[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

llvm/test/Reduce/Inputs/remove-global-vars.py

@@ -0,0 +1,10 @@
+#!/usr/bin/env python
+
+import sys
+
+input = open(sys.argv[1], "r")
+for line in input:
+  if "@interesting = global" in line:
+    sys.exit(0)
+
+sys.exit(1) # IR isn't interesting

llvm/test/Reduce/remove-global-vars.ll

@@ -0,0 +1,29 @@
+; Test that llvm-reduce can remove uninteresting Global Variables as well as
+; their direct uses (which in turn are replaced with 'undef').
+;
+; RUN: llvm-reduce --test %p/Inputs/remove-global-vars.py %s -o - | FileCheck %s
+; REQUIRES: plugins
+
+; CHECK: @interesting = global
+@interesting = global i32 0, align 4
+; CHECK-NOT: global
+@uninteresting = global i32 1, align 4
+
+define i32 @main() {
+entry:
+  ; CHECK-NOT: load i32, i32* @uninteresting, align 4
+  %0 = load i32, i32* @uninteresting, align 4
+  ; CHECK: store i32 undef, i32* @interesting, align 4
+  store i32 %0, i32* @interesting, align 4
+
+  ; CHECK: load i32, i32* @interesting, align 4
+  %1 = load i32, i32* @interesting, align 4
+  ; CHECK-NOT: store i32 %1, i32* @uninteresting, align 4
+  store i32 %1, i32* @uninteresting, align 4
+
+  ; CHECK: %inc = add nsw i32 undef, 1
+  %inc = add nsw i32 %0, 1
+  ; CHECK: store i32 %inc, i32* @interesting, align 4
+  store i32 %inc, i32* @interesting, align 4
+  ret i32 0
+}

llvm/tools/llvm-reduce/CMakeLists.txt

@@ -18,6 +18,7 @@ add_llvm_tool(llvm-reduce
   TestRunner.cpp
   deltas/Delta.cpp
   deltas/ReduceFunctions.cpp
+  deltas/ReduceGlobalVars.cpp
 
   DEPENDS
   intrinsics_gen

llvm/tools/llvm-reduce/DeltaManager.h

@@ -14,11 +14,16 @@
 #include "TestRunner.h"
 #include "deltas/Delta.h"
 #include "deltas/ReduceFunctions.h"
+#include "deltas/ReduceGlobalVars.h"
 
 namespace llvm {
 
+// TODO: Add CLI option to run only specified Passes (for unit tests)
 inline void runDeltaPasses(TestRunner &Tester) {
+  outs() << "Reducing functions...\n";
   reduceFunctionsDeltaPass(Tester);
+  outs() << "Reducing GVs...\n";
+  reduceGlobalsDeltaPass(Tester);
   // TODO: Implement the remaining Delta Passes
 }
 

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);
+}

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