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
58using namespace llvm;
59
60namespace {
61
62#define DEBUG_TYPE "bool-ret-to-int"
63
64STATISTIC(NumBoolRetPromotion,
65          "Number of times a bool feeding a RetInst was promoted to an int");
66STATISTIC(NumBoolCallPromotion,
67          "Number of times a bool feeding a CallInst was promoted to an int");
68STATISTIC(NumBoolToIntPromotion,
69          "Total number of times a bool was promoted to an int");
70
71class 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
276private:
277  const PPCSubtarget *ST;
278};
279
280} // end anonymous namespace
281
282char PPCBoolRetToInt::ID = 0;
283INITIALIZE_PASS(PPCBoolRetToInt, "bool-ret-to-int",
284                "Convert i1 constants to i32/i64 if they are returned",
285                false, false)
286
287FunctionPass *llvm::createPPCBoolRetToIntPass() { return new PPCBoolRetToInt(); }
288