llvm/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 "ppc-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.pop_back_val();
  79       auto *CurrUser = dyn_cast<User>(Curr);
  80       // Operands of CallInst/Constant are skipped because they may not be Bool
  81       // type. For CallInst, their positions are defined by ABI.
  82       if (CurrUser && !isa<CallInst>(Curr) && !isa<Constant>(Curr))
  83         for (auto &Op : CurrUser->operands())
  84           if (Defs.insert(Op).second)
  85             WorkList.push_back(Op);
  86     }
  87     return Defs;
  88   }
  89
  90   // Translate a i1 value to an equivalent i32/i64 value:
  91   Value *translate(Value *V) {
  92     assert(V->getType() == Type::getInt1Ty(V->getContext()) &&
  93            "Expect an i1 value");
  94
  95     Type *IntTy = ST->isPPC64() ? Type::getInt64Ty(V->getContext())
  96                                 : Type::getInt32Ty(V->getContext());
  97
  98     if (auto *C = dyn_cast<Constant>(V))
  99       return ConstantExpr::getZExt(C, IntTy);
 100     if (auto *P = dyn_cast<PHINode>(V)) {
 101       // Temporarily set the operands to 0. We'll fix this later in
 102       // runOnUse.
 103       Value *Zero = Constant::getNullValue(IntTy);
 104       PHINode *Q =
 105         PHINode::Create(IntTy, P->getNumIncomingValues(), P->getName(), P);
 106       for (unsigned i = 0; i < P->getNumOperands(); ++i)
 107         Q->addIncoming(Zero, P->getIncomingBlock(i));
 108       return Q;
 109     }
 110
 111     auto *A = dyn_cast<Argument>(V);
 112     auto *I = dyn_cast<Instruction>(V);
 113     assert((A || I) && "Unknown value type");
 114
 115     auto InstPt =
 116       A ? &*A->getParent()->getEntryBlock().begin() : I->getNextNode();
 117     return new ZExtInst(V, IntTy, "", InstPt);
 118   }
 119
 120   typedef SmallPtrSet<const PHINode *, 8> PHINodeSet;
 121
 122   // A PHINode is Promotable if:
 123   // 1. Its type is i1 AND
 124   // 2. All of its uses are ReturnInt, CallInst, PHINode, or DbgInfoIntrinsic
 125   // AND
 126   // 3. All of its operands are Constant or Argument or
 127   //    CallInst or PHINode AND
 128   // 4. All of its PHINode uses are Promotable AND
 129   // 5. All of its PHINode operands are Promotable
 130   static PHINodeSet getPromotablePHINodes(const Function &F) {
 131     PHINodeSet Promotable;
 132     // Condition 1
 133     for (auto &BB : F)
 134       for (auto &I : BB)
 135         if (const auto *P = dyn_cast<PHINode>(&I))
 136           if (P->getType()->isIntegerTy(1))
 137             Promotable.insert(P);
 138
 139     SmallVector<const PHINode *, 8> ToRemove;
 140     for (const PHINode *P : Promotable) {
 141       // Condition 2 and 3
 142       auto IsValidUser = [] (const Value *V) -> bool {
 143         return isa<ReturnInst>(V) || isa<CallInst>(V) || isa<PHINode>(V) ||
 144         isa<DbgInfoIntrinsic>(V);
 145       };
 146       auto IsValidOperand = [] (const Value *V) -> bool {
 147         return isa<Constant>(V) || isa<Argument>(V) || isa<CallInst>(V) ||
 148         isa<PHINode>(V);
 149       };
 150       const auto &Users = P->users();
 151       const auto &Operands = P->operands();
 152       if (!llvm::all_of(Users, IsValidUser) ||
 153           !llvm::all_of(Operands, IsValidOperand))
 154         ToRemove.push_back(P);
 155     }
 156
 157     // Iterate to convergence
 158     auto IsPromotable = [&Promotable] (const Value *V) -> bool {
 159       const auto *Phi = dyn_cast<PHINode>(V);
 160       return !Phi || Promotable.count(Phi);
 161     };
 162     while (!ToRemove.empty()) {
 163       for (auto &User : ToRemove)
 164         Promotable.erase(User);
 165       ToRemove.clear();
 166
 167       for (const PHINode *P : Promotable) {
 168         // Condition 4 and 5
 169         const auto &Users = P->users();
 170         const auto &Operands = P->operands();
 171         if (!llvm::all_of(Users, IsPromotable) ||
 172             !llvm::all_of(Operands, IsPromotable))
 173           ToRemove.push_back(P);
 174       }
 175     }
 176
 177     return Promotable;
