lib/Target/Hexagon/HexagonFixupHwLoops.cpp

   1 //===---- HexagonFixupHwLoops.cpp - Fixup HW loops too far from LOOPn. ----===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 // The loop start address in the LOOPn instruction is encoded as a distance
   8 // from the LOOPn instruction itself. If the start address is too far from
   9 // the LOOPn instruction, the instruction needs to use a constant extender.
  10 // This pass will identify and convert such LOOPn instructions to a proper
  11 // form.
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "Hexagon.h"
  15 #include "HexagonTargetMachine.h"
  16 #include "llvm/ADT/DenseMap.h"
  17 #include "llvm/CodeGen/MachineFunction.h"
  18 #include "llvm/CodeGen/MachineFunctionPass.h"
  19 #include "llvm/CodeGen/MachineInstrBuilder.h"
  20 #include "llvm/CodeGen/Passes.h"
  21 #include "llvm/CodeGen/TargetInstrInfo.h"
  22 #include "llvm/Support/MathExtras.h"
  23 #include "llvm/PassSupport.h"
  24
  25 using namespace llvm;
  26
  27 static cl::opt<unsigned> MaxLoopRange(
  28     "hexagon-loop-range", cl::Hidden, cl::init(200),
  29     cl::desc("Restrict range of loopN instructions (testing only)"));
  30
  31 namespace llvm {
  32   FunctionPass *createHexagonFixupHwLoops();
  33   void initializeHexagonFixupHwLoopsPass(PassRegistry&);
  34 }
  35
  36 namespace {
  37   struct HexagonFixupHwLoops : public MachineFunctionPass {
  38   public:
  39     static char ID;
  40
  41     HexagonFixupHwLoops() : MachineFunctionPass(ID) {
  42       initializeHexagonFixupHwLoopsPass(*PassRegistry::getPassRegistry());
  43     }
  44
  45     bool runOnMachineFunction(MachineFunction &MF) override;
  46
  47     MachineFunctionProperties getRequiredProperties() const override {
  48       return MachineFunctionProperties().set(
  49           MachineFunctionProperties::Property::NoVRegs);
  50     }
  51
  52     StringRef getPassName() const override {
  53       return "Hexagon Hardware Loop Fixup";
  54     }
  55
  56     void getAnalysisUsage(AnalysisUsage &AU) const override {
  57       AU.setPreservesCFG();
  58       MachineFunctionPass::getAnalysisUsage(AU);
  59     }
  60
  61   private:
  62     /// Check the offset between each loop instruction and
  63     /// the loop basic block to determine if we can use the LOOP instruction
  64     /// or if we need to set the LC/SA registers explicitly.
  65     bool fixupLoopInstrs(MachineFunction &MF);
  66
  67     /// Replace loop instruction with the constant extended
  68     /// version if the loop label is too far from the loop instruction.
  69     void useExtLoopInstr(MachineFunction &MF,
  70                          MachineBasicBlock::iterator &MII);
  71   };
  72
  73   char HexagonFixupHwLoops::ID = 0;
  74 }
  75
  76 INITIALIZE_PASS(HexagonFixupHwLoops, "hwloopsfixup",
  77                 "Hexagon Hardware Loops Fixup", false, false)
  78
  79 FunctionPass *llvm::createHexagonFixupHwLoops() {
  80   return new HexagonFixupHwLoops();
  81 }
  82
  83 /// Returns true if the instruction is a hardware loop instruction.
  84 static bool isHardwareLoop(const MachineInstr &MI) {
  85   return MI.getOpcode() == Hexagon::J2_loop0r ||
  86          MI.getOpcode() == Hexagon::J2_loop0i ||
  87          MI.getOpcode() == Hexagon::J2_loop1r ||
  88          MI.getOpcode() == Hexagon::J2_loop1i;
  89 }
  90
  91 bool HexagonFixupHwLoops::runOnMachineFunction(MachineFunction &MF) {
  92   if (skipFunction(MF.getFunction()))
  93     return false;
  94   return fixupLoopInstrs(MF);
  95 }
  96
  97 /// For Hexagon, if the loop label is to far from the
  98 /// loop instruction then we need to set the LC0 and SA0 registers
  99 /// explicitly instead of using LOOP(start,count).  This function
 100 /// checks the distance, and generates register assignments if needed.
