C and C Compilers with Garbage Collection: Libraries, Optimizations, and Generated Code

In contrast to higher-level languages like Java and C#, traditional C and C do not come with built-in garbage collection (GC) mechanisms. However, several compilers and libraries can provide GC functionality or enable the integration of such features into your projects. This article explores the available options, delves into optimizations, and discusses the implications for generated code.

Compilers with Garbage Collection

Several C and C compilers can integrate garbage collection through libraries, although these compilers themselves do not natively provide GC functionality.

GCC (GNU Compiler Collection)

While GCC itself does not support garbage collection, it can be linked with external libraries like the Boehm-Demers-Weiser Garbage Collector (Boehm GC) for automatic memory management. This library provides extensive support for conservative garbage collection in C and C programs.

Clang

Similar to GCC, Clang also lacks built-in garbage collection capabilities. Integration with external libraries like the Boehm GC can enable GC features in your projects.

MSVC (Microsoft Visual C)

MSVC does not have built-in garbage collection. You can use external libraries like the Boehm GC to achieve this functionality.

Libraries for Garbage Collection

Besides integrating with external GC libraries, C and C libraries like Mimalloc can be configured to work with garbage collection patterns. Additionally, C11 introduced smart pointers, which provide a form of automatic memory management, though not traditional garbage collection.

Boehm-Demers-Weiser Garbage Collector

This widely used conservative garbage collector is designed for C and C programs. It can be integrated into your projects to simplify memory management, reducing the need for manual memory handling.

Mimalloc

Primarily a memory allocator, Mimalloc can be configured to work with garbage collection patterns. It is a versatile tool for managing memory in C and C environments.

Smart Pointers in C

C11 introduced smart pointers that enhance automatic memory management, though they are not true garbage collection. These tools can significantly reduce the risk of memory leaks and other related issues.

Generated Code

For code generated by C and C compilers, garbage collection typically does not apply as it does in higher-level languages. The responsibility for memory management lies with the developer or libraries used. If a library providing garbage collection is utilized, the generated code can be designed to work within that system.

Internal vs. Emitted Code

It is important to distinguish between a compiler having internal garbage collection machinery and a compiler emitting code for your programs that uses garbage collection. GCC, for instance, does have some internal garbage collection machinery, but this is primarily used during optimization rather than directly integrated into the emitted code.

For industrial-strength C and C compilers like GCC and Clang, optimization is a crucial aspect of their functionality. These compilers are designed to produce highly optimized code, often requiring millions of lines of code. Basic optimizations like inlining, constant folding, and loop unrolling are performed in the middle-end of the compiler, separate from memory management concerns.

The GCC middle-end contains more than two hundred optimization passes, many of which perform specific tasks. The garbage collector in GCC, called GGC, is triggered between optimization passes and works slightly faster than the Boehm GC. However, it is not as robust as the Boehm GC for handling cyclic data, which is common in compilers.

Clang, on the other hand, uses traditional C programming techniques like reference counting and weak pointers. This approach can be less effective for handling cyclic data. The Garbage Collection Handbook explains why this might be a suboptimal approach.

Summary

In summary, while traditional C and C compilers do not include garbage collection functionality, third-party libraries like the Boehm GC can be used to add such features to your projects. Smart pointers in C provide a form of automatic memory management but do not constitute traditional garbage collection. The process of optimization in compilers is distinct from the integration of garbage collection.