[clang] [llvm] [PowerPC] Tune AIX shared library TLS model at function level by heuristic (PR #84132)

[Hubert Tong via cfe-commits]

================
@@ -3362,6 +3362,64 @@ SDValue PPCTargetLowering::LowerGlobalTLSAddress(SDValue Op,
   return LowerGlobalTLSAddressLinux(Op, DAG);
 }
 
+/// updateForAIXShLibTLSModelOpt - Helper to initialize TLS model opt settings,
+/// and then apply the update.
+static void updateForAIXShLibTLSModelOpt(TLSModel::Model &Model,
+                                         SelectionDAG &DAG,
+                                         const TargetMachine &TM) {
+  // Initialize TLS model opt setting lazily:
+  // (1) Use initial-exec for single TLS var references within current function.
+  // (2) Use local-dynamic for multiple TLS var references within current
+  // function.
+  PPCFunctionInfo *FuncInfo =
+      DAG.getMachineFunction().getInfo<PPCFunctionInfo>();
+  if (!FuncInfo->isAIXFuncUseInitDone()) {
+    SmallPtrSet<const GlobalValue *, 8> TLSGV;
+    // Iterate over all instructions within current function, collect all TLS
+    // global variables (global variables taken as the first parameter to
+    // Intrinsic::threadlocal_address).
+    const Function &Func = DAG.getMachineFunction().getFunction();
+    for (Function::const_iterator BI = Func.begin(), BE = Func.end(); BI != BE;
+         ++BI)
+      for (BasicBlock::const_iterator II = BI->begin(), IE = BI->end();
+           II != IE; ++II)
+        if (II->getOpcode() == Instruction::Call)
+          if (const CallInst *CI = dyn_cast<const CallInst>(&*II))
+            if (Function *CF = CI->getCalledFunction())
+              if (CF->isDeclaration() &&
+                  CF->getIntrinsicID() == Intrinsic::threadlocal_address)
+                if (const GlobalValue *GV =
+                        dyn_cast<GlobalValue>(II->getOperand(0))) {
+                  TLSModel::Model GVModel = TM.getTLSModel(GV);
+                  if (GVModel == TLSModel::InitialExec ||
+                      GVModel == TLSModel::LocalDynamic)
+                    TLSGV.insert(GV);
+                }
+
+    unsigned TLSGVCnt = TLSGV.size();
+    LLVM_DEBUG(dbgs() << format("TLSGV count:%d\n", TLSGVCnt));
+    if (TLSGVCnt == 1)
+      FuncInfo->setAIXFuncUseTLSIE();
+    else if (TLSGVCnt > 1)
+      FuncInfo->setAIXFuncUseTLSLD();
----------------
hubert-reinterpretcast wrote:

We should need to set only one thing (to represent "use IE instead of LD"). The threshold number should not be repeated in more than one place.

Additionally, the threshold number may need to be increased (tests via experiments).

https://github.com/llvm/llvm-project/pull/84132