[DevMSAN] Skip device globals without users (#16760)

Author: zhaomaosu

llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp

@@ -775,6 +775,8 @@ Constant *getOrCreateGlobalString(Module &M, StringRef Name, StringRef Value,
 }
 
 static bool isUnsupportedDeviceGlobal(const GlobalVariable *G) {
+  if (G->user_empty())
+    return true;
   // Skip instrumenting on "__MsanKernelMetadata" etc.
   if (G->getName().starts_with("__Msan"))
     return true;

llvm/test/Instrumentation/MemorySanitizer/SPIRV/instrument_device_global.ll

@@ -4,7 +4,15 @@ target triple = "spir64-unknown-unknown"
 
 @.str = external addrspace(1) constant [59 x i8]
 @__spirv_BuiltInGlobalInvocationId = external addrspace(1) constant <3 x i64>
+@dev_global_no_users = dso_local addrspace(1) global { [4 x i32] } zeroinitializer
+
+define spir_func void @_ZZZ4mainENKUlRN4sycl3_V17handlerEE_clES2_ENKUlvE_clEv() {
+entry:
+  %call = call spir_func ptr addrspace(4) null(ptr addrspace(4) addrspacecast (ptr addrspace(1) @.str to ptr addrspace(4)), i64 0)
+  ret void
+}
 
 ; CHECK: @__MsanDeviceGlobalMetadata
 ; CHECK-NOT: @__spirv_BuiltInGlobalInvocationId
+; CHECK-NOT: @dev_global_no_users
 ; CHECK-SAME: @.str