fix[codegen]: fix make_setter overlap in dynarray_append (#4059)

`make_setter` can potentially run into overlap when called from
`dynarray_append`; this commit copies to a temporary intermediate buffer
(as is done in `AnnAssign`) before copying to the destination if the
condition is detected.

this is a variant of the bugs fixed in ad9c10b and 1c8349e.

this commit also adds a util function to detect overlap, and adds an
assertion directly in `make_setter` so that future variants panic
instead of generating bad code.

tests/functional/codegen/types/test_dynamic_array.py

@@ -1865,3 +1865,25 @@ def test_dynarray_length_no_clobber(get_contract, tx_failed, code):
     c = get_contract(code)
     with tx_failed():
         c.should_revert()
+
+
+def test_dynarray_make_setter_overlap(get_contract):
+    # GH 4056, variant of GH 3503
+    code = """
+a: DynArray[DynArray[uint256, 10], 10]
+
+@external
+def foo() -> DynArray[uint256, 10]:
+    self.a.append([1, 2, self.boo(), 4])
+    return self.a[0] # returns [11, 12, 3, 4]
+
+@internal
+def boo() -> uint256:
+    self.a.append([11, 12, 13, 14, 15, 16])
+    self.a.pop()
+    # it should now be impossible to read any of [11, 12, 13, 14, 15, 16]
+    return 3
+    """
+
+    c = get_contract(code)
+    assert c.foo() == [1, 2, 3, 4]

vyper/codegen/context.py

@@ -67,7 +67,6 @@ def as_ir_node(self):
             mutable=self.mutable,
             location=self.location,
         )
-        ret._referenced_variables = {self}
         if self.alloca is not None:
             ret.passthrough_metadata["alloca"] = self.alloca
         return ret

vyper/codegen/core.py

@@ -901,10 +901,33 @@ def _abi_payload_size(ir_node):
     raise CompilerPanic("unreachable")  # pragma: nocover
 
 
+def potential_overlap(left, right):
+    """
+    Return true if make_setter(left, right) could potentially trample
+    src or dst during evaluation.
+    """
+    if left.typ._is_prim_word and right.typ._is_prim_word:
+        return False
+
+    if len(left.referenced_variables & right.referenced_variables) > 0:
+        return True
+
+    if len(left.referenced_variables) > 0 and right.contains_risky_call:
+        return True
+
+    if left.contains_risky_call and len(right.referenced_variables) > 0:
+        return True
+
+    return False
+
+
 # Create an x=y statement, where the types may be compound
 def make_setter(left, right, hi=None):
     check_assign(left, right)
 
+    if potential_overlap(left, right):
+        raise CompilerPanic("overlap between src and dst!")
+
     # we need bounds checks when decoding from memory, otherwise we can
     # get oob reads.
     #

vyper/codegen/expr.py

@@ -18,7 +18,9 @@
     is_flag_type,
     is_numeric_type,
     is_tuple_like,
+    make_setter,
     pop_dyn_array,
+    potential_overlap,
     sar,
     shl,
     shr,
@@ -165,17 +167,24 @@ def parse_NameConstant(self):
 
     # Variable names
     def parse_Name(self):
-        if self.expr.id == "self":
+        varname = self.expr.id
+
+        if varname == "self":
             return IRnode.from_list(["address"], typ=AddressT())
-        elif self.expr.id in self.context.vars:
-            return self.context.lookup_var(self.expr.id).as_ir_node()
 
-        elif (varinfo := self.expr._expr_info.var_info) is not None:
-            if varinfo.is_constant:
-                return Expr.parse_value_expr(varinfo.decl_node.value, self.context)
+        varinfo = self.expr._expr_info.var_info
+        assert varinfo is not None
 
-            assert varinfo.is_immutable, "not an immutable!"
+        # local variable
+        if varname in self.context.vars:
+            ret = self.context.lookup_var(varname).as_ir_node()
+            ret._referenced_variables = {varinfo}
+            return ret
 
+        if varinfo.is_constant:
+            return Expr.parse_value_expr(varinfo.decl_node.value, self.context)
+
+        if varinfo.is_immutable:
             mutable = self.context.is_ctor_context
 
             location = data_location_to_address_space(
@@ -186,12 +195,14 @@ def parse_Name(self):
                 varinfo.position.position,
                 typ=varinfo.typ,
                 location=location,
-                annotation=self.expr.id,
+                annotation=varname,
                 mutable=mutable,
             )
             ret._referenced_variables = {varinfo}
             return ret
 
+        raise CompilerPanic("unreachable")  # pragma: nocover
+
     # x.y or x[5]
     def parse_Attribute(self):
         typ = self.expr._metadata["type"]
@@ -691,7 +702,16 @@ def parse_Call(self):
                 check_assign(
                     dummy_node_for_type(darray.typ.value_type), dummy_node_for_type(arg.typ)
                 )
-                return append_dyn_array(darray, arg)
+
+                ret = ["seq"]
+                if potential_overlap(darray, arg):
+                    tmp = self.context.new_internal_variable(arg.typ)
+                    tmp = IRnode.from_list(tmp, typ=arg.typ, location=MEMORY)
+                    ret.append(make_setter(tmp, arg))
+                    arg = tmp
+
+                ret.append(append_dyn_array(darray, arg))
+                return IRnode.from_list(ret)
 
         assert isinstance(func_t, ContractFunctionT)
         assert func_t.is_internal or func_t.is_constructor

vyper/codegen/stmt.py

@@ -13,6 +13,7 @@
     get_element_ptr,
     get_type_for_exact_size,
     make_setter,
+    potential_overlap,
     wrap_value_for_external_return,
     writeable,
 )
@@ -70,10 +71,7 @@ def parse_Assign(self):
         dst = self._get_target(self.stmt.target)
 
         ret = ["seq"]
-        overlap = len(dst.referenced_variables & src.referenced_variables) > 0
-        overlap |= len(dst.referenced_variables) > 0 and src.contains_risky_call
-        overlap |= dst.contains_risky_call and len(src.referenced_variables) > 0
-        if overlap and not dst.typ._is_prim_word:
+        if potential_overlap(dst, src):
             # there is overlap between the lhs and rhs, and the type is
             # complex - i.e., it spans multiple words. for safety, we
             # copy to a temporary buffer before copying to the destination.