[Hexagon] Merge adjacent stores

llvm-svn: 250542

lib/Target/Hexagon/CMakeLists.txt

@@ -40,6 +40,7 @@ add_llvm_target(HexagonCodeGen
   HexagonRemoveSZExtArgs.cpp
   HexagonSelectionDAGInfo.cpp
   HexagonSplitConst32AndConst64.cpp
+  HexagonStoreWidening.cpp
   HexagonSubtarget.cpp
   HexagonTargetMachine.cpp
   HexagonTargetObjectFile.cpp

lib/Target/Hexagon/HexagonStoreWidening.cpp

@@ -0,0 +1,616 @@
+//===--- HexagonStoreWidening.cpp------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// Replace sequences of "narrow" stores to adjacent memory locations with
+// a fewer "wide" stores that have the same effect.
+// For example, replace:
+//   S4_storeirb_io  %vreg100, 0, 0   ; store-immediate-byte
+//   S4_storeirb_io  %vreg100, 1, 0   ; store-immediate-byte
+// with
+//   S4_storeirh_io  %vreg100, 0, 0   ; store-immediate-halfword
+// The above is the general idea.  The actual cases handled by the code
+// may be a bit more complex.
+// The purpose of this pass is to reduce the number of outstanding stores,
+// or as one could say, "reduce store queue pressure".  Also, wide stores
+// mean fewer stores, and since there are only two memory instructions allowed
+// per packet, it also means fewer packets, and ultimately fewer cycles.
+//===---------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "hexagon-widen-stores"
+
+#include "HexagonTargetMachine.h"
+
+#include "llvm/PassSupport.h"
+#include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/MC/MCInstrDesc.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Target/TargetMachine.h"
+#include "llvm/Target/TargetRegisterInfo.h"
+#include "llvm/Target/TargetInstrInfo.h"
+
+#include <algorithm>
+
+
+using namespace llvm;
+
+namespace llvm {
+  FunctionPass *createHexagonStoreWidening();
+  void initializeHexagonStoreWideningPass(PassRegistry&);
+}
+
+namespace {
+  struct HexagonStoreWidening : public MachineFunctionPass {
+    const HexagonInstrInfo      *TII;
+    const HexagonRegisterInfo   *TRI;
+    const MachineRegisterInfo   *MRI;
+    AliasAnalysis               *AA;
+    MachineFunction             *MF;
+
+  public:
+    static char ID;
+    HexagonStoreWidening() : MachineFunctionPass(ID) {
+      initializeHexagonStoreWideningPass(*PassRegistry::getPassRegistry());
+    }
+
+    bool runOnMachineFunction(MachineFunction &MF) override;
+
+    const char *getPassName() const override {
+      return "Hexagon Store Widening";
+    }
+
+    void getAnalysisUsage(AnalysisUsage &AU) const override {
+      AU.addRequired<AAResultsWrapperPass>();
+      AU.addPreserved<AAResultsWrapperPass>();
+      MachineFunctionPass::getAnalysisUsage(AU);
+    }
+
+    static bool handledStoreType(const MachineInstr *MI);
+
+  private:
+    static const int MaxWideSize = 4;
+
+    typedef std::vector<MachineInstr*> InstrGroup;
+    typedef std::vector<InstrGroup> InstrGroupList;
+
+    bool instrAliased(InstrGroup &Stores, const MachineMemOperand &MMO);
+    bool instrAliased(InstrGroup &Stores, const MachineInstr *MI);
+    void createStoreGroup(MachineInstr *BaseStore, InstrGroup::iterator Begin,
+        InstrGroup::iterator End, InstrGroup &Group);
+    void createStoreGroups(MachineBasicBlock &MBB,
+        InstrGroupList &StoreGroups);
+    bool processBasicBlock(MachineBasicBlock &MBB);
+    bool processStoreGroup(InstrGroup &Group);
+    bool selectStores(InstrGroup::iterator Begin, InstrGroup::iterator End,
+        InstrGroup &OG, unsigned &TotalSize, unsigned MaxSize);
