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From: "segher at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/101865] _ARCH_PWR8 is not defined when using -mcpu=power8
Date: Tue, 31 Aug 2021 16:37:31 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101865

--- Comment #15 from Segher Boessenkool <segher at gcc dot gnu.org> ---
(In reply to HaoChen Gui from comment #9)
> For this example, let's suppose that we set mcpu=3Dpower8 and mno-vsx in =
the
> command line. Thus, _ARCH_PWR8 should be defined as mcpu=3Dpower8. But if=
 the
> Power8-specific codes contain VSX codes, could the asm be executed? I thi=
nk
> we just use the macro _ARCH_PWR8 here to guard which instructions are
> available.

Yes, it can be executed just fine.  The only thing the compiler -mno-vsx fl=
ag
does is make the compiler not generate any code that uses the VSRs (or any =
VSX
insns).  Whether the program tries to use VSX resources by itself is up to =
it.

The CPU certainly does not think it does not have those insns.  The kernel =
will
not think it does not, either.  Things will just work, by default anyway.=