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-exception
6//
7//===----------------------------------------------------------------------===//
8// Inspect a basic block and if its single basic block loop with a small
9// number of instructions, set the prefLoopAlignment to 32 bytes (5).
10//===----------------------------------------------------------------------===//
11
12#define DEBUG_TYPE "hexagon-loop-align"
13
14#include "HexagonTargetMachine.h"
15#include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
16#include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
17#include "llvm/CodeGen/SchedulerRegistry.h"
18#include "llvm/Support/Debug.h"
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(Val: 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(Val: 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(Val: 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(Val: 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(Val: 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(Val: 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(Val: 7500),
53 cl::desc("Set hexagon loop align edge theshold"));
54
55namespace llvm {
56FunctionPass *createHexagonLoopAlign();
57void initializeHexagonLoopAlignPass(PassRegistry &);
58} // namespace llvm
59
60namespace {
61
62class HexagonLoopAlign : public MachineFunctionPass {
63 const HexagonSubtarget *HST = nullptr;
64 const TargetMachine *HTM = nullptr;
65 const HexagonInstrInfo *HII = nullptr;
66
67public:
68 static char ID;
69 HexagonLoopAlign() : MachineFunctionPass(ID) {
70 initializeHexagonLoopAlignPass(*PassRegistry::getPassRegistry());
71 }
72 bool shouldBalignLoop(MachineBasicBlock &BB, bool AboveThres);
73 bool isSingleLoop(MachineBasicBlock &MBB);
74 bool attemptToBalignSmallLoop(MachineFunction &MF, MachineBasicBlock &MBB);
75
76 void getAnalysisUsage(AnalysisUsage &AU) const override {
77 AU.addRequired<MachineBranchProbabilityInfo>();
78 AU.addRequired<MachineBlockFrequencyInfo>();
79 MachineFunctionPass::getAnalysisUsage(AU);
80 }
81
82 StringRef getPassName() const override { return "Hexagon LoopAlign pass"; }
83 bool runOnMachineFunction(MachineFunction &MF) override;
84};
85
86char HexagonLoopAlign::ID = 0;
87
88bool HexagonLoopAlign::shouldBalignLoop(MachineBasicBlock &BB,
89 bool AboveThres) {
90 bool isVec = false;
91 unsigned InstCnt = 0;
92 unsigned BndlCnt = 0;
93
94 for (MachineBasicBlock::instr_iterator II = BB.instr_begin(),
95 IE = BB.instr_end();
96 II != IE; ++II) {
97
98 // End if the instruction is endloop.
99 if (HII->isEndLoopN(Opcode: II->getOpcode()))
100 break;
101 // Count the number of bundles.
102 if (II->isBundle()) {
103 BndlCnt++;
104 continue;
105 }
106 // Skip over debug instructions.
107 if (II->isDebugInstr())
108 continue;
109 // Check if there are any HVX instructions in loop.
110 isVec |= HII->isHVXVec(MI: *II);
111 // Count the number of instructions.
112 InstCnt++;
113 }
114
115 LLVM_DEBUG({
116 dbgs() << "Bundle Count : " << BndlCnt << "\n";
117 dbgs() << "Instruction Count : " << InstCnt << "\n";
118 });
119
120 unsigned LimitUB = 0;
121 unsigned LimitBndl = LoopBndlAlignLimit;
122 // The conditions in the order of priority.
123 if (HST->isTinyCore()) {
124 LimitUB = TinyLoopAlignLimitUB;
125 LimitBndl = TinyLoopBndlAlignLimit;
126 } else if (isVec)
127 LimitUB = HVXLoopAlignLimitUB;
128 else if (AboveThres)
129 LimitUB = LoopAlignLimitUB;
130
131 // if the upper bound is not set to a value, implies we didn't meet
132 // the criteria.
133 if (LimitUB == 0)
134 return false;
135
136 return InstCnt >= LoopAlignLimitLB && InstCnt <= LimitUB &&
137 BndlCnt <= LimitBndl;
138}
139
140bool HexagonLoopAlign::isSingleLoop(MachineBasicBlock &MBB) {
141 int Succs = MBB.succ_size();
142 return (MBB.isSuccessor(MBB: &MBB) && (Succs == 2));
143}
144
145bool HexagonLoopAlign::attemptToBalignSmallLoop(MachineFunction &MF,
146 MachineBasicBlock &MBB) {
147 if (!isSingleLoop(MBB))
148 return false;
149
150 const MachineBranchProbabilityInfo *MBPI =
151 &getAnalysis<MachineBranchProbabilityInfo>();
152 const MachineBlockFrequencyInfo *MBFI =
153 &getAnalysis<MachineBlockFrequencyInfo>();
154
155 // Compute frequency of back edge,
156 BlockFrequency BlockFreq = MBFI->getBlockFreq(MBB: &MBB);
157 BranchProbability BrProb = MBPI->getEdgeProbability(Src: &MBB, Dst: &MBB);
158 BlockFrequency EdgeFreq = BlockFreq * BrProb;
159 LLVM_DEBUG({
160 dbgs() << "Loop Align Pass:\n";
161 dbgs() << "\tedge with freq(" << EdgeFreq.getFrequency() << ")\n";
162 });
163
164 bool AboveThres = EdgeFreq.getFrequency() > LoopEdgeThreshold;
165 if (shouldBalignLoop(BB&: MBB, AboveThres)) {
166 // We found a loop, change its alignment to be 32 (5).
167 MBB.setAlignment(llvm::Align(1 << 5));
168 return true;
169 }
170 return false;
171}
172
173// Inspect each basic block, and if its a single BB loop, see if it
174// meets the criteria for increasing alignment to 32.
175
176bool HexagonLoopAlign::runOnMachineFunction(MachineFunction &MF) {
177
178 HST = &MF.getSubtarget<HexagonSubtarget>();
179 HII = HST->getInstrInfo();
180 HTM = &MF.getTarget();
181
182 if (skipFunction(F: MF.getFunction()))
183 return false;
184 if (DisableLoopAlign)
185 return false;
186
187 // This optimization is performed at
188 // i) -O2 and above, and when the loop has a HVX instruction.
189 // ii) -O3
190 if (HST->useHVXOps()) {
191 if (HTM->getOptLevel() < CodeGenOptLevel::Default)
192 return false;
193 } else {
194 if (HTM->getOptLevel() < CodeGenOptLevel::Aggressive)
195 return false;
196 }
197
198 bool Changed = false;
199 for (MachineFunction::iterator MBBi = MF.begin(), MBBe = MF.end();
200 MBBi != MBBe; ++MBBi) {
201 MachineBasicBlock &MBB = *MBBi;
202 Changed |= attemptToBalignSmallLoop(MF, MBB);
203 }
204 return Changed;
205}
206
207} // namespace
208
209INITIALIZE_PASS(HexagonLoopAlign, "hexagon-loop-align",
210 "Hexagon LoopAlign pass", false, false)
211
212//===----------------------------------------------------------------------===//
213// Public Constructor Functions
214//===----------------------------------------------------------------------===//
215
216FunctionPass *llvm::createHexagonLoopAlign() { return new HexagonLoopAlign(); }
217

source code of llvm/lib/Target/Hexagon/HexagonLoopAlign.cpp