+    bool createWideStores(InstrGroup &OG, InstrGroup &NG, unsigned TotalSize);
+    bool replaceStores(InstrGroup &OG, InstrGroup &NG);
+    bool storesAreAdjacent(const MachineInstr *S1, const MachineInstr *S2);
+  };
+
+} // namespace
+
+
+namespace {
+
+// Some local helper functions...
+unsigned getBaseAddressRegister(const MachineInstr *MI) {
+  const MachineOperand &MO = MI->getOperand(0);
+  assert(MO.isReg() && "Expecting register operand");
+  return MO.getReg();
+}
+
+int64_t getStoreOffset(const MachineInstr *MI) {
+  unsigned OpC = MI->getOpcode();
+  assert(HexagonStoreWidening::handledStoreType(MI) && "Unhandled opcode");
+
+  switch (OpC) {
+    case Hexagon::S4_storeirb_io:
+    case Hexagon::S4_storeirh_io:
+    case Hexagon::S4_storeiri_io: {
+      const MachineOperand &MO = MI->getOperand(1);
+      assert(MO.isImm() && "Expecting immediate offset");
+      return MO.getImm();
+    }
+  }
+  dbgs() << *MI;
+  llvm_unreachable("Store offset calculation missing for a handled opcode");
+  return 0;
+}
+
+const MachineMemOperand &getStoreTarget(const MachineInstr *MI) {
+  assert(!MI->memoperands_empty() && "Expecting memory operands");
+  return **MI->memoperands_begin();
+}
+
+} // namespace
+
+
+char HexagonStoreWidening::ID = 0;
+
+INITIALIZE_PASS_BEGIN(HexagonStoreWidening, "hexagon-widen-stores",
+                "Hexason Store Widening", false, false)
+INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
+INITIALIZE_PASS_END(HexagonStoreWidening, "hexagon-widen-stores",
+                "Hexagon Store Widening", false, false)
+
+
+// Filtering function: any stores whose opcodes are not "approved" of by
+// this function will not be subjected to widening.
+inline bool HexagonStoreWidening::handledStoreType(const MachineInstr *MI) {
+  // For now, only handle stores of immediate values.
+  // Also, reject stores to stack slots.
+  unsigned Opc = MI->getOpcode();
+  switch (Opc) {
+    case Hexagon::S4_storeirb_io:
+    case Hexagon::S4_storeirh_io:
+    case Hexagon::S4_storeiri_io:
+      // Base address must be a register. (Implement FI later.)
+      return MI->getOperand(0).isReg();
+    default:
+      return false;
+  }
+}
+
+
+// Check if the machine memory operand MMO is aliased with any of the
+// stores in the store group Stores.
+bool HexagonStoreWidening::instrAliased(InstrGroup &Stores,
+      const MachineMemOperand &MMO) {
+  if (!MMO.getValue())
+    return true;
+
+  MemoryLocation L(MMO.getValue(), MMO.getSize(), MMO.getAAInfo());
+
+  for (auto SI : Stores) {
+    const MachineMemOperand &SMO = getStoreTarget(SI);
+    if (!SMO.getValue())
+      return true;
+
+    MemoryLocation SL(SMO.getValue(), SMO.getSize(), SMO.getAAInfo());
+    if (AA->alias(L, SL))
+      return true;
+  }
+
+  return false;
+}
+
+
+// Check if the machine instruction MI accesses any storage aliased with
+// any store in the group Stores.
+bool HexagonStoreWidening::instrAliased(InstrGroup &Stores,
+      const MachineInstr *MI) {
+  for (auto &I : MI->memoperands())
+    if (instrAliased(Stores, *I))
+      return true;
+  return false;
+}
+
+
+// Inspect a machine basic block, and generate store groups out of stores
+// encountered in the block.
+//
+// A store group is a group of stores that use the same base register,
+// and which can be reordered within that group without altering the
+// semantics of the program.  A single store group could be widened as
+// a whole, if there existed a single store instruction with the same
