Merge "Update aosp/master LLVM for rebase to r230699."

1 files changed, 411 insertions, 0 deletions

diff --git a/lib/Transforms/Scalar/BDCE.cpp b/lib/Transforms/Scalar/BDCE.cpp
new file mode 100644
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+++ b/lib/Transforms/Scalar/BDCE.cpp
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+//===---- BDCE.cpp - Bit-tracking dead code elimination -------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the Bit-Tracking Dead Code Elimination pass. Some
+// instructions (shifts, some ands, ors, etc.) kill some of their input bits.
+// We track these dead bits and remove instructions that compute only these
+// dead bits.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/DepthFirstIterator.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/AssumptionCache.h"
+#include "llvm/Analysis/ValueTracking.h"
+#include "llvm/IR/BasicBlock.h"
+#include "llvm/IR/CFG.h"
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/InstIterator.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/Operator.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+
+using namespace llvm;
+
+#define DEBUG_TYPE "bdce"
+
+STATISTIC(NumRemoved, "Number of instructions removed (unused)");
+STATISTIC(NumSimplified, "Number of instructions trivialized (dead bits)");
+
+namespace {
+struct BDCE : public FunctionPass {
+  static char ID; // Pass identification, replacement for typeid
+  BDCE() : FunctionPass(ID) {
+    initializeBDCEPass(*PassRegistry::getPassRegistry());
+  }
+
+  bool runOnFunction(Function& F) override;
+
+  void getAnalysisUsage(AnalysisUsage& AU) const override {
+    AU.setPreservesCFG();
+    AU.addRequired<AssumptionCacheTracker>();
+    AU.addRequired<DominatorTreeWrapperPass>();
+  }
+
+  void determineLiveOperandBits(const Instruction *UserI,
+                                const Instruction *I, unsigned OperandNo,
+                                const APInt &AOut, APInt &AB,
+                                APInt &KnownZero, APInt &KnownOne,
+                                APInt &KnownZero2, APInt &KnownOne2);
+
+  AssumptionCache *AC;
+  const DataLayout *DL;
+  DominatorTree *DT;
+};
+}
+
+char BDCE::ID = 0;
+INITIALIZE_PASS_BEGIN(BDCE, "bdce", "Bit-Tracking Dead Code Elimination",
+                      false, false)
+INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
+INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
+INITIALIZE_PASS_END(BDCE, "bdce", "Bit-Tracking Dead Code Elimination",
+                    false, false)
+
+static bool isAlwaysLive(Instruction *I) {
+  return isa<TerminatorInst>(I) || isa<DbgInfoIntrinsic>(I) ||
+         isa<LandingPadInst>(I) || I->mayHaveSideEffects();
+}
+
+void BDCE::determineLiveOperandBits(const Instruction *UserI,
+                                    const Instruction *I, unsigned OperandNo,
+                                    const APInt &AOut, APInt &AB,
+                                    APInt &KnownZero, APInt &KnownOne,
+                                    APInt &KnownZero2, APInt &KnownOne2) {
+  unsigned BitWidth = AB.getBitWidth();
+
+  // We're called once per operand, but for some instructions, we need to
+  // compute known bits of both operands in order to determine the live bits of
+  // either (when both operands are instructions themselves). We don't,
+  // however, want to do this twice, so we cache the result in APInts that live
+  // in the caller. For the two-relevant-operands case, both operand values are
+  // provided here.
+  auto ComputeKnownBits = [&](unsigned BitWidth, const Value *V1,
+                              const Value *V2) {
+    KnownZero = APInt(BitWidth, 0);
+    KnownOne =  APInt(BitWidth, 0);
+    computeKnownBits(const_cast<Value*>(V1), KnownZero, KnownOne, DL, 0, AC,
+                     UserI, DT);
+
+    if (V2) {
+      KnownZero2 = APInt(BitWidth, 0);
+      KnownOne2 =  APInt(BitWidth, 0);
+      computeKnownBits(const_cast<Value*>(V2), KnownZero2, KnownOne2, DL, 0, AC,
+                       UserI, DT);
+    }
+  };
+
+  switch (UserI->getOpcode()) {
+  default: break;
+  case Instruction::Call:
+  case Instruction::Invoke:
+    if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(UserI))
+      switch (II->getIntrinsicID()) {
+      default: break;
+      case Intrinsic::bswap:
+        // The alive bits of the input are the swapped alive bits of
+        // the output.
