llvm/tools/llvm-reduce/deltas/ReduceArguments.cpp

   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 }