[llvm] [PowerPC]redesign the target flags (PR #69695)

[Qiu Chaofan via llvm-commits]

================
@@ -102,79 +102,99 @@ class ModulePass;
     // PPC Specific MachineOperand flags.
     MO_NO_FLAG,
 
+    /// On PPC, the 12 bits are not enough for all target operand flags.
+    /// Treat all PPC target flags as direct flags. This also means we can not
+    /// use a bitmask flag, so if one operand has two or more flags, a fake
+    /// combination flag must be created. See example MO_GOT_TPREL_PCREL_FLAG.
+
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ecnelises wrote:

```cpp
    /// On PPC, 12 bits are not enough as orthogonal masks. Define flags in
    /// sequence to save space. To define new flag, add new enum entry instead
    /// of combining existing flags. See MO_GOT_TPREL_PCREL_FLAG as example.
```

https://github.com/llvm/llvm-project/pull/69695