From: Colin LeMahieu <colinl@codeaurora.org>
Date: Mon, 8 Jun 2015 16:34:47 +0000 (+0000)
Subject: [Hexagon] Adding functionality for searching for compound instruction pairs.  Compoun... 
X-Git-Url: http://plrg.eecs.uci.edu/git/?a=commitdiff_plain;h=838271c858c35f4aa0622c52b549074318e18f4e;p=oota-llvm.git

[Hexagon] Adding functionality for searching for compound instruction pairs.  Compound instructions reduce slot resource requirements freeing those packet slots up for more instructions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239307 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Target/Hexagon/HexagonAsmPrinter.cpp b/lib/Target/Hexagon/HexagonAsmPrinter.cpp
index 45d953ff40a..93ae7ef876c 100644
--- a/lib/Target/Hexagon/HexagonAsmPrinter.cpp
+++ b/lib/Target/Hexagon/HexagonAsmPrinter.cpp
@@ -200,11 +200,17 @@ void HexagonAsmPrinter::EmitInstruction(const MachineInstr *MI) {
     HexagonLowerToMC(MI, MCB, *this);
     HexagonMCInstrInfo::padEndloop(MCB);
   }
+  // Examine the packet and try to find instructions that can be converted
+  // to compounds.
+  HexagonMCInstrInfo::tryCompound(*Subtarget->getInstrInfo(),
+                                  OutStreamer->getContext(), MCB);
   // Examine the packet and convert pairs of instructions to duplex
   // instructions when possible.
   SmallVector<DuplexCandidate, 8> possibleDuplexes;
-  possibleDuplexes = HexagonMCInstrInfo::getDuplexPossibilties(*Subtarget->getInstrInfo(), MCB);
-  HexagonMCShuffle(*Subtarget->getInstrInfo(), *Subtarget, OutStreamer->getContext(), MCB, possibleDuplexes);
+  possibleDuplexes = HexagonMCInstrInfo::getDuplexPossibilties(
+      *Subtarget->getInstrInfo(), MCB);
+  HexagonMCShuffle(*Subtarget->getInstrInfo(), *Subtarget,
+                   OutStreamer->getContext(), MCB, possibleDuplexes);
   EmitToStreamer(*OutStreamer, MCB);
 }
 
diff --git a/lib/Target/Hexagon/MCTargetDesc/CMakeLists.txt b/lib/Target/Hexagon/MCTargetDesc/CMakeLists.txt
index d0fae8a5192..6253686b499 100644
--- a/lib/Target/Hexagon/MCTargetDesc/CMakeLists.txt
+++ b/lib/Target/Hexagon/MCTargetDesc/CMakeLists.txt
@@ -4,6 +4,7 @@ add_llvm_library(LLVMHexagonDesc
   HexagonInstPrinter.cpp
   HexagonMCAsmInfo.cpp
   HexagonMCCodeEmitter.cpp
+  HexagonMCCompound.cpp
   HexagonMCDuplexInfo.cpp
   HexagonMCInstrInfo.cpp
   HexagonMCShuffler.cpp
diff --git a/lib/Target/Hexagon/MCTargetDesc/HexagonBaseInfo.h b/lib/Target/Hexagon/MCTargetDesc/HexagonBaseInfo.h
index 4f84e0d79e6..f4d162ccf6a 100644
--- a/lib/Target/Hexagon/MCTargetDesc/HexagonBaseInfo.h
+++ b/lib/Target/Hexagon/MCTargetDesc/HexagonBaseInfo.h
@@ -202,6 +202,14 @@ namespace HexagonII {
     HSIG_Compound
   };
 
+  // Hexagon Compound classes.
