Strip non-kernel functions from RS2SPIRV compilation

Added a pass to trim out non-kernel functions from the rest of SPIR-V
compilation passes. Also changed/enforced the pass ordering so that dead
globals exposed by this pass are removed prior of SPIR-V compilation.

Bug: 30964317

Test: RSoV, RSTest, RSoV LIT tests on Angler
Change-Id: I689758ae0977bca694341e948842b668f68caac8
diff --git a/rsov/compiler/RemoveNonkernelsPass.cpp b/rsov/compiler/RemoveNonkernelsPass.cpp
new file mode 100644
index 0000000..fb2d9ea
--- /dev/null
+++ b/rsov/compiler/RemoveNonkernelsPass.cpp
@@ -0,0 +1,95 @@
+/*
+ * Copyright 2017, The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "RemoveNonkernelsPass.h"
+
+#include "bcinfo/MetadataExtractor.h"
+
+#include "llvm/ADT/StringSet.h"
+#include "llvm/IR/Attributes.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/PassManager.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/Debug.h"
+
+#define DEBUG_TYPE "rs2spirv-remove"
+
+using namespace llvm;
+
+namespace rs2spirv {
+
+namespace {
+
+class RemoveNonkernelsPass : public ModulePass {
+  bcinfo::MetadataExtractor &ME;
+
+public:
+  static char ID;
+  explicit RemoveNonkernelsPass(bcinfo::MetadataExtractor &Extractor)
+      : ModulePass(ID), ME(Extractor) {}
+
+  const char *getPassName() const override { return "RemoveNonkernelsPass"; }
+
+  bool runOnModule(Module &M) override {
+    DEBUG(dbgs() << "RemoveNonkernelsPass\n");
+    DEBUG(M.dump());
+
+    const size_t RSKernelNum = ME.getExportForEachSignatureCount();
+    const char **RSKernelNames = ME.getExportForEachNameList();
+    if (RSKernelNum == 0)
+      DEBUG(dbgs() << "RemoveNonkernelsPass detected no kernel\n");
+
+    StringSet<> KNames;
+    for (size_t i = 0; i < RSKernelNum; ++i)
+      KNames.insert(RSKernelNames[i]);
+
+    std::vector<Function *> Functions;
+    for (auto &F : M.functions()) {
+      Functions.push_back(&F);
+    }
+
+    for (auto &F : Functions) {
+      if (F->isDeclaration())
+        continue;
+
+      const StringRef FName = F->getName();
+
+      if (KNames.count(FName) != 0)
+        continue; // Skip kernels.
+
+      F->replaceAllUsesWith(UndefValue::get((Type *)F->getType()));
+      F->eraseFromParent();
+
+      DEBUG(dbgs() << "Removed:\t" << FName << '\n');
+    }
+
+    // Return true, as the pass modifies module.
+    DEBUG(M.dump());
+    DEBUG(dbgs() << "Done removal\n");
+
+    return true;
+  }
+};
+}
+
+char RemoveNonkernelsPass::ID = 0;
+
+ModulePass *createRemoveNonkernelsPass(bcinfo::MetadataExtractor &ME) {
+  return new RemoveNonkernelsPass(ME);
+}
+
+} // namespace rs2spirv