From 4dfb4ef88ef10d4c1d7afafcdcf7ece117f9b36e Mon Sep 17 00:00:00 2001
From: "codeflash-ai[bot]"
 <148906541+codeflash-ai[bot]@users.noreply.github.com>
Date: Sun, 1 Feb 2026 14:31:00 +0000
Subject: [PATCH] Optimize function_has_return_statement
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The optimization achieves a **77% speedup** (from 1.29ms to 725μs) by restructuring the depth-first search to check the most common locations for return statements first, avoiding unnecessary traversal overhead.

## Key Optimizations

1. **Fast-path for top-level returns**: The optimized version first scans `function_node.body` directly before initiating the full DFS. Since most functions with returns have them at the top level, this short-circuits the expensive `ast.iter_child_nodes()` calls in the majority of cases.

2. **Reduced stack initialization overhead**: Instead of initializing the stack with `[function_node]` and then iterating over its children, the optimized code starts the stack with `list(body)`, skipping the wrapper function node entirely. This saves one unnecessary iteration.

3. **Early empty-body check**: By checking `if not body` upfront, the code avoids creating an empty stack and entering the while loop for functions with no statements.

## Performance Impact by Test Pattern

The optimization excels when:
- **Return is at top-level** (e.g., simple functions with direct returns): **300-500% faster** - the fast-path loop finds the return immediately without DFS overhead
- **Return is early in a large function**: **3,800-26,000% faster** for functions with 100+ statements - avoids traversing all subsequent AST nodes
- **Functions without returns but minimal nesting**: **10-20% faster** - benefits from reduced stack initialization overhead

The optimization shows minimal or slight regression when:
- **Return is deeply nested** (e.g., inside if/try/for blocks at level 2+): **0-5% slower** - the fast-path check adds overhead before falling back to DFS
- **Very complex nested structures**: **~4% slower** - the additional top-level scan doesn't help when returns are buried deep

## Line Profiler Evidence

The key improvement is visible in the line profiler: `ast.iter_child_nodes()` was called **1,366 times** (82.4% of runtime) in the original versus **679 times** (73.2% of runtime) in the optimized version - nearly a 50% reduction in expensive child node iterations, achieved by the fast-path detecting returns before the full DFS begins.
---
 codeflash/discovery/functions_to_optimize.py | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/codeflash/discovery/functions_to_optimize.py b/codeflash/discovery/functions_to_optimize.py
index 2a19f0a36..9770f2ff3 100644
--- a/codeflash/discovery/functions_to_optimize.py
+++ b/codeflash/discovery/functions_to_optimize.py
@@ -1001,7 +1001,19 @@ def filter_files_optimized(file_path: Path, tests_root: Path, ignore_paths: list
 
 def function_has_return_statement(function_node: FunctionDef | AsyncFunctionDef) -> bool:
     # Custom DFS, return True as soon as a Return node is found
-    stack: list[ast.AST] = [function_node]
+    # Handle edge case where a Return node is passed directly
+    if isinstance(function_node, ast.Return):
+        return True
+    
+    body = function_node.body
+    if not body:
+        return False
+    # Fast-path: check top-level body statements first (common case)
+    for node in body:
+        if isinstance(node, ast.Return):
+            return True
+    # Continue DFS from the body nodes (skip the wrapper function node)
+    stack: list[ast.AST] = list(body)
     while stack:
         node = stack.pop()
         if isinstance(node, ast.Return):