1 //===-- SIAnnotateControlFlow.cpp - ------------------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 /// \file
11 /// Annotates the control flow with hardware specific intrinsics.
12 //
13 //===----------------------------------------------------------------------===//
14
15 #include "AMDGPU.h"
16 #include "llvm/ADT/DepthFirstIterator.h"
17 #include "llvm/Analysis/LoopInfo.h"
18 #include "llvm/IR/Constants.h"
19 #include "llvm/IR/Dominators.h"
20 #include "llvm/IR/Instructions.h"
21 #include "llvm/IR/Module.h"
22 #include "llvm/Pass.h"
23 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
24 #include "llvm/Transforms/Utils/SSAUpdater.h"
25
26 using namespace llvm;
27
28 #define DEBUG_TYPE "si-annotate-control-flow"
29
30 namespace {
31
32 // Complex types used in this pass
33 typedef std::pair<BasicBlock *, Value *> StackEntry;
34 typedef SmallVector<StackEntry, 16> StackVector;
35
36 // Intrinsic names the control flow is annotated with
37 static const char *const IfIntrinsic = "llvm.SI.if";
38 static const char *const ElseIntrinsic = "llvm.SI.else";
39 static const char *const BreakIntrinsic = "llvm.SI.break";
40 static const char *const IfBreakIntrinsic = "llvm.SI.if.break";
41 static const char *const ElseBreakIntrinsic = "llvm.SI.else.break";
42 static const char *const LoopIntrinsic = "llvm.SI.loop";
43 static const char *const EndCfIntrinsic = "llvm.SI.end.cf";
44
45 class SIAnnotateControlFlow : public FunctionPass {
46
47 static char ID;
48
49 Type *Boolean;
50 Type *Void;
51 Type *Int64;
52 Type *ReturnStruct;
53
54 ConstantInt *BoolTrue;
55 ConstantInt *BoolFalse;
56 UndefValue *BoolUndef;
57 Constant *Int64Zero;
58
59 Constant *If;
60 Constant *Else;
61 Constant *Break;
62 Constant *IfBreak;
63 Constant *ElseBreak;
64 Constant *Loop;
65 Constant *EndCf;
66
67 DominatorTree *DT;
68 StackVector Stack;
69
70 LoopInfo *LI;
71
72 bool isTopOfStack(BasicBlock *BB);
73
74 Value *popSaved();
75
76 void push(BasicBlock *BB, Value *Saved);
77
78 bool isElse(PHINode *Phi);
79
80 void eraseIfUnused(PHINode *Phi);
81
82 void openIf(BranchInst *Term);
83
84 void insertElse(BranchInst *Term);
85
86 Value *handleLoopCondition(Value *Cond, PHINode *Broken, llvm::Loop *L);
87
88 void handleLoop(BranchInst *Term);
89
90 void closeControlFlow(BasicBlock *BB);
91
92 public:
SIAnnotateControlFlow()93 SIAnnotateControlFlow():
94 FunctionPass(ID) { }
95
96 bool doInitialization(Module &M) override;
97
98 bool runOnFunction(Function &F) override;
99
getPassName() const100 const char *getPassName() const override {
101 return "SI annotate control flow";
102 }
103
getAnalysisUsage(AnalysisUsage & AU) const104 void getAnalysisUsage(AnalysisUsage &AU) const override {
105 AU.addRequired<LoopInfoWrapperPass>();
106 AU.addRequired<DominatorTreeWrapperPass>();
107 AU.addPreserved<DominatorTreeWrapperPass>();
108 FunctionPass::getAnalysisUsage(AU);
109 }
110
111 };
112
113 } // end anonymous namespace
114
115 char SIAnnotateControlFlow::ID = 0;
116
117 /// \brief Initialize all the types and constants used in the pass
doInitialization(Module & M)118 bool SIAnnotateControlFlow::doInitialization(Module &M) {
119 LLVMContext &Context = M.getContext();
120
121 Void = Type::getVoidTy(Context);
122 Boolean = Type::getInt1Ty(Context);
123 Int64 = Type::getInt64Ty(Context);
124 ReturnStruct = StructType::get(Boolean, Int64, (Type *)nullptr);
125
126 BoolTrue = ConstantInt::getTrue(Context);
127 BoolFalse = ConstantInt::getFalse(Context);
128 BoolUndef = UndefValue::get(Boolean);
129 Int64Zero = ConstantInt::get(Int64, 0);
130
131 If = M.getOrInsertFunction(
132 IfIntrinsic, ReturnStruct, Boolean, (Type *)nullptr);
133
134 Else = M.getOrInsertFunction(
135 ElseIntrinsic, ReturnStruct, Int64, (Type *)nullptr);
136
137 Break = M.getOrInsertFunction(
138 BreakIntrinsic, Int64, Int64, (Type *)nullptr);
139
140 IfBreak = M.getOrInsertFunction(
141 IfBreakIntrinsic, Int64, Boolean, Int64, (Type *)nullptr);
142
143 ElseBreak = M.getOrInsertFunction(
144 ElseBreakIntrinsic, Int64, Int64, Int64, (Type *)nullptr);
145
146 Loop = M.getOrInsertFunction(
147 LoopIntrinsic, Boolean, Int64, (Type *)nullptr);
148
149 EndCf = M.getOrInsertFunction(
150 EndCfIntrinsic, Void, Int64, (Type *)nullptr);
151
152 return false;
153 }
154
155 /// \brief Is BB the last block saved on the stack ?
