Optimize remove_unused_definitions_by_function_names

The optimized code achieves a **15% speedup** through three key optimizations that target expensive operations identified in the profiler:

**1. Early Exit for Empty Qualified Functions (Major Impact)**
- Added a guard clause in `collect_top_level_defs_with_usages()` that returns early if `qualified_function_names` is empty
- This completely skips the expensive CST visitor pattern (`wrapper.visit(dependency_collector)`) which accounts for 82.6% of the function's runtime
- Test results show dramatic speedups (706-3748% faster) for cases with empty function sets, indicating this optimization has substantial impact when no specific functions need to be preserved

**2. Loop Optimization with Local Variable Caching**
- Cached `new_children.append` as `append_child` and `remove_unused_definitions_recursively` as `rr` to eliminate repeated attribute lookups in the hot loop
- The profiler shows this loop executing 2,777 times and consuming 9.5% of total runtime through recursive calls
- Attribute lookups in Python are relatively expensive, so caching these references provides measurable improvement in tight loops

**3. Tuple Unpacking Elimination**
- Replaced tuple unpacking `modified_module, _ = remove_unused_definitions_recursively(...)` with direct indexing to avoid creating temporary tuples
- While a micro-optimization, it reduces object allocation overhead in the main execution path

**Impact Based on Function Usage:**
The function references show this is called from `extract_code_string_context_from_files()` and `extract_code_markdown_context_from_files()`, both of which process multiple files and function sets during code context extraction. The early exit optimization is particularly valuable here since many files may have empty qualified function sets, allowing the system to skip expensive dependency analysis entirely.

The optimizations are most effective for:
- Large codebases where many files don't contain target functions (early exit benefit)
- Complex AST structures with deep nesting (loop optimization benefit) 
- Batch processing scenarios where the function is called repeatedly (cumulative micro-optimization benefits)

Author: codeflash-ai[bot]

codeflash/context/unused_definition_remover.py

@@ -447,10 +447,13 @@ def remove_unused_definitions_recursively(  # noqa: PLR0911
             new_children = []
             section_found_used = False
 
+            append_child = new_children.append  # Local for speed
+            # Minimize attribute lookup in loop
+            rr = remove_unused_definitions_recursively
             for child in original_content:
-                filtered, used = remove_unused_definitions_recursively(child, definitions)
+                filtered, used = rr(child, definitions)
                 if filtered:
-                    new_children.append(filtered)
+                    append_child(filtered)
                 section_found_used |= used
 
             if new_children or section_found_used:
@@ -478,6 +481,12 @@ def collect_top_level_defs_with_usages(
     definitions = collect_top_level_definitions(module)
 
     # Collect dependencies between definitions using the visitor pattern
+
+    # DependencyCollector uses CST visitor, very expensive! Use only if qualified_function_names is not empty
+    if not qualified_function_names:
+        return definitions
+
+    # Only instantiate and visit if needed
     wrapper = cst.MetadataWrapper(module)
     dependency_collector = DependencyCollector(definitions)
     wrapper.visit(dependency_collector)
@@ -510,7 +519,8 @@ def remove_unused_definitions_by_function_names(code: str, qualified_function_na
         defs_with_usages = collect_top_level_defs_with_usages(module, qualified_function_names)
 
         # Apply the recursive removal transformation
-        modified_module, _ = remove_unused_definitions_recursively(module, defs_with_usages)
+        result = remove_unused_definitions_recursively(module, defs_with_usages)
+        modified_module = result[0]
 
         return modified_module.code if modified_module else ""  # noqa: TRY300
     except Exception as e: