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/Pass.h"
24
25using namespace llvm;
26
27static cl::opt<unsigned> MaxLoopRange(
28 "hexagon-loop-range", cl::Hidden, cl::init(Val: 200),
29 cl::desc("Restrict range of loopN instructions (testing only)"));
30
31namespace llvm {
32 FunctionPass *createHexagonFixupHwLoops();
33 void initializeHexagonFixupHwLoopsPass(PassRegistry&);
34}
35
36namespace {
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
76INITIALIZE_PASS(HexagonFixupHwLoops, "hwloopsfixup",
77 "Hexagon Hardware Loops Fixup", false, false)
78
79FunctionPass *llvm::createHexagonFixupHwLoops() {
80 return new HexagonFixupHwLoops();
81}
82
83/// Returns true if the instruction is a hardware loop instruction.
84static 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
91bool HexagonFixupHwLoops::runOnMachineFunction(MachineFunction &MF) {
92 if (skipFunction(F: 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.
105bool 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(1)) {
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(Size: InstOffset, A: 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(MI: *MII);
140 if (MII->isMetaInstruction()) {
141 ++MII;
142 continue;
143 }
144 if (isHardwareLoop(MI: *MII)) {
145 assert(MII->getOperand(0).isMBB() &&
146 "Expect a basic block as loop operand");
147 MachineBasicBlock *TargetBB = MII->getOperand(i: 0).getMBB();
148 unsigned Diff = AbsoluteDifference(X: InstOffset,
149 Y: BlockToInstOffset[TargetBB]);
150 if (Diff > MaxLoopRange) {
151 useExtLoopInstr(MF, MII);
152 MII = MBB.erase(I: 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.
168void 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(BB&: *MBB, I: MII, MIMD: DL, MCID: TII->get(Opcode: newOp));
192
193 for (unsigned i = 0; i < MII->getNumOperands(); ++i)
194 MIB.add(MO: MII->getOperand(i));
195}
196

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