+  enum CompoundGroup {
+    HCG_None = 0,
+    HCG_A,
+    HCG_B,
+    HCG_C
+  };
+
   enum InstParseBits {
     INST_PARSE_MASK       = 0x0000c000,
     INST_PARSE_PACKET_END = 0x0000c000,
diff --git a/lib/Target/Hexagon/MCTargetDesc/HexagonMCCompound.cpp b/lib/Target/Hexagon/MCTargetDesc/HexagonMCCompound.cpp
new file mode 100644
index 00000000000..108093547f8
--- /dev/null
+++ b/lib/Target/Hexagon/MCTargetDesc/HexagonMCCompound.cpp
@@ -0,0 +1,420 @@
+
+//=== HexagonMCCompound.cpp - Hexagon Compound checker  -------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file is looks at a packet and tries to form compound insns
+//
+//===----------------------------------------------------------------------===//
+#include "Hexagon.h"
+#include "MCTargetDesc/HexagonBaseInfo.h"
+#include "MCTargetDesc/HexagonMCShuffler.h"
+#include "llvm/ADT/StringExtras.h"
+#include "llvm/MC/MCAssembler.h"
+#include "llvm/MC/MCContext.h"
+#include "llvm/MC/MCInst.h"
+#include "llvm/MC/MCSectionELF.h"
+#include "llvm/MC/MCStreamer.h"
+#include "llvm/MC/MCSymbol.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+
+using namespace llvm;
+using namespace Hexagon;
+
+#define DEBUG_TYPE "hexagon-mccompound"
+
+enum OpcodeIndex {
+  fp0_jump_nt = 0,
+  fp0_jump_t,
+  fp1_jump_nt,
+  fp1_jump_t,
+  tp0_jump_nt,
+  tp0_jump_t,
+  tp1_jump_nt,
+  tp1_jump_t
+};
+
+unsigned tstBitOpcode[8] = {J4_tstbit0_fp0_jump_nt, J4_tstbit0_fp0_jump_t,
+                            J4_tstbit0_fp1_jump_nt, J4_tstbit0_fp1_jump_t,
+                            J4_tstbit0_tp0_jump_nt, J4_tstbit0_tp0_jump_t,
+                            J4_tstbit0_tp1_jump_nt, J4_tstbit0_tp1_jump_t};
+unsigned cmpeqBitOpcode[8] = {J4_cmpeq_fp0_jump_nt, J4_cmpeq_fp0_jump_t,
+                              J4_cmpeq_fp1_jump_nt, J4_cmpeq_fp1_jump_t,
+                              J4_cmpeq_tp0_jump_nt, J4_cmpeq_tp0_jump_t,
+                              J4_cmpeq_tp1_jump_nt, J4_cmpeq_tp1_jump_t};
+unsigned cmpgtBitOpcode[8] = {J4_cmpgt_fp0_jump_nt, J4_cmpgt_fp0_jump_t,
+                              J4_cmpgt_fp1_jump_nt, J4_cmpgt_fp1_jump_t,
+                              J4_cmpgt_tp0_jump_nt, J4_cmpgt_tp0_jump_t,
+                              J4_cmpgt_tp1_jump_nt, J4_cmpgt_tp1_jump_t};
+unsigned cmpgtuBitOpcode[8] = {J4_cmpgtu_fp0_jump_nt, J4_cmpgtu_fp0_jump_t,
+                               J4_cmpgtu_fp1_jump_nt, J4_cmpgtu_fp1_jump_t,
+                               J4_cmpgtu_tp0_jump_nt, J4_cmpgtu_tp0_jump_t,
+                               J4_cmpgtu_tp1_jump_nt, J4_cmpgtu_tp1_jump_t};
+unsigned cmpeqiBitOpcode[8] = {J4_cmpeqi_fp0_jump_nt, J4_cmpeqi_fp0_jump_t,
+                               J4_cmpeqi_fp1_jump_nt, J4_cmpeqi_fp1_jump_t,
+                               J4_cmpeqi_tp0_jump_nt, J4_cmpeqi_tp0_jump_t,
+                               J4_cmpeqi_tp1_jump_nt, J4_cmpeqi_tp1_jump_t};
+unsigned cmpgtiBitOpcode[8] = {J4_cmpgti_fp0_jump_nt, J4_cmpgti_fp0_jump_t,
+                               J4_cmpgti_fp1_jump_nt, J4_cmpgti_fp1_jump_t,
+                               J4_cmpgti_tp0_jump_nt, J4_cmpgti_tp0_jump_t,
+                               J4_cmpgti_tp1_jump_nt, J4_cmpgti_tp1_jump_t};
+unsigned cmpgtuiBitOpcode[8] = {J4_cmpgtui_fp0_jump_nt, J4_cmpgtui_fp0_jump_t,
+                                J4_cmpgtui_fp1_jump_nt, J4_cmpgtui_fp1_jump_t,
+                                J4_cmpgtui_tp0_jump_nt, J4_cmpgtui_tp0_jump_t,
+                                J4_cmpgtui_tp1_jump_nt, J4_cmpgtui_tp1_jump_t};
+unsigned cmpeqn1BitOpcode[8] = {J4_cmpeqn1_fp0_jump_nt, J4_cmpeqn1_fp0_jump_t,
+                                J4_cmpeqn1_fp1_jump_nt, J4_cmpeqn1_fp1_jump_t,
+                                J4_cmpeqn1_tp0_jump_nt, J4_cmpeqn1_tp0_jump_t,
+                                J4_cmpeqn1_tp1_jump_nt, J4_cmpeqn1_tp1_jump_t};
+unsigned cmpgtn1BitOpcode[8] = {
+    J4_cmpgtn1_fp0_jump_nt, J4_cmpgtn1_fp0_jump_t,  J4_cmpgtn1_fp1_jump_nt,
+    J4_cmpgtn1_fp1_jump_t,  J4_cmpgtn1_tp0_jump_nt, J4_cmpgtn1_tp0_jump_t,
+    J4_cmpgtn1_tp1_jump_nt, J4_cmpgtn1_tp1_jump_t,
+};
+
+// enum HexagonII::CompoundGroup
+namespace {
+unsigned getCompoundCandidateGroup(MCInst const &MI, bool IsExtended) {
+  unsigned DstReg, SrcReg, Src1Reg, Src2Reg;
+
+  switch (MI.getOpcode()) {
+  default:
+    return HexagonII::HCG_None;
+  //
+  // Compound pairs.
