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

[Amy Kwan via llvm-commits]

================
@@ -145,9 +164,97 @@ 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 node that loads the variable
+            // offset from the TOC, and the .__tls_get_mod node is being tuned
+            // here. It is better to put the variable offset TOC load after the
+            // call, since this node can use clobbers r4/r5.
+            // Search for the pattern of the two nodes that load from the TOC
+            // (either for the variable offset or for the module handle), and
+            // then move the variable offset TOC load 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 that loads from the TOC.
+              // Check the pattern and do the movement if the pattern matches.
+              if (UseIter != MBB.end()) {
+                // Collect all associated nodes that load from the TOC. 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 corresponding
+                      // node that loads from the TOC for the InReg. Otherwise,
+                      // Temp probably pointed to the variable offset TOC load
+                      // 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 nodes that load from the TOC: one should be
+                // _$TLSML, and the other will be moved before the node that
----------------
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
```
Minor comment update.

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