First take on constant propagation

4 files changed, 73 insertions, 26 deletions

diff --git a/lcode.c b/lcode.c
index eccb8380..1005f1b7 100644
--- a/lcode.c
+++ b/lcode.c
@@ -52,7 +52,7 @@ l_noret luaK_semerror (LexState *ls, const char *msg) {
 ** If expression is a numeric constant, fills 'v' with its value
 ** and returns 1. Otherwise, returns 0.
 */
-static int tonumeral(const expdesc *e, TValue *v) {
+int luaK_tonumeral (FuncState *fs, const expdesc *e, TValue *v) {
   if (hasjumps(e))
     return 0;  /* not a numeral */
   switch (e->k) {
@@ -62,12 +62,42 @@ static int tonumeral(const expdesc *e, TValue *v) {
     case VKFLT:
       if (v) setfltvalue(v, e->u.nval);
       return 1;
+    case VUPVAL: {  /* may be a constant */
+      Vardesc *vd = luaY_getvardesc(&fs, e);
+      if (v && vd && !ttisnil(&vd->val)) {
+        setobj(fs->ls->L, v, &vd->val);
+        return 1;
+      }  /* else */
+    }  /* FALLTHROUGH */
     default: return 0;
   }
 }
 
 
 /*
+** If expression 'e' is a constant, change 'e' to represent
+** the constant value.
+*/
+static int const2exp (FuncState *fs, expdesc *e) {
+  Vardesc *vd = luaY_getvardesc(&fs, e);
+  if (vd) {
+    TValue *v = &vd->val;
+    switch (ttypetag(v)) {
+      case LUA_TNUMINT:
+        e->k = VKINT;
+        e->u.ival = ivalue(v);
+        return 1;
+      case LUA_TNUMFLT:
+        e->k = VKFLT;
+        e->u.nval = fltvalue(v);
+        return 1;
+    }
+  }
+  return 0;
+}
+
+
+/*
 ** Return the previous instruction of the current code. If there
 ** may be a jump target between the current instruction and the
 ** previous one, return an invalid instruction (to avoid wrong
@@ -683,8 +713,10 @@ void luaK_dischargevars (FuncState *fs, expdesc *e) {
       break;
     }
     case VUPVAL: {  /* move value to some (pending) register */
-      e->u.info = luaK_codeABC(fs, OP_GETUPVAL, 0, e->u.var.idx, 0);
-      e->k = VRELOC;
+      if (!const2exp(fs, e)) {
+        e->u.info = luaK_codeABC(fs, OP_GETUPVAL, 0, e->u.var.idx, 0);
+        e->k = VRELOC;
+      }
       break;
     }
     case VINDEXUP: {
@@ -1218,9 +1250,11 @@ static int validop (int op, TValue *v1, TValue *v2) {
 ** (In this case, 'e1' has the final result.)
 */
 static int constfolding (FuncState *fs, int op, expdesc *e1,
-                                                const expdesc *e2) {
+                                        const expdesc *e2) {
   TValue v1, v2, res;
-  if (!tonumeral(e1, &v1) || !tonumeral(e2, &v2) || !validop(op, &v1, &v2))
+  if (!luaK_tonumeral(fs, e1, &v1) ||
+      !luaK_tonumeral(fs, e2, &v2) ||
+      !validop(op, &v1, &v2))
     return 0;  /* non-numeric operands or not safe to fold */
   luaO_rawarith(fs->ls->L, op, &v1, &v2, &res);  /* does operation */
   if (ttisinteger(&res)) {
@@ -1307,7 +1341,7 @@ static void codearith (FuncState *fs, OpCode op,
                        expdesc *e1, expdesc *e2, int flip, int line) {
   if (isSCint(e2))  /* immediate operand? */
     codebini(fs, cast(OpCode, op - OP_ADD + OP_ADDI), e1, e2, flip, line);
-  else if (tonumeral(e2, NULL) && luaK_exp2K(fs, e2)) {  /* K operand? */
+  else if (luaK_tonumeral(fs, e2, NULL) && luaK_exp2K(fs, e2)) {  /* K operand? */
     int v2 = e2->u.info;  /* K index */
     op = cast(OpCode, op - OP_ADD + OP_ADDK);
     finishbinexpval(fs, e1, e2, op, v2, flip, line);
