use buf_target in expand_index

tinygrad/codegen/late/devectorizer.py

@@ -60,7 +60,9 @@ load_store_indexing = PatternMatcher([
 def expand_index(buf:UOp, vec:UOp):
   if getenv("UNSAFE_DISABLE_MASK", 0): vec = vec.get_idx()
   # generate the individual indexes
-  midx = graph_rewrite(UOp.sink(*[buf.index(vec.gep(i), ptr=True) for i in range(vec.dtype.count)]),
+  # we use `.buf_target()` here to avoid traversing into the AFTER
+  buf_target = buf.buf_target().rtag() if buf.op is Ops.AFTER else buf
+  midx = graph_rewrite(UOp.sink(*[buf_target.index(vec.gep(i), ptr=True) for i in range(vec.dtype.count)]),
                        symbolic+load_store_indexing, name=f"index_buf_{buf.arg}")
   # extract all the relevant offsets
   offsets_rootsrc: defaultdict[Any, dict[int, list[int]]] = defaultdict(dict)
@@ -93,7 +95,7 @@ def expand_index(buf:UOp, vec:UOp):
   assert None not in idxs, f"some idxs are missing {idxs}"
   # this base thing is for image, we want the CAT to be a normal pointer
   post_cat = UOp(Ops.PTRCAT, buf.ptrdtype.base.ptr(size=buf.ptrdtype.size, addrspace=buf.ptrdtype.addrspace).vec(global_offset), tuple(ret))
-  return post_cat.gep(tuple(cast(list[int], idxs)))
+  return post_cat.gep(tuple(cast(list[int], idxs))).substitute({buf_target:buf})
 
 def cat_after_store(cat:UOp, data:UOp, sto:UOp):
   # TODO: this is written in many places

tinygrad/uop/ops.py

@@ -615,6 +615,7 @@ class UOp(OpMixin, metaclass=UOpMetaClass):
 
   def buf_target(self) -> UOp:
     # the buffer that's being loaded from or store to
+    # NOTE: this is the good one to keep
     match self.op:
       case Ops.DEFINE_GLOBAL | Ops.DEFINE_LOCAL | Ops.DEFINE_REG: return self
       case Ops.AFTER | Ops.INDEX | Ops.STORE | Ops.LOAD: return self.src[0].buf_target()