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@mpage Thanks for your feedback! I've pushed an update that should address cases like the one you mentioned.

The main change involves doing, as suggested, a cfg analysis (using dfs via is_borrow_safe and check_borrow_safety_globally functions). This analysis now:

• Tracks the borrowed value across basic block boundaries if it's live at the end of a block.
• Checks along all execution paths if the original local variable backing the borrow is overwritten before the borrowed value is consumed.
• Verifies that the borrowed value itself isn't stored into another local variable.
• Detects and handles cycles in the CFG to ensure termination and safety.

I think this way we are properly handling the scenarios like the one you provided and ensuring the LOAD_FAST_BORROW optimization is applied safely.

Could you please take another look when you have a moment?

To be honest, this dived deeper into flowgraph.c than I initially anticipated, and it's a bit outside my usual comfort zone, so any further guidance would be much appreciated if I've missed something or if there are better ways to approach this.