Messages in this thread | | | Subject | Re: [PATCH] slab: Remove unnecessary __builtin_constant_p() | From | Steven Rostedt <> | Date | Mon, 22 Apr 2013 19:15:18 -0400 |
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On Mon, 2013-04-22 at 14:16 -0700, Andrew Morton wrote: > On Mon, 22 Apr 2013 16:58:21 -0400 Steven Rostedt <rostedt@goodmis.org> wrote:
> > When looking into this, we found the only two users of the index_of() > > static function that has this issue, passes in size_of(), which will > > always be a constant, making the check redundant. > > Looking at the current callers is cheating. What happens if someone > adds another caller which doesn't use sizeof?
Well, as it required a size of something, if it was dynamic then what would the size be of?
> > > Note, this is a bug in Clang that will hopefully be fixed soon. But for > > now, this strange redundant compile time check is preventing Clang from > > even testing the Linux kernel build. > > </little birdie voice> > > > > And I still think the original change log has rational for the change, > > as it does make it rather confusing to what is happening there. > > The patch made index_of() weaker! > > It's probably all a bit academic, given that linux-next does > > -/* > - * This function must be completely optimized away if a constant is passed to > - * it. Mostly the same as what is in linux/slab.h except it returns an index. > - */ > -static __always_inline int index_of(const size_t size) > -{ > - extern void __bad_size(void); > - > - if (__builtin_constant_p(size)) { > - int i = 0; > - > -#define CACHE(x) \ > - if (size <=x) \ > - return i; \ > - else \ > - i++; > -#include <linux/kmalloc_sizes.h> > -#undef CACHE > - __bad_size(); > - } else > - __bad_size(); > - return 0; > -} > -
Looks like someone just ate the bird.
-- Steve
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