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Add 'undef' operator.

    Marks values as undefined, useful for reaching defn
    dummy analysis.

--- a/6/isel.c

+++ b/6/isel.c

@@ -777,6 +777,7 @@

                 g(s, Icvttss2sd, a, r, NULL);

             break;

         case Odead:

+        case Oundef:

             /* nothing */

             break;

--- a/6/simp.c

+++ b/6/simp.c

@@ -1518,6 +1518,9 @@

         case Ogt: case Oge: case Olt: case Ole:

             r = compare(s, n, 0);

             break;

+        case Obad:

+            die("bad operator");

+            break;

         default:

             if (istyfloat(exprtype(n))) {

                 switch (exprop(n)) {

@@ -1530,9 +1533,6 @@

             }

             r = visit(s, n);

             break;

-        case Obad:

-            die("bad operator");

-            break;

     }

     return r;

 }

@@ -1587,11 +1587,14 @@

         case Ndecl:

             declarelocal(s, n);

-            if (!n->decl.init)

-                break;

             t = mkexpr(n->loc, Ovar, n->decl.name, NULL);

-            u = mkexpr(n->loc, Oasn, t, n->decl.init, NULL);

-            u->expr.type = n->decl.type;

+            if (!n->decl.init) {

+                u = mkexpr(n->loc, Oundef, t, NULL);

+                u->expr.type = mktype(n->loc, Tyvoid);

+            } else {

+                u = mkexpr(n->loc, Oasn, t, n->decl.init, NULL);

+                u->expr.type = n->decl.type;

+            }

             t->expr.type = n->decl.type;

             t->expr.did = n->decl.did;

             simp(s, u);

--- a/parse/infer.c

+++ b/parse/infer.c

@@ -517,19 +517,21 @@

 /* Gets the type of a literal value */

 static Type *littype(Node *n)

 {

-    if (n->lit.type)

-        return n->lit.type;

-    switch (n->lit.littype) {

-        case Lchr:      return mktype(n->loc, Tychar);                         break;

-        case Lbool:     return mktype(n->loc, Tybool);                         break;

-        case Lint:      return mktylike(n->loc, Tyint);                        break;

-        case Lflt:      return mktylike(n->loc, Tyflt64);                    break;

-        case Lstr:      return mktyslice(n->loc, mktype(n->loc, Tybyte));     break;

-        case Llbl:      return mktyptr(n->loc, mktype(n->loc, Tyvoid));       break;

-        case Lfunc:     return n->lit.fnval->func.type;                         break;

-    };

-    die("Bad lit type %d", n->lit.littype);

-    return NULL;

+    Type *t;

+

+    if (!n->lit.type) {

+        switch (n->lit.littype) {

+            case Lchr:      t = mktype(n->loc, Tychar);                         break;

+            case Lbool:     t = mktype(n->loc, Tybool);                         break;

+            case Lint:      t = mktylike(n->loc, Tyint);                        break;

+            case Lflt:      t = mktylike(n->loc, Tyflt64);                      break;

+            case Lstr:      t = mktyslice(n->loc, mktype(n->loc, Tybyte));      break;

+            case Llbl:      t = mktyptr(n->loc, mktype(n->loc, Tyvoid));        break;

+            case Lfunc:     t = n->lit.fnval->func.type;                        break;

+        }

+        n->lit.type = t;

+    }

+    return n->lit.type;

 }

 static Type *delayeducon(Inferstate *st, Type *fallback)

@@ -1446,7 +1448,8 @@

             }

             settype(st, n, type(st, args[0]));

             break;

-        case Obad: case Ocjmp: case Ojtab: case Oset: case Odead:

+        case Obad: case Ocjmp: case Ojtab: case Oset:

+        case Odead: case Oundef:

         case Oslbase: case Osllen: case Outag:

         case Oblit: case  Oclear: case Oudata:

         case Otrunc: case Oswiden: case Ozwiden:

--- a/parse/ops.def

+++ b/parse/ops.def

@@ -56,7 +56,8 @@

 O(Oarr,	        1,	OTmisc, NULL)

 /* all below this point are backend-only */

-O(Odead,        0,      OTmisc, "DEAD")         /*  code */

+O(Odead,        0,      OTmisc, "DEAD")         /* dead code */

+O(Oundef,       0,      OTmisc, "UNDEF")        /* undefined var */

 O(Ocjmp,	1,	OTmisc, "CJMP")         /* conditional jump */

 O(Ojtab,	1,	OTmisc, "JTAB")		/* jump table */

 O(Oset,	        1,	OTbin,  "=")            /* store to var */