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diff --git a/llvm/lib/Transforms/Scalar/BDCE.cpp b/llvm/lib/Transforms/Scalar/BDCE.cpp
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+++ b/llvm/lib/Transforms/Scalar/BDCE.cpp
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+//===---- BDCE.cpp - Bit-tracking dead code elimination -------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// 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/BDCE.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/DemandedBits.h"
+#include "llvm/Analysis/GlobalsModRef.h"
+#include "llvm/Transforms/Utils/Local.h"
+#include "llvm/IR/InstIterator.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Transforms/Scalar.h"
+using namespace llvm;
+
+#define DEBUG_TYPE "bdce"
+
+STATISTIC(NumRemoved, "Number of instructions removed (unused)");
+STATISTIC(NumSimplified, "Number of instructions trivialized (dead bits)");
+
+/// If an instruction is trivialized (dead), then the chain of users of that
+/// instruction may need to be cleared of assumptions that can no longer be
+/// guaranteed correct.
+static void clearAssumptionsOfUsers(Instruction *I, DemandedBits &DB) {
+  assert(I->getType()->isIntOrIntVectorTy() &&
+         "Trivializing a non-integer value?");
+
+  // Initialize the worklist with eligible direct users.
+  SmallPtrSet<Instruction *, 16> Visited;
+  SmallVector<Instruction *, 16> WorkList;
+  for (User *JU : I->users()) {
+    // If all bits of a user are demanded, then we know that nothing below that
+    // in the def-use chain needs to be changed.
+    auto *J = dyn_cast<Instruction>(JU);
+    if (J && J->getType()->isIntOrIntVectorTy() &&
+        !DB.getDemandedBits(J).isAllOnesValue()) {
+      Visited.insert(J);
+      WorkList.push_back(J);
+    }
+
+    // Note that we need to check for non-int types above before asking for
+    // demanded bits. Normally, the only way to reach an instruction with an
+    // non-int type is via an instruction that has side effects (or otherwise
+    // will demand its input bits). However, if we have a readnone function
+    // that returns an unsized type (e.g., void), we must avoid asking for the
+    // demanded bits of the function call's return value. A void-returning
+    // readnone function is always dead (and so we can stop walking the use/def
+    // chain here), but the check is necessary to avoid asserting.
+  }
+
+  // DFS through subsequent users while tracking visits to avoid cycles.
+  while (!WorkList.empty()) {
+    Instruction *J = WorkList.pop_back_val();
+
+    // NSW, NUW, and exact are based on operands that might have changed.
+    J->dropPoisonGeneratingFlags();
+
+    // We do not have to worry about llvm.assume or range metadata:
+    // 1. llvm.assume demands its operand, so trivializing can't change it.
+    // 2. range metadata only applies to memory accesses which demand all bits.
+
+    for (User *KU : J->users()) {
+      // If all bits of a user are demanded, then we know that nothing below
+      // that in the def-use chain needs to be changed.
+      auto *K = dyn_cast<Instruction>(KU);
+      if (K && Visited.insert(K).second && K->getType()->isIntOrIntVectorTy() &&
+          !DB.getDemandedBits(K).isAllOnesValue())
+        WorkList.push_back(K);
+    }
+  }
+}
+
+static bool bitTrackingDCE(Function &F, DemandedBits &DB) {
+  SmallVector<Instruction*, 128> Worklist;
+  bool Changed = false;
+  for (Instruction &I : instructions(F)) {
+    // If the instruction has side effects and no non-dbg uses,
+    // skip it. This way we avoid computing known bits on an instruction
+    // that will not help us.
+    if (I.mayHaveSideEffects() && I.use_empty())
+      continue;
+
+    // Remove instructions that are dead, either because they were not reached
+    // during analysis or have no demanded bits.
+    if (DB.isInstructionDead(&I) ||
+        (I.getType()->isIntOrIntVectorTy() &&
+         DB.getDemandedBits(&I).isNullValue() &&
+         wouldInstructionBeTriviallyDead(&I))) {
+      salvageDebugInfo(I);
+      Worklist.push_back(&I);
+      I.dropAllReferences();
+      Changed = true;
+      continue;
+    }
+
+    for (Use &U : I.operands()) {
+      // DemandedBits only detects dead integer uses.
+      if (!U->getType()->isIntOrIntVectorTy())
+        continue;
+
+      if (!isa<Instruction>(U) && !isa<Argument>(U))
+        continue;
+
+      if (!DB.isUseDead(&U))
+        continue;
+
+      LLVM_DEBUG(dbgs() << "BDCE: Trivializing: " << U << " (all bits dead)\n");
+
+      clearAssumptionsOfUsers(&I, DB);
+
+      // 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.
+      U.set(ConstantInt::get(U->getType(), 0));
+      ++NumSimplified;
+      Changed = true;
+    }
+  }
+
+  for (Instruction *&I : Worklist) {
+    ++NumRemoved;
+    I->eraseFromParent();
+  }
+
+  return Changed;
+}
+
+PreservedAnalyses BDCEPass::run(Function &F, FunctionAnalysisManager &AM) {
+  auto &DB = AM.getResult<DemandedBitsAnalysis>(F);
+  if (!bitTrackingDCE(F, DB))
+    return PreservedAnalyses::all();
+
+  PreservedAnalyses PA;
+  PA.preserveSet<CFGAnalyses>();
+  PA.preserve<GlobalsAA>();
+  return PA;
+}
+
+namespace {
+struct BDCELegacyPass : public FunctionPass {
+  static char ID; // Pass identification, replacement for typeid
+  BDCELegacyPass() : FunctionPass(ID) {
+    initializeBDCELegacyPassPass(*PassRegistry::getPassRegistry());
+  }
+
+  bool runOnFunction(Function &F) override {
+    if (skipFunction(F))
+      return false;
+    auto &DB = getAnalysis<DemandedBitsWrapperPass>().getDemandedBits();
+    return bitTrackingDCE(F, DB);
+  }
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.setPreservesCFG();
+    AU.addRequired<DemandedBitsWrapperPass>();
+    AU.addPreserved<GlobalsAAWrapperPass>();
+  }
+};
+}
+
+char BDCELegacyPass::ID = 0;
+INITIALIZE_PASS_BEGIN(BDCELegacyPass, "bdce",
+                      "Bit-Tracking Dead Code Elimination", false, false)
+INITIALIZE_PASS_DEPENDENCY(DemandedBitsWrapperPass)
+INITIALIZE_PASS_END(BDCELegacyPass, "bdce",
+                    "Bit-Tracking Dead Code Elimination", false, false)
+
+FunctionPass *llvm::createBitTrackingDCEPass() { return new BDCELegacyPass(); }