+  // "p0=cmp.eq(Rs16,Rt16); if (p0.new) jump:nt #r9:2"
+  // "Rd16=#U6 ; jump #r9:2"
+  // "Rd16=Rs16 ; jump #r9:2"
+  //
+  case Hexagon::C2_cmpeq:
+  case Hexagon::C2_cmpgt:
+  case Hexagon::C2_cmpgtu:
+    if (IsExtended)
+      return false;
+    DstReg = MI.getOperand(0).getReg();
+    Src1Reg = MI.getOperand(1).getReg();
+    Src2Reg = MI.getOperand(2).getReg();
+    if ((Hexagon::P0 == DstReg || Hexagon::P1 == DstReg) &&
+        HexagonMCInstrInfo::isIntRegForSubInst(Src1Reg) &&
+        HexagonMCInstrInfo::isIntRegForSubInst(Src2Reg))
+      return HexagonII::HCG_A;
+    break;
+  case Hexagon::C2_cmpeqi:
+  case Hexagon::C2_cmpgti:
+  case Hexagon::C2_cmpgtui:
+    if (IsExtended)
+      return false;
+    // P0 = cmp.eq(Rs,#u2)
+    DstReg = MI.getOperand(0).getReg();
+    SrcReg = MI.getOperand(1).getReg();
+    if ((Hexagon::P0 == DstReg || Hexagon::P1 == DstReg) &&
+        HexagonMCInstrInfo::isIntRegForSubInst(SrcReg) &&
+        MI.getOperand(2).isImm() && ((isUInt<5>(MI.getOperand(2).getImm())) ||
+                                     (MI.getOperand(2).getImm() == -1)))
+      return HexagonII::HCG_A;
+    break;
+  case Hexagon::A2_tfr:
+    if (IsExtended)
+      return false;
+    // Rd = Rs
+    DstReg = MI.getOperand(0).getReg();
+    SrcReg = MI.getOperand(1).getReg();
+    if (HexagonMCInstrInfo::isIntRegForSubInst(DstReg) &&
+        HexagonMCInstrInfo::isIntRegForSubInst(SrcReg))
+      return HexagonII::HCG_A;
+    break;
+  case Hexagon::A2_tfrsi:
+    if (IsExtended)
+      return false;
+    // Rd = #u6
+    DstReg = MI.getOperand(0).getReg();
+    if (MI.getOperand(1).isImm() && MI.getOperand(1).getImm() <= 63 &&
+        MI.getOperand(1).getImm() >= 0 &&
+        HexagonMCInstrInfo::isIntRegForSubInst(DstReg))
+      return HexagonII::HCG_A;
+    break;
+  case Hexagon::S2_tstbit_i:
+    if (IsExtended)
+      return false;
+    DstReg = MI.getOperand(0).getReg();
+    Src1Reg = MI.getOperand(1).getReg();
+    if ((Hexagon::P0 == DstReg || Hexagon::P1 == DstReg) &&
+        MI.getOperand(2).isImm() &&
+        HexagonMCInstrInfo::isIntRegForSubInst(Src1Reg) &&
+        (MI.getOperand(2).getImm() == 0))
+      return HexagonII::HCG_A;
+    break;
+  // The fact that .new form is used pretty much guarantees
+  // that predicate register will match. Nevertheless,
+  // there could be some false positives without additional
+  // checking.
