[TargetLowering] Fix the problem of emulated-TLS implementation witho… (#101490)

For a __thread variable x, when emulated TLS is enabled and there is an
access to x, the compiler first looks up the symbol __emutls_v.x within
the module. However, the issue arises with an alias y of x, the compiler
still tries to look up __emutls_v.y instead of __emutls_v.x. As a
result, the lookup returns a nullptr, causing the compiler to crash. The
purpose of this MR (Merge Request) is to ensure that in emulated TLS,
before checking __emutls_v.y, the compiler first identifies which global
value y is an alias of.

Author: cceerczw

llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp

@@ -10245,10 +10245,13 @@ SDValue TargetLowering::LowerToTLSEmulatedModel(const GlobalAddressSDNode *GA,
 
   ArgListTy Args;
   ArgListEntry Entry;
-  std::string NameString = ("__emutls_v." + GA->getGlobal()->getName()).str();
-  Module *VariableModule = const_cast<Module*>(GA->getGlobal()->getParent());
+  const GlobalValue *GV =
+      cast<GlobalValue>(GA->getGlobal()->stripPointerCastsAndAliases());
+  SmallString<32> NameString("__emutls_v.");
+  NameString += GV->getName();
   StringRef EmuTlsVarName(NameString);
-  GlobalVariable *EmuTlsVar = VariableModule->getNamedGlobal(EmuTlsVarName);
+  const GlobalVariable *EmuTlsVar =
+      GV->getParent()->getNamedGlobal(EmuTlsVarName);
   assert(EmuTlsVar && "Cannot find EmuTlsVar ");
   Entry.Node = DAG.getGlobalAddress(EmuTlsVar, dl, PtrVT);
   Entry.Ty = VoidPtrType;

llvm/test/CodeGen/AArch64/emutls_alias.ll

@@ -0,0 +1,17 @@
+; RUN: llc < %s -emulated-tls -mtriple=aarch64-linux-ohos \
+; RUN:     | FileCheck -check-prefix=EMUTLS_CHECK %s
+ 
+%struct.__res_state = type { [5 x i8] }
+ 
+@foo = dso_local thread_local global %struct.__res_state { [5 x i8] c"\01\02\03\04\05" }, align 1
+ 
+@bar = hidden thread_local(initialexec) alias %struct.__res_state, ptr @foo
+ 
+define dso_local i32 @main() {
+  %1 = alloca i32, align 4
+  store i32 0, ptr %1, align 4
+  store i8 0, ptr @bar, align 1
+  ; EMUTLS_CHECK: adrp    x0, __emutls_v.foo
+  ; EMUTLS_CHECK-NEXT: add     x0, x0, :lo12:__emutls_v.foo
+  ret i32 0
+}