[TBAA][DSE] bitfield store is incorrectly optimized out

[dtcxzyw]

Reproducer: https://godbolt.org/z/jKrGW5jEh

#include <stdint.h>

struct S1 {
   signed f0 : 9;
   unsigned f1 : 2;
   int8_t  f2;
};

struct S1 g;

struct S1 func(struct S1* x) {
    x->f2 = 3;
    *x = g;
    return *x;
}

x->f2 = 3 is incorrectly eliminated by DSEPass.
This miscompilation is caused by recent commit #81313.

[dtcxzyw]

Another reproducer: https://godbolt.org/z/Y3bnsMqd7

[fhahn]

Let me take a look. It seems like clang emits tbaa .struct with overlapping fields. Need to check what exactly is going on