+  case Hexagon::J2_jumptnew:
+  case Hexagon::J2_jumpfnew:
+  case Hexagon::J2_jumptnewpt:
+  case Hexagon::J2_jumpfnewpt:
+    Src1Reg = MI.getOperand(0).getReg();
+    if (Hexagon::P0 == Src1Reg || Hexagon::P1 == Src1Reg)
+      return HexagonII::HCG_B;
+    break;
+  // Transfer and jump:
+  // Rd=#U6 ; jump #r9:2
+  // Rd=Rs ; jump #r9:2
+  // Do not test for jump range here.
+  case Hexagon::J2_jump:
+  case Hexagon::RESTORE_DEALLOC_RET_JMP_V4:
+    return HexagonII::HCG_C;
+    break;
+  }
+
+  return HexagonII::HCG_None;
+}
+}
+
+/// getCompoundOp - Return the index from 0-7 into the above opcode lists.
+namespace {
+unsigned getCompoundOp(MCInst const &HMCI) {
+  const MCOperand &Predicate = HMCI.getOperand(0);
+  unsigned PredReg = Predicate.getReg();
+
+  assert((PredReg == Hexagon::P0) || (PredReg == Hexagon::P1) ||
+         (PredReg == Hexagon::P2) || (PredReg == Hexagon::P3));
+
+  switch (HMCI.getOpcode()) {
+  default:
+    llvm_unreachable("Expected match not found.\n");
+    break;
+  case Hexagon::J2_jumpfnew:
+    return (PredReg == Hexagon::P0) ? fp0_jump_nt : fp1_jump_nt;
+  case Hexagon::J2_jumpfnewpt:
+    return (PredReg == Hexagon::P0) ? fp0_jump_t : fp1_jump_t;
+  case Hexagon::J2_jumptnew:
+    return (PredReg == Hexagon::P0) ? tp0_jump_nt : tp1_jump_nt;
+  case Hexagon::J2_jumptnewpt:
+    return (PredReg == Hexagon::P0) ? tp0_jump_t : tp1_jump_t;
+  }
+}
+}
+
+namespace {
+MCInst *getCompoundInsn(MCContext &Context, MCInst const &L, MCInst const &R) {
+  MCInst *CompoundInsn = 0;
+  unsigned compoundOpcode;
+  MCOperand Rs, Rt;
+
+  switch (L.getOpcode()) {
+  default:
+    DEBUG(dbgs() << "Possible compound ignored\n");
+    return CompoundInsn;
+
+  case Hexagon::A2_tfrsi:
+    Rt = L.getOperand(0);
+    compoundOpcode = J4_jumpseti;
+    CompoundInsn = new (Context) MCInst;
+    CompoundInsn->setOpcode(compoundOpcode);
+
+    CompoundInsn->addOperand(Rt);
+    CompoundInsn->addOperand(L.getOperand(1)); // Immediate
+    CompoundInsn->addOperand(R.getOperand(0)); // Jump target
+    break;
+
+  case Hexagon::A2_tfr:
+    Rt = L.getOperand(0);
+    Rs = L.getOperand(1);
+
+    compoundOpcode = J4_jumpsetr;
+    CompoundInsn = new (Context) MCInst;
+    CompoundInsn->setOpcode(compoundOpcode);
+    CompoundInsn->addOperand(Rt);
+    CompoundInsn->addOperand(Rs);
+    CompoundInsn->addOperand(R.getOperand(0)); // Jump target.
