Yingwei Zheng 3d795bdd4d [InstCombine] Handle a bitreverse idiom which ends with a bswap (#77677) ...

This patch handles the following `bitreverse` idiom, which is found in
8bd6445acc/absl/crc/internal/crc.cc (L75-L80):

```
uint32_t ReverseBits(uint32_t bits) {
  bits = (bits & 0xaaaaaaaau) >> 1 | (bits & 0x55555555u) << 1;
  bits = (bits & 0xccccccccu) >> 2 | (bits & 0x33333333u) << 2;
  bits = (bits & 0xf0f0f0f0u) >> 4 | (bits & 0x0f0f0f0fu) << 4;
  return absl::gbswap_32(bits);
}
```

Alive2: https://alive2.llvm.org/ce/z/ZYXNmj

2024-01-11 15:15:12 +08:00

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