[llvm-dev] Forcing loop optimization

[Michael Kruse via llvm-dev]

For forcing transformations via source code annotations, see [1].

However, there may be other reasons for an optimization to be not implied,
such as the loop not having been normalized. See [2]

[1]
https://clang.llvm.org/docs/LanguageExtensions.html#extensions-for-loop-hint-optimizations
[2] https://llvm.org/docs/LoopTerminology.html

Michael

Am Mo., 14. Juni 2021 um 08:23 Uhr schrieb Sudakshina Dutta via llvm-dev <
llvm-dev at lists.llvm.org>:

> Dear all,
>
> Good day to you. Is it possible to have forced application of loop
> unrolling or any other loop optimization ? I have tried applying loop
> unrolling on the following code. However, the optimization has not been
> applied by Clang.
>
> *Code (code.c)*
> int main()
> {
>     int i1, i2, N;
>     int In[50], A[50], D[50];
>
>     N = 25;
>     A[0] = In[0] + 5;
>     #pragma clang loop unroll (enable)
>     for(i1 = 1; i1 <= 25; i1++)
>     {
>             A[i1] = In[i1];
>             D[i1] = A[i1];
>     }
>     return D[N];
> }
>
> *The applied commands*
>
>    1. clang -S -emit-llvm code.c  -o code.ll -Xclang -disable-O0-optnon
>    2. opt -loop-unroll -S code.ll -o code-opt.ll -opt-bisect-limit=300
>    -unroll-count=3 -print-after=loop-unroll
>
> Regards,
> Sudakshina
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