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diff --git a/gnu/llvm/lib/Transforms/Scalar/BDCE.cpp b/gnu/llvm/lib/Transforms/Scalar/BDCE.cpp
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index 00000000000..cb9b8b6fffc
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+++ b/gnu/llvm/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/SmallVector.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/GlobalsModRef.h"
+#include "llvm/Analysis/DemandedBits.h"
+#include "llvm/IR/CFG.h"
+#include "llvm/IR/InstIterator.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.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<DemandedBits>();
+    AU.addPreserved<GlobalsAAWrapperPass>();
+  }
+};
+}
+
+char BDCE::ID = 0;
+INITIALIZE_PASS_BEGIN(BDCE, "bdce", "Bit-Tracking Dead Code Elimination",
+                      false, false)
+INITIALIZE_PASS_DEPENDENCY(DemandedBits)
+INITIALIZE_PASS_END(BDCE, "bdce", "Bit-Tracking Dead Code Elimination",
+                    false, false)
+
+bool BDCE::runOnFunction(Function& F) {
+  if (skipOptnoneFunction(F))
+    return false;
+  DemandedBits &DB = getAnalysis<DemandedBits>();
+
+  SmallVector<Instruction*, 128> Worklist;
+  bool Changed = false;
+  for (Instruction &I : instructions(F)) {
+    if (I.getType()->isIntegerTy() &&
+        !DB.getDemandedBits(&I).getBoolValue()) {
+      // 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.
+      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;
+    }
+    if (!DB.isInstructionDead(&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();
+}
+