+// semantics as the entire group.  In many cases, a single store group
+// may need more than one wide store.
+void HexagonStoreWidening::createStoreGroups(MachineBasicBlock &MBB,
+      InstrGroupList &StoreGroups) {
+  InstrGroup AllInsns;
+
+  // Copy all instruction pointers from the basic block to a temporary
+  // list.  This will allow operating on the list, and modifying its
+  // elements without affecting the basic block.
+  for (auto &I : MBB)
+    AllInsns.push_back(&I);
+
+  // Traverse all instructions in the AllInsns list, and if we encounter
+  // a store, then try to create a store group starting at that instruction
+  // i.e. a sequence of independent stores that can be widened.
+  for (auto I = AllInsns.begin(), E = AllInsns.end(); I != E; ++I) {
+    MachineInstr *MI = *I;
+    // Skip null pointers (processed instructions).
+    if (!MI || !handledStoreType(MI))
+      continue;
+
+    // Found a store.  Try to create a store group.
+    InstrGroup G;
+    createStoreGroup(MI, I+1, E, G);
+    if (G.size() > 1)
+      StoreGroups.push_back(G);
+  }
+}
+
+
+// Create a single store group.  The stores need to be independent between
+// themselves, and also there cannot be other instructions between them
+// that could read or modify storage being stored into.
+void HexagonStoreWidening::createStoreGroup(MachineInstr *BaseStore,
+      InstrGroup::iterator Begin, InstrGroup::iterator End, InstrGroup &Group) {
+  assert(handledStoreType(BaseStore) && "Unexpected instruction");
+  unsigned BaseReg = getBaseAddressRegister(BaseStore);
+  InstrGroup Other;
+
+  Group.push_back(BaseStore);
+
+  for (auto I = Begin; I != End; ++I) {
+    MachineInstr *MI = *I;
+    if (!MI)
+      continue;
+
+    if (handledStoreType(MI)) {
+      // If this store instruction is aliased with anything already in the
+      // group, terminate the group now.
+      if (instrAliased(Group, getStoreTarget(MI)))
+        return;
+      // If this store is aliased to any of the memory instructions we have
+      // seen so far (that are not a part of this group), terminate the group.
+      if (instrAliased(Other, getStoreTarget(MI)))
+        return;
+
+      unsigned BR = getBaseAddressRegister(MI);
+      if (BR == BaseReg) {
+        Group.push_back(MI);
+        *I = 0;
+        continue;
+      }
+    }
+
+    // Assume calls are aliased to everything.
+    if (MI->isCall() || MI->hasUnmodeledSideEffects())
+      return;
+
+    if (MI->mayLoad() || MI->mayStore()) {
+      if (MI->hasOrderedMemoryRef() || instrAliased(Group, MI))
+        return;
+      Other.push_back(MI);
+    }
+  } // for
+}
+
+
+// Check if store instructions S1 and S2 are adjacent.  More precisely,
+// S2 has to access memory immediately following that accessed by S1.
+bool HexagonStoreWidening::storesAreAdjacent(const MachineInstr *S1,
+      const MachineInstr *S2) {
+  if (!handledStoreType(S1) || !handledStoreType(S2))
+    return false;
+
+  const MachineMemOperand &S1MO = getStoreTarget(S1);
+
+  // Currently only handling immediate stores.
+  int Off1 = S1->getOperand(1).getImm();
+  int Off2 = S2->getOperand(1).getImm();
+
+  return (Off1 >= 0) ? Off1+S1MO.getSize() == unsigned(Off2)
+                     : int(Off1+S1MO.getSize()) == Off2;
+}
+
+
+/// Given a sequence of adjacent stores, and a maximum size of a single wide
+/// store, pick a group of stores that  can be replaced by a single store
+/// of size not exceeding MaxSize.  The selected sequence will be recorded
