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diff --git a/lib/Target/X86/X86DiscriminateMemOps.cpp b/lib/Target/X86/X86DiscriminateMemOps.cpp
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index 000000000000..3654bf04f4e9
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+++ b/lib/Target/X86/X86DiscriminateMemOps.cpp
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+//===- X86DiscriminateMemOps.cpp - Unique IDs for Mem Ops -----------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+///
+/// This pass aids profile-driven cache prefetch insertion by ensuring all
+/// instructions that have a memory operand are distinguishible from each other.
+///
+//===----------------------------------------------------------------------===//
+
+#include "X86.h"
+#include "X86InstrBuilder.h"
+#include "X86InstrInfo.h"
+#include "X86MachineFunctionInfo.h"
+#include "X86Subtarget.h"
+#include "llvm/CodeGen/MachineModuleInfo.h"
+#include "llvm/IR/DebugInfoMetadata.h"
+#include "llvm/ProfileData/SampleProf.h"
+#include "llvm/ProfileData/SampleProfReader.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Transforms/IPO/SampleProfile.h"
+using namespace llvm;
+
+#define DEBUG_TYPE "x86-discriminate-memops"
+
+namespace {
+
+using Location = std::pair<StringRef, unsigned>;
+
+Location diToLocation(const DILocation *Loc) {
+  return std::make_pair(Loc->getFilename(), Loc->getLine());
+}
+
+/// Ensure each instruction having a memory operand has a distinct <LineNumber,
+/// Discriminator> pair.
+void updateDebugInfo(MachineInstr *MI, const DILocation *Loc) {
+  DebugLoc DL(Loc);
+  MI->setDebugLoc(DL);
+}
+
+class X86DiscriminateMemOps : public MachineFunctionPass {
+  bool runOnMachineFunction(MachineFunction &MF) override;
+  StringRef getPassName() const override {
+    return "X86 Discriminate Memory Operands";
+  }
+
+public:
+  static char ID;
+
+  /// Default construct and initialize the pass.
+  X86DiscriminateMemOps();
+};
+
+} // end anonymous namespace
+
+//===----------------------------------------------------------------------===//
+//            Implementation
+//===----------------------------------------------------------------------===//
+
+char X86DiscriminateMemOps::ID = 0;
+
+/// Default construct and initialize the pass.
+X86DiscriminateMemOps::X86DiscriminateMemOps() : MachineFunctionPass(ID) {}
+
+bool X86DiscriminateMemOps::runOnMachineFunction(MachineFunction &MF) {
+  DISubprogram *FDI = MF.getFunction().getSubprogram();
+  if (!FDI || !FDI->getUnit()->getDebugInfoForProfiling())
+    return false;
+
+  // Have a default DILocation, if we find instructions with memops that don't
+  // have any debug info.
+  const DILocation *ReferenceDI =
+      DILocation::get(FDI->getContext(), FDI->getLine(), 0, FDI);
+
+  DenseMap<Location, unsigned> MemOpDiscriminators;
+  MemOpDiscriminators[diToLocation(ReferenceDI)] = 0;
+
+  // Figure out the largest discriminator issued for each Location. When we
+  // issue new discriminators, we can thus avoid issuing discriminators
+  // belonging to instructions that don't have memops. This isn't a requirement
+  // for the goals of this pass, however, it avoids unnecessary ambiguity.
+  for (auto &MBB : MF) {
+    for (auto &MI : MBB) {
+      const auto &DI = MI.getDebugLoc();
+      if (!DI)
+        continue;
+      Location Loc = diToLocation(DI);
+      MemOpDiscriminators[Loc] =
+          std::max(MemOpDiscriminators[Loc], DI->getBaseDiscriminator());
+    }
+  }
+
+  // Keep track of the discriminators seen at each Location. If an instruction's
+  // DebugInfo has a Location and discriminator we've already seen, replace its
+  // discriminator with a new one, to guarantee uniqueness.
+  DenseMap<Location, DenseSet<unsigned>> Seen;
+
+  bool Changed = false;
+  for (auto &MBB : MF) {
+    for (auto &MI : MBB) {
+      if (X86II::getMemoryOperandNo(MI.getDesc().TSFlags) < 0)
+        continue;
+      const DILocation *DI = MI.getDebugLoc();
+      if (!DI) {
+        DI = ReferenceDI;
+      }
+      Location L = diToLocation(DI);
+      DenseSet<unsigned> &Set = Seen[L];
+      const std::pair<DenseSet<unsigned>::iterator, bool> TryInsert =
+          Set.insert(DI->getBaseDiscriminator());
+      if (!TryInsert.second) {
+        unsigned BF, DF, CI = 0;
+        DILocation::decodeDiscriminator(DI->getDiscriminator(), BF, DF, CI);
+        Optional<unsigned> EncodedDiscriminator = DILocation::encodeDiscriminator(
+            MemOpDiscriminators[L] + 1, DF, CI);
+
+        if (!EncodedDiscriminator) {
+          // FIXME(mtrofin): The assumption is that this scenario is infrequent/OK
+          // not to support. If evidence points otherwise, we can explore synthesizeing
+          // unique DIs by adding fake line numbers, or by constructing 64 bit
+          // discriminators.
+          LLVM_DEBUG(dbgs() << "Unable to create a unique discriminator "
+                     "for instruction with memory operand in: "
+                     << DI->getFilename() << " Line: " << DI->getLine()
+                     << " Column: " << DI->getColumn()
+                     << ". This is likely due to a large macro expansion. \n");
+          continue;
+        }
+        // Since we were able to encode, bump the MemOpDiscriminators.
+        ++MemOpDiscriminators[L];
+        DI = DI->cloneWithDiscriminator(EncodedDiscriminator.getValue());
+        updateDebugInfo(&MI, DI);
+        Changed = true;
+        std::pair<DenseSet<unsigned>::iterator, bool> MustInsert =
+            Set.insert(DI->getBaseDiscriminator());
+        (void)MustInsert; // Silence warning in release build.
+        assert(MustInsert.second && "New discriminator shouldn't be present in set");
+      }
+
+      // Bump the reference DI to avoid cramming discriminators on line 0.
+      // FIXME(mtrofin): pin ReferenceDI on blocks or first instruction with DI
+      // in a block. It's more consistent than just relying on the last memop
+      // instruction we happened to see.
+      ReferenceDI = DI;
+    }
+  }
+  return Changed;
+}
+
+FunctionPass *llvm::createX86DiscriminateMemOpsPass() {
+  return new X86DiscriminateMemOps();
+}