By taking advantage of three-operand IMUL, we can eliminate a MOV
instruction. This is a small code size win. However, due to IMUL sign
extending the immediate value to 64 bits, we can only apply this when
the magic number's most significant bit is zero.
To ensure this can actually happen, we also minimize the magic number by
checking for trailing zeroes.
Example (Unsigned division by 18)
Before:
41 BE E4 38 8E E3 mov r14d,0E38E38E4h
4D 0F AF F5 imul r14,r13
49 C1 EE 24 shr r14,24h
After:
4D 69 F5 39 8E E3 38 imul r14,r13,38E38E39h
49 C1 EE 22 shr r14,22h
2cafa0a960