What are the microarchitecural differences between 32 and 64 bit X86?

HeavenPR

Pushq %rax # 1 byte instruction encoded as pushl %eax in 32 bits
Pushq %r10 # 2 byte instruction encoded as pushl preceeded by REX.


这个从一个方面解释了为什么附加的 registers 使用起来要慢，因为 code 变大了