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

[Amy Kwan via cfe-commits]

================
@@ -145,9 +164,96 @@ namespace {
                                                               .addImm(0);
 
         if (IsAIX) {
-          // The variable offset and region handle are copied in r4 and r3. The
-          // copies are followed by GETtlsADDR32AIX/GETtlsADDR64AIX.
-          if (!IsTLSTPRelMI) {
+          if (IsTLSLDAIXMI) {
+            // The relative order between the LoadOffset at toc node (for the
+            // variable offset), and the .__tls_get_mod node is being tuned
+            // here. It is better to put the LoadOffset at toc node after the call,
+            // since the LoadOffset at toc node can use clobbers r4/r5. Search for
+            // the pattern of two Load at toc nodes (either for the variable offset
+            // or for the module handle), and then move the LoadOffset at toc node
+            // right before the node that uses the OutReg of the .__tls_get_mod
+            // node.
+            unsigned LDTocOp =
+                Is64Bit ? (IsLargeModel ? PPC::LDtocL : PPC::LDtoc)
+                        : (IsLargeModel ? PPC::LWZtocL : PPC::LWZtoc);
+            if (!RegInfo.use_empty(OutReg)) {
+              std::set<MachineInstr *> Uses;
+              // Collect all instructions that use the OutReg.
+              for (MachineOperand &MO : RegInfo.use_operands(OutReg))
+                Uses.insert(MO.getParent());
+              // Find the first user (e.g.: lwax/stfdx) of the OutReg within the
+              // current BB.
+              MachineBasicBlock::iterator UseIter = MBB.begin();
+              for (MachineBasicBlock::iterator IE = MBB.end(); UseIter != IE;
+                   ++UseIter)
+                if (Uses.count(&*UseIter))
+                  break;
+
+              // Additional handling is required when UserIter (the first user
+              // of OutReg) is pointing to a valid node. Check the pattern and
+              // do the movement if the pattern matches.
+              if (UseIter != MBB.end()) {
+                // Collect associated Load at toc nodes. Use hasOneDef() to guard
+                // against unexpected scenarios.
+                std::set<MachineInstr *> LoadFromTocs;
+                for (MachineOperand &MO : UseIter->operands())
+                  if (MO.isReg() && MO.isUse()) {
+                    Register MOReg = MO.getReg();
+                    if (RegInfo.hasOneDef(MOReg)) {
+                      MachineInstr *Temp =
+                          RegInfo.getOneDef(MOReg)->getParent();
+                      // For the current TLSLDAIX node, get the Load at toc node
+                      // for the InReg. Otherwise, Temp probably pointed to the
+                      // LoadOffset at toc node that we would like to move.
+                      if (Temp == &MI && RegInfo.hasOneDef(InReg))
+                        Temp = RegInfo.getOneDef(InReg)->getParent();
+                      if (Temp->getOpcode() == LDTocOp)
+                        LoadFromTocs.insert(Temp);
+                    } else {
+                      // FIXME: analyze this scenario if there is one.
+                      LoadFromTocs.clear();
+                      break;
+                    }
+                  }
+
+                // Check the two Load at toc nodes: one should be _$TLSML, and the
+                // other will be moved before the node that uses the OutReg of
+                // the .__tls_get_mod node.
----------------
amy-kwan wrote:

```suggestion
                // Check the two nodes that loaded from the TOC: one should be _$TLSML,
                // and the other will be moved before the node that uses the OutReg of
                // the .__tls_get_mod node.
```

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