micro-optimization

问题 Consider a simple instruction like mov RCX, RDI # 48 89 f9 The 48 is the REX prefix for x86_64. It is not an LCP. But consider adding an LCP (for alignment purposes): .byte 0x67 mov RCX, RDI # 67 48 89 f9 67 is an address size prefix which in this case is for an instruction without addresses. This instruction also has no immediates, and it doesn't use the F7 opcode (False LCP stalls; F7 would be TEST, NOT, NEG, MUL, IMUL, DIV + IDIV). Assume that it doesn't cross a 16-byte boundary either.

问题 Consider a simple instruction like mov RCX, RDI # 48 89 f9 The 48 is the REX prefix for x86_64. It is not an LCP. But consider adding an LCP (for alignment purposes): .byte 0x67 mov RCX, RDI # 67 48 89 f9 67 is an address size prefix which in this case is for an instruction without addresses. This instruction also has no immediates, and it doesn't use the F7 opcode (False LCP stalls; F7 would be TEST, NOT, NEG, MUL, IMUL, DIV + IDIV). Assume that it doesn't cross a 16-byte boundary either.

来源： https://stackoverflow.com/questions/63433790/optimizing-percpu-2-level-bit-vector-in-restartable-sequence-on-x86-64-skylake

来源： https://stackoverflow.com/questions/50222531/conflicting-signs-in-x86-assembly-movsx-then-unsigned-compare-branch

来源： https://stackoverflow.com/questions/50222531/conflicting-signs-in-x86-assembly-movsx-then-unsigned-compare-branch

来源： https://stackoverflow.com/questions/50222531/conflicting-signs-in-x86-assembly-movsx-then-unsigned-compare-branch

来源： https://stackoverflow.com/questions/50222531/conflicting-signs-in-x86-assembly-movsx-then-unsigned-compare-branch

来源： https://stackoverflow.com/questions/50222531/conflicting-signs-in-x86-assembly-movsx-then-unsigned-compare-branch

来源： https://stackoverflow.com/questions/50222531/conflicting-signs-in-x86-assembly-movsx-then-unsigned-compare-branch

来源： https://stackoverflow.com/questions/50222531/conflicting-signs-in-x86-assembly-movsx-then-unsigned-compare-branch