[llvm-dev] Which optimization pass deals with heap values?

[Florian Hahn via llvm-dev]

> On Jan 17, 2022, at 08:07, Russell Wallace via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
> All the optimization passes I can find in the documentation, deal with register, stack or global values; I cannot find any mention of anything trying to optimize values on the heap. But this:
> 
> #include <stdlib.h>
> 
> int main(int argc, char **argv) {
>   int *a = malloc(10 * sizeof(int));
>   for (int i = 0; i < 10; i++)
>     a[i] = i;
>   return a[5];
> }
> 
> compiles to 'ret 5' (as it should). Which pass does that?
> _____________________________________________


You can use `-mllvm -print-changed` with clang when built with assertions to find this out, e.g. see https://clang.godbolt.org/z/aM18Tr7Mr <https://clang.godbolt.org/z/aM18Tr7Mr>

It will be multiple optimizations working together. There are several passes that optimize memory operation, like DSE, GVN, EarlyCSE +MemorySSA.


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