+/// in OG ("old group" of instructions).
+/// OG should be empty on entry, and should be left empty if the function
+/// fails.
+bool HexagonStoreWidening::selectStores(InstrGroup::iterator Begin,
+      InstrGroup::iterator End, InstrGroup &OG, unsigned &TotalSize,
+      unsigned MaxSize) {
+  assert(Begin != End && "No instructions to analyze");
+  assert(OG.empty() && "Old group not empty on entry");
+
+  if (std::distance(Begin, End) <= 1)
+    return false;
+
+  MachineInstr *FirstMI = *Begin;
+  assert(!FirstMI->memoperands_empty() && "Expecting some memory operands");
+  const MachineMemOperand &FirstMMO = getStoreTarget(FirstMI);
+  unsigned Alignment = FirstMMO.getAlignment();
+  unsigned SizeAccum = FirstMMO.getSize();
+  unsigned FirstOffset = getStoreOffset(FirstMI);
+
+  // The initial value of SizeAccum should always be a power of 2.
+  assert(isPowerOf2_32(SizeAccum) && "First store size not a power of 2");
+
+  // If the size of the first store equals to or exceeds the limit, do nothing.
+  if (SizeAccum >= MaxSize)
+    return false;
+
+  // If the size of the first store is greater than or equal to the address
+  // stored to, then the store cannot be made any wider.
+  if (SizeAccum >= Alignment)
+    return false;
+
+  // The offset of a store will put restrictions on how wide the store can be.
+  // Offsets in stores of size 2^n bytes need to have the n lowest bits be 0.
+  // If the first store already exhausts the offset limits, quit.  Test this
+  // by checking if the next wider size would exceed the limit.
+  if ((2*SizeAccum-1) & FirstOffset)
+    return false;
+
+  OG.push_back(FirstMI);
+  MachineInstr *S1 = FirstMI, *S2 = *(Begin+1);
+  InstrGroup::iterator I = Begin+1;
+
+  // Pow2Num will be the largest number of elements in OG such that the sum
+  // of sizes of stores 0...Pow2Num-1 will be a power of 2.
+  unsigned Pow2Num = 1;
+  unsigned Pow2Size = SizeAccum;
+
+  // Be greedy: keep accumulating stores as long as they are to adjacent
+  // memory locations, and as long as the total number of bytes stored
+  // does not exceed the limit (MaxSize).
+  // Keep track of when the total size covered is a power of 2, since
+  // this is a size a single store can cover.
+  while (I != End) {
+    S2 = *I;
+    // Stores are sorted, so if S1 and S2 are not adjacent, there won't be
+    // any other store to fill the "hole".
+    if (!storesAreAdjacent(S1, S2))
+      break;
+
+    unsigned S2Size = getStoreTarget(S2).getSize();
+    if (SizeAccum + S2Size > std::min(MaxSize, Alignment))
+      break;
+
+    OG.push_back(S2);
+    SizeAccum += S2Size;
+    if (isPowerOf2_32(SizeAccum)) {
+      Pow2Num = OG.size();
+      Pow2Size = SizeAccum;
+    }
+    if ((2*Pow2Size-1) & FirstOffset)
+      break;
+
+    S1 = S2;
+    ++I;
+  }
+
+  // The stores don't add up to anything that can be widened.  Clean up.
+  if (Pow2Num <= 1) {
+    OG.clear();
+    return false;
+  }
+
+  // Only leave the stored being widened.
+  OG.resize(Pow2Num);
+  TotalSize = Pow2Size;
+  return true;
+}
+
+
+/// Given an "old group" OG of stores, create a "new group" NG of instructions
+/// to replace them.  Ideally, NG would only have a single instruction in it,
+/// but that may only be possible for store-immediate.
+bool HexagonStoreWidening::createWideStores(InstrGroup &OG, InstrGroup &NG,
+      unsigned TotalSize) {
+  // XXX Current limitations:
+  // - only expect stores of immediate values in OG,
+  // - only handle a TotalSize of up to 4.
+
+  if (TotalSize > 4)
