fix[venom]: fix _stack_reorder() routine

tests/unit/compiler/venom/test_stack_reorder.py

@@ -0,0 +1,28 @@
+from vyper.venom import generate_assembly_experimental
+from vyper.venom.context import IRContext
+
+
+def test_stack_reorder():
+    """
+    Test to was created from the example in the
+    issue https://github.com/vyperlang/vyper/issues/4215
+    this example should fail with original stack reorder
+    algorithm but succeed with new one
+    """
+    ctx = IRContext()
+    fn = ctx.create_function("_global")
+
+    bb = fn.get_basic_block()
+    var0 = bb.append_instruction("store", 1)
+    var1 = bb.append_instruction("store", 2)
+    var2 = bb.append_instruction("store", 3)
+    var3 = bb.append_instruction("store", 4)
+    var4 = bb.append_instruction("store", 5)
+
+    bb.append_instruction("staticcall", var0, var1, var2, var3, var4, var3)
+
+    ret_val = bb.append_instruction("add", var4, var4)
+
+    bb.append_instruction("ret", ret_val)
+
+    generate_assembly_experimental(ctx)

vyper/venom/venom_to_assembly.py

@@ -1,4 +1,5 @@
-from collections import Counter
+from bisect import insort
+from collections import Counter, defaultdict
 from typing import Any
 
 from vyper.exceptions import CompilerPanic, StackTooDeep
@@ -205,14 +206,29 @@ def _stack_reorder(
             stack = stack.copy()
 
         stack_ops_count = len(stack_ops)
+        if stack_ops_count == 0:
+            return 0
 
         counts = Counter(stack_ops)
 
+        # positions stores the positions of relevant operands
+        # on stack for example operand %82 is on positions [0, 3]
+        # this operand could ocure even more deeper in the stack
+        # but only those that are needed/relevant in calculation
+        # are considered
+        positions: dict[IROperand, list[int]] = defaultdict(list)
+        for op in stack_ops:
+            positions[op] = []
+            for i in range(counts[op]):
+                positions[op].append(stack.get_depth(op, i + 1))
+
         for i in range(stack_ops_count):
             op = stack_ops[i]
             final_stack_depth = -(stack_ops_count - i - 1)
-            depth = stack.get_depth(op, counts[op])  # type: ignore
-            counts[op] -= 1
+            depth = positions[op].pop()  # type: ignore
+            assert depth not in range(
+                -stack_ops_count + 1, final_stack_depth
+            ), f"{depth} : ({-stack_ops_count - 1}, {final_stack_depth})"
 
             if depth == StackModel.NOT_IN_STACK:
                 raise CompilerPanic(f"Variable {op} not in stack")
@@ -223,9 +239,26 @@ def _stack_reorder(
             if op == stack.peek(final_stack_depth):
                 continue
 
+            # moves the top item to original position
+            top_item_positions = positions[stack.peek(0)]
+            if len(top_item_positions) != 0:
+                top_item_positions.remove(0)
+                insort(top_item_positions, depth)
+
             cost += self.swap(assembly, stack, depth)
+
+            # moves the item from final position to top
+            final_item_positions = positions[stack.peek(final_stack_depth)]
+            if final_stack_depth in final_item_positions:
+                final_item_positions.remove(final_stack_depth)
+                final_item_positions.insert(0, 0)
+            else:
+                final_item_positions.insert(0, 0)
+
             cost += self.swap(assembly, stack, final_stack_depth)
 
+        assert stack._stack[-len(stack_ops) :] == stack_ops, (stack, stack_ops)
+
         return cost
 
     def _emit_input_operands(