+
+    break;
+
+  case Hexagon::C2_cmpeq:
+    DEBUG(dbgs() << "CX: C2_cmpeq\n");
+    Rs = L.getOperand(1);
+    Rt = L.getOperand(2);
+
+    compoundOpcode = cmpeqBitOpcode[getCompoundOp(R)];
+    CompoundInsn = new (Context) MCInst;
+    CompoundInsn->setOpcode(compoundOpcode);
+    CompoundInsn->addOperand(Rs);
+    CompoundInsn->addOperand(Rt);
+    CompoundInsn->addOperand(R.getOperand(1));
+    break;
+
+  case Hexagon::C2_cmpgt:
+    DEBUG(dbgs() << "CX: C2_cmpgt\n");
+    Rs = L.getOperand(1);
+    Rt = L.getOperand(2);
+
+    compoundOpcode = cmpgtBitOpcode[getCompoundOp(R)];
+    CompoundInsn = new (Context) MCInst;
+    CompoundInsn->setOpcode(compoundOpcode);
+    CompoundInsn->addOperand(Rs);
+    CompoundInsn->addOperand(Rt);
+    CompoundInsn->addOperand(R.getOperand(1));
+    break;
+
+  case Hexagon::C2_cmpgtu:
+    DEBUG(dbgs() << "CX: C2_cmpgtu\n");
+    Rs = L.getOperand(1);
+    Rt = L.getOperand(2);
+
+    compoundOpcode = cmpgtuBitOpcode[getCompoundOp(R)];
+    CompoundInsn = new (Context) MCInst;
+    CompoundInsn->setOpcode(compoundOpcode);
+    CompoundInsn->addOperand(Rs);
+    CompoundInsn->addOperand(Rt);
+    CompoundInsn->addOperand(R.getOperand(1));
+    break;
+
+  case Hexagon::C2_cmpeqi:
+    DEBUG(dbgs() << "CX: C2_cmpeqi\n");
+    if (L.getOperand(2).getImm() == -1)
+      compoundOpcode = cmpeqn1BitOpcode[getCompoundOp(R)];
+    else
+      compoundOpcode = cmpeqiBitOpcode[getCompoundOp(R)];
+
+    Rs = L.getOperand(1);
+    CompoundInsn = new (Context) MCInst;
+    CompoundInsn->setOpcode(compoundOpcode);
+    CompoundInsn->addOperand(Rs);
+    if (L.getOperand(2).getImm() != -1)
+      CompoundInsn->addOperand(L.getOperand(2));
+    CompoundInsn->addOperand(R.getOperand(1));
+    break;
+
+  case Hexagon::C2_cmpgti:
+    DEBUG(dbgs() << "CX: C2_cmpgti\n");
+    if (L.getOperand(2).getImm() == -1)
+      compoundOpcode = cmpgtn1BitOpcode[getCompoundOp(R)];
+    else
+      compoundOpcode = cmpgtiBitOpcode[getCompoundOp(R)];
+
+    Rs = L.getOperand(1);
+    CompoundInsn = new (Context) MCInst;
+    CompoundInsn->setOpcode(compoundOpcode);
+    CompoundInsn->addOperand(Rs);
+    if (L.getOperand(2).getImm() != -1)
+      CompoundInsn->addOperand(L.getOperand(2));
+    CompoundInsn->addOperand(R.getOperand(1));
+    break;
+
+  case Hexagon::C2_cmpgtui:
+    DEBUG(dbgs() << "CX: C2_cmpgtui\n");
+    Rs = L.getOperand(1);
+    compoundOpcode = cmpgtuiBitOpcode[getCompoundOp(R)];
+    CompoundInsn = new (Context) MCInst;
+    CompoundInsn->setOpcode(compoundOpcode);
+    CompoundInsn->addOperand(Rs);
+    CompoundInsn->addOperand(L.getOperand(2));
+    CompoundInsn->addOperand(R.getOperand(1));
+    break;
+
+  case Hexagon::S2_tstbit_i:
+    DEBUG(dbgs() << "CX: S2_tstbit_i\n");
+    Rs = L.getOperand(1);
+    compoundOpcode = tstBitOpcode[getCompoundOp(R)];
+    CompoundInsn = new (Context) MCInst;
+    CompoundInsn->setOpcode(compoundOpcode);
+    CompoundInsn->addOperand(Rs);
+    CompoundInsn->addOperand(R.getOperand(1));
+    break;
+  }
+
+  return CompoundInsn;
+}
+}
+
+/// Non-Symmetrical. See if these two instructions are fit for compound pair.
+namespace {
+bool isOrderedCompoundPair(MCInst const &MIa, bool IsExtendedA,
+                           MCInst const &MIb, bool IsExtendedB) {
+  unsigned MIaG = getCompoundCandidateGroup(MIa, IsExtendedA);
+  unsigned MIbG = getCompoundCandidateGroup(MIb, IsExtendedB);
+  // We have two candidates - check that this is the same register
+  // we are talking about.
