We normally check for division by zero to know if we should set the
destination register to zero with a XOR. However, when the divisor and
destination registers are the same the explicit zeroing can be omitted.
In addition, some of the surrounding branching can be simplified as
well.
Before:
45 85 FF test r15d,r15d
75 05 jne normal_path
45 33 FF xor r15d,r15d
EB 0C jmp done
normal_path:
B8 5A 00 00 00 mov eax,5Ah
99 cdq
41 F7 FF idiv eax,r15d
44 8B F8 mov r15d,eax
done:
After:
45 85 FF test r15d,r15d
74 0C je done
B8 5A 00 00 00 mov eax,5Ah
99 cdq
41 F7 FF idiv eax,r15d
44 8B F8 mov r15d,eax
done:
Sintendo
47e16133e5