[dfsan] Refactor defining TLS variables

[stephan.yichao.zhao]

Summary

This is a part of https://reviews.llvm.org/D95835.

[morehouse]

llvm/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp

1073

Considering this function is only useful inside runImpl, it might be better to use a lambda there instead. Then we can also capture Mod and Changed instead of passing them every time.

Then we could also probably avoid passing the Ty.

[stephan.yichao.zhao]

chanegd getOrInsertGlobal to be a lambda.

We still keep Ty because it is different at callsites.

[morehouse]

LGTM

llvm/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp

 bool DataFlowSanitizer::runImpl(Module &M) {
   init(M);
 
   if (ABIList.isIn(M, "skip"))
     return false;
 
   const unsigned InitialGlobalSize = M.global_size();
   const unsigned InitialModuleSize = M.size();
 
   bool Changed = false;
 
-  Type *ArgTLSTy = ArrayType::get(Type::getInt64Ty(*Ctx), kArgTLSSize / 8);
-  ArgTLS = Mod->getOrInsertGlobal("__dfsan_arg_tls", ArgTLSTy);
-  if (GlobalVariable *G = dyn_cast<GlobalVariable>(ArgTLS)) {
-    Changed |= G->getThreadLocalMode() != GlobalVariable::InitialExecTLSModel;
-    G->setThreadLocalMode(GlobalVariable::InitialExecTLSModel);
-  }
-  Type *RetvalTLSTy =
-      ArrayType::get(Type::getInt64Ty(*Ctx), kRetvalTLSSize / 8);
-  RetvalTLS = Mod->getOrInsertGlobal("__dfsan_retval_tls", RetvalTLSTy);
-  if (GlobalVariable *G = dyn_cast<GlobalVariable>(RetvalTLS)) {
+  auto getOrInsertGlobal = [this, &Changed](StringRef Name,
+                                            Type *Ty) -> Constant * {
+    Constant *C = Mod->getOrInsertGlobal(Name, Ty);
+    if (GlobalVariable *G = dyn_cast<GlobalVariable>(C)) {
       Changed |= G->getThreadLocalMode() != GlobalVariable::InitialExecTLSModel;
       G->setThreadLocalMode(GlobalVariable::InitialExecTLSModel);
     }
+    return C;
+  };
+
+  // These globals must be kept in sync with the ones in dfsan.cpp.
+  ArgTLS = getOrInsertGlobal(
+      "__dfsan_arg_tls",
+      ArrayType::get(Type::getInt64Ty(*Ctx), kArgTLSSize / 8));
+  RetvalTLS = getOrInsertGlobal(
+      "__dfsan_retval_tls",
+      ArrayType::get(Type::getInt64Ty(*Ctx), kRetvalTLSSize / 8));
 
   ExternalShadowMask =
       Mod->getOrInsertGlobal(kDFSanExternShadowPtrMask, IntptrTy);
 
   initializeCallbackFunctions(M);
   initializeRuntimeFunctions(M);
 
   std::vector<Function *> FnsToInstrument;