1 //===--- HexagonBranchRelaxation.cpp - Identify and relax long jumps ------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 #define DEBUG_TYPE "hexagon-brelax"
13 #include "HexagonInstrInfo.h"
14 #include "HexagonSubtarget.h"
15 #include "llvm/ADT/DenseMap.h"
16 #include "llvm/ADT/SmallVector.h"
17 #include "llvm/ADT/StringRef.h"
18 #include "llvm/CodeGen/MachineBasicBlock.h"
19 #include "llvm/CodeGen/MachineFunction.h"
20 #include "llvm/CodeGen/MachineFunctionPass.h"
21 #include "llvm/CodeGen/MachineInstr.h"
22 #include "llvm/CodeGen/MachineOperand.h"
23 #include "llvm/CodeGen/Passes.h"
24 #include "llvm/Pass.h"
25 #include "llvm/Support/CommandLine.h"
26 #include "llvm/Support/Debug.h"
27 #include "llvm/Support/raw_ostream.h"
35 // Since we have no exact knowledge of code layout, allow some safety buffer
36 // for jump target. This is measured in bytes.
37 static cl::opt<uint32_t> BranchRelaxSafetyBuffer("branch-relax-safety-buffer",
38 cl::init(200), cl::Hidden, cl::ZeroOrMore, cl::desc("safety buffer size"));
42 FunctionPass *createHexagonBranchRelaxation();
43 void initializeHexagonBranchRelaxationPass(PassRegistry&);
45 } // end namespace llvm
49 struct HexagonBranchRelaxation : public MachineFunctionPass {
53 HexagonBranchRelaxation() : MachineFunctionPass(ID) {
54 initializeHexagonBranchRelaxationPass(*PassRegistry::getPassRegistry());
57 bool runOnMachineFunction(MachineFunction &MF) override;
59 StringRef getPassName() const override {
60 return "Hexagon Branch Relaxation";
63 void getAnalysisUsage(AnalysisUsage &AU) const override {
65 MachineFunctionPass::getAnalysisUsage(AU);
69 const HexagonInstrInfo *HII;
70 const HexagonRegisterInfo *HRI;
72 bool relaxBranches(MachineFunction &MF);
73 void computeOffset(MachineFunction &MF,
74 DenseMap<MachineBasicBlock*, unsigned> &BlockToInstOffset);
75 bool reGenerateBranch(MachineFunction &MF,
76 DenseMap<MachineBasicBlock*, unsigned> &BlockToInstOffset);
77 bool isJumpOutOfRange(MachineInstr &MI,
78 DenseMap<MachineBasicBlock*, unsigned> &BlockToInstOffset);
81 char HexagonBranchRelaxation::ID = 0;
83 } // end anonymous namespace
85 INITIALIZE_PASS(HexagonBranchRelaxation, "hexagon-brelax",
86 "Hexagon Branch Relaxation", false, false)
88 FunctionPass *llvm::createHexagonBranchRelaxation() {
89 return new HexagonBranchRelaxation();
92 bool HexagonBranchRelaxation::runOnMachineFunction(MachineFunction &MF) {
93 LLVM_DEBUG(dbgs() << "****** Hexagon Branch Relaxation ******\n");
95 auto &HST = MF.getSubtarget<HexagonSubtarget>();
96 HII = HST.getInstrInfo();
97 HRI = HST.getRegisterInfo();
100 Changed = relaxBranches(MF);
104 void HexagonBranchRelaxation::computeOffset(MachineFunction &MF,
105 DenseMap<MachineBasicBlock*, unsigned> &OffsetMap) {
106 // offset of the current instruction from the start.
107 unsigned InstOffset = 0;
109 if (B.getAlignment()) {
110 // Although we don't know the exact layout of the final code, we need
111 // to account for alignment padding somehow. This heuristic pads each
112 // aligned basic block according to the alignment value.
113 int ByteAlign = (1u << B.getAlignment()) - 1;
114 InstOffset = (InstOffset + ByteAlign) & ~(ByteAlign);
116 OffsetMap[&B] = InstOffset;
117 for (auto &MI : B.instrs()) {
118 InstOffset += HII->getSize(MI);
119 // Assume that all extendable branches will be extended.
