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Re: x86: combined usage of "-Os -mregparm=3" leads to broken codes


On Tue, Sep 23, 2014 at 5:11 PM, Bin Meng <bmeng.cn@gmail.com> wrote:
>
> Sorry I still don't get it. The inline-asm codes are put in the very end
> of the test function just before return, so the clobbered registers are
> not used by gcc. The %edx gets overwritten before the inline-asm block.
>
> I just did a modification to the inline-asm codes to indicate to gcc that
> %edx is clobbered, but it did not help.
>

PS: if turning on WORKAROUND define in my test code, the generated codes
are correct.

I believe the issue is not with the inline assembly constraints but with
'-Os' plus '-regparm=3' combination. With '-Os' gcc optimization goes too
far to generate nothing for the C code 'params.a = d;' and gcc simply
takes %edx (supposed to be the 2nd parameter of test function) for a
scratch register.

Regards,
Bin


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