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 "HexagonTargetMachine.h"
11 #include "HexagonSubtarget.h"
12 #include "HexagonMachineFunctionInfo.h"
13 #include "llvm/CodeGen/MachineDominators.h"
14 #include "llvm/CodeGen/MachineFunctionPass.h"
15 #include "llvm/CodeGen/MachineInstrBuilder.h"
16 #include "llvm/CodeGen/MachineLoopInfo.h"
17 #include "llvm/CodeGen/MachineRegisterInfo.h"
18 #include "llvm/CodeGen/Passes.h"
19 #include "llvm/Target/TargetMachine.h"
20 #include "llvm/Target/TargetInstrInfo.h"
21 #include "llvm/Target/TargetRegisterInfo.h"
22 #include "llvm/Support/Compiler.h"
23 #include "llvm/Support/Debug.h"
24 #include "llvm/Support/MathExtras.h"
25
26 using namespace llvm;
27
28 namespace {
29
30 class HexagonCFGOptimizer : public MachineFunctionPass {
31
32 private:
33 HexagonTargetMachine& QTM;
34 const HexagonSubtarget &QST;
35
36 void InvertAndChangeJumpTarget(MachineInstr*, MachineBasicBlock*);
37
38 public:
39 static char ID;
HexagonCFGOptimizer(HexagonTargetMachine & TM)40 HexagonCFGOptimizer(HexagonTargetMachine& TM) : MachineFunctionPass(ID),
41 QTM(TM),
42 QST(*TM.getSubtargetImpl()) {}
43
getPassName() const44 const char *getPassName() const {
45 return "Hexagon CFG Optimizer";
46 }
47 bool runOnMachineFunction(MachineFunction &Fn);
48 };
49
50
51 char HexagonCFGOptimizer::ID = 0;
52
IsConditionalBranch(int Opc)53 static bool IsConditionalBranch(int Opc) {
54 return (Opc == Hexagon::JMP_c) || (Opc == Hexagon::JMP_cNot)
55 || (Opc == Hexagon::JMP_cdnPt) || (Opc == Hexagon::JMP_cdnNotPt);
56 }
57
58
IsUnconditionalJump(int Opc)59 static bool IsUnconditionalJump(int Opc) {
60 return (Opc == Hexagon::JMP);
61 }
62
63
64 void
InvertAndChangeJumpTarget(MachineInstr * MI,MachineBasicBlock * NewTarget)65 HexagonCFGOptimizer::InvertAndChangeJumpTarget(MachineInstr* MI,
66 MachineBasicBlock* NewTarget) {
67 const HexagonInstrInfo *QII = QTM.getInstrInfo();
68 int NewOpcode = 0;
69 switch(MI->getOpcode()) {
70 case Hexagon::JMP_c:
71 NewOpcode = Hexagon::JMP_cNot;
72 break;
73
74 case Hexagon::JMP_cNot:
75 NewOpcode = Hexagon::JMP_c;
76 break;
77
78 case Hexagon::JMP_cdnPt:
79 NewOpcode = Hexagon::JMP_cdnNotPt;
80 break;
81
82 case Hexagon::JMP_cdnNotPt:
83 NewOpcode = Hexagon::JMP_cdnPt;
84 break;
85
86 default:
87 llvm_unreachable("Cannot handle this case");
88 }
89
90 MI->setDesc(QII->get(NewOpcode));
91 MI->getOperand(1).setMBB(NewTarget);
92 }
93
94
runOnMachineFunction(MachineFunction & Fn)95 bool HexagonCFGOptimizer::runOnMachineFunction(MachineFunction &Fn) {
96
97 // Loop over all of the basic blocks.
98 for (MachineFunction::iterator MBBb = Fn.begin(), MBBe = Fn.end();
99 MBBb != MBBe; ++MBBb) {
100 MachineBasicBlock* MBB = MBBb;
101
102 // Traverse the basic block.
103 MachineBasicBlock::iterator MII = MBB->getFirstTerminator();
104 if (MII != MBB->end()) {
105 MachineInstr *MI = MII;
106 int Opc = MI->getOpcode();
107 if (IsConditionalBranch(Opc)) {
108
109 //
110 // (Case 1) Transform the code if the following condition occurs:
111 // BB1: if (p0) jump BB3
112 // ...falls-through to BB2 ...
113 // BB2: jump BB4
114 // ...next block in layout is BB3...
115 // BB3: ...
116 //
117 // Transform this to:
118 // BB1: if (!p0) jump BB4
119 // Remove BB2
120 // BB3: ...
121 //
122 // (Case 2) A variation occurs when BB3 contains a JMP to BB4:
123 // BB1: if (p0) jump BB3
124 // ...falls-through to BB2 ...
125 // BB2: jump BB4
126 // ...other basic blocks ...
