lib/Target/PowerPC/PPCBoolRetToInt.cpp

   1 //===- PPCBoolRetToInt.cpp ------------------------------------------------===//
   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 converting i1 values to i32/i64 if they could be more
  10 // profitably allocated as GPRs rather than CRs. This pass will become totally
  11 // unnecessary if Register Bank Allocation and Global Instruction Selection ever
  12 // go upstream.
  13 //
  14 // Presently, the pass converts i1 Constants, and Arguments to i32/i64 if the
  15 // transitive closure of their uses includes only PHINodes, CallInsts, and
  16 // ReturnInsts. The rational is that arguments are generally passed and returned
  17 // in GPRs rather than CRs, so casting them to i32/i64 at the LLVM IR level will
  18 // actually save casts at the Machine Instruction level.
  19 //
  20 // It might be useful to expand this pass to add bit-wise operations to the list
  21 // of safe transitive closure types. Also, we miss some opportunities when LLVM
  22 // represents logical AND and OR operations with control flow rather than data
  23 // flow. For example by lowering the expression: return (A && B && C)
  24 //
  25 // as: return A ? true : B && C.
  26 //
  27 // There's code in SimplifyCFG that code be used to turn control flow in data
  28 // flow using SelectInsts. Selects are slow on some architectures (P7/P8), so
  29 // this probably isn't good in general, but for the special case of i1, the
  30 // Selects could be further lowered to bit operations that are fast everywhere.
  31 //
  32 //===----------------------------------------------------------------------===//
  33
  34 #include "PPC.h"
  35 #include "PPCTargetMachine.h"
  36 #include "llvm/ADT/DenseMap.h"
  37 #include "llvm/ADT/STLExtras.h"
  38 #include "llvm/ADT/SmallPtrSet.h"
  39 #include "llvm/ADT/SmallVector.h"
  40 #include "llvm/ADT/Statistic.h"
  41 #include "llvm/IR/Argument.h"
  42 #include "llvm/IR/Constants.h"
  43 #include "llvm/IR/Dominators.h"
  44 #include "llvm/IR/Function.h"
  45 #include "llvm/IR/Instruction.h"
  46 #include "llvm/IR/Instructions.h"
  47 #include "llvm/IR/IntrinsicInst.h"
  48 #include "llvm/IR/OperandTraits.h"
  49 #include "llvm/IR/Type.h"
  50 #include "llvm/IR/Use.h"
  51 #include "llvm/IR/User.h"
  52 #include "llvm/IR/Value.h"
  53 #include "llvm/Pass.h"
  54 #include "llvm/CodeGen/TargetPassConfig.h"
  55 #include "llvm/Support/Casting.h"
  56 #include <cassert>
  57
  58 using namespace llvm;
  59
  60 namespace {
  61
  62 #define DEBUG_TYPE "bool-ret-to-int"
  63
  64 STATISTIC(NumBoolRetPromotion,
  65           "Number of times a bool feeding a RetInst was promoted to an int");
  66 STATISTIC(NumBoolCallPromotion,
  67           "Number of times a bool feeding a CallInst was promoted to an int");
  68 STATISTIC(NumBoolToIntPromotion,
  69           "Total number of times a bool was promoted to an int");
  70
  71 class PPCBoolRetToInt : public FunctionPass {
  72   static SmallPtrSet<Value *, 8> findAllDefs(Value *V) {
  73     SmallPtrSet<Value *, 8> Defs;
  74     SmallVector<Value *, 8> WorkList;
  75     WorkList.push_back(V);
  76     Defs.insert(V);
  77     while (!WorkList.empty()) {
  78       Value *Curr = WorkList.back();
  79       WorkList.pop_back();
  80       auto *CurrUser = dyn_cast<User>(Curr);
  81       // Operands of CallInst are skipped because they may not be Bool type,
  82       // and their positions are defined by ABI.
