[llvm-dev] Naming clash: -DCLS=n and CLS in code

[Bruce Hoult via llvm-dev]

I'm prepared to give the benefit of the doubt and assume there's a "#ifndef
#define ..." somewhere, not shown for brevity.


On Tue, Jun 19, 2018 at 12:49 PM, Tim Northover <t.p.northover at gmail.com>
wrote:

> On Tue, 19 Jun 2018 at 20:46, Bruce Hoult <brucehoult at sifive.com> wrote:
> > Furthermore .. in the articles you reference, the -DCLS=$(getconf
> LEVEL1_DCACHE_LINESIZE) is passed when compiling the user's program -- one
> doing extensive blocked matrix operations -- and not when building the
> *compiler*.
>
> It's worse. At least in the first case, the code looks like it
> wouldn't even compile without that definition. That's not an
> optimization flag, that's a weird build system.
> >
> >
> > On Tue, Jun 19, 2018 at 12:12 PM, U.Mutlu via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
> >>
> >> Tim Northover wrote on 06/19/2018 08:54 PM:
> >>>>>
> >>>>> Why are you passing that argument in the first place? The compiler
> >>>>> completely ignores it.
> >>>>
> >>>>
> >>>> CLS stands for cacheline size. It is an important parameter
> >>>> for optimization of the generated code, at least with gcc/g++.
> >>>> -DCLS=n should have the same importance like for example -DNDEBUG.
> >>>
> >>>
> >>> The GCC source doesn't appear to mention it, and neither does any
> >>> documentation I can find. NDEBUG on the other hand is in both the C
> >>> and C++ standards.
> >>>
> >>> I still think there's some weird library out there that interprets it
> >>> the way you're suggesting, and Clang is not that weird library.
> >>
> >>
> >> This is from a famous article series titled "What every programmer
> should know about memory":
> >>   gcc -DCLS=$(getconf LEVEL1_DCACHE_LINESIZE) ...
> >>
> >> https://lwn.net/Articles/255364/
> >> http://mosermichael.github.io/cstuff/all/blog/2015/12/11/wepskn.html
> >> https://www.dcl.hpi.uni-potsdam.de/teaching/numasem/
> slides/NUMASem_Matrix_multiplication.pdf
> >>
> >> You can find more examples by searching for "DCLS getconf
> LEVEL1_DCACHE_LINESIZE".
> >>
> >>
> >>
> >> _______________________________________________
> >> LLVM Developers mailing list
> >> llvm-dev at lists.llvm.org
> >> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> >
> >
>
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