Testcase:

#include <vector>
bool f(const std::vector<int>& v) {
  return v == std::vector<int>{42};
}

We should, but don't, optimize out the allocation / deallocation here. We get IR that resembles this after optimization:

  %call = tail call noalias noundef nonnull dereferenceable(4) ptr @_Znwm(i64 noundef 4) #5
  store i32 42, ptr %call, align 4
  ; ...
  %bcmp = tail call i32 @bcmp(ptr noundef nonnull dereferenceable(4) %1, ptr noundef nonnull dereferenceable(4) %call, i64 
  ; ...
  tail call void @_ZdlPvm(ptr noundef nonnull %call, i64 noundef 4) #6

... with no other non-assumption uses of %call. It seems to me that we should be able to convert the @bcmp call to a load and an icmp, or perhaps to promote the constant argument to a global, and either way we should then be able to remove the heap allocation.

Similar testcase with the C++ standard library usage removed:

#include <stdlib.h>
#include <strings.h>
int f(int *p) {
  int *q = (int*)malloc(4);
  *q = 42;
  int r = bcmp(p, q, 4);
  free(q);
  return r == 0;
}

Again, we are unable to remove the heap allocation here.