[AMDGPU] Request module used variables from LDS lowering as internal

[rampitec]

Summary

I do not see any practical difference but technically
used.* variables are internal and a call to getGlobalVariable
misses true as a second argument. NFC as far as I can tell.

[JonChesterfield]

Ah, apologies. I misread/misremembered this. The global variable looked up here is llvm.used / llvm.compiler.used, and not the LDS variable that is going to be removed.

I can't tell if AppendingLinkage qualifies as internal or not from the documentation. From going code reading, it isn't. Control flow hits AllowLocal || !Result->hasLocalLinkage(), and appending linkage will return false for hasLocalLinkage.

I don't know if we're better off with getGlobalVariable or getNamedGlobal here. Functionally, no difference.

llvm/lib/Target/AMDGPU/AMDGPULowerModuleLDSPass.cpp

 using namespace llvm;
 
 namespace {
 
 class AMDGPULowerModuleLDS : public ModulePass {
 
   static void removeFromUsedList(Module &M, StringRef Name,
                                  SmallPtrSetImpl<Constant *> &ToRemove) {
-    GlobalVariable *GV = M.getGlobalVariable(Name);
+    GlobalVariable *GV = M.getNamedGlobal(Name);
     if (!GV || ToRemove.empty()) {
       return;
     }
 
     SmallVector<Constant *, 16> Init;
     auto *CA = cast<ConstantArray>(GV->getInitializer());
     for (auto &Op : CA->operands()) {
       // ModuleUtils::appendToUsed only inserts Constants