 101 ///
 102 /// This function makes two passes over the basic blocks.  The first
 103 /// pass computes the offset of the basic block from the start.
 104 /// The second pass checks all the loop instructions.
 105 bool HexagonFixupHwLoops::fixupLoopInstrs(MachineFunction &MF) {
 106
 107   // Offset of the current instruction from the start.
 108   unsigned InstOffset = 0;
 109   // Map for each basic block to it's first instruction.
 110   DenseMap<const MachineBasicBlock *, unsigned> BlockToInstOffset;
 111
 112   const HexagonInstrInfo *HII =
 113       static_cast<const HexagonInstrInfo *>(MF.getSubtarget().getInstrInfo());
 114
 115   // First pass - compute the offset of each basic block.
 116   for (const MachineBasicBlock &MBB : MF) {
 117     if (MBB.getAlignment() != Align::None()) {
 118       // Although we don't know the exact layout of the final code, we need
 119       // to account for alignment padding somehow. This heuristic pads each
 120       // aligned basic block according to the alignment value.
 121       InstOffset = alignTo(InstOffset, MBB.getAlignment());
 122     }
 123
 124     BlockToInstOffset[&MBB] = InstOffset;
 125     for (const MachineInstr &MI : MBB)
 126       InstOffset += HII->getSize(MI);
 127   }
 128
 129   // Second pass - check each loop instruction to see if it needs to be
 130   // converted.
 131   bool Changed = false;
 132   for (MachineBasicBlock &MBB : MF) {
 133     InstOffset = BlockToInstOffset[&MBB];
 134
 135     // Loop over all the instructions.
 136     MachineBasicBlock::iterator MII = MBB.begin();
 137     MachineBasicBlock::iterator MIE = MBB.end();
 138     while (MII != MIE) {
 139       unsigned InstSize = HII->getSize(*MII);
 140       if (MII->isMetaInstruction()) {
 141         ++MII;
 142         continue;
 143       }
 144       if (isHardwareLoop(*MII)) {
 145         assert(MII->getOperand(0).isMBB() &&
 146                "Expect a basic block as loop operand");
 147         MachineBasicBlock *TargetBB = MII->getOperand(0).getMBB();
 148         unsigned Diff = AbsoluteDifference(InstOffset,
 149                                            BlockToInstOffset[TargetBB]);
 150         if (Diff > MaxLoopRange) {
 151           useExtLoopInstr(MF, MII);
 152           MII = MBB.erase(MII);
 153           Changed = true;
 154         } else {
 155           ++MII;
 156         }
 157       } else {
 158         ++MII;
 159       }
 160       InstOffset += InstSize;
 161     }
 162   }
 163
 164   return Changed;
 165 }
 166
 167 /// Replace loop instructions with the constant extended version.
 168 void HexagonFixupHwLoops::useExtLoopInstr(MachineFunction &MF,
 169                                           MachineBasicBlock::iterator &MII) {
 170   const TargetInstrInfo *TII = MF.getSubtarget().getInstrInfo();
 171   MachineBasicBlock *MBB = MII->getParent();
 172   DebugLoc DL = MII->getDebugLoc();
 173   MachineInstrBuilder MIB;
 174   unsigned newOp;
 175   switch (MII->getOpcode()) {
 176   case Hexagon::J2_loop0r:
 177     newOp = Hexagon::J2_loop0rext;
 178     break;
 179   case Hexagon::J2_loop0i:
 180     newOp = Hexagon::J2_loop0iext;
 181     break;
 182   case Hexagon::J2_loop1r:
 183     newOp = Hexagon::J2_loop1rext;
 184     break;
 185   case Hexagon::J2_loop1i:
 186     newOp = Hexagon::J2_loop1iext;
 187     break;
 188   default:
 189     llvm_unreachable("Invalid Hardware Loop Instruction.");
 190   }
 191   MIB = BuildMI(*MBB, MII, DL, TII->get(newOp));
 192
 193   for (unsigned i = 0; i < MII->getNumOperands(); ++i)
 194     MIB.add(MII->getOperand(i));
 195 }