1 //===-- HexagonCFGOptimizer.cpp - CFG optimizations -----------------------===//
2 // The LLVM Compiler Infrastructure
3 //
4 // This file is distributed under the University of Illinois Open Source
5 // License. See LICENSE.TXT for details.
6 //
7 //===----------------------------------------------------------------------===//
8
9 #define DEBUG_TYPE "hexagon_cfg"
10 #include "Hexagon.h"
11 #include "HexagonMachineFunctionInfo.h"
12 #include "HexagonSubtarget.h"
13 #include "HexagonTargetMachine.h"
14 #include "llvm/CodeGen/MachineDominators.h"
15 #include "llvm/CodeGen/MachineFunctionPass.h"
16 #include "llvm/CodeGen/MachineInstrBuilder.h"
17 #include "llvm/CodeGen/MachineLoopInfo.h"
18 #include "llvm/CodeGen/MachineRegisterInfo.h"
19 #include "llvm/CodeGen/Passes.h"
20 #include "llvm/Support/Compiler.h"
21 #include "llvm/Support/Debug.h"
22 #include "llvm/Support/MathExtras.h"
23 #include "llvm/Target/TargetInstrInfo.h"
24 #include "llvm/Target/TargetMachine.h"
25 #include "llvm/Target/TargetRegisterInfo.h"
26
27 using namespace llvm;
28
29 namespace {
30
31 class HexagonCFGOptimizer : public MachineFunctionPass {
32
33 private:
34 HexagonTargetMachine& QTM;
35 const HexagonSubtarget &QST;
36
37 void InvertAndChangeJumpTarget(MachineInstr*, MachineBasicBlock*);
38
39 public:
40 static char ID;
HexagonCFGOptimizer(HexagonTargetMachine & TM)41 HexagonCFGOptimizer(HexagonTargetMachine& TM) : MachineFunctionPass(ID),
42 QTM(TM),
43 QST(*TM.getSubtargetImpl()) {}
44
getPassName() const45 const char *getPassName() const {
46 return "Hexagon CFG Optimizer";
47 }
48 bool runOnMachineFunction(MachineFunction &Fn);
49 };
50
51
52 char HexagonCFGOptimizer::ID = 0;
53
IsConditionalBranch(int Opc)54 static bool IsConditionalBranch(int Opc) {
55 return (Opc == Hexagon::JMP_c) || (Opc == Hexagon::JMP_cNot)
56 || (Opc == Hexagon::JMP_cdnPt) || (Opc == Hexagon::JMP_cdnNotPt);
57 }
58
59
IsUnconditionalJump(int Opc)60 static bool IsUnconditionalJump(int Opc) {
61 return (Opc == Hexagon::JMP);
62 }
63
64
65 void
InvertAndChangeJumpTarget(MachineInstr * MI,MachineBasicBlock * NewTarget)66 HexagonCFGOptimizer::InvertAndChangeJumpTarget(MachineInstr* MI,
67 MachineBasicBlock* NewTarget) {
68 const HexagonInstrInfo *QII = QTM.getInstrInfo();
69 int NewOpcode = 0;
70 switch(MI->getOpcode()) {
71 case Hexagon::JMP_c:
72 NewOpcode = Hexagon::JMP_cNot;
73 break;
74
75 case Hexagon::JMP_cNot:
76 NewOpcode = Hexagon::JMP_c;
77 break;
78
79 case Hexagon::JMP_cdnPt:
80 NewOpcode = Hexagon::JMP_cdnNotPt;
81 break;
82
83 case Hexagon::JMP_cdnNotPt:
84 NewOpcode = Hexagon::JMP_cdnPt;
85 break;
86
87 default:
88 llvm_unreachable("Cannot handle this case");
89 }
90
91 MI->setDesc(QII->get(NewOpcode));
92 MI->getOperand(1).setMBB(NewTarget);
93 }
94
95
runOnMachineFunction(MachineFunction & Fn)96 bool HexagonCFGOptimizer::runOnMachineFunction(MachineFunction &Fn) {
97
98 // Loop over all of the basic blocks.
99 for (MachineFunction::iterator MBBb = Fn.begin(), MBBe = Fn.end();
100 MBBb != MBBe; ++MBBb) {
101 MachineBasicBlock* MBB = MBBb;
102
103 // Traverse the basic block.
104 MachineBasicBlock::iterator MII = MBB->getFirstTerminator();
105 if (MII != MBB->end()) {
106 MachineInstr *MI = MII;
107 int Opc = MI->getOpcode();
108 if (IsConditionalBranch(Opc)) {
109
110 //
111 // (Case 1) Transform the code if the following condition occurs:
112 // BB1: if (p0) jump BB3
113 // ...falls-through to BB2 ...
114 // BB2: jump BB4
115 // ...next block in layout is BB3...
116 // BB3: ...
117 //
118 // Transform this to:
119 // BB1: if (!p0) jump BB4
120 // Remove BB2
121 // BB3: ...
