1//===---- HexagonFixupHwLoops.cpp - Fixup HW loops too far from LOOPn. ----===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8// The loop start address in the LOOPn instruction is encoded as a distance
9// from the LOOPn instruction itself. If the start address is too far from
10// the LOOPn instruction, the instruction needs to use a constant extender.
11// This pass will identify and convert such LOOPn instructions to a proper
12// form.
13//===----------------------------------------------------------------------===//
14
15
16#include "llvm/ADT/DenseMap.h"
17#include "Hexagon.h"
18#include "HexagonTargetMachine.h"
19#include "llvm/CodeGen/MachineFunction.h"
20#include "llvm/CodeGen/MachineFunctionPass.h"
21#include "llvm/CodeGen/MachineInstrBuilder.h"
22#include "llvm/CodeGen/Passes.h"
23#include "llvm/PassSupport.h"
24#include "llvm/Target/TargetInstrInfo.h"
25
26using namespace llvm;
27
28static cl::opt<unsigned> MaxLoopRange(
29    "hexagon-loop-range", cl::Hidden, cl::init(200),
30    cl::desc("Restrict range of loopN instructions (testing only)"));
31
32namespace llvm {
33  FunctionPass *createHexagonFixupHwLoops();
34  void initializeHexagonFixupHwLoopsPass(PassRegistry&);
35}
36
37namespace {
38  struct HexagonFixupHwLoops : public MachineFunctionPass {
39  public:
40    static char ID;
41
42    HexagonFixupHwLoops() : MachineFunctionPass(ID) {
43      initializeHexagonFixupHwLoopsPass(*PassRegistry::getPassRegistry());
44    }
45
46    bool runOnMachineFunction(MachineFunction &MF) override;
47
48    const char *getPassName() const override {
49      return "Hexagon Hardware Loop Fixup";
50    }
51
52    void getAnalysisUsage(AnalysisUsage &AU) const override {
53      AU.setPreservesCFG();
54      MachineFunctionPass::getAnalysisUsage(AU);
55    }
56
57  private:
58    /// \brief Check the offset between each loop instruction and
59    /// the loop basic block to determine if we can use the LOOP instruction
60    /// or if we need to set the LC/SA registers explicitly.
61    bool fixupLoopInstrs(MachineFunction &MF);
62
63    /// \brief Replace loop instruction with the constant extended
64    /// version if the loop label is too far from the loop instruction.
65    void useExtLoopInstr(MachineFunction &MF,
66                         MachineBasicBlock::iterator &MII);
67  };
68
69  char HexagonFixupHwLoops::ID = 0;
70}
71
72INITIALIZE_PASS(HexagonFixupHwLoops, "hwloopsfixup",
73                "Hexagon Hardware Loops Fixup", false, false)
74
75FunctionPass *llvm::createHexagonFixupHwLoops() {
76  return new HexagonFixupHwLoops();
77}
78
79/// \brief Returns true if the instruction is a hardware loop instruction.
80static bool isHardwareLoop(const MachineInstr *MI) {
81  return MI->getOpcode() == Hexagon::J2_loop0r ||
82         MI->getOpcode() == Hexagon::J2_loop0i ||
83         MI->getOpcode() == Hexagon::J2_loop1r ||
84         MI->getOpcode() == Hexagon::J2_loop1i;
85}
86
87bool HexagonFixupHwLoops::runOnMachineFunction(MachineFunction &MF) {
88  return fixupLoopInstrs(MF);
89}
90
91/// \brief For Hexagon, if the loop label is to far from the
92/// loop instruction then we need to set the LC0 and SA0 registers
93/// explicitly instead of using LOOP(start,count).  This function
94/// checks the distance, and generates register assignments if needed.
95///
96/// This function makes two passes over the basic blocks.  The first
97/// pass computes the offset of the basic block from the start.
98/// The second pass checks all the loop instructions.
99bool HexagonFixupHwLoops::fixupLoopInstrs(MachineFunction &MF) {
100
101  // Offset of the current instruction from the start.
102  unsigned InstOffset = 0;
103  // Map for each basic block to it's first instruction.
104  DenseMap<const MachineBasicBlock *, unsigned> BlockToInstOffset;
105
106  const HexagonInstrInfo *HII =
107      static_cast<const HexagonInstrInfo *>(MF.getSubtarget().getInstrInfo());
108
109  // First pass - compute the offset of each basic block.
110  for (const MachineBasicBlock &MBB : MF) {
111    if (MBB.getAlignment()) {
112      // Although we don't know the exact layout of the final code, we need
113      // to account for alignment padding somehow. This heuristic pads each
114      // aligned basic block according to the alignment value.
115      int ByteAlign = (1u << MBB.getAlignment()) - 1;
116      InstOffset = (InstOffset + ByteAlign) & ~(ByteAlign);
117    }
118
119    BlockToInstOffset[&MBB] = InstOffset;
120    for (const MachineInstr &MI : MBB)
121      InstOffset += HII->getSize(&MI);
122  }
123
124  // Second pass - check each loop instruction to see if it needs to be
125  // converted.
126  InstOffset = 0;
127  bool Changed = false;
128  for (MachineBasicBlock &MBB : MF) {
129    InstOffset = BlockToInstOffset[&MBB];
130
131    // Loop over all the instructions.
132    MachineBasicBlock::iterator MII = MBB.begin();
133    MachineBasicBlock::iterator MIE = MBB.end();
134    while (MII != MIE) {
135      InstOffset += HII->getSize(&*MII);
136      if (MII->isDebugValue()) {
137        ++MII;
138        continue;
139      }
140      if (isHardwareLoop(MII)) {
141        assert(MII->getOperand(0).isMBB() &&
142               "Expect a basic block as loop operand");
143        int diff = InstOffset - BlockToInstOffset[MII->getOperand(0).getMBB()];
144        if ((unsigned)abs(diff) > MaxLoopRange) {
145          useExtLoopInstr(MF, MII);
146          MII = MBB.erase(MII);
147          Changed = true;
148        } else {
149          ++MII;
150        }
151      } else {
152        ++MII;
153      }
154    }
155  }
156
157  return Changed;
158}
159
160/// \brief Replace loop instructions with the constant extended version.
161void HexagonFixupHwLoops::useExtLoopInstr(MachineFunction &MF,
162                                          MachineBasicBlock::iterator &MII) {
163  const TargetInstrInfo *TII = MF.getSubtarget().getInstrInfo();
164  MachineBasicBlock *MBB = MII->getParent();
165  DebugLoc DL = MII->getDebugLoc();
166  MachineInstrBuilder MIB;
167  unsigned newOp;
168  switch (MII->getOpcode()) {
169  case Hexagon::J2_loop0r:
170    newOp = Hexagon::J2_loop0rext;
171    break;
172  case Hexagon::J2_loop0i:
173    newOp = Hexagon::J2_loop0iext;
174    break;
175  case Hexagon::J2_loop1r:
176    newOp = Hexagon::J2_loop1rext;
177    break;
178  case Hexagon::J2_loop1i:
179    newOp = Hexagon::J2_loop1iext;
180    break;
181  default:
182    llvm_unreachable("Invalid Hardware Loop Instruction.");
183  }
184  MIB = BuildMI(*MBB, MII, DL, TII->get(newOp));
185
186  for (unsigned i = 0; i < MII->getNumOperands(); ++i)
187    MIB.addOperand(MII->getOperand(i));
188}
189