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Make improved pattern matching work for unions.

--- a/6/simp.c

+++ b/6/simp.c

@@ -1218,8 +1218,14 @@

 static Node *simpuget(Simp *s, Node *n, Node *dst)

 {

-    die("No uget simplification yet");

-	return NULL;

+    Node *u, *p;

+

+    if (!dst)

+        dst = temp(s, n);

+    u = n->expr.args[0];

+    p = addk(addr(s, u, exprtype(n)), Wordsz);

+    assign(s, dst, load(p));

+    return dst;

 }

 /* simplifies 

--- a/mi/match.c

+++ b/mi/match.c

@@ -154,16 +154,22 @@

 static Dtree *addunion(Dtree *t, Node *pat, Node *val, Node ***cap, size_t *ncap)

 {

-    Node *elt, *tag;

+    Node *elt, *tag, *id;

+    int32_t t1, t2;

     Dtree *sub;

+    Ucon *uc;

     size_t i;

     if (t->any)

         return t->any;

+    uc = finducon(tybase(exprtype(pat)), pat->expr.args[0]);

+    t2 = uc->id;

     /* if we have the value already... */

     sub = NULL;

     for (i = 0; i < t->nval; i++) {

-        if (nameeq(t->val[i], pat->expr.args[0])) {

+        tag = t->val[i]->expr.args[0];

+        t1 = tag->lit.intval;

+        if (t1 == t2) {

             if (pat->expr.nargs > 1) {

                 elt = uvalue(val, exprtype(pat->expr.args[1])); 

                 return addpat(t->sub[i], pat->expr.args[1], elt, cap, ncap);

@@ -173,11 +179,16 @@

         }

     }

+    /* otherwise create a new match */

     sub = mkdtree();

     sub->patexpr = pat;

     tag = mkexpr(pat->loc, Outag, val, NULL);

     tag->expr.type = mktype(pat->loc, Tyint32);

-    lappend(&t->val, &t->nval, pat->expr.args[0]);

+

+    id = mkintlit(pat->loc, uc->id);

+    id->expr.type = mktype(pat->loc, Tyint32);

+

+    lappend(&t->val, &t->nval, id);

     lappend(&t->sub, &t->nsub, sub);

     lappend(&t->load, &t->nload, tag);

     if (pat->expr.nargs == 2) {