● Covered by 1 source · 1 reportLow impact1 neutral
Tail-call optimization in C compilers is a relatively recent development
Key points
- C calling conventions historically hindered tail-call optimization.
- Mark Probst implemented TCO in GCC in 2001 with limitations.
- Modern GCC and Clang now support TCO for specific tail-call patterns.
- This enables techniques needing many code snippets, like in Gforth.
Historical Limitations of Tail-Call Optimization in C
Historically, the C calling convention, where the caller is responsible for removing arguments from the stack, prevented effective tail-call optimization. This design meant that a call could not be directly replaced by a jump, as the caller needed to perform cleanup after the callee returned, turning what could be a tail call into a non-tail call.
Early Implementations and Challenges
In 1994, C compilers generally did not perform tail-call optimization for common usage patterns. Mark Probst introduced tail-call optimization in GCC in 2001, but it came with limitations, such as an inability to handle indirect calls, which are crucial for scenarios like interpreter dispatch.
Recent Advancements in C Compilers
Recent observations, prompted by the "Copy-and-Patch Compilation" paper by Xu and Kjolstad, indicate that modern GCC and Clang compilers now successfully perform tail-call optimization for specific types of tail calls. This represents a significant change from earlier compiler capabilities.
Impact on Code Generation Techniques
The improved tail-call optimization support in C compilers enables the use of techniques that require a large number of distinct code snippets. For example, in projects like Gforth, which currently limits itself to fewer than 2,000 code snippets, this advancement could allow for the implementation of more complex and efficient VM instructions or static superinstructions, potentially supporting up to 100,000 snippets.
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Primary sources
GitHub lpereira/lwanReporting from
Tail-call optimization (TCO) in C compilers like GCC and Clang for specific use cases is a recent development, despite the general concept existing for some time. This advancement allows for more efficient code generation in scenarios requiring numerous code snippets, such as interpreter dispatch.