 178   }
 179
 180   typedef DenseMap<Value *, Value *> B2IMap;
 181
 182  public:
 183   static char ID;
 184
 185   PPCBoolRetToInt() : FunctionPass(ID) {
 186     initializePPCBoolRetToIntPass(*PassRegistry::getPassRegistry());
 187   }
 188
 189   bool runOnFunction(Function &F) override {
 190     if (skipFunction(F))
 191       return false;
 192
 193     auto *TPC = getAnalysisIfAvailable<TargetPassConfig>();
 194     if (!TPC)
 195       return false;
 196
 197     auto &TM = TPC->getTM<PPCTargetMachine>();
 198     ST = TM.getSubtargetImpl(F);
 199
 200     PHINodeSet PromotablePHINodes = getPromotablePHINodes(F);
 201     B2IMap Bool2IntMap;
 202     bool Changed = false;
 203     for (auto &BB : F) {
 204       for (auto &I : BB) {
 205         if (auto *R = dyn_cast<ReturnInst>(&I))
 206           if (F.getReturnType()->isIntegerTy(1))
 207             Changed |=
 208               runOnUse(R->getOperandUse(0), PromotablePHINodes, Bool2IntMap);
 209
 210         if (auto *CI = dyn_cast<CallInst>(&I))
 211           for (auto &U : CI->operands())
 212             if (U->getType()->isIntegerTy(1))
 213               Changed |= runOnUse(U, PromotablePHINodes, Bool2IntMap);
 214       }
 215     }
 216
 217     return Changed;
 218   }
 219
 220   bool runOnUse(Use &U, const PHINodeSet &PromotablePHINodes,
 221                        B2IMap &BoolToIntMap) {
 222     auto Defs = findAllDefs(U);
 223
 224     // If the values are all Constants or Arguments, don't bother
 225     if (llvm::none_of(Defs, [](Value *V) { return isa<Instruction>(V); }))
 226       return false;
 227
 228     // Presently, we only know how to handle PHINode, Constant, Arguments and
 229     // CallInst. Potentially, bitwise operations (AND, OR, XOR, NOT) and sign
 230     // extension could also be handled in the future.
 231     for (Value *V : Defs)
 232       if (!isa<PHINode>(V) && !isa<Constant>(V) &&
 233           !isa<Argument>(V) && !isa<CallInst>(V))
 234         return false;
 235
 236     for (Value *V : Defs)
 237       if (const auto *P = dyn_cast<PHINode>(V))
 238         if (!PromotablePHINodes.count(P))
 239           return false;
 240
 241     if (isa<ReturnInst>(U.getUser()))
 242       ++NumBoolRetPromotion;
 243     if (isa<CallInst>(U.getUser()))
 244       ++NumBoolCallPromotion;
 245     ++NumBoolToIntPromotion;
 246
 247     for (Value *V : Defs)
 248       if (!BoolToIntMap.count(V))
 249         BoolToIntMap[V] = translate(V);
 250
 251     // Replace the operands of the translated instructions. They were set to
 252     // zero in the translate function.
 253     for (auto &Pair : BoolToIntMap) {
 254       auto *First = dyn_cast<User>(Pair.first);
 255       auto *Second = dyn_cast<User>(Pair.second);
 256       assert((!First || Second) && "translated from user to non-user!?");
 257       // Operands of CallInst/Constant are skipped because they may not be Bool
 258       // type. For CallInst, their positions are defined by ABI.
 259       if (First && !isa<CallInst>(First) && !isa<Constant>(First))
 260         for (unsigned i = 0; i < First->getNumOperands(); ++i)
 261           Second->setOperand(i, BoolToIntMap[First->getOperand(i)]);
 262     }
 263
 264     Value *IntRetVal = BoolToIntMap[U];
 265     Type *Int1Ty = Type::getInt1Ty(U->getContext());
 266     auto *I = cast<Instruction>(U.getUser());
 267     Value *BackToBool = new TruncInst(IntRetVal, Int1Ty, "backToBool", I);
 268     U.set(BackToBool);
 269
 270     return true;
 271   }
 272
 273   void getAnalysisUsage(AnalysisUsage &AU) const override {
 274     AU.addPreserved<DominatorTreeWrapperPass>();
 275     FunctionPass::getAnalysisUsage(AU);
 276   }
 277
 278 private:
 279   const PPCSubtarget *ST;
 280 };
 281
 282 } // end anonymous namespace
 283
 284 char PPCBoolRetToInt::ID = 0;
 285 INITIALIZE_PASS(PPCBoolRetToInt, "ppc-bool-ret-to-int",
 286                 "Convert i1 constants to i32/i64 if they are returned", false,
 287                 false)
 288
 289 FunctionPass *llvm::createPPCBoolRetToIntPass() { return new PPCBoolRetToInt(); }