210 lines · cpp
1//===----- HexagonLoopAlign.cpp - Generate loop alignment directives -----===//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-exception6//7//===----------------------------------------------------------------------===//8// Inspect a basic block and if its single basic block loop with a small9// number of instructions, set the prefLoopAlignment to 32 bytes (5).10//===----------------------------------------------------------------------===//11 12#include "Hexagon.h"13#include "HexagonTargetMachine.h"14#include "llvm/CodeGen/MachineBlockFrequencyInfo.h"15#include "llvm/CodeGen/MachineBranchProbabilityInfo.h"16#include "llvm/Support/Debug.h"17 18#define DEBUG_TYPE "hexagon-loop-align"19 20using namespace llvm;21 22static cl::opt<bool>23 DisableLoopAlign("disable-hexagon-loop-align", cl::Hidden,24 cl::desc("Disable Hexagon loop alignment pass"));25 26static cl::opt<uint32_t> HVXLoopAlignLimitUB(27 "hexagon-hvx-loop-align-limit-ub", cl::Hidden, cl::init(16),28 cl::desc("Set hexagon hvx loop upper bound align limit"));29 30static cl::opt<uint32_t> TinyLoopAlignLimitUB(31 "hexagon-tiny-loop-align-limit-ub", cl::Hidden, cl::init(16),32 cl::desc("Set hexagon tiny-core loop upper bound align limit"));33 34static cl::opt<uint32_t>35 LoopAlignLimitUB("hexagon-loop-align-limit-ub", cl::Hidden, cl::init(8),36 cl::desc("Set hexagon loop upper bound align limit"));37 38static cl::opt<uint32_t>39 LoopAlignLimitLB("hexagon-loop-align-limit-lb", cl::Hidden, cl::init(4),40 cl::desc("Set hexagon loop lower bound align limit"));41 42static cl::opt<uint32_t>43 LoopBndlAlignLimit("hexagon-loop-bundle-align-limit", cl::Hidden,44 cl::init(4),45 cl::desc("Set hexagon loop align bundle limit"));46 47static cl::opt<uint32_t> TinyLoopBndlAlignLimit(48 "hexagon-tiny-loop-bundle-align-limit", cl::Hidden, cl::init(8),49 cl::desc("Set hexagon tiny-core loop align bundle limit"));50 51static cl::opt<uint32_t>52 LoopEdgeThreshold("hexagon-loop-edge-threshold", cl::Hidden, cl::init(7500),53 cl::desc("Set hexagon loop align edge threshold"));54 55namespace {56 57class HexagonLoopAlign : public MachineFunctionPass {58 const HexagonSubtarget *HST = nullptr;59 const TargetMachine *HTM = nullptr;60 const HexagonInstrInfo *HII = nullptr;61 62public:63 static char ID;64 HexagonLoopAlign() : MachineFunctionPass(ID) {}65 bool shouldBalignLoop(MachineBasicBlock &BB, bool AboveThres);66 bool isSingleLoop(MachineBasicBlock &MBB);67 bool attemptToBalignSmallLoop(MachineFunction &MF, MachineBasicBlock &MBB);68 69 void getAnalysisUsage(AnalysisUsage &AU) const override {70 AU.addRequired<MachineBranchProbabilityInfoWrapperPass>();71 AU.addRequired<MachineBlockFrequencyInfoWrapperPass>();72 MachineFunctionPass::getAnalysisUsage(AU);73 }74 75 StringRef getPassName() const override { return "Hexagon LoopAlign pass"; }76 bool runOnMachineFunction(MachineFunction &MF) override;77};78 79char HexagonLoopAlign::ID = 0;80 81bool HexagonLoopAlign::shouldBalignLoop(MachineBasicBlock &BB,82 bool AboveThres) {83 bool isVec = false;84 unsigned InstCnt = 0;85 unsigned BndlCnt = 0;86 87 for (MachineBasicBlock::instr_iterator II = BB.instr_begin(),88 IE = BB.instr_end();89 II != IE; ++II) {90 91 // End if the instruction is endloop.92 if (HII->isEndLoopN(II->getOpcode()))93 break;94 // Count the number of bundles.95 if (II->isBundle()) {96 BndlCnt++;97 continue;98 }99 // Skip over debug