122 //
123 // (Case 2) A variation occurs when BB3 contains a JMP to BB4:
124 // BB1: if (p0) jump BB3
125 // ...falls-through to BB2 ...
126 // BB2: jump BB4
127 // ...other basic blocks ...
128 // BB4:
129 // ...not a fall-thru
130 // BB3: ...
131 // jump BB4
132 //
133 // Transform this to:
134 // BB1: if (!p0) jump BB4
135 // Remove BB2
136 // BB3: ...
137 // BB4: ...
138 //
139 unsigned NumSuccs = MBB->succ_size();
140 MachineBasicBlock::succ_iterator SI = MBB->succ_begin();
141 MachineBasicBlock* FirstSucc = *SI;
142 MachineBasicBlock* SecondSucc = *(++SI);
143 MachineBasicBlock* LayoutSucc = NULL;
144 MachineBasicBlock* JumpAroundTarget = NULL;
145
146 if (MBB->isLayoutSuccessor(FirstSucc)) {
147 LayoutSucc = FirstSucc;
148 JumpAroundTarget = SecondSucc;
149 } else if (MBB->isLayoutSuccessor(SecondSucc)) {
150 LayoutSucc = SecondSucc;
151 JumpAroundTarget = FirstSucc;
152 } else {
153 // Odd case...cannot handle.
154 }
155
156 // The target of the unconditional branch must be JumpAroundTarget.
157 // TODO: If not, we should not invert the unconditional branch.
158 MachineBasicBlock* CondBranchTarget = NULL;
159 if ((MI->getOpcode() == Hexagon::JMP_c) ||
160 (MI->getOpcode() == Hexagon::JMP_cNot)) {
161 CondBranchTarget = MI->getOperand(1).getMBB();
162 }
163
164 if (!LayoutSucc || (CondBranchTarget != JumpAroundTarget)) {
165 continue;
166 }
167
168 if ((NumSuccs == 2) && LayoutSucc && (LayoutSucc->pred_size() == 1)) {
169
170 // Ensure that BB2 has one instruction -- an unconditional jump.
171 if ((LayoutSucc->size() == 1) &&
172 IsUnconditionalJump(LayoutSucc->front().getOpcode())) {
173 MachineBasicBlock* UncondTarget =
174 LayoutSucc->front().getOperand(0).getMBB();
175 // Check if the layout successor of BB2 is BB3.
176 bool case1 = LayoutSucc->isLayoutSuccessor(JumpAroundTarget);
177 bool case2 = JumpAroundTarget->isSuccessor(UncondTarget) &&
178 JumpAroundTarget->size() >= 1 &&
179 IsUnconditionalJump(JumpAroundTarget->back().getOpcode()) &&
180 JumpAroundTarget->pred_size() == 1 &&
181 JumpAroundTarget->succ_size() == 1;
182
183 if (case1 || case2) {
184 InvertAndChangeJumpTarget(MI, UncondTarget);
185 MBB->removeSuccessor(JumpAroundTarget);
186 MBB->addSuccessor(UncondTarget);
187
188 // Remove the unconditional branch in LayoutSucc.
189 LayoutSucc->erase(LayoutSucc->begin());
190 LayoutSucc->removeSuccessor(UncondTarget);
191 LayoutSucc->addSuccessor(JumpAroundTarget);
192
193 // This code performs the conversion for case 2, which moves
194 // the block to the fall-thru case (BB3 in the code above).
195 if (case2 && !case1) {
196 JumpAroundTarget->moveAfter(LayoutSucc);
197 // only move a block if it doesn't have a fall-thru. otherwise
198 // the CFG will be incorrect.
199 if (!UncondTarget->canFallThrough()) {
200 UncondTarget->moveAfter(JumpAroundTarget);
201 }
202 }
203
204 //
205 // Correct live-in information. Is used by post-RA scheduler
206 // The live-in to LayoutSucc is now all values live-in to
207 // JumpAroundTarget.
208 //
209 std::vector<unsigned> OrigLiveIn(LayoutSucc->livein_begin(),
210 LayoutSucc->livein_end());
211 std::vector<unsigned> NewLiveIn(JumpAroundTarget->livein_begin(),
212 JumpAroundTarget->livein_end());
213 for (unsigned i = 0; i < OrigLiveIn.size(); ++i) {
214 LayoutSucc->removeLiveIn(OrigLiveIn[i]);
215 }
216 for (unsigned i = 0; i < NewLiveIn.size(); ++i) {
217 LayoutSucc->addLiveIn(NewLiveIn[i]);
218 }
219 }
220 }
221 }
222 }
223 }
224 }
225 return true;
226 }
227 }
228
229
230 //===----------------------------------------------------------------------===//
231 // Public Constructor Functions
232 //===----------------------------------------------------------------------===//
233
createHexagonCFGOptimizer(HexagonTargetMachine & TM)234 FunctionPass *llvm::createHexagonCFGOptimizer(HexagonTargetMachine &TM) {
235 return new HexagonCFGOptimizer(TM);
236 }
237