[llvm-dev] DSE: Remove useless stores between malloc & memset

[Friedman, Eli via llvm-dev]

On 5/17/2018 8:58 AM, Dávid Bolvanský via llvm-dev wrote:
> Hello,
>
> I would like to find a way to do this removal properly. I found DSE 
> and "eliminateNoopStore" can be useful for this thing.
>
> What I mean?
> int *test = malloc(15 * sizeof(int));
> test[10] = 12; < ----- remove this store
> memset(test,0,sizeof(int) * 15);

This is classic dead store elimination, and it's already handled by DSE. 
At least, we optimize the following testcase:

#include <stdlib.h>
#include <string.h>
void bar(int*);
void f() {
   int *test = malloc(15 * sizeof(int));
   test[10] = 12;
   memset(test,0,sizeof(int) * 15);
   bar(test);
}

You should be able to look at the existing code to understand how it's 
handled (using MemoryDependenceAnalysis).

-Eli

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