Register-sensitive selection, duplication, and sequencing of instructions

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https://dl.acm.org/doi/10.1145/377792.377849

https://github.com/llvm/llvm-project/tree/bc8726b16bacc1790cee9a27302f556f5ca7ba39/llvm/lib/Target/X86

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Instruction Selection and Duplication:

• Works on general dependence graphs with both true and non-true dependences
• Considers register pressure when selecting instructions
• Duplicates instructions if it reduces overall register pressure

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• X86RegisterInfo.cpp: Defines register classes, allocation order, etc.
• X86InstrInfo.cpp: Implements instruction selection and scheduling logic
• X86FrameLowering.cpp: Handles stack frame and register spilling

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Uses backwards scheduling algorithm Prioritizes instructions that free up registers Delays instructions that increase register pressure