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