+        AB = AOut.byteSwap();
+        break;
+      case Intrinsic::ctlz:
+        if (OperandNo == 0) {
+          // We need some output bits, so we need all bits of the
+          // input to the left of, and including, the leftmost bit
+          // known to be one.
+          ComputeKnownBits(BitWidth, I, nullptr);
+          AB = APInt::getHighBitsSet(BitWidth,
+                 std::min(BitWidth, KnownOne.countLeadingZeros()+1));
+        }
+        break;
+      case Intrinsic::cttz:
+        if (OperandNo == 0) {
+          // We need some output bits, so we need all bits of the
+          // input to the right of, and including, the rightmost bit
+          // known to be one.
+          ComputeKnownBits(BitWidth, I, nullptr);
+          AB = APInt::getLowBitsSet(BitWidth,
+                 std::min(BitWidth, KnownOne.countTrailingZeros()+1));
+        }
+        break;
+      }
+    break;
+  case Instruction::Add:
+  case Instruction::Sub:
+    // Find the highest live output bit. We don't need any more input
+    // bits than that (adds, and thus subtracts, ripple only to the
+    // left).
+    AB = APInt::getLowBitsSet(BitWidth, AOut.getActiveBits());
+    break;
+  case Instruction::Shl:
+    if (OperandNo == 0)
+      if (ConstantInt *CI =
+            dyn_cast<ConstantInt>(UserI->getOperand(1))) {
+        uint64_t ShiftAmt = CI->getLimitedValue(BitWidth-1);
+        AB = AOut.lshr(ShiftAmt);
+
+        // If the shift is nuw/nsw, then the high bits are not dead
+        // (because we've promised that they *must* be zero).
+        const ShlOperator *S = cast<ShlOperator>(UserI);
+        if (S->hasNoSignedWrap())
+          AB |= APInt::getHighBitsSet(BitWidth, ShiftAmt+1);
+        else if (S->hasNoUnsignedWrap())
+          AB |= APInt::getHighBitsSet(BitWidth, ShiftAmt);
+      }
+    break;
+  case Instruction::LShr:
+    if (OperandNo == 0)
+      if (ConstantInt *CI =
+            dyn_cast<ConstantInt>(UserI->getOperand(1))) {
+        uint64_t ShiftAmt = CI->getLimitedValue(BitWidth-1);
+        AB = AOut.shl(ShiftAmt);
+
+        // If the shift is exact, then the low bits are not dead
+        // (they must be zero).
+        if (cast<LShrOperator>(UserI)->isExact())
+          AB |= APInt::getLowBitsSet(BitWidth, ShiftAmt);
+      }
+    break;
+  case Instruction::AShr:
+    if (OperandNo == 0)
+      if (ConstantInt *CI =
+            dyn_cast<ConstantInt>(UserI->getOperand(1))) {
+        uint64_t ShiftAmt = CI->getLimitedValue(BitWidth-1);
+        AB = AOut.shl(ShiftAmt);
+        // Because the high input bit is replicated into the
+        // high-order bits of the result, if we need any of those
+        // bits, then we must keep the highest input bit.
+        if ((AOut & APInt::getHighBitsSet(BitWidth, ShiftAmt))
+            .getBoolValue())
+          AB.setBit(BitWidth-1);
+
+        // If the shift is exact, then the low bits are not dead
+        // (they must be zero).
+        if (cast<AShrOperator>(UserI)->isExact())
+          AB |= APInt::getLowBitsSet(BitWidth, ShiftAmt);
+      }
+    break;
+  case Instruction::And:
+    AB = AOut;
+
+    // For bits that are known zero, the corresponding bits in the
+    // other operand are dead (unless they're both zero, in which
+    // case they can't both be dead, so just mark the LHS bits as
+    // dead).
