-mno-bmi doesn't work in GCC4.8.2

[hanhwi]

Hi, all,

I'm using GCC 4.8.2 on x86-64 machine. The compiler emits tzcnt instruction
unlike previous gcc. I want to prevent using tzcnt instruction. As I know,
tzcnt instruction is BMI extension. To disable the feature, I set -mno-bmi
but it didn't work.

Is there any way to disable tzcnt instruction?

Thanks,
Hanhwi



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[Ryan Mansfield]

Post by hanhwi
Hi, all,
I'm using GCC 4.8.2 on x86-64 machine. The compiler emits tzcnt instruction
unlike previous gcc. I want to prevent using tzcnt instruction. As I know,
tzcnt instruction is BMI extension. To disable the feature, I set -mno-bmi
but it didn't work.

I believe starting with 4.8 gcc unconditionally emits tzcnt, as non-bmi
targets will handle it as rep;bsf, and bmi targets will treat it as a tzcnt.

Regards,

Ryan Mansfield