[llvm-dev] Disabling DCE pass from opt

[serge guelton via llvm-dev]

Hi Alex,

That's probably not the answer you're looking for, but declaring tmpToBeDCE as volatile has the
side effect of preventing DCE :-)


On Tue, Nov 15, 2016 at 04:00:21PM +0200, Alex Susu via llvm-dev wrote:
>   Hello.
>     Could you please tell me which passes in opt perform DCE for the
> following code (I am aware of the passes from the source file
> lib/Transforms/IPO/PassManagerBuilder.cpp):
>         void foo(TYPE *A, TYPE *B, TYPE *C, TYPE N) {
>           int tmpToBeDCE;
> 
>           for (TYPE i = 0; i < N; ++i) {
>               C[i] = A[i] + B[i];
>               tmpToBeDCE = 2;
>           }
> 
>           tmpToBeDCE++;
>         }
> 
>     I ask because when I give this code to clang -O3 (I require -O3 to
> perform vectorization), in the resulting .ll file there is no reference to
> the tmpToBeDCE variable - it was eliminated since it has no real use.
>     I would like to still have this variable implemented in the output .ll file.
> 
>   Thank you,
>     Alex
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