+    if (OperandNo == 0) {
+      ComputeKnownBits(BitWidth, I, UserI->getOperand(1));
+      AB &= ~KnownZero2;
+    } else {
+      if (!isa<Instruction>(UserI->getOperand(0)))
+        ComputeKnownBits(BitWidth, UserI->getOperand(0), I);
+      AB &= ~(KnownZero & ~KnownZero2);
+    }
+    break;
+  case Instruction::Or:
+    AB = AOut;
+
+    // For bits that are known one, the corresponding bits in the
+    // other operand are dead (unless they're both one, in which
+    // case they can't both be dead, so just mark the LHS bits as
+    // dead).
+    if (OperandNo == 0) {
+      ComputeKnownBits(BitWidth, I, UserI->getOperand(1));
+      AB &= ~KnownOne2;
+    } else {
+      if (!isa<Instruction>(UserI->getOperand(0)))
+        ComputeKnownBits(BitWidth, UserI->getOperand(0), I);
+      AB &= ~(KnownOne & ~KnownOne2);
+    }
+    break;
+  case Instruction::Xor:
+  case Instruction::PHI:
+    AB = AOut;
+    break;
+  case Instruction::Trunc:
+    AB = AOut.zext(BitWidth);
+    break;
+  case Instruction::ZExt:
+    AB = AOut.trunc(BitWidth);
+    break;
+  case Instruction::SExt:
+    AB = AOut.trunc(BitWidth);
+    // Because the high input bit is replicated into the
+    // high-order bits of the result, if we need any of those
+    // bits, then we must keep the highest input bit.
+    if ((AOut & APInt::getHighBitsSet(AOut.getBitWidth(),
+                                      AOut.getBitWidth() - BitWidth))
+        .getBoolValue())
+      AB.setBit(BitWidth-1);
+    break;
+  case Instruction::Select:
+    if (OperandNo != 0)
+      AB = AOut;
+    break;
+  }
+}
+
+bool BDCE::runOnFunction(Function& F) {
+  if (skipOptnoneFunction(F))
+    return false;
+
+  AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
+  DL = F.getParent()->getDataLayout();
+  DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
+
+  DenseMap<Instruction *, APInt> AliveBits;
+  SmallVector<Instruction*, 128> Worklist;
+
+  // The set of visited instructions (non-integer-typed only).
+  SmallPtrSet<Instruction*, 128> Visited;
+
+  // Collect the set of "root" instructions that are known live.
+  for (Instruction &I : inst_range(F)) {
+    if (!isAlwaysLive(&I))
+      continue;
+
+    DEBUG(dbgs() << "BDCE: Root: " << I << "\n");
+    // For integer-valued instructions, set up an initial empty set of alive
+    // bits and add the instruction to the work list. For other instructions
+    // add their operands to the work list (for integer values operands, mark
+    // all bits as live).
+    if (IntegerType *IT = dyn_cast<IntegerType>(I.getType())) {
+      if (!AliveBits.count(&I)) {
+        AliveBits[&I] = APInt(IT->getBitWidth(), 0);
+        Worklist.push_back(&I);
+      }
+
+      continue;
+    }
+
+    // Non-integer-typed instructions...
+    for (Use &OI : I.operands()) {
+      if (Instruction *J = dyn_cast<Instruction>(OI)) {
+        if (IntegerType *IT = dyn_cast<IntegerType>(J->getType()))
+          AliveBits[J] = APInt::getAllOnesValue(IT->getBitWidth());
+        Worklist.push_back(J);
+      }
+    }
+    // To save memory, we don't add I to the Visited set here. Instead, we
+    // check isAlwaysLive on every instruction when searching for dead
+    // instructions later (we need to check isAlwaysLive for the
+    // integer-typed instructions anyway).
+  }
+
+  // Propagate liveness backwards to operands.
