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/Constants.h"
18 #include "llvm/IR/Instructions.h"
19 #include "llvm/IR/Intrinsics.h"
20 #include <set>
21 #include <vector>
22 
23 using namespace llvm;
24 
25 /// Goes over OldF calls and replaces them with a call to NewF
26 static void replaceFunctionCalls(Function &OldF, Function &NewF,
27                                  const std::set<int> &ArgIndexesToKeep) {
28   const auto &Users = OldF.users();
29   for (auto I = Users.begin(), E = Users.end(); I != E; )
30     if (auto *CI = dyn_cast<CallInst>(*I++)) {
31       // Skip uses in call instructions where OldF isn't the called function
32       // (e.g. if OldF is an argument of the call).
33       if (CI->getCalledFunction() != &OldF)
34         continue;
35       SmallVector<Value *, 8> Args;
36       for (auto ArgI = CI->arg_begin(), E = CI->arg_end(); ArgI != E; ++ArgI)
37         if (ArgIndexesToKeep.count(ArgI - CI->arg_begin()))
38           Args.push_back(*ArgI);
39 
40       CallInst *NewCI = CallInst::Create(&NewF, Args);
41       NewCI->setCallingConv(NewF.getCallingConv());
42       if (!CI->use_empty())
43         CI->replaceAllUsesWith(NewCI);
44       ReplaceInstWithInst(CI, NewCI);
45     }
46 }
47 
48 /// Returns whether or not this function should be considered a candidate for
49 /// argument removal. Currently, functions with no arguments and intrinsics are
50 /// not considered. Intrinsics aren't considered because their signatures are
51 /// fixed.
52 static bool shouldRemoveArguments(const Function &F) {
53   return !F.arg_empty() && !F.isIntrinsic();
54 }
55 
56 /// Removes out-of-chunk arguments from functions, and modifies their calls
57 /// accordingly. It also removes allocations of out-of-chunk arguments.
58 static void extractArgumentsFromModule(Oracle &O, Module &Program) {
59   std::vector<Argument *> InitArgsToKeep;
60   std::vector<Function *> Funcs;
61   // Get inside-chunk arguments, as well as their parent function
62   for (auto &F : Program)
63     if (shouldRemoveArguments(F)) {
64       Funcs.push_back(&F);
65       for (auto &A : F.args())
66         if (O.shouldKeep())
67           InitArgsToKeep.push_back(&A);
68     }
69 
70   // We create a vector first, then convert it to a set, so that we don't have
71   // to pay the cost of rebalancing the set frequently if the order we insert
72   // the elements doesn't match the order they should appear inside the set.
73   std::set<Argument *> ArgsToKeep(InitArgsToKeep.begin(), InitArgsToKeep.end());
74 
75   for (auto *F : Funcs) {
76     ValueToValueMapTy VMap;
77     std::vector<WeakVH> InstToDelete;
78     for (auto &A : F->args())
79       if (!ArgsToKeep.count(&A)) {
80         // By adding undesired arguments to the VMap, CloneFunction will remove
81         // them from the resulting Function
82         VMap[&A] = UndefValue::get(A.getType());
83         for (auto *U : A.users())
84           if (auto *I = dyn_cast<Instruction>(*&U))
85             InstToDelete.push_back(I);
86       }
87     // Delete any (unique) instruction that uses the argument
88     for (Value *V : InstToDelete) {
89       if (!V)
90         continue;
91       auto *I = cast<Instruction>(V);
92       I->replaceAllUsesWith(UndefValue::get(I->getType()));
93       if (!I->isTerminator())
94         I->eraseFromParent();
95     }
96 
97     // No arguments to reduce
98     if (VMap.empty())
99       continue;
100 
101     std::set<int> ArgIndexesToKeep;
102     for (auto &Arg : enumerate(F->args()))
103       if (ArgsToKeep.count(&Arg.value()))
104         ArgIndexesToKeep.insert(Arg.index());
105 
106     auto *ClonedFunc = CloneFunction(F, VMap);
107     // In order to preserve function order, we move Clone after old Function
108     ClonedFunc->removeFromParent();
109     Program.getFunctionList().insertAfter(F->getIterator(), ClonedFunc);
110 
111     replaceFunctionCalls(*F, *ClonedFunc, ArgIndexesToKeep);
112     // Rename Cloned Function to Old's name
113     std::string FName = std::string(F->getName());
114     F->replaceAllUsesWith(ConstantExpr::getBitCast(ClonedFunc, F->getType()));
115     F->eraseFromParent();
116     ClonedFunc->setName(FName);
117   }
118 }
119 
120 void llvm::reduceArgumentsDeltaPass(TestRunner &Test) {
121   outs() << "*** Reducing Arguments...\n";
122   runDeltaPass(Test, extractArgumentsFromModule);
123 }
124