Paulo Matos, FEX x87 Stack Optimization

Summary
This blog post discusses recent optimizations made to the FEX emulator, an ARM64 emulator of Intel assembly, to improve its handling of x87 code. The author explains the workings of the x87 FPU, highlighting its stack-based operations and its components, including the status register and the tag register. The post then dives into the implementation of a new pass in FEX that optimizes x87 instruction blocks by utilizing virtual stacks and generating more efficient code. This pass achieves substantial code size reductions and performance improvements, as evidenced by benchmarks from popular games like Half-Life and Oblivion. However, the author notes that some issues still require further investigation, specifically related to the interaction between the FPU state and the MMX state.

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