Messages in this thread | | | Date | Fri, 7 Sep 2018 15:02:08 -0700 | From | Paul Burton <> | Subject | Re: [PATCH] mips: bug: add unlikely() to BUG_ON() |
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Hi Igor,
On Fri, Sep 07, 2018 at 09:03:02PM +0300, Igor Stoppa wrote: > diff --git a/arch/mips/include/asm/bug.h b/arch/mips/include/asm/bug.h > index 745dc160a069..02101b54aec2 100644 > --- a/arch/mips/include/asm/bug.h > +++ b/arch/mips/include/asm/bug.h > @@ -31,7 +31,7 @@ static inline void __BUG_ON(unsigned long condition) > : : "r" (condition), "i" (BRK_BUG)); > } > > -#define BUG_ON(C) __BUG_ON((unsigned long)(C)) > +#define BUG_ON(C) __BUG_ON(unlikely((unsigned long)(C))) > > #define HAVE_ARCH_BUG_ON >
I'm not sure this will actually do anything.
__BUG_ON() doesn't use the value of its condition argument for regular control flow unless it's compile-time constant anyway, in which case unlikely() should be redundant because the compiler knows the value already.
If the condition isn't compile-time constant then we just emit a tne (trap-if-not-equal) instruction using inline asm. That will generate an exception if the value is non-zero at runtime. I don't see how adding unlikely() is going to help the compiler do anything differently with that.
Thanks, Paul
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