  83       if (CurrUser && !isa<CallInst>(Curr))
  84         for (auto &Op : CurrUser->operands())
  85           if (Defs.insert(Op).second)
  86             WorkList.push_back(Op);
  87     }
  88     return Defs;
  89   }
  90
  91   // Translate a i1 value to an equivalent i32/i64 value:
  92   Value *translate(Value *V) {
  93     Type *IntTy = ST->isPPC64() ? Type::getInt64Ty(V->getContext())
  94                                 : Type::getInt32Ty(V->getContext());
  95
  96     if (auto *C = dyn_cast<Constant>(V))
  97       return ConstantExpr::getZExt(C, IntTy);
  98     if (auto *P = dyn_cast<PHINode>(V)) {
  99       // Temporarily set the operands to 0. We'll fix this later in
 100       // runOnUse.
 101       Value *Zero = Constant::getNullValue(IntTy);
 102       PHINode *Q =
 103         PHINode::Create(IntTy, P->getNumIncomingValues(), P->getName(), P);
 104       for (unsigned i = 0; i < P->getNumOperands(); ++i)
 105         Q->addIncoming(Zero, P->getIncomingBlock(i));
 106       return Q;
 107     }
 108
 109     auto *A = dyn_cast<Argument>(V);
 110     auto *I = dyn_cast<Instruction>(V);
 111     assert((A || I) && "Unknown value type");
 112
 113     auto InstPt =
 114       A ? &*A->getParent()->getEntryBlock().begin() : I->getNextNode();
 115     return new ZExtInst(V, IntTy, "", InstPt);
 116   }
 117
 118   typedef SmallPtrSet<const PHINode *, 8> PHINodeSet;
 119
 120   // A PHINode is Promotable if:
 121   // 1. Its type is i1 AND
 122   // 2. All of its uses are ReturnInt, CallInst, PHINode, or DbgInfoIntrinsic
 123   // AND
 124   // 3. All of its operands are Constant or Argument or
 125   //    CallInst or PHINode AND
 126   // 4. All of its PHINode uses are Promotable AND
 127   // 5. All of its PHINode operands are Promotable
 128   static PHINodeSet getPromotablePHINodes(const Function &F) {
 129     PHINodeSet Promotable;
 130     // Condition 1
 131     for (auto &BB : F)
 132       for (auto &I : BB)
 133         if (const auto *P = dyn_cast<PHINode>(&I))
 134           if (P->getType()->isIntegerTy(1))
 135             Promotable.insert(P);
 136
 137     SmallVector<const PHINode *, 8> ToRemove;
 138     for (const PHINode *P : Promotable) {
 139       // Condition 2 and 3
 140       auto IsValidUser = [] (const Value *V) -> bool {
 141         return isa<ReturnInst>(V) || isa<CallInst>(V) || isa<PHINode>(V) ||
 142         isa<DbgInfoIntrinsic>(V);
 143       };
 144       auto IsValidOperand = [] (const Value *V) -> bool {
 145         return isa<Constant>(V) || isa<Argument>(V) || isa<CallInst>(V) ||
 146         isa<PHINode>(V);
 147       };
 148       const auto &Users = P->users();
 149       const auto &Operands = P->operands();
 150       if (!llvm::all_of(Users, IsValidUser) ||
 151           !llvm::all_of(Operands, IsValidOperand))
 152         ToRemove.push_back(P);
 153     }
 154
 155     // Iterate to convergence
 156     auto IsPromotable = [&Promotable] (const Value *V) -> bool {
 157       const auto *Phi = dyn_cast<PHINode>(V);
 158       return !Phi || Promotable.count(Phi);
 159     };
 160     while (!ToRemove.empty()) {
 161       for (auto &User : ToRemove)
 162         Promotable.erase(User);
 163       ToRemove.clear();
 164
 165       for (const PHINode *P : Promotable) {
 166         // Condition 4 and 5
 167         const auto &Users = P->users();
 168         const auto &Operands = P->operands();
 169         if (!llvm::all_of(Users, IsPromotable) ||
 170             !llvm::all_of(Operands, IsPromotable))
 171           ToRemove.push_back(P);
 172       }
 173     }
 174
 175     return Promotable;
 176   }
 177
 178   typedef DenseMap<Value *, Value *> B2IMap;
 179
 180  public:
 181   static char ID;
 182
 183   PPCBoolRetToInt() : FunctionPass(ID) {
 184     initializePPCBoolRetToIntPass(*PassRegistry::getPassRegistry());