120 if (MI.isBranch() && HII->isExtendable(MI))
121 InstOffset += HEXAGON_INSTR_SIZE;
126 /// relaxBranches - For Hexagon, if the jump target/loop label is too far from
127 /// the jump/loop instruction then, we need to make sure that we have constant
128 /// extenders set for jumps and loops.
130 /// There are six iterations in this phase. It's self explanatory below.
131 bool HexagonBranchRelaxation::relaxBranches(MachineFunction &MF) {
132 // Compute the offset of each basic block
133 // offset of the current instruction from the start.
134 // map for each instruction to the beginning of the function
135 DenseMap<MachineBasicBlock*, unsigned> BlockToInstOffset;
136 computeOffset(MF, BlockToInstOffset);
138 return reGenerateBranch(MF, BlockToInstOffset);
141 /// Check if a given instruction is:
142 /// - a jump to a distant target
143 /// - that exceeds its immediate range
144 /// If both conditions are true, it requires constant extension.
145 bool HexagonBranchRelaxation::isJumpOutOfRange(MachineInstr &MI,
146 DenseMap<MachineBasicBlock*, unsigned> &BlockToInstOffset) {
147 MachineBasicBlock &B = *MI.getParent();
148 auto FirstTerm = B.getFirstInstrTerminator();
149 if (FirstTerm == B.instr_end())
152 if (HII->isExtended(MI))
155 unsigned InstOffset = BlockToInstOffset[&B];
156 unsigned Distance = 0;
158 // To save time, estimate exact position of a branch instruction
159 // as one at the end of the MBB.
160 // Number of instructions times typical instruction size.
161 InstOffset += HII->nonDbgBBSize(&B) * HEXAGON_INSTR_SIZE;
163 MachineBasicBlock *TBB = nullptr, *FBB = nullptr;
164 SmallVector<MachineOperand, 4> Cond;
166 // Try to analyze this branch.
167 if (HII->analyzeBranch(B, TBB, FBB, Cond, false)) {
168 // Could not analyze it. See if this is something we can recognize.
169 // If it is a NVJ, it should always have its target in
171 if (HII->isNewValueJump(*FirstTerm))
172 TBB = FirstTerm->getOperand(HII->getCExtOpNum(*FirstTerm)).getMBB();
174 if (TBB && &MI == &*FirstTerm) {
175 Distance = std::abs((long long)InstOffset - BlockToInstOffset[TBB])
176 + BranchRelaxSafetyBuffer;
177 return !HII->isJumpWithinBranchRange(*FirstTerm, Distance);
180 // Look for second terminator.
181 auto SecondTerm = std::next(FirstTerm);
182 assert(SecondTerm != B.instr_end() &&
183 (SecondTerm->isBranch() || SecondTerm->isCall()) &&
184 "Bad second terminator");
185 if (&MI != &*SecondTerm)
187 // Analyze the second branch in the BB.
188 Distance = std::abs((long long)InstOffset - BlockToInstOffset[FBB])
189 + BranchRelaxSafetyBuffer;
190 return !HII->isJumpWithinBranchRange(*SecondTerm, Distance);
195 bool HexagonBranchRelaxation::reGenerateBranch(MachineFunction &MF,
196 DenseMap<MachineBasicBlock*, unsigned> &BlockToInstOffset) {
197 bool Changed = false;
201 if (!MI.isBranch() || !isJumpOutOfRange(MI, BlockToInstOffset))
203 LLVM_DEBUG(dbgs() << "Long distance jump. isExtendable("
204 << HII->isExtendable(MI) << ") isConstExtended("
205 << HII->isConstExtended(MI) << ") " << MI);
207 // Since we have not merged HW loops relaxation into
208 // this code (yet), soften our approach for the moment.
209 if (!HII->isExtendable(MI) && !HII->isExtended(MI)) {
210 LLVM_DEBUG(dbgs() << "\tUnderimplemented relax branch instruction.\n");
212 // Find which operand is expandable.
213 int ExtOpNum = HII->getCExtOpNum(MI);
214 MachineOperand &MO = MI.getOperand(ExtOpNum);
215 // This need to be something we understand. So far we assume all
216 // branches have only MBB address as expandable field.
217 // If it changes, this will need to be expanded.
218 assert(MO.isMBB() && "Branch with unknown expandable field type");
219 // Mark given operand as extended.
220 MO.addTargetFlag(HexagonII::HMOTF_ConstExtended);