+    return false;
+
+  unsigned Acc = 0;  // Value accumulator.
+  unsigned Shift = 0;
+
+  for (InstrGroup::iterator I = OG.begin(), E = OG.end(); I != E; ++I) {
+    MachineInstr *MI = *I;
+    const MachineMemOperand &MMO = getStoreTarget(MI);
+    MachineOperand &SO = MI->getOperand(2);  // Source.
+    assert(SO.isImm() && "Expecting an immediate operand");
+
+    unsigned NBits = MMO.getSize()*8;
+    unsigned Mask = (0xFFFFFFFFU >> (32-NBits));
+    unsigned Val = (SO.getImm() & Mask) << Shift;
+    Acc |= Val;
+    Shift += NBits;
+  }
+
+
+  MachineInstr *FirstSt = OG.front();
+  DebugLoc DL = OG.back()->getDebugLoc();
+  const MachineMemOperand &OldM = getStoreTarget(FirstSt);
+  MachineMemOperand *NewM =
+    MF->getMachineMemOperand(OldM.getPointerInfo(), OldM.getFlags(),
+                             TotalSize, OldM.getAlignment(),
+                             OldM.getAAInfo());
+
+  if (Acc < 0x10000) {
+    // Create mem[hw] = #Acc
+    unsigned WOpc = (TotalSize == 2) ? Hexagon::S4_storeirh_io :
+                    (TotalSize == 4) ? Hexagon::S4_storeiri_io : 0;
+    assert(WOpc && "Unexpected size");
+
+    int Val = (TotalSize == 2) ? int16_t(Acc) : int(Acc);
+    const MCInstrDesc &StD = TII->get(WOpc);
+    MachineOperand &MR = FirstSt->getOperand(0);
+    int64_t Off = FirstSt->getOperand(1).getImm();
+    MachineInstr *StI = BuildMI(*MF, DL, StD)
+                          .addReg(MR.getReg(), getKillRegState(MR.isKill()))
+                          .addImm(Off)
+                          .addImm(Val);
+    StI->addMemOperand(*MF, NewM);
+    NG.push_back(StI);
+  } else {
+    // Create vreg = A2_tfrsi #Acc; mem[hw] = vreg
+    const MCInstrDesc &TfrD = TII->get(Hexagon::A2_tfrsi);
+    const TargetRegisterClass *RC = TII->getRegClass(TfrD, 0, TRI, *MF);
+    unsigned VReg = MF->getRegInfo().createVirtualRegister(RC);
+    MachineInstr *TfrI = BuildMI(*MF, DL, TfrD, VReg)
+                           .addImm(int(Acc));
+    NG.push_back(TfrI);
+
+    unsigned WOpc = (TotalSize == 2) ? Hexagon::S2_storerh_io :
+                    (TotalSize == 4) ? Hexagon::S2_storeri_io : 0;
+    assert(WOpc && "Unexpected size");
+
+    const MCInstrDesc &StD = TII->get(WOpc);
+    MachineOperand &MR = FirstSt->getOperand(0);
+    int64_t Off = FirstSt->getOperand(1).getImm();
+    MachineInstr *StI = BuildMI(*MF, DL, StD)
+                          .addReg(MR.getReg(), getKillRegState(MR.isKill()))
+                          .addImm(Off)
+                          .addReg(VReg, RegState::Kill);
+    StI->addMemOperand(*MF, NewM);
+    NG.push_back(StI);
+  }
+
+  return true;
+}
+
+
+// Replace instructions from the old group OG with instructions from the
+// new group NG.  Conceptually, remove all instructions in OG, and then
+// insert all instructions in NG, starting at where the first instruction
+// from OG was (in the order in which they appeared in the basic block).
+// (The ordering in OG does not have to match the order in the basic block.)
+bool HexagonStoreWidening::replaceStores(InstrGroup &OG, InstrGroup &NG) {
+  DEBUG({
+    dbgs() << "Replacing:\n";
+    for (auto I : OG)
+      dbgs() << "  " << *I;
+    dbgs() << "with\n";
+    for (auto I : NG)
+      dbgs() << "  " << *I;
+  });
+
+  MachineBasicBlock *MBB = OG.back()->getParent();
+  MachineBasicBlock::iterator InsertAt = MBB->end();
+
+  // Need to establish the insertion point.  The best one is right before
+  // the first store in the OG, but in the order in which the stores occur
