1//===- ReduceGlobalVars.cpp - Specialized Delta Pass ----------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file implements a function which calls the Generic Delta pass in order
10// to reduce Global Variables in the provided Module.
11//
12//===----------------------------------------------------------------------===//
13
14#include "ReduceGlobalVars.h"
15#include "Utils.h"
16#include "llvm/IR/Constants.h"
17#include "llvm/Transforms/Utils/ModuleUtils.h"
18
19using namespace llvm;
20
21static bool shouldAlwaysKeep(const GlobalVariable &GV) {
22 return GV.getName() == "llvm.used" || GV.getName() == "llvm.compiler.used";
23}
24
25/// Removes all the GVs that aren't inside the desired Chunks.
26static void extractGVsFromModule(Oracle &O, ReducerWorkItem &WorkItem) {
27 Module &Program = WorkItem.getModule();
28
29 // Get GVs inside desired chunks
30 std::vector<Constant *> InitGVsToKeep;
31 for (auto &GV : Program.globals()) {
32 if (shouldAlwaysKeep(GV) || O.shouldKeep())
33 InitGVsToKeep.push_back(x: &GV);
34 }
35
36 // We create a vector first, then convert it to a set, so that we don't have
37 // to pay the cost of rebalancing the set frequently if the order we insert
38 // the elements doesn't match the order they should appear inside the set.
39 DenseSet<Constant *> GVsToKeep(InitGVsToKeep.begin(), InitGVsToKeep.end());
40
41 // Delete out-of-chunk GVs and their uses
42 DenseSet<Constant *> ToRemove;
43 for (auto &GV : Program.globals()) {
44 if (!GVsToKeep.count(V: &GV))
45 ToRemove.insert(V: &GV);
46 }
47
48 removeFromUsedLists(M&: Program,
49 ShouldRemove: [&ToRemove](Constant *C) { return ToRemove.count(V: C); });
50
51 for (auto *GV : ToRemove) {
52 GV->replaceAllUsesWith(V: getDefaultValue(T: GV->getType()));
53 cast<GlobalVariable>(Val: GV)->eraseFromParent();
54 }
55}
56
57void llvm::reduceGlobalsDeltaPass(TestRunner &Test) {
58 runDeltaPass(Test, ExtractChunksFromModule: extractGVsFromModule, Message: "Reducing GlobalVariables");
59}
60