Lower private global variables in functions

Usually the functions are inlined into one entry functions before the
SpirvLowerGlobal Pass, However in one case,
llpc-raytracing-mode=continuations, the module does not inline library
functions to entry function. the private global variables are used in
multi functions. These private global variables are coming from
gpurt hlsl module, usually are enum values hence, these global
variables are loaded, but not stored. So we are probably safe lower
these variables in there used functions.

wer

llpc/lower/llpcSpirvLowerGlobal.cpp

@@ -590,27 +590,44 @@ void SpirvLowerGlobal::mapGlobalVariableToProxy(GlobalVariable *globalVar) {
   const auto &dataLayout = m_module->getDataLayout();
   Type *globalVarTy = globalVar->getValueType();
 
-  m_builder->SetInsertPointPastAllocas(m_entryPoint);
-
   Value *proxy = nullptr;
-
+  removeConstantExpr(m_context, globalVar);
   // Handle special globals, regular allocas will be removed by SROA pass.
-  if (globalVar->getName().startswith(RtName::HitAttribute))
+  if (globalVar->getName().startswith(RtName::HitAttribute)) {
     proxy = m_entryPoint->getArg(1);
-  else if (globalVar->getName().startswith(RtName::IncomingRayPayLoad))
+    globalVar->replaceAllUsesWith(proxy);
+  } else if (globalVar->getName().startswith(RtName::IncomingRayPayLoad)) {
     proxy = m_entryPoint->getArg(0);
-  else if (globalVar->getName().startswith(RtName::IncomingCallableData))
+    globalVar->replaceAllUsesWith(proxy);
+  } else if (globalVar->getName().startswith(RtName::IncomingCallableData)) {
     proxy = m_entryPoint->getArg(0);
-  else
-    proxy = m_builder->CreateAlloca(globalVarTy, dataLayout.getAllocaAddrSpace(), nullptr,
-                                    Twine(LlpcName::GlobalProxyPrefix) + globalVar->getName());
+    globalVar->replaceAllUsesWith(proxy);
+  } else {
+    // Collect used functions
+    SmallSet<Function *, 4> funcs;
+    for (User *user : globalVar->users()) {
+      auto inst = cast<Instruction>(user);
+      funcs.insert(inst->getFunction());
+    }
+    for (Function *func : funcs) {
+      assert(m_entryPoint);
+      m_builder->SetInsertPointPastAllocas(func);
+      proxy = m_builder->CreateAlloca(globalVarTy, dataLayout.getAllocaAddrSpace(), nullptr,
+                                      Twine(LlpcName::GlobalProxyPrefix) + globalVar->getName());
 
-  if (globalVar->hasInitializer()) {
-    auto initializer = globalVar->getInitializer();
-    m_builder->CreateStore(initializer, proxy);
+      if (globalVar->hasInitializer()) {
+        auto initializer = globalVar->getInitializer();
+        m_builder->CreateStore(initializer, proxy);
+      }
+      globalVar->mutateType(proxy->getType());
+      globalVar->replaceUsesWithIf(proxy, [func](Use &U) {
+        Instruction *userInst = cast<Instruction>(U.getUser());
+        return userInst->getFunction() == func;
+      });
+    }
   }
 
-  m_globalVarProxyMap[globalVar] = proxy;
+  m_globalVarProxy.insert(globalVar);
 }
 
 // =====================================================================================================================
@@ -687,20 +704,17 @@ void SpirvLowerGlobal::mapOutputToProxy(GlobalVariable *output) {
 // =====================================================================================================================
 // Does lowering operations for SPIR-V global variables, replaces global variables with proxy variables.
 void SpirvLowerGlobal::lowerGlobalVar() {
-  if (m_globalVarProxyMap.empty()) {
+  if (m_globalVarProxy.empty()) {
     // Skip lowering if there is no global variable
     return;
   }
 
-  // Replace global variable with proxy variable
-  for (auto globalVarMap : m_globalVarProxyMap) {
-    auto globalVar = cast<GlobalVariable>(globalVarMap.first);
-    auto proxy = globalVarMap.second;
-    globalVar->mutateType(proxy->getType()); // To clear address space for pointer to make replacement valid
-    globalVar->replaceAllUsesWith(proxy);
+  // remove global variables
+  for (auto globalVar : m_globalVarProxy) {
     globalVar->dropAllReferences();
     globalVar->eraseFromParent();
   }
+  m_globalVarProxy.clear();
 }
 
 // =====================================================================================================================

llpc/lower/llpcSpirvLowerGlobal.h

@@ -115,8 +115,8 @@ class SpirvLowerGlobal : public SpirvLower, public llvm::PassInfoMixin<SpirvLowe
   void addCallInstForXfbOutput(const ShaderInOutMetadata &outputMeta, Value *outputValue, unsigned xfbBufferAdjust,
                                unsigned xfbOffsetAdjust, unsigned locOffset, lgc::InOutInfo outputInfo);
 
-  std::unordered_map<llvm::Value *, llvm::Value *> m_globalVarProxyMap; // Proxy map for lowering global variables
-  std::unordered_map<llvm::Value *, llvm::Value *> m_inputProxyMap;     // Proxy map for lowering inputs
+  std::unordered_set<llvm::GlobalVariable *> m_globalVarProxy;      // The unordered_set for lowering global variables
+  std::unordered_map<llvm::Value *, llvm::Value *> m_inputProxyMap; // Proxy map for lowering inputs
 
   // NOTE: Here we use list to store pairs of output proxy mappings. This is because we want output patching to be
   // "ordered" (resulting LLVM IR for the patching always be consistent).