[AArch64] Simplify some masked integer comparisons. (#153783)

Specifically, `X & M ?= C --> (C << clz(M)) ?= (X << clz(M))` where M is
a non-empty sequence of ones starting at the least significant bit with
the remainder zero and C is a constant subset of M that cannot be
materialised into a SUBS (immediate). Proof:
https://alive2.llvm.org/ce/z/haqdJ4.

This improves the comparison in isinf, for example:
```cpp
int isinf(float x) {
  return __builtin_isinf(x);
}
```

Before:
```
isinf:
  fmov    w9, s0
  mov     w8, #2139095040
  and     w9, w9, #0x7fffffff
  cmp     w9, w8
  cset    w0, eq
  ret
```

After:
```
isinf:
  fmov    w9, s0
  mov     w8, #-16777216
  cmp     w8, w9, lsl #1
  cset    w0, eq
  ret
```

0 files changed, 0 insertions, 0 deletions