For the following test-case,

int a;

static void foo()
  a = 3;

int main()
  a = 4;
  foo ();
  return a;

I assume it's safe to remove "a = 4"  since 'a' would be overwritten
by call to foo ?
IIUC, ipa-reference pass does mod/ref analysis to compute side-effects
of function call,
so could we perhaps use ipa_reference_get_not_written_global() in dse
pass to check if a global variable will be killed on call to a
function ? If not, I suppose we could write a similar ipa pass that
computes the set of killed global variables per function but I am not
sure if that's the correct approach.


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