@@ -1328,7 +1362,7 @@ static void codearith (FuncState *fs, OpCode op,
 static void codecommutative (FuncState *fs, OpCode op,
                              expdesc *e1, expdesc *e2, int line) {
   int flip = 0;
-  if (tonumeral(e1, NULL)) {  /* is first operand a numeric constant? */
+  if (luaK_tonumeral(fs, e1, NULL)) {  /* is first operand a numeric constant? */
     swapexps(e1, e2);  /* change order */
     flip = 1;
   }
@@ -1451,7 +1485,7 @@ void luaK_prefix (FuncState *fs, UnOpr op, expdesc *e, int line) {
     case OPR_MINUS: case OPR_BNOT:  /* use 'ef' as fake 2nd operand */
       if (constfolding(fs, op + LUA_OPUNM, e, &ef))
         break;
-      /* FALLTHROUGH */
+      /* else */ /* FALLTHROUGH */
     case OPR_LEN:
       codeunexpval(fs, cast(OpCode, op + OP_UNM), e, line);
       break;
@@ -1466,6 +1500,7 @@ void luaK_prefix (FuncState *fs, UnOpr op, expdesc *e, int line) {
 ** 2nd operand.
 */
 void luaK_infix (FuncState *fs, BinOpr op, expdesc *v) {
+  luaK_dischargevars(fs, v);
   switch (op) {
     case OPR_AND: {
       luaK_goiftrue(fs, v);  /* go ahead only if 'v' is true */
@@ -1484,13 +1519,13 @@ void luaK_infix (FuncState *fs, BinOpr op, expdesc *v) {
     case OPR_MOD: case OPR_POW:
     case OPR_BAND: case OPR_BOR: case OPR_BXOR:
     case OPR_SHL: case OPR_SHR: {
-      if (!tonumeral(v, NULL))
+      if (!luaK_tonumeral(fs, v, NULL))
         luaK_exp2anyreg(fs, v);
       /* else keep numeral, which may be folded with 2nd operand */
       break;
     }
     case OPR_EQ: case OPR_NE: {
-      if (!tonumeral(v, NULL))
+      if (!luaK_tonumeral(fs, v, NULL))
         luaK_exp2RK(fs, v);
       /* else keep numeral, which may be an immediate operand */
       break;
@@ -1535,17 +1570,16 @@ static void codeconcat (FuncState *fs, expdesc *e1, expdesc *e2, int line) {
 */
 void luaK_posfix (FuncState *fs, BinOpr opr,
                   expdesc *e1, expdesc *e2, int line) {
+  luaK_dischargevars(fs, e2);
   switch (opr) {
     case OPR_AND: {
-      lua_assert(e1->t == NO_JUMP);  /* list closed by 'luK_infix' */
-      luaK_dischargevars(fs, e2);
+      lua_assert(e1->t == NO_JUMP);  /* list closed by 'luaK_infix' */
       luaK_concat(fs, &e2->f, e1->f);
       *e1 = *e2;
       break;
     }
     case OPR_OR: {
-      lua_assert(e1->f == NO_JUMP);  /* list closed by 'luK_infix' */
-      luaK_dischargevars(fs, e2);
+      lua_assert(e1->f == NO_JUMP);  /* list closed by 'luaK_infix' */
       luaK_concat(fs, &e2->t, e1->t);
       *e1 = *e2;
       break;
diff --git a/lcode.h b/lcode.h
index 0758f88d..c4953295 100644
--- a/lcode.h
+++ b/lcode.h
@@ -51,6 +51,7 @@ typedef enum UnOpr { OPR_MINUS, OPR_BNOT, OPR_NOT, OPR_LEN, OPR_NOUNOPR } UnOpr;
 
 #define luaK_jumpto(fs,t)       luaK_patchlist(fs, luaK_jump(fs), t)
 
+LUAI_FUNC int luaK_tonumeral (FuncState *fs, const expdesc *e, TValue *v);
 LUAI_FUNC int luaK_codeABx (FuncState *fs, OpCode o, int A, unsigned int Bx);
 LUAI_FUNC int luaK_codeAsBx (FuncState *fs, OpCode o, int A, int Bx);
 LUAI_FUNC int luaK_codeABCk (FuncState *fs, OpCode o, int A,
diff --git a/lparser.c b/lparser.c
index 3c68f2d7..875f7d04 100644
--- a/lparser.c
+++ b/lparser.c
@@ -206,6 +206,7 @@ static Vardesc *new_localvar (LexState *ls, TString *name) {
   var = &dyd->actvar.arr[dyd->actvar.n++];
   var->idx = cast(short, reg);
   var->ro = 0;
+  setnilvalue(&var->val);
   return var;
 }
 
