[clang] [llvm] [X86] Add Support for X86 TLSDESC Relocations (PR #83136)

[via cfe-commits]

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@@ -18543,7 +18552,19 @@ GetTLSADDR(SelectionDAG &DAG, SDValue Chain, GlobalAddressSDNode *GA,
   MFI.setHasCalls(true);
 
   SDValue Glue = Chain.getValue(1);
-  return DAG.getCopyFromReg(Chain, dl, ReturnReg, PtrVT, Glue);
+  SDValue Ret = DAG.getCopyFromReg(Chain, dl, ReturnReg, PtrVT, Glue);
+
+  if (!UseTLSDESC)
+    return Ret;
+
+  const X86Subtarget &Subtarget = DAG.getSubtarget<X86Subtarget>();
+  unsigned Seg = Subtarget.is64Bit() ? X86AS::FS : X86AS::GS;
+
+  Value *Ptr = Constant::getNullValue(PointerType::get(*DAG.getContext(), Seg));
+  SDValue Offset =
+      DAG.getLoad(PtrVT, dl, DAG.getEntryNode(), DAG.getIntPtrConstant(0, dl),
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goldsteinn wrote:

Why add `0`?

https://github.com/llvm/llvm-project/pull/83136