[llvm] [PowerPC] Utilize getReservedRegs to find asm clobberable registers. (PR #107863)

[Amy Kwan via llvm-commits]

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@@ -3434,6 +3434,10 @@ SDValue PPCTargetLowering::LowerGlobalTLSAddressAIX(SDValue Op,
   if (Subtarget.hasAIXShLibTLSModelOpt())
     updateForAIXShLibTLSModelOpt(Model, DAG, getTargetMachine());
 
+  // Whenever accessing the TLS variable, it is done through the TC entries.
+  // Therefore, we set the DAG to use the TOC base.
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amy-kwan wrote:

```suggestion
  // TLS variables are accessed through TOC entries.
  // To support this, set the DAG to use the TOC base pointer.
```

https://github.com/llvm/llvm-project/pull/107863