Fixed stripping unused inputs in remove_unused_interface_variables_pass for OpenGL

Fixed stripping unused inputs in remove_unused_interface_variables_pass for OpenGL
Re-added previous fix for preserve storage
Fixed remove_unused_interface_variables_pass removing outputs from fragment shaders

Author: EpicJeanNoeMorissette

source/opt/aggressive_dead_code_elim_pass.cpp

@@ -612,11 +612,11 @@ void AggressiveDCEPass::InitializeModuleScopeLiveInstructions() {
         // without an associated output. Don't remove outputs unless explicitly
         // allowed.
         // UE Change Begin: Fix to override the stripping of input variables, this should be allowed in the spec, but we rely on this data for some platforms to match inputs/outputs
-        if (!remove_outputs_) {
-          if (spv::StorageClass(storage_class) == spv::StorageClass::Input ||
-              spv::StorageClass(storage_class) == spv::StorageClass::Output) {
-            AddToWorklist(var);
-          }
+        if ((context()->preserve_storage_input() &&
+             spv::StorageClass(storage_class) == spv::StorageClass::Input) ||
+            (!remove_outputs_ &&
+             spv::StorageClass(storage_class) == spv::StorageClass::Output)) {
+          AddToWorklist(var);
         }
         // UE Change End: Fix to override the stripping of input variables, this should be allowed in the spec, but we rely on this data for some platforms to match inputs/outputs
       }

source/opt/optimizer.cpp

@@ -230,7 +230,7 @@ Optimizer& Optimizer::RegisterPerformancePasses(bool preserve_interface) {
       .RegisterPass(CreateLocalMultiStoreElimPass())
       .RegisterPass(CreateRedundancyEliminationPass())
       .RegisterPass(CreateSimplificationPass())
-      .RegisterPass(CreateAggressiveDCEPass())
+      .RegisterPass(CreateAggressiveDCEPass(preserve_interface))
       .RegisterPass(CreateCFGCleanupPass());
       // UE Change End
       ;

source/opt/remove_unused_interface_variables_pass.cpp

@@ -63,6 +63,17 @@ class RemoveUnusedInterfaceVariablesContext {
     std::unordered_set<uint32_t> old_variables;
     for (int i = entry_.NumInOperands() - 1; i >= 3; --i) {
       auto variable = entry_.GetInOperand(i).words[0];
+      // UE Change Begin: Fix to override the stripping of input variables and fragement outputs, this should be allowed in the spec, but we rely on this data for some platforms to match inputs/outputs
+      auto* var = parent_.get_def_use_mgr()->GetDef(variable);
+      
+      bool is_fragment_model = parent_.context()->GetStage() == spv::ExecutionModel::Fragment;
+      spv::StorageClass storage_class = spv::StorageClass(var->GetSingleWordInOperand(0));
+      if ((storage_class == spv::StorageClass::Input && parent_.context()->preserve_storage_input()) ||
+          (storage_class == spv::StorageClass::Output && is_fragment_model))
+      {
+        return false;
+      }
+      // UE Change End: Fix to override the stripping of input variables and fragement outputs, this should be allowed in the spec, but we rely on this data for some platforms to match inputs/outputs
       if (!used_variables_.count(variable)) return true;  // It is unused.
       if (old_variables.count(variable)) return true;     // It is duplicate.
       old_variables.insert(variable);