+  // in the program list.  Since the ordering in OG does not correspond
+  // to the order in the program list, we need to do some work to find
+  // the insertion point.
+
+  // Create a set of all instructions in OG (for quick lookup).
+  SmallPtrSet<MachineInstr*, 4> InstrSet;
+  for (auto I : OG)
+    InstrSet.insert(I);
+
+  // Traverse the block, until we hit an instruction from OG.
+  for (auto &I : *MBB) {
+    if (InstrSet.count(&I)) {
+      InsertAt = I;
+      break;
+    }
+  }
+
+  assert((InsertAt != MBB->end()) && "Cannot locate any store from the group");
+
+  bool AtBBStart = false;
+
+  // InsertAt points at the first instruction that will be removed.  We need
+  // to move it out of the way, so it remains valid after removing all the
+  // old stores, and so we are able to recover it back to the proper insertion
+  // position.
+  if (InsertAt != MBB->begin())
+    --InsertAt;
+  else
+    AtBBStart = true;
+
+  for (auto I : OG)
+    I->eraseFromParent();
+
+  if (!AtBBStart)
+    ++InsertAt;
+  else
+    InsertAt = MBB->begin();
+
+  for (auto I : NG)
+    MBB->insert(InsertAt, I);
+
+  return true;
+}
+
+
+// Break up the group into smaller groups, each of which can be replaced by
+// a single wide store.  Widen each such smaller group and replace the old
+// instructions with the widened ones.
+bool HexagonStoreWidening::processStoreGroup(InstrGroup &Group) {
+  bool Changed = false;
+  InstrGroup::iterator I = Group.begin(), E = Group.end();
+  InstrGroup OG, NG;   // Old and new groups.
+  unsigned CollectedSize;
+
+  while (I != E) {
+    OG.clear();
+    NG.clear();
+
+    bool Succ = selectStores(I++, E, OG, CollectedSize, MaxWideSize) &&
+                createWideStores(OG, NG, CollectedSize)              &&
+                replaceStores(OG, NG);
+    if (!Succ)
+      continue;
+
+    assert(OG.size() > 1 && "Created invalid group");
+    assert(distance(I, E)+1 >= int(OG.size()) && "Too many elements");
+    I += OG.size()-1;
+
+    Changed = true;
+  }
+
+  return Changed;
+}
+
+
+// Process a single basic block: create the store groups, and replace them
+// with the widened stores, if possible.  Processing of each basic block
+// is independent from processing of any other basic block.  This transfor-
+// mation could be stopped after having processed any basic block without
+// any ill effects (other than not having performed widening in the unpro-
+// cessed blocks).  Also, the basic blocks can be processed in any order.
+bool HexagonStoreWidening::processBasicBlock(MachineBasicBlock &MBB) {
+  InstrGroupList SGs;
+  bool Changed = false;
+
+  createStoreGroups(MBB, SGs);
+
+  auto Less = [] (const MachineInstr *A, const MachineInstr *B) -> bool {
+    return getStoreOffset(A) < getStoreOffset(B);
+  };
+  for (auto &G : SGs) {
+    assert(G.size() > 1 && "Store group with fewer than 2 elements");
+    std::sort(G.begin(), G.end(), Less);
+
+    Changed |= processStoreGroup(G);
+  }
+
+  return Changed;
+}
+
+
+bool HexagonStoreWidening::runOnMachineFunction(MachineFunction &MFn) {
+  MF = &MFn;
+  auto &ST = MFn.getSubtarget<HexagonSubtarget>();
+  TII = ST.getInstrInfo();
+  TRI = ST.getRegisterInfo();
+  MRI = &MFn.getRegInfo();
+  AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
+
+  bool Changed = false;
+
+  for (auto &B : MFn)
+    Changed |= processBasicBlock(B);
+
+  return Changed;
+}
+
+
+FunctionPass *llvm::createHexagonStoreWidening() {
+  return new HexagonStoreWidening();
+}
+

