collatz checks

1 files changed, 51 insertions, 0 deletions

diff --git a/src/type.cff b/src/type.cff
index 1d224cc..e3989c7 100644
--- a/src/type.cff
+++ b/src/type.cff
@@ -202,6 +202,31 @@ fn rank2numtype(r int) *const Type {
    return *types[r];
 }
 
+fn arraydecay(ty *const Type) *const Type {
+   switch ty.u {
+   case Arr arr; return mkptrtype(arr.child);
+   case else; return ty;
+   }
+}
+
+fn constifychild(ty *const Type) *const Type {
+   let ty2 = *ty;
+   switch ty.u {
+   case Ptr child;
+      let cchild = constify(child);
+      if child == cchild { return ty; }
+      ty2.u.Ptr = child;
+      return interntype(ty2);
+   case Slice child;
+      let cchild = constify(child);
+      if child == cchild { return ty; }
+      ty2.u.Slice = child;
+      return interntype(ty2);
+   case else;
+      assert(#f, "constifychild: not ptr or slice");
+   }
+}
+
 extern fn typeof2(a *const Type, b *const Type) *const Type {
    if a == b and !a->is(:Int) {
       return a;
@@ -217,5 +242,31 @@ extern fn typeof2(a *const Type, b *const Type) *const Type {
    if a == unconstify(b) {
       return b;
    }
+   if a->is(:Arr) and b->is(:Arr) {
+      a = arraydecay(a);
+   }
+   if a->is(:Ptr) and b->is(:Arr) {
+      b = arraydecay(b);
+   }
+   if a->is(:Arr) and b->is(:Ptr) {
+      a = arraydecay(a);
+   }
+   if a.u.#tag == b.u.#tag and (a->is(:Ptr) or a->is(:Slice)) {
+      let akonst = a.u.Ptr.konst,
+          bkonst = b.u.Ptr.konst,
+          uac = unconstify(a.u.Ptr),
+          ubc = unconstify(b.u.Ptr);
+      if uac == ubc {
+         return akonst ? a : b;
+      }
+      if uac == ty_void {
+         if bkonst and !akonst { return constifychild(a); }
+         return a;
+      }
+      if ubc == ty_void {
+         if akonst and !bkonst { return constifychild(b); }
+         return b;
+      }
+   }
    return #null;
 }