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Constrain conditional tests to be testable

--- a/parse/infer.c

+++ b/parse/infer.c

@@ -145,7 +145,7 @@

     return s;

 }

-static void matchcstrs(Node *ctx, Type *a, Type *b)

+static void mergecstrs(Node *ctx, Type *a, Type *b)

 {

     if (b->type == Tyvar) {

         /* make sure that if a = b, both have same cstrs */

@@ -181,7 +181,7 @@

         b = t;

     }

-    matchcstrs(ctx, a, b);

+    mergecstrs(ctx, a, b);

     if (a->type != b->type) {

         if (a->type == Tyvar)

             tytab[a->tid] = b;

@@ -195,7 +195,7 @@

                 fatal(ctx->line, "%s incompatible with %s near %s", tystr(a), tystr(b), ctxstr(ctx));

             /* FIXME: recurse properly.

-               matchcstrs(ctx, a, b);

+               mergecstrs(ctx, a, b);

                unify(ctx, a->sub[i], b->sub[i]);

                */

         }

@@ -382,12 +382,14 @@

             infernode(n->ifstmt.cond, NULL, sawret);

             infernode(n->ifstmt.iftrue, ret, sawret);

             infernode(n->ifstmt.iffalse, ret, sawret);

+            constrain(type(n->ifstmt.cond), cstrtab[Tctest]);

             break;

         case Nloopstmt:

-            infernode(n->loopstmt.cond, NULL, sawret);

             infernode(n->loopstmt.init, ret, sawret);

+            infernode(n->loopstmt.cond, NULL, sawret);

             infernode(n->loopstmt.step, ret, sawret);

             infernode(n->loopstmt.body, ret, sawret);

+            constrain(type(n->loopstmt.cond), cstrtab[Tctest]);

             break;

         case Nexpr:

             inferexpr(n, ret, sawret);