Purpose of cmove instruction in x86 assembly?

2018-06-03 17:55:55

disassembling an executable I encountered the cmove instruction. I've already searched on internet but I've only found that it's a conditional move, and if the source and destination are equal the mov occurs. what i haven't understood yet is why should I need it, since it doesn't change the operands. please could you explain me its purpose, using an example too if necessary

thanks

The CMOVcc instructions doesn't compare the source and destination. It uses the flags from a previous comparison (or other operation that sets the flags) which determines if the move should be done or not.

Example; this copies edx to ecx if eax and ebx are equal:

cmp eax, ebx
cmoveq ecx, edx

This does the same as:

cmp eax, ebx
jne skip
  mov ecx, edx
skip:

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