Why Don't Modern Compilers Use Push/Pop for Gradual Stack Frame Building?

Compilers that Use Push/Pop Instructions for Local Variables

Modern C/C compilers like clang, ICC, MSVC, and gcc avoid using push/pop instructions directly. Instead, they optimize code by using more efficient sub/mov or lea instructions. Push/pop is still utilized for specific scenarios like saving/restoring callee-saved registers and passing stack arguments.

Compiler Support for Gradual Stack Frame Building

Compilers do not typically support building stack frames gradually using push/pop instructions. This is because it conflicts with unwinding mechanisms for error handling and debugging, and may result in larger unwind info sections. Additionally, mixing push and [rsp] addressing modes can introduce inefficiencies on Intel CPUs due to stack-sync uops.

Reasons for Avoiding Gradual Stack Frame Building

• Stack Unwinding and Debugging Support: It's crucial for stack unwinding during exceptions or debugging to maintain a precise stack state. Gradual frame building would complicate this process.
• Code Size and Efficiency: Sub/mov instructions provide more compact code and are generally more efficient than push/pop, especially for small constant values.
• Complexity in Implementation: Compilers would require additional checks and special-case handling to support gradual stack frame building, which can slow down the compilation process.

Conclusion

While push/pop instructions may seem beneficial for creating local variables, compilers currently prioritize more efficient and reliable techniques like sub/mov or lea. There are certain scenarios where push/pop is still used, but it is not typically employed for gradual stack frame building.

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