+  unsigned Opca = MIa.getOpcode();
+  if (MIaG == HexagonII::HCG_A && MIbG == HexagonII::HCG_C &&
+      (Opca == Hexagon::A2_tfr || Opca == Hexagon::A2_tfrsi))
+    return true;
+  return ((MIaG == HexagonII::HCG_A && MIbG == HexagonII::HCG_B) &&
+          (MIa.getOperand(0).getReg() == MIb.getOperand(0).getReg()));
+}
+}
+
+namespace {
+bool lookForCompound(MCInstrInfo const &MCII, MCContext &Context, MCInst &MCI) {
+  assert(HexagonMCInstrInfo::isBundle(MCI));
+  bool JExtended = false;
+  for (MCInst::iterator J =
+           MCI.begin() + HexagonMCInstrInfo::bundleInstructionsOffset;
+       J != MCI.end(); ++J) {
+    MCInst const *JumpInst = J->getInst();
+    if (HexagonMCInstrInfo::isImmext(*JumpInst)) {
+      JExtended = true;
+      continue;
+    }
+    if (llvm::HexagonMCInstrInfo::getType(MCII, *JumpInst) ==
+        HexagonII::TypeJ) {
+      // Try to pair with another insn (B)undled with jump.
+      bool BExtended = false;
+      for (MCInst::iterator B =
+               MCI.begin() + HexagonMCInstrInfo::bundleInstructionsOffset;
+           B != MCI.end(); ++B) {
+        MCInst const *Inst = B->getInst();
+        if (JumpInst == Inst)
+          continue;
+        if (HexagonMCInstrInfo::isImmext(*Inst)) {
+          BExtended = true;
+          continue;
+        }
+        DEBUG(dbgs() << "J,B: " << JumpInst->getOpcode() << ","
+                     << Inst->getOpcode() << "\n");
+        if (isOrderedCompoundPair(*Inst, BExtended, *JumpInst, JExtended)) {
+          MCInst *CompoundInsn = getCompoundInsn(Context, *Inst, *JumpInst);
+          if (CompoundInsn) {
+            DEBUG(dbgs() << "B: " << Inst->getOpcode() << ","
+                         << JumpInst->getOpcode() << " Compounds to "
+                         << CompoundInsn->getOpcode() << "\n");
+            J->setInst(CompoundInsn);
+            MCI.erase(B);
+            return true;
+          }
+        }
+        BExtended = false;
+      }
+    }
+    JExtended = false;
+  }
+  return false;
+}
+}
+
+/// tryCompound - Given a bundle check for compound insns when one
+/// is found update the contents fo the bundle with the compound insn.
+/// If a compound instruction is found then the bundle will have one
+/// additional slot.
+void HexagonMCInstrInfo::tryCompound(MCInstrInfo const &MCII,
+                                     MCContext &Context, MCInst &MCI) {
+  assert(MCI.getOpcode() == Hexagon::BUNDLE &&
+         "Non-Bundle where Bundle expected");
+
+  // By definition a compound must have 2 insn.
+  if (MCI.size() < 2)
+    return;
+
+  // Look for compounds until none are found, only update the bundle when
+  // a compound is found.
+  while (lookForCompound(MCII, Context, MCI))
+    ;
+
+  return;
+}
diff --git a/lib/Target/Hexagon/MCTargetDesc/HexagonMCInstrInfo.h b/lib/Target/Hexagon/MCTargetDesc/HexagonMCInstrInfo.h
index f09dfd8cf47..09f305f638e 100644
--- a/lib/Target/Hexagon/MCTargetDesc/HexagonMCInstrInfo.h
+++ b/lib/Target/Hexagon/MCTargetDesc/HexagonMCInstrInfo.h
@@ -223,6 +223,9 @@ void setOuterLoop(MCInst &MCI);
 
 // Would duplexing this instruction create a requirement to extend
 bool subInstWouldBeExtended(MCInst const &potentialDuplex);
+
+// Attempt to find and replace compound pairs 
+void tryCompound(MCInstrInfo const &MCII, MCContext &Context, MCInst &MCI);
 }
 }
 
diff --git a/test/CodeGen/Hexagon/compound.ll b/test/CodeGen/Hexagon/compound.ll
new file mode 100644
index 00000000000..f8d36b8b77d
--- /dev/null
+++ b/test/CodeGen/Hexagon/compound.ll
@@ -0,0 +1,17 @@
+; RUN: llc -march=hexagon -filetype=obj -o - %s | llvm-objdump -d - | FileCheck %s
+
+; CHECK: p0 = cmp.gt(r0,#-1); if (!p0.new) jump:nt
+
+declare void @a()
+declare void @b()
+
+define void @foo(i32 %a) {
+%b = icmp sgt i32 %a, -1
+br i1 %b, label %x, label %y
+x:
+call void @a()
+ret void
+y:
+call void @b()
+ret void
+}
\ No newline at end of file