isTopOfStack(BasicBlock * BB)156 bool SIAnnotateControlFlow::isTopOfStack(BasicBlock *BB) {
157 return !Stack.empty() && Stack.back().first == BB;
158 }
159
160 /// \brief Pop the last saved value from the control flow stack
popSaved()161 Value *SIAnnotateControlFlow::popSaved() {
162 return Stack.pop_back_val().second;
163 }
164
165 /// \brief Push a BB and saved value to the control flow stack
push(BasicBlock * BB,Value * Saved)166 void SIAnnotateControlFlow::push(BasicBlock *BB, Value *Saved) {
167 Stack.push_back(std::make_pair(BB, Saved));
168 }
169
170 /// \brief Can the condition represented by this PHI node treated like
171 /// an "Else" block?
isElse(PHINode * Phi)172 bool SIAnnotateControlFlow::isElse(PHINode *Phi) {
173 BasicBlock *IDom = DT->getNode(Phi->getParent())->getIDom()->getBlock();
174 for (unsigned i = 0, e = Phi->getNumIncomingValues(); i != e; ++i) {
175 if (Phi->getIncomingBlock(i) == IDom) {
176
177 if (Phi->getIncomingValue(i) != BoolTrue)
178 return false;
179
180 } else {
181 if (Phi->getIncomingValue(i) != BoolFalse)
182 return false;
183
184 }
185 }
186 return true;
187 }
188
189 // \brief Erase "Phi" if it is not used any more
eraseIfUnused(PHINode * Phi)190 void SIAnnotateControlFlow::eraseIfUnused(PHINode *Phi) {
191 if (!Phi->hasNUsesOrMore(1))
192 Phi->eraseFromParent();
193 }
194
195 /// \brief Open a new "If" block
openIf(BranchInst * Term)196 void SIAnnotateControlFlow::openIf(BranchInst *Term) {
197 Value *Ret = CallInst::Create(If, Term->getCondition(), "", Term);
198 Term->setCondition(ExtractValueInst::Create(Ret, 0, "", Term));
199 push(Term->getSuccessor(1), ExtractValueInst::Create(Ret, 1, "", Term));
200 }
201
202 /// \brief Close the last "If" block and open a new "Else" block
insertElse(BranchInst * Term)203 void SIAnnotateControlFlow::insertElse(BranchInst *Term) {
204 Value *Ret = CallInst::Create(Else, popSaved(), "", Term);
205 Term->setCondition(ExtractValueInst::Create(Ret, 0, "", Term));
206 push(Term->getSuccessor(1), ExtractValueInst::Create(Ret, 1, "", Term));
207 }
208
209 /// \brief Recursively handle the condition leading to a loop
handleLoopCondition(Value * Cond,PHINode * Broken,llvm::Loop * L)210 Value *SIAnnotateControlFlow::handleLoopCondition(Value *Cond, PHINode *Broken,
211 llvm::Loop *L) {
212
213 // Only search through PHI nodes which are inside the loop. If we try this
214 // with PHI nodes that are outside of the loop, we end up inserting new PHI
215 // nodes outside of the loop which depend on values defined inside the loop.
216 // This will break the module with
217 // 'Instruction does not dominate all users!' errors.