lib/Target/Hexagon/HexagonTargetMachine.cpp

@@ -33,6 +33,9 @@ static cl::opt<bool> DisableHexagonCFGOpt("disable-hexagon-cfgopt",
   cl::Hidden, cl::ZeroOrMore, cl::init(false),
   cl::desc("Disable Hexagon CFG Optimization"));
 
+static cl::opt<bool> DisableStoreWidening("disable-store-widen",
+  cl::Hidden, cl::init(false), cl::desc("Disable store widening"));
+
 static cl::opt<bool> EnableExpandCondsets("hexagon-expand-condsets",
   cl::init(true), cl::Hidden, cl::ZeroOrMore,
   cl::desc("Early expansion of MUX"));
@@ -97,6 +100,7 @@ namespace llvm {
   FunctionPass *createHexagonPeephole();
   FunctionPass *createHexagonRemoveExtendArgs(const HexagonTargetMachine &TM);
   FunctionPass *createHexagonSplitConst32AndConst64();
+  FunctionPass *createHexagonStoreWidening();
 } // end namespace llvm;
 
 /// HexagonTargetMachine ctor - Create an ILP32 architecture model.
@@ -226,9 +230,12 @@ bool HexagonPassConfig::addInstSelector() {
 }
 
 void HexagonPassConfig::addPreRegAlloc() {
-  if (getOptLevel() != CodeGenOpt::None)
+  if (getOptLevel() != CodeGenOpt::None) {
+    if (!DisableStoreWidening)
+      addPass(createHexagonStoreWidening(), false);
     if (!DisableHardwareLoops)
       addPass(createHexagonHardwareLoops(), false);
+  }
 }
 
 void HexagonPassConfig::addPostRegAlloc() {

test/CodeGen/Hexagon/store-widen-aliased-load.ll

@@ -0,0 +1,21 @@
+; RUN: llc -march=hexagon < %s | FileCheck %s
+; CHECK-NOT: memh
+; Check that store widening does not merge the two stores.
+
+target datalayout = "e-p:32:32:32-i64:64:64-i32:32:32-i16:16:16-i1:32:32-f64:64:64-f32:32:32-v64:64:64-v32:32:32-a0:0-n16:32"
+target triple = "hexagon"
+
+%struct.type_t = type { i8, i8, [2 x i8] }
+
+define zeroext i8 @foo(%struct.type_t* nocapture %p) nounwind {
+entry:
+  %a = getelementptr inbounds %struct.type_t, %struct.type_t* %p, i32 0, i32 0
+  store i8 0, i8* %a, align 2, !tbaa !0
+  %b = getelementptr inbounds %struct.type_t, %struct.type_t* %p, i32 0, i32 1
+  %0 = load i8, i8* %b, align 1, !tbaa !0
+  store i8 0, i8* %b, align 1, !tbaa !0
+  ret i8 %0
+}
+
+!0 = !{!"omnipotent char", !1}
+!1 = !{!"Simple C/C++ TBAA"}

test/CodeGen/Hexagon/store-widen-negv.ll

@@ -0,0 +1,11 @@
+; RUN: llc -march=hexagon < %s | FileCheck %s
+; We shouldn't see a 32-bit expansion of -120, just the uint8 value.
+; CHECK: #136
+define i32 @foo([4 x i8]* %ptr) {
+entry:
+  %msb = getelementptr inbounds [4 x i8], [4 x i8]* %ptr, i32 0, i32 3
+  %lsb = getelementptr inbounds [4 x i8], [4 x i8]* %ptr, i32 0, i32 2
+  store i8 0, i8* %msb
+  store i8 -120, i8* %lsb, align 2
+  ret i32 0
+}

test/CodeGen/Hexagon/store-widen-negv2.ll

@@ -0,0 +1,19 @@
+; RUN: llc -march=hexagon < %s | FileCheck %s
+; CHECK-LABEL: foo:
+; CHECK: memh(r0+#0){{.*}}={{.*}}#-2
+; Don't use memh(r0+#0)=##65534.
+
+target datalayout = "e-m:e-p:32:32-i1:32-i64:64-a:0-v32:32-n16:32"
+target triple = "hexagon"
+
+; Function Attrs: nounwind
+define void @foo(i16* nocapture %s) #0 {
+entry:
+  %0 = bitcast i16* %s to i8*
+  store i8 -2, i8* %0, align 2
+  %add.ptr = getelementptr inbounds i8, i8* %0, i32 1
+  store i8 -1, i8* %add.ptr, align 1
+  ret void
+}
+
+attributes #0 = { nounwind }

test/CodeGen/Hexagon/store-widen.ll

@@ -0,0 +1,18 @@
+; RUN: llc -march=hexagon < %s | FileCheck %s
+target datalayout = "e-p:32:32:32-i64:64:64-i32:32:32-i16:16:16-i1:32:32-f64:64:64-f32:32:32-v64:64:64-v32:32:32-a0:0-n16:32"
+target triple = "hexagon"
+
+define void @foo(i16* nocapture %a) nounwind {
+entry:
+; There should be a memw, not memh.
+; CHECK: memw
+  ; Cheated on the alignment, just to trigger the widening.
+  store i16 0, i16* %a, align 4, !tbaa !0
+  %arrayidx1 = getelementptr inbounds i16, i16* %a, i32 1
+  store i16 0, i16* %arrayidx1, align 2, !tbaa !0
+  ret void
+}
+
+!0 = !{!"short", !1}
+!1 = !{!"omnipotent char", !2}
+!2 = !{!"Simple C/C++ TBAA"}