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- Safe case: When A value is NOT used after STA, both the LDA #$00 is removed and STA is converted to STZ
- LDA #$00 / STA $1000 / STA $1001 → STZ $1000 / STZ $1001
- Critical case: When A value IS used later (like in ADC), LDA #$00 is preserved and STA is still converted to STZ
- LDA #$00 / STA $1000 / CLC / ADC $1001 / STA $1002 → LDA #$00 / STZ $1000 / CLC / ADC $1001 / STA $1002
The optimizer now correctly distinguishes between:
- Instructions that USE A value (can't remove LDA): ADC, SBC, AND, ORA, EOR, CMP, BIT, PHA, TAX, TAY
- Instructions that MODIFY A (safe to remove LDA): LDA, PLA, TXA, TYA
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The optimizer now correctly distinguishes between: