++++++-------
 ldebug.c   |  6 +++---
 lopcodes.c |  4 ++--
 lopcodes.h |  4 ++--
 lvm.c      |  8 ++++----
 5 files changed, 22 insertions(+), 18 deletions(-)

diff --git a/lcode.c b/lcode.c
index ab2a8295..d2d4b819 100644
--- a/lcode.c
+++ b/lcode.c
@@ -1,5 +1,5 @@
 /*
-** $Id: lcode.c,v 2.51 2011/02/01 18:03:10 roberto Exp roberto $
+** $Id: lcode.c,v 2.52 2011/04/07 18:14:12 roberto Exp roberto $
 ** Code generator for Lua
 ** See Copyright Notice in lua.h
 */
@@ -35,19 +35,23 @@ static int isnumeral(expdesc *e) {
 
 void luaK_nil (FuncState *fs, int from, int n) {
   Instruction *previous;
+  int l = from + n - 1;  /* last register to set nil */
   if (fs->pc > fs->lasttarget) {  /* no jumps to current position? */
     previous = &fs->f->code[fs->pc-1];
     if (GET_OPCODE(*previous) == OP_LOADNIL) {
       int pfrom = GETARG_A(*previous);
-      int pto = GETARG_B(*previous);
-      if (pfrom <= from && from <= pto+1) {  /* can connect both? */
-        if (from+n-1 > pto)
-          SETARG_B(*previous, from+n-1);
+      int pl = pfrom + GETARG_B(*previous);
+      if ((pfrom <= from && from <= pl + 1) ||
+          (from <= pfrom && pfrom <= l + 1)) {  /* can connect both? */
+        if (pfrom < from) from = pfrom;  /* from = min(from, pfrom) */ 
+        if (pl > l) l = pl;  /* l = max(l, pl) */ 
+        SETARG_A(*previous, from);
+        SETARG_B(*previous, l - from);
         return;
       }
-    }
+    }  /* else go through */
   }
-  luaK_codeABC(fs, OP_LOADNIL, from, from+n-1, 0);  /* else no optimization */
+  luaK_codeABC(fs, OP_LOADNIL, from, n - 1, 0);  /* else no optimization */
 }
 
 
diff --git a/ldebug.c b/ldebug.c
index 65b79090..1d0be89e 100644
--- a/ldebug.c
+++ b/ldebug.c
@@ -1,5 +1,5 @@
 /*
-** $Id: ldebug.c,v 2.78 2011/04/18 15:02:37 roberto Exp roberto $
+** $Id: ldebug.c,v 2.79 2011/04/18 19:49:13 roberto Exp roberto $
 ** Debug Interface
 ** See Copyright Notice in lua.h
 */
@@ -355,8 +355,8 @@ static const char *getobjname (lua_State *L, CallInfo *ci, int reg,
         break;
       }
       case OP_LOADNIL: {
-        int b = GETARG_B(i);  /* move from 'b' to 'a' */
-        if (a <= reg && reg <= b)  /* set registers from 'a' to 'b' */
+        int b = GETARG_B(i);
+        if (a <= reg && reg <= a + b)  /* set registers from 'a' to 'a+b' */
           what = NULL;
         break;
       }
diff --git a/lopcodes.c b/lopcodes.c
index dbacf317..d289ae7d 100644
--- a/lopcodes.c
+++ b/lopcodes.c
@@ -1,5 +1,5 @@
 /*
-** $Id: lopcodes.c,v 1.46 2011/04/07 18:14:12 roberto Exp roberto $
+** $Id: lopcodes.c,v 1.47 2011/04/12 17:27:35 roberto Exp roberto $
 ** See Copyright Notice in lua.h
 */
 
@@ -66,7 +66,7 @@ LUAI_DDEF const lu_byte luaP_opmodes[NUM_OPCODES] = {
  ,opmode(0, 1, OpArgK, OpArgN, iABx)		/* OP_LOADK */
  ,opmode(0, 1, OpArgN, OpArgN, iABx)		/* OP_LOADKX */
  ,opmode(0, 1, OpArgU, OpArgU, iABC)		/* OP_LOADBOOL */
- ,opmode(0, 1, OpArgR, OpArgN, iABC)		/* OP_LOADNIL */
+ ,opmode(0, 1, OpArgU, OpArgN, iABC)		/* OP_LOADNIL */
  ,opmode(0, 1, OpArgU, OpArgN, iABC)		/* OP_GETUPVAL */
  ,opmode(0, 1, OpArgU, OpArgK, iABC)		/* OP_GETTABUP */
  ,opmode(0, 1, OpArgR, OpArgK, iABC)		/* OP_GETTABLE */
diff --git a/lopcodes.h b/lopcodes.h
index 60d1492d..5ab88228 100644
--- a/lopcodes.h
+++ b/lopcodes.h
@@ -1,5 +1,5 @@
 /*
-** $Id: lopcodes.h,v 1.139 2011/02/07 12:24:42 roberto Exp roberto $
+** $Id: lopcodes.h,v 1.140 2011/04/07 18:14:12 roberto Exp roberto $
 ** Opcodes for Lua virtual machine
 ** See Copyright Notice in lua.h
 */
@@ -170,7 +170,7 @@ OP_MOVE,/*	A B	R(A) := R(B)					*/
 OP_LOADK,/*	A Bx	R(A) := Kst(Bx)					*/
 OP_LOADKX,/*	A 	R(A) := Kst(extra arg)				*/
 OP_LOADBOOL,/*	A B C	R(A) := (Bool)B; if (C) pc++			*/
-OP_LOADNIL,/*	A B	R(A) := ... := R(B) := nil			*/
+OP_LOADNIL,/*	A B	R(A), R(A+1), ..., R(A+B) := nil		*/
 OP_GETUPVAL,/*	A B	R(A) := UpValue[B]				*/
 
 OP_GETTABUP,/*	A B C	R(A) := UpValue[B][RK(C)]			*/
diff --git a/lvm.c b/lvm.c
index 7356a398..decd2219 100644
--- a/lvm.c
+++ b/lvm.c
@@ -1,5 +1,5 @@
 /*
-** $Id: lvm.c,v 2.134 2011/04/07 18:14:12 roberto Exp roberto $
+** $Id: lvm.c,v 2.135 2011/04/18 19:48:53 roberto Exp roberto $
 ** Lua virtual machine
 ** See Copyright Notice in lua.h
 */
@@ -541,10 +541,10 @@ void luaV_execute (lua_State *L) {
         if (GETARG_C(i)) ci->u.l.savedpc++;  /* skip next instruction (if C) */
       )
       vmcase(OP_LOADNIL,
-        TValue *rb = RB(i);
+        int b = GETARG_B(i);
         do {
-          setnilvalue(rb--);
-        } while (rb >= ra);
+          setnilvalue(ra++);
+        } while (b--);
       )
       vmcase(OP_GETUPVAL,
         int b = GETARG_B(i);