[llvm] [GlobalIsel] Combine freeze (PR #93239)

[Thorsten Schütt via llvm-commits]

================
@@ -1745,18 +1778,55 @@ static bool canCreateUndefOrPoison(Register Reg, const MachineRegisterInfo &MRI,
                                    UndefPoisonKind Kind) {
   MachineInstr *RegDef = MRI.getVRegDef(Reg);
 
-  if (auto *GMI = dyn_cast<GenericMachineInstr>(RegDef)) {
-    if (ConsiderFlagsAndMetadata && includesPoison(Kind) &&
-        GMI->hasPoisonGeneratingFlags())
-      return true;
-  } else {
-    // Conservatively return true.
-    return true;
-  }
----------------
tschuett wrote:

ValueTracking writes it as follows:
```
if (ConsiderFlagsAndMetadata && includesPoison(Kind) &&
      Op->hasPoisonGeneratingAnnotations())
    return true;
```
The question is how to handle non `GenericMachineInstr`.

https://github.com/llvm/llvm-project/pull/93239