On 14/02/18 12:08, zhenzhong.duan wrote: > > > @@ -286,13 +286,13 @@ > > setz %dl > > and %dl, STACK_CPUINFO_FIELD(use_shadow_spec_ctrl)(%r14) > Is it safe to remove the 'xor %edx, %edx' above? setz set whole byte 1 > or 0. >
It is safe, but it is not a good idea. Using setz is an 8bit operation, which will suffer a register merge stall in the pipeline as we know for certain at this point that the upper bits of %edx are nonzero at this point. (An encoding which allowed setz %eax would have been far more useful in 64bit code.) ~Andrew _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
