Andres-Salamanca 577ee97d4e
[CIR] Fix access to bitfields inside a union (#154398)
This PR fixes the access to bitfields inside a union.
Previously, we were using a `getMemberOp` to access the field, but
because it is a union, `getMemberOp` would always use index `0`.

For example, given:
```c
typedef union {
  int x;
  int y : 4;
  int z : 8;
} demo;
```
```mlir
!rec_demo = !cir.record<union "demo" {!s32i, !u8i, !u8i}>
```

In the case of:

```c
d.y = 2;
```

It would generate:

```mlir
cir.get_member %0[0] {name = "y"} : !cir.ptr<!rec_demo> -> !cir.ptr<!s32i>
```

with a return type of `!s32i`, when it should be `!u8i`.
the get_member verifier would detect that the return type does not match
the `y` member.
To fix this, we now use `bitcast` to get the start of the union.
2025-08-19 17:43:13 -05:00

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