[Bug tree-optimization/103168] New: Value numbering of pure functions can be improved

[hubicka at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103168

            Bug ID: 103168
           Summary: Value numbering of pure functions can be improved
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hubicka at gcc dot gnu.org
  Target Milestone: ---

In the following testcase the call to test is loop invariant because memory
modified is not escaping. While value numbering of pure functions we however
add value number of the vdef corresponding to vuse.

I think we want to walk the chain to aliasing store?

__attribute__((const)) int test();
int
main()
{
        int ret;
        int a[10];
        for (int i=0; i<10;i++)
          if (test())
                  a[i]++;
        for (int i=0; i<10;i++)
                ret *= a[i];
        return ret;
}