[llvm] [clang] [PowerPC] Support local-dynamic TLS relocation on AIX (PR #66316)

[Amy Kwan via cfe-commits]

================
@@ -3413,13 +3415,34 @@ SDValue PPCTargetLowering::LowerGlobalTLSAddressAIX(SDValue Op,
     return DAG.getNode(PPCISD::ADD_TLS, dl, PtrVT, TLSReg, VariableOffset);
   }
 
-  // Only Local-Exec, Initial-Exec and General-Dynamic TLS models are currently
-  // supported models. If Local- or Initial-exec are not possible or specified,
-  // all GlobalTLSAddress nodes are lowered using the general-dynamic model.
-  // We need to generate two TOC entries, one for the variable offset, one for
-  // the region handle. The global address for the TOC entry of the region
-  // handle is created with the MO_TLSGDM_FLAG flag and the global address
-  // for the TOC entry of the variable offset is created with MO_TLSGD_FLAG.
+  if (Model == TLSModel::LocalDynamic) {
+    // For local-dynamic on AIX, we need to generate one TOC entry for each
+    // variable offset, and a single module-handle TOC entry for the entire
+    // file.
+
+    SDValue VariableOffsetTGA =
----------------
amy-kwan wrote:

nit: I think it is easier to follow if we group the `VariableOffsetTGA`/`VariableOffset` together, and the module handle code together.
```
    SDValue VariableOffsetTGA =
        DAG.getTargetGlobalAddress(GV, dl, PtrVT, 0, PPCII::MO_TLSLD_FLAG);
    SDValue VariableOffset = getTOCEntry(DAG, dl, VariableOffsetTGA);

  // module handle code . . .
```

https://github.com/llvm/llvm-project/pull/66316