[Bugpoint redesign] Added Pass to Remove Global Variables

Summary:
This pass tries to remove Global Variables, as well as their derived uses. For example if a variable `@x` is used by `%call1` and `%call2`, both these uses and the definition of `@x` are deleted. Moreover if `%call1` or `%call2` are used elsewhere those uses are also deleted, and so on recursively.

I'm still uncertain if this pass should remove derived uses, I'm open to suggestions.

Subscribers: mgorny, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D64176

> llvm-svn: 368918

llvm-svn: 369061

2 files changed, 92 insertions, 0 deletions

diff --git a/llvm/tools/llvm-reduce/deltas/ReduceGlobalVars.cpp b/llvm/tools/llvm-reduce/deltas/ReduceGlobalVars.cpp
new file mode 100644
index 00000000000..15bb5a79cb3
--- /dev/null
+++ b/llvm/tools/llvm-reduce/deltas/ReduceGlobalVars.cpp
@@ -0,0 +1,72 @@
+//===- ReduceGlobalVars.cpp - Specialized Delta Pass ----------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements a function which calls the Generic Delta pass in order
+// to reduce initialized Global Variables in the provided Module.
+//
+//===----------------------------------------------------------------------===//
+
+#include "ReduceGlobalVars.h"
+
+/// Removes all the Initialized GVs that aren't inside the desired Chunks.
+/// @returns the Module stripped of out-of-chunk GVs
+static void extractGVsFromModule(std::vector<Chunk> ChunksToKeep,
+                                 Module *Program) {
+  // Get GVs inside desired chunks
+  std::set<GlobalVariable *> GVsToKeep;
+  unsigned I = 0, GVCount = 0;
+  for (auto &GV : Program->globals())
+    if (GV.hasInitializer() && I < ChunksToKeep.size()) {
+      if (ChunksToKeep[I].contains(++GVCount))
+        GVsToKeep.insert(&GV);
+      if (GVCount == ChunksToKeep[I].end)
+        ++I;
+    }
+
+  // Delete out-of-chunk GVs and their uses
+  std::vector<GlobalVariable *> ToRemove;
+  std::vector<Instruction *> InstToRemove;
+  for (auto &GV : Program->globals())
+    if (GV.hasInitializer() && !GVsToKeep.count(&GV)) {
+      for (auto U : GV.users())
+        if (auto *Inst = dyn_cast<Instruction>(U))
+          InstToRemove.push_back(Inst);
+
+      GV.replaceAllUsesWith(UndefValue::get(GV.getType()));
+      ToRemove.push_back(&GV);
+    }
+
+  // Delete Instruction uses of unwanted GVs
+  for (auto *Inst : InstToRemove) {
+    Inst->replaceAllUsesWith(UndefValue::get(Inst->getType()));
+    Inst->eraseFromParent();
+  }
+
+  for (auto *GV : ToRemove)
+    GV->eraseFromParent();
+}
+
+/// Counts the amount of initialized GVs and displays their
+/// respective name & index
+static int countGVs(Module *Program) {
+  // TODO: Silence index with --quiet flag
+  outs() << "----------------------------\n";
+  outs() << "GlobalVariable Index Reference:\n";
+  int GVCount = 0;
+  for (auto &GV : Program->globals())
+    if (GV.hasInitializer())
+      outs() << "\t" << ++GVCount << ": " << GV.getName() << "\n";
+  outs() << "----------------------------\n";
+  return GVCount;
+}
+
+void llvm::reduceGlobalsDeltaPass(TestRunner &Test) {
+  outs() << "*** Reducing GVs...\n";
+  unsigned GVCount = countGVs(Test.getProgram());
+  runDeltaPass(Test, GVCount, extractGVsFromModule);
+}
diff --git a/llvm/tools/llvm-reduce/deltas/ReduceGlobalVars.h b/llvm/tools/llvm-reduce/deltas/ReduceGlobalVars.h
new file mode 100644
index 00000000000..d4a870aded5
--- /dev/null
+++ b/llvm/tools/llvm-reduce/deltas/ReduceGlobalVars.h
@@ -0,0 +1,20 @@
+//===- ReduceGlobalVars.h - Specialized Delta Pass ------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements a function which calls the Generic Delta pass in order
+// to reduce initialized Global Variables in the provided Module.
+//
+//===----------------------------------------------------------------------===//
+
+#include "Delta.h"
+#include "llvm/IR/Value.h"
+#include "llvm/Transforms/Utils/Cloning.h"
+
+namespace llvm {
+void reduceGlobalsDeltaPass(TestRunner &Test);
+} // namespace llvm