218 PHINode *Phi = nullptr;
219 if ((Phi = dyn_cast<PHINode>(Cond)) && L->contains(Phi)) {
220
221 BasicBlock *Parent = Phi->getParent();
222 PHINode *NewPhi = PHINode::Create(Int64, 0, "", &Parent->front());
223 Value *Ret = NewPhi;
224
225 // Handle all non-constant incoming values first
226 for (unsigned i = 0, e = Phi->getNumIncomingValues(); i != e; ++i) {
227 Value *Incoming = Phi->getIncomingValue(i);
228 BasicBlock *From = Phi->getIncomingBlock(i);
229 if (isa<ConstantInt>(Incoming)) {
230 NewPhi->addIncoming(Broken, From);
231 continue;
232 }
233
234 Phi->setIncomingValue(i, BoolFalse);
235 Value *PhiArg = handleLoopCondition(Incoming, Broken, L);
236 NewPhi->addIncoming(PhiArg, From);
237 }
238
239 BasicBlock *IDom = DT->getNode(Parent)->getIDom()->getBlock();
240
241 for (unsigned i = 0, e = Phi->getNumIncomingValues(); i != e; ++i) {
242
243 Value *Incoming = Phi->getIncomingValue(i);
244 if (Incoming != BoolTrue)
245 continue;
246
247 BasicBlock *From = Phi->getIncomingBlock(i);
248 if (From == IDom) {
249 CallInst *OldEnd = dyn_cast<CallInst>(Parent->getFirstInsertionPt());
250 if (OldEnd && OldEnd->getCalledFunction() == EndCf) {
251 Value *Args[] = { OldEnd->getArgOperand(0), NewPhi };
252 Ret = CallInst::Create(ElseBreak, Args, "", OldEnd);
253 continue;
254 }
255 }
256 TerminatorInst *Insert = From->getTerminator();
257 Value *PhiArg = CallInst::Create(Break, Broken, "", Insert);
258 NewPhi->setIncomingValue(i, PhiArg);
259 }
260 eraseIfUnused(Phi);
261 return Ret;
262
263 } else if (Instruction *Inst = dyn_cast<Instruction>(Cond)) {
264 BasicBlock *Parent = Inst->getParent();
265 Instruction *Insert;
266 if (L->contains(Inst)) {
267 Insert = Parent->getTerminator();
268 } else {
269 Insert = L->getHeader()->getFirstNonPHIOrDbgOrLifetime();
270 }
271 Value *Args[] = { Cond, Broken };
272 return CallInst::Create(IfBreak, Args, "", Insert);
273
274 } else {
275 llvm_unreachable("Unhandled loop condition!");
276 }
277 return 0;
278 }
279
280 /// \brief Handle a back edge (loop)
handleLoop(BranchInst * Term)281 void SIAnnotateControlFlow::handleLoop(BranchInst *Term) {
282 BasicBlock *BB = Term->getParent();
283 llvm::Loop *L = LI->getLoopFor(BB);
284 BasicBlock *Target = Term->getSuccessor(1);
285 PHINode *Broken = PHINode::Create(Int64, 0, "", &Target->front());
286
287 Value *Cond = Term->getCondition();
288 Term->setCondition(BoolTrue);
289 Value *Arg = handleLoopCondition(Cond, Broken, L);
290
291 for (pred_iterator PI = pred_begin(Target), PE = pred_end(Target);
292 PI != PE; ++PI) {
293
294 Broken->addIncoming(*PI == BB ? Arg : Int64Zero, *PI);
295 }
296
297 Term->setCondition(CallInst::Create(Loop, Arg, "", Term));
298 push(Term->getSuccessor(0), Arg);
299 }/// \brief Close the last opened control flow
closeControlFlow(BasicBlock * BB)300 void SIAnnotateControlFlow::closeControlFlow(BasicBlock *BB) {
301 llvm::Loop *L = LI->getLoopFor(BB);
302
303 if (L && L->getHeader() == BB) {
304 // We can't insert an EndCF call into a loop header, because it will
305 // get executed on every iteration of the loop, when it should be
306 // executed only once before the loop.
307 SmallVector <BasicBlock*, 8> Latches;
308 L->getLoopLatches(Latches);
309
310 std::vector<BasicBlock*> Preds;
311 for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB); PI != PE; ++PI) {
312 if (std::find(Latches.begin(), Latches.end(), *PI) == Latches.end())
313 Preds.push_back(*PI);
314 }
315 BB = llvm::SplitBlockPredecessors(BB, Preds, "endcf.split", DT, LI, false);
316 }
317
318 CallInst::Create(EndCf, popSaved(), "", &*BB->getFirstInsertionPt());
319 }
320
321 /// \brief Annotate the control flow with intrinsics so the backend can
322 /// recognize if/then/else and loops.
runOnFunction(Function & F)323 bool SIAnnotateControlFlow::runOnFunction(Function &F) {
324 DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
325 LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
326
327 for (df_iterator<BasicBlock *> I = df_begin(&F.getEntryBlock()),
328 E = df_end(&F.getEntryBlock()); I != E; ++I) {
329
330 BranchInst *Term = dyn_cast<BranchInst>((*I)->getTerminator());
331
332 if (!Term || Term->isUnconditional()) {
333 if (isTopOfStack(*I))
334 closeControlFlow(*I);
335 continue;
336 }
337
338 if (I.nodeVisited(Term->getSuccessor(1))) {
339 if (isTopOfStack(*I))
340 closeControlFlow(*I);
341 handleLoop(Term);
342 continue;
343 }
344
345 if (isTopOfStack(*I)) {
346 PHINode *Phi = dyn_cast<PHINode>(Term->getCondition());
347 if (Phi && Phi->getParent() == *I && isElse(Phi)) {
348 insertElse(Term);
349 eraseIfUnused(Phi);
350 continue;
351 }
352 closeControlFlow(*I);
353 }
354 openIf(Term);
355 }
356
357 assert(Stack.empty());
358 return true;
359 }
360
361 /// \brief Create the annotation pass
createSIAnnotateControlFlowPass()362 FunctionPass *llvm::createSIