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

Bruce Hoult via llvm-dev llvm-dev at lists.llvm.org
Tue Jun 19 12:46:47 PDT 2018

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

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
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