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re: toolchain/45673: gcc on i386 current generates bad code for assembler code in lock.h

>  On Sun, 11 Mar 2012, Kai-Uwe Eckhardt wrote:
>  > it looks like a problem in the toolchain. The gcc in 
>  > 6.0_BETA and current i386 is built with --with-march=i486 
>  > --with-tune=nocona. Nocona has the 64 bit registers available 
>  > and this leads to wrong code.
>  According to my reading of "man gcc", -march is supposed 
>  to control the available set of CPU features, registers, 
>  instructions, and the like, while -mtune is supposed to affect 
>  the cost of using the available CPU features (while not affecting 
>  the set of available features).  If a feature is not present in 
>  the CPU type specified with "-march", but is present in the CPU 
>  type specified with "-mtune", then I believe that GCC should NOT 
>  attempt to use that feature.
>  If GCC is invoked with "-march=i486 -mtune=nocona" and is using 
>  features that are present in the nocona CPU but not present in the 
>  i486 CPU, then I believe that indicates a GCC bug.

i had a read through the i386 gcc code and i couldn't see anyway
that -mtune=nocona would change the available instructions.  i
agree that this would be a bug if it does so.

fortunately, the real bug seems to be the register constraints.


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