instructions.100 if (II->isDebugInstr())101 continue;102 // Check if there are any HVX instructions in loop.103 isVec |= HII->isHVXVec(*II);104 // Count the number of instructions.105 InstCnt++;106 }107 108 LLVM_DEBUG({109 dbgs() << "Bundle Count : " << BndlCnt << "\n";110 dbgs() << "Instruction Count : " << InstCnt << "\n";111 });112 113 unsigned LimitUB = 0;114 unsigned LimitBndl = LoopBndlAlignLimit;115 // The conditions in the order of priority.116 if (HST->isTinyCore()) {117 LimitUB = TinyLoopAlignLimitUB;118 LimitBndl = TinyLoopBndlAlignLimit;119 } else if (isVec)120 LimitUB = HVXLoopAlignLimitUB;121 else if (AboveThres)122 LimitUB = LoopAlignLimitUB;123 124 // if the upper bound is not set to a value, implies we didn't meet125 // the criteria.126 if (LimitUB == 0)127 return false;128 129 return InstCnt >= LoopAlignLimitLB && InstCnt <= LimitUB &&130 BndlCnt <= LimitBndl;131}132 133bool HexagonLoopAlign::isSingleLoop(MachineBasicBlock &MBB) {134 int Succs = MBB.succ_size();135 return (MBB.isSuccessor(&MBB) && (Succs == 2));136}137 138bool HexagonLoopAlign::attemptToBalignSmallLoop(MachineFunction &MF,139 MachineBasicBlock &MBB) {140 if (!isSingleLoop(MBB))141 return false;142 143 const MachineBranchProbabilityInfo *MBPI =144 &getAnalysis<MachineBranchProbabilityInfoWrapperPass>().getMBPI();145 const MachineBlockFrequencyInfo *MBFI =146 &getAnalysis<MachineBlockFrequencyInfoWrapperPass>().getMBFI();147 148 // Compute frequency of back edge,149 BlockFrequency BlockFreq = MBFI->getBlockFreq(&MBB);150 BranchProbability BrProb = MBPI->getEdgeProbability(&MBB, &MBB);151 BlockFrequency EdgeFreq = BlockFreq * BrProb;152 LLVM_DEBUG({153 dbgs() << "Loop Align Pass:\n";154 dbgs() << "\tedge with freq(" << EdgeFreq.getFrequency() << ")\n";155 });156 157 bool AboveThres = EdgeFreq.getFrequency() > LoopEdgeThreshold;158 if (shouldBalignLoop(MBB, AboveThres)) {159 // We found a loop, change its alignment to be 32 (5).160 MBB.setAlignment(llvm::Align(1 << 5));161 return true;162 }163 return false;164}165 166// Inspect each basic block, and if its a single BB loop, see if it167// meets the criteria for increasing alignment to 32.168 169bool HexagonLoopAlign::runOnMachineFunction(MachineFunction &MF) {170 171 HST = &MF.getSubtarget<HexagonSubtarget>();172 HII = HST->getInstrInfo();173 HTM = &MF.getTarget();174 175 if (skipFunction(MF.getFunction()))176 return false;177 if (DisableLoopAlign)178 return false;179 180 // This optimization is performed at181 // i) -O2 and above, and when the loop has a HVX instruction.182 // ii) -O3183 if (HST->useHVXOps()) {184 if (HTM->getOptLevel() < CodeGenOptLevel::Default)185 return false;186 } else {187 if (HTM->getOptLevel() < CodeGenOptLevel::Aggressive)188 return false;189 }190 191 bool Changed = false;192 for (MachineFunction::iterator MBBi = MF.begin(), MBBe = MF.end();193 MBBi != MBBe; ++MBBi) {194 MachineBasicBlock &MBB = *MBBi;195 Changed |= attemptToBalignSmallLoop(MF, MBB);196 }197 return Changed;198}199 200} // namespace201 202INITIALIZE_PASS(HexagonLoopAlign, "hexagon-loop-align",203 "Hexagon LoopAlign pass", false, false)204 205//===----------------------------------------------------------------------===//206// Public Constructor Functions207//===----------------------------------------------------------------------===//208 209FunctionPass *llvm::createHexagonLoopAlign() { return new HexagonLoopAlign(); }210