 185   }
 186
 187   bool runOnFunction(Function &F) override {
 188     if (skipFunction(F))
 189       return false;
 190
 191     auto *TPC = getAnalysisIfAvailable<TargetPassConfig>();
 192     if (!TPC)
 193       return false;
 194
 195     auto &TM = TPC->getTM<PPCTargetMachine>();
 196     ST = TM.getSubtargetImpl(F);
 197
 198     PHINodeSet PromotablePHINodes = getPromotablePHINodes(F);
 199     B2IMap Bool2IntMap;
 200     bool Changed = false;
 201     for (auto &BB : F) {
 202       for (auto &I : BB) {
 203         if (auto *R = dyn_cast<ReturnInst>(&I))
 204           if (F.getReturnType()->isIntegerTy(1))
 205             Changed |=
 206               runOnUse(R->getOperandUse(0), PromotablePHINodes, Bool2IntMap);
 207
 208         if (auto *CI = dyn_cast<CallInst>(&I))
 209           for (auto &U : CI->operands())
 210             if (U->getType()->isIntegerTy(1))
 211               Changed |= runOnUse(U, PromotablePHINodes, Bool2IntMap);
 212       }
 213     }
 214
 215     return Changed;
 216   }
 217
 218   bool runOnUse(Use &U, const PHINodeSet &PromotablePHINodes,
 219                        B2IMap &BoolToIntMap) {
 220     auto Defs = findAllDefs(U);
 221
 222     // If the values are all Constants or Arguments, don't bother
 223     if (llvm::none_of(Defs, isa<Instruction, Value *>))
 224       return false;
 225
 226     // Presently, we only know how to handle PHINode, Constant, Arguments and
 227     // CallInst. Potentially, bitwise operations (AND, OR, XOR, NOT) and sign
 228     // extension could also be handled in the future.
 229     for (Value *V : Defs)
 230       if (!isa<PHINode>(V) && !isa<Constant>(V) &&
 231           !isa<Argument>(V) && !isa<CallInst>(V))
 232         return false;
 233
 234     for (Value *V : Defs)
 235       if (const auto *P = dyn_cast<PHINode>(V))
 236         if (!PromotablePHINodes.count(P))
 237           return false;
 238
 239     if (isa<ReturnInst>(U.getUser()))
 240       ++NumBoolRetPromotion;
 241     if (isa<CallInst>(U.getUser()))
 242       ++NumBoolCallPromotion;
 243     ++NumBoolToIntPromotion;
 244
 245     for (Value *V : Defs)
 246       if (!BoolToIntMap.count(V))
 247         BoolToIntMap[V] = translate(V);
 248
 249     // Replace the operands of the translated instructions. They were set to
 250     // zero in the translate function.
 251     for (auto &Pair : BoolToIntMap) {
 252       auto *First = dyn_cast<User>(Pair.first);
 253       auto *Second = dyn_cast<User>(Pair.second);
 254       assert((!First || Second) && "translated from user to non-user!?");
 255       // Operands of CallInst are skipped because they may not be Bool type,
 256       // and their positions are defined by ABI.
 257       if (First && !isa<CallInst>(First))
 258         for (unsigned i = 0; i < First->getNumOperands(); ++i)
 259           Second->setOperand(i, BoolToIntMap[First->getOperand(i)]);
 260     }
 261
 262     Value *IntRetVal = BoolToIntMap[U];
 263     Type *Int1Ty = Type::getInt1Ty(U->getContext());
 264     auto *I = cast<Instruction>(U.getUser());
 265     Value *BackToBool = new TruncInst(IntRetVal, Int1Ty, "backToBool", I);
 266     U.set(BackToBool);
 267
 268     return true;
 269   }
 270
 271   void getAnalysisUsage(AnalysisUsage &AU) const override {
 272     AU.addPreserved<DominatorTreeWrapperPass>();
 273     FunctionPass::getAnalysisUsage(AU);
 274   }
 275
 276 private:
 277   const PPCSubtarget *ST;
 278 };
 279
 280 } // end anonymous namespace
 281
 282 char PPCBoolRetToInt::ID = 0;
 283 INITIALIZE_PASS(PPCBoolRetToInt, "bool-ret-to-int",
 284                 "Convert i1 constants to i32/i64 if they are returned",
 285                 false, false)
 286
 287 FunctionPass *llvm::createPPCBoolRetToIntPass() { return new PPCBoolRetToInt(); }