[llvm] [InstCombine] Try optimizing with knownbits which determined from Cond (PR #91762)

[via llvm-commits]

ParkHanbum wrote:

this is why test failed in windows.

```
================
[this have problem with cl.exe but not clang]
  unsigned CmpLHSOpc;
  bool IsDisjoint = false;
  // Specially handling for X^Y==0 transformed to X==Y
  if (match(TVal, m_c_BitwiseLogic(m_Specific(CmpLHS), m_Specific(CmpRHS)))) {
    X = CmpLHS;
    Y = CmpRHS;
>>>>>>>>>>>
    APInt ZeroVal = APInt::getZero(CmpLHS->getType()->getScalarSizeInBits());
    C = const_cast<APInt *>(&ZeroVal);

================
[this have not a problem]
  unsigned CmpLHSOpc;
  bool IsDisjoint = false;
  APInt ZeroVal;
  // Specially handling for X^Y==0 transformed to X==Y
  if (match(TVal, m_c_BitwiseLogic(m_Specific(CmpLHS), m_Specific(CmpRHS)))) {
    X = CmpLHS;
    Y = CmpRHS;
>>>>>>>>>>>
    ZeroVal = APInt::getZero(CmpLHS->getType()->getScalarSizeInBits());
    C = const_cast<APInt *>(&ZeroVal);
```
I declare ZeroVal in if-match block, but used its reference after off the block. 

window compiler didn't allow this, I could see garbage value was setted in `C` through debug message.

```
APInt(32b, 1616897802336u 1990099040s)
```

it obviouly my mistake. 
but clang seems allow this as roughly.

how do you think? 


https://github.com/llvm/llvm-project/pull/91762