127 // BB4:
128 // ...not a fall-thru
129 // BB3: ...
130 // jump BB4
131 //
132 // Transform this to:
133 // BB1: if (!p0) jump BB4
134 // Remove BB2
135 // BB3: ...
136 // BB4: ...
137 //
138 unsigned NumSuccs = MBB->succ_size();
139 MachineBasicBlock::succ_iterator SI = MBB->succ_begin();
140 MachineBasicBlock* FirstSucc = *SI;
141 MachineBasicBlock* SecondSucc = *(++SI);
142 MachineBasicBlock* LayoutSucc = NULL;
143 MachineBasicBlock* JumpAroundTarget = NULL;
144
145 if (MBB->isLayoutSuccessor(FirstSucc)) {
146 LayoutSucc = FirstSucc;
147 JumpAroundTarget = SecondSucc;
148 } else if (MBB->isLayoutSuccessor(SecondSucc)) {
149 LayoutSucc = SecondSucc;
150 JumpAroundTarget = FirstSucc;
151 } else {
152 // Odd case...cannot handle.
153 }
154
155 // The target of the unconditional branch must be JumpAroundTarget.
156 // TODO: If not, we should not invert the unconditional branch.
157 MachineBasicBlock* CondBranchTarget = NULL;
158 if ((MI->getOpcode() == Hexagon::JMP_c) ||
159 (MI->getOpcode() == Hexagon::JMP_cNot)) {
160 CondBranchTarget = MI->getOperand(1).getMBB();
161 }
162
163 if (!LayoutSucc || (CondBranchTarget != JumpAroundTarget)) {
164 continue;
165 }
166
167 if ((NumSuccs == 2) && LayoutSucc && (LayoutSucc->pred_size() == 1)) {
168
169 // Ensure that BB2 has one instruction -- an unconditional jump.
170 if ((LayoutSucc->size() == 1) &&
171 IsUnconditionalJump(LayoutSucc->front().getOpcode())) {
172 MachineBasicBlock* UncondTarget =
173 LayoutSucc->front().getOperand(0).getMBB();
174 // Check if the layout successor of BB2 is BB3.
175 bool case1 = LayoutSucc->isLayoutSuccessor(JumpAroundTarget);
176 bool case2 = JumpAroundTarget->isSuccessor(UncondTarget) &&
177 JumpAroundTarget->size() >= 1 &&
178 IsUnconditionalJump(JumpAroundTarget->back().getOpcode()) &&
179 JumpAroundTarget->pred_size() == 1 &&
180 JumpAroundTarget->succ_size() == 1;
181
182 if (case1 || case2) {
183 InvertAndChangeJumpTarget(MI, UncondTarget);
184 MBB->removeSuccessor(JumpAroundTarget);
185 MBB->addSuccessor(UncondTarget);
186
187 // Remove the unconditional branch in LayoutSucc.
188 LayoutSucc->erase(LayoutSucc->begin());
189 LayoutSucc->removeSuccessor(UncondTarget);
190 LayoutSucc->addSuccessor(JumpAroundTarget);
191
192 // This code performs the conversion for case 2, which moves
193 // the block to the fall-thru case (BB3 in the code above).
194 if (case2 && !case1) {
195 JumpAroundTarget->moveAfter(LayoutSucc);
196 // only move a block if it doesn't have a fall-thru. otherwise
197 // the CFG will be incorrect.
198 if (!UncondTarget->canFallThrough()) {
199 UncondTarget->moveAfter(JumpAroundTarget);
200 }
201 }
202
203 //
204 // Correct live-in information. Is used by post-RA scheduler
205 // The live-in to LayoutSucc is now all values live-in to
206 // JumpAroundTarget.
207 //
208 std::vector<unsigned> OrigLiveIn(LayoutSucc->livein_begin(),
209 LayoutSucc->livein_end());
210 std::vector<unsigned> NewLiveIn(JumpAroundTarget->livein_begin(),
211 JumpAroundTarget->livein_end());
212 for (unsigned i = 0; i < OrigLiveIn.size(); ++i) {
213 LayoutSucc->removeLiveIn(OrigLiveIn[i]);
214 }
215 for (unsigned i = 0; i < NewLiveIn.size(); ++i) {
216 LayoutSucc->addLiveIn(NewLiveIn[i]);
217 }
218 }
219 }
220 }
221 }
222 }
223 }
224 return true;
225 }
226 }
227
228
229 //===----------------------------------------------------------------------===//
230 // Public Constructor Functions
231 //===----------------------------------------------------------------------===//
232
createHexagonCFGOptimizer(HexagonTargetMachine & TM)233 FunctionPass *llvm::createHexagonCFGOptimizer(HexagonTargetMachine &TM) {
234 return new HexagonCFGOptimizer(TM);
235 }
236