@@ -238,7 +239,7 @@ static LocVar *getlocvar (FuncState *fs, int i) {
 ** where that variable was defined. Return NULL if expression
 ** is neither a local variable nor an upvalue.
 */
-static Vardesc *getvardesc (FuncState **fs, expdesc *e) {
+Vardesc *luaY_getvardesc (FuncState **fs, const expdesc *e) {
   if (e->k == VLOCAL)
     return getlocalvardesc(*fs, e->u.var.idx);
   else if (e->k != VUPVAL)
@@ -261,7 +262,7 @@ static Vardesc *getvardesc (FuncState **fs, expdesc *e) {
 
 static void check_readonly (LexState *ls, expdesc *e) {
   FuncState *fs = ls->fs;
-  Vardesc *vardesc = getvardesc(&fs, e);
+  Vardesc *vardesc = luaY_getvardesc(&fs, e);
   if (vardesc && vardesc->ro) {  /* is variable local and const? */
     const char *msg = luaO_pushfstring(ls->L,
        "attempt to assign to const variable '%s'",
@@ -1678,20 +1679,13 @@ static void commonlocalstat (LexState *ls) {
 static void tocloselocalstat (LexState *ls, Vardesc *var) {
   FuncState *fs = ls->fs;
   var->ro = 1;  /* to-be-closed variables are always read-only */
-  markupval(fs, fs->nactvar);
+  markupval(fs, fs->nactvar + 1);
   fs->bl->insidetbc = 1;  /* in the scope of a to-be-closed variable */
-  luaK_codeABC(fs, OP_TBC, fs->nactvar - 1, 0, 0);
+  luaK_codeABC(fs, OP_TBC, fs->nactvar, 0, 0);
 }
 
 
-static void attriblocalstat (LexState *ls) {
-  Vardesc *var;
-  TString *attr = str_checkname(ls);
-  testnext(ls, '>');
-  var = new_localvar(ls, str_checkname(ls));
-  checknext(ls, '=');
-  exp1(ls);
-  adjustlocalvars(ls, 1);
+static void checkattrib (LexState *ls, TString *attr, Vardesc *var) {
   if (strcmp(getstr(attr), "const") == 0)
     var->ro = 1;  /* set variable as read-only */
   else if (strcmp(getstr(attr), "toclose") == 0)
@@ -1702,6 +1696,22 @@ static void attriblocalstat (LexState *ls) {
 }
 
 
+static void attriblocalstat (LexState *ls) {
+  FuncState *fs = ls->fs;
+  Vardesc *var;
+  expdesc e;
+  TString *attr = str_checkname(ls);
+  testnext(ls, '>');
+  var = new_localvar(ls, str_checkname(ls));
+  checknext(ls, '=');
+  expr(ls, &e);
+  checkattrib(ls, attr, var);
+  luaK_tonumeral(fs, &e, &var->val);
+  luaK_exp2nextreg(fs, &e);
+  adjustlocalvars(ls, 1);
+}
+
+
 static void localstat (LexState *ls) {
   /* stat -> LOCAL NAME {',' NAME} ['=' explist]
            | LOCAL *toclose NAME '=' exp */
diff --git a/lparser.h b/lparser.h
index 228d4a5c..b708de25 100644
--- a/lparser.h
+++ b/lparser.h
@@ -81,6 +81,7 @@ typedef struct expdesc {
 
 /* description of an active local variable */
 typedef struct Vardesc {
+  TValue val;  /* constant value (if variable is 'const') */
   short idx;  /* index of the variable in the Proto's 'locvars' array */
   lu_byte ro;  /* true if variable is 'const' */
 } Vardesc;
@@ -143,6 +144,7 @@ typedef struct FuncState {
 } FuncState;
 
 
+LUAI_FUNC Vardesc *luaY_getvardesc (FuncState **fs, const expdesc *e);
 LUAI_FUNC LClosure *luaY_parser (lua_State *L, ZIO *z, Mbuffer *buff,
                                  Dyndata *dyd, const char *name, int firstchar);