1 //===- ReduceArguments.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 uninteresting Arguments from declared and defined functions.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "ReduceArguments.h"
15 #include "Delta.h"
16 #include "llvm/ADT/SmallVector.h"
17 #include "llvm/IR/Intrinsics.h"
18 #include <set>
19 #include <vector>
20 
21 using namespace llvm;
22 
23 /// Goes over OldF calls and replaces them with a call to NewF
24 static void replaceFunctionCalls(Function &OldF, Function &NewF,
25                                  const std::set<int> &ArgIndexesToKeep) {
26   const auto &Users = OldF.users();
27   for (auto I = Users.begin(), E = Users.end(); I != E; )
28     if (auto *CI = dyn_cast<CallInst>(*I++)) {
29       // Skip uses in call instructions where OldF isn't the called function
30       // (e.g. if OldF is an argument of the call).
31       if (CI->getCalledFunction() != &OldF)
32         continue;
33       SmallVector<Value *, 8> Args;
34       for (auto ArgI = CI->arg_begin(), E = CI->arg_end(); ArgI != E; ++ArgI)
35         if (ArgIndexesToKeep.count(ArgI - CI->arg_begin()))
36           Args.push_back(*ArgI);
37 
38       CallInst *NewCI = CallInst::Create(&NewF, Args);
39       NewCI->setCallingConv(NewF.getCallingConv());
40       if (!CI->use_empty())
41         CI->replaceAllUsesWith(NewCI);
42       ReplaceInstWithInst(CI, NewCI);
43     }
44 }
45 
46 /// Returns whether or not this function should be considered a candidate for
47 /// argument removal. Currently, functions with no arguments and intrinsics are
48 /// not considered. Intrinsics aren't considered because their signatures are
49 /// fixed.
50 static bool shouldRemoveArguments(const Function &F) {
51   return !F.arg_empty() && !F.isIntrinsic();
52 }
53 
54 /// Removes out-of-chunk arguments from functions, and modifies their calls
55 /// accordingly. It also removes allocations of out-of-chunk arguments.
56 static void extractArgumentsFromModule(Oracle &O, Module &Program) {
57   std::vector<Argument *> InitArgsToKeep;
58   std::vector<Function *> Funcs;
59   // Get inside-chunk arguments, as well as their parent function
60   for (auto &F : Program)
61     if (shouldRemoveArguments(F)) {
62       Funcs.push_back(&F);
63       for (auto &A : F.args())
64         if (O.shouldKeep())
65           InitArgsToKeep.push_back(&A);
66     }
67 
68   // We create a vector first, then convert it to a set, so that we don't have
69   // to pay the cost of rebalancing the set frequently if the order we insert
70   // the elements doesn't match the order they should appear inside the set.
71   std::set<Argument *> ArgsToKeep(InitArgsToKeep.begin(), InitArgsToKeep.end());
72 
73   for (auto *F : Funcs) {
74     ValueToValueMapTy VMap;
75     std::vector<WeakVH> InstToDelete;
76     for (auto &A : F->args())
77       if (!ArgsToKeep.count(&A)) {
78         // By adding undesired arguments to the VMap, CloneFunction will remove
79         // them from the resulting Function
80         VMap[&A] = UndefValue::get(A.getType());
81         for (auto *U : A.users())
82           if (auto *I = dyn_cast<Instruction>(*&U))
83             InstToDelete.push_back(I);
84       }
85     // Delete any (unique) instruction that uses the argument
86     for (Value *V : InstToDelete) {
87       if (!V)
88         continue;
89       auto *I = cast<Instruction>(V);
90       I->replaceAllUsesWith(UndefValue::get(I->getType()));
91       if (!I->isTerminator())
92         I->eraseFromParent();
93     }
94 
95     // No arguments to reduce
96     if (VMap.empty())
97       continue;
98 
99     std::set<int> ArgIndexesToKeep;
100     for (auto &Arg : enumerate(F->args()))
101       if (ArgsToKeep.count(&Arg.value()))
102         ArgIndexesToKeep.insert(Arg.index());
103 
104     auto *ClonedFunc = CloneFunction(F, VMap);
105     // In order to preserve function order, we move Clone after old Function
106     ClonedFunc->removeFromParent();
107     Program.getFunctionList().insertAfter(F->getIterator(), ClonedFunc);
108 
109     replaceFunctionCalls(*F, *ClonedFunc, ArgIndexesToKeep);
110     // Rename Cloned Function to Old's name
111     std::string FName = std::string(F->getName());
112     F->replaceAllUsesWith(ConstantExpr::getBitCast(ClonedFunc, F->getType()));
113     F->eraseFromParent();
114     ClonedFunc->setName(FName);
115   }
116 }
117 
118 void llvm::reduceArgumentsDeltaPass(TestRunner &Test) {
119   outs() << "*** Reducing Arguments...\n";
120   runDeltaPass(Test, extractArgumentsFromModule);
121 }
122