+  while (!Worklist.empty()) {
+    Instruction *UserI = Worklist.pop_back_val();
+
+    DEBUG(dbgs() << "BDCE: Visiting: " << *UserI);
+    APInt AOut;
+    if (UserI->getType()->isIntegerTy()) {
+      AOut = AliveBits[UserI];
+      DEBUG(dbgs() << " Alive Out: " << AOut);
+    }
+    DEBUG(dbgs() << "\n");
+
+    if (!UserI->getType()->isIntegerTy())
+      Visited.insert(UserI);
+
+    APInt KnownZero, KnownOne, KnownZero2, KnownOne2;
+    // Compute the set of alive bits for each operand. These are anded into the
+    // existing set, if any, and if that changes the set of alive bits, the
+    // operand is added to the work-list.
+    for (Use &OI : UserI->operands()) {
+      if (Instruction *I = dyn_cast<Instruction>(OI)) {
+        if (IntegerType *IT = dyn_cast<IntegerType>(I->getType())) {
+          unsigned BitWidth = IT->getBitWidth();
+          APInt AB = APInt::getAllOnesValue(BitWidth);
+          if (UserI->getType()->isIntegerTy() && !AOut &&
+              !isAlwaysLive(UserI)) {
+            AB = APInt(BitWidth, 0);
+          } else {
+            // If all bits of the output are dead, then all bits of the input 
+            // Bits of each operand that are used to compute alive bits of the
+            // output are alive, all others are dead.
+            determineLiveOperandBits(UserI, I, OI.getOperandNo(), AOut, AB,
+                                     KnownZero, KnownOne,
+                                     KnownZero2, KnownOne2);
+          }
+
+          // If we've added to the set of alive bits (or the operand has not
+          // been previously visited), then re-queue the operand to be visited
+          // again.
+          APInt ABPrev(BitWidth, 0);
+          auto ABI = AliveBits.find(I);
+          if (ABI != AliveBits.end())
+            ABPrev = ABI->second;
+
+          APInt ABNew = AB | ABPrev;
+          if (ABNew != ABPrev || ABI == AliveBits.end()) {
+            AliveBits[I] = std::move(ABNew);
+            Worklist.push_back(I);
+          }
+        } else if (!Visited.count(I)) {
+          Worklist.push_back(I);
+        }
+      }
+    }
+  }
+
+  bool Changed = false;
+  // The inverse of the live set is the dead set.  These are those instructions
+  // which have no side effects and do not influence the control flow or return
+  // value of the function, and may therefore be deleted safely.
+  // NOTE: We reuse the Worklist vector here for memory efficiency.
+  for (Instruction &I : inst_range(F)) {
+    // For live instructions that have all dead bits, first make them dead by
+    // replacing all uses with something else. Then, if they don't need to
+    // remain live (because they have side effects, etc.) we can remove them.
+    if (I.getType()->isIntegerTy()) {
+      auto ABI = AliveBits.find(&I);
+      if (ABI != AliveBits.end()) {
+        if (ABI->second.getBoolValue())
+          continue;
+
+        DEBUG(dbgs() << "BDCE: Trivializing: " << I << " (all bits dead)\n");
+        // FIXME: In theory we could substitute undef here instead of zero.
+        // This should be reconsidered once we settle on the semantics of
+        // undef, poison, etc.
+        Value *Zero = ConstantInt::get(I.getType(), 0);
+        ++NumSimplified;
+        I.replaceAllUsesWith(Zero);
+        Changed = true;
+      }
+    } else if (Visited.count(&I)) {
+      continue;
+    }
+
+    if (isAlwaysLive(&I))
+      continue;
+
+    Worklist.push_back(&I);
+    I.dropAllReferences();
+    Changed = true;
+  }
+
+  for (Instruction *&I : Worklist) {
+    ++NumRemoved;
+    I->eraseFromParent();
+  }
+
+  return Changed;
+}
+
+FunctionPass *llvm::createBitTrackingDCEPass() {
+  return new BDCE();
+}
+