[JIT] Optimization for CMP REG, 0xFFFFFFFF(FFFFFFFF) -> INC REG #52523
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If def DISPLAY_SIZES = 1 in jit.h, then gives and error
If def DISPLAY_SIZES = 1, gives an error
because of intersection of names "dataSize" between "compiler.h" and in "codegenarm64.cpp"
transfer local declaration for dataSize
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May 9, 2021
| // "INC REG" instead of "CMP REG, 0xFFFFFFFF" (or just - if "CMP REG, -1") | ||
| if (op1->isUsedFromReg() && op2->IsIntegralConst(-1) && targetReg != REG_NA) | ||
| { | ||
| emit->emitIns_R(INS_inc, emitTypeSize(tree), op1->GetRegNum()); |
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Not sure I understand this optimization - doesn't it modify op1 reg?
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Oh, good point! My big mistake. Yes, it changes the logic of the program by modify op1 value. Thank you.
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Per Agner (see https://www.agner.org/optimize/microarchitecture.pdf, Sec. 12.6, Table 12.1), this might suppress macro-op fusion? |
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Optimization for (example):
If in REG 0xFFFFFFFF, then instead of CMP => INC REG, thus the ZF flag changes in 1, and SETcc set byte in returned REG
If there are any pitfalls here, please explain to me.
Before:
After:
SPMI:
https://gist.github.com/DarkBullNull/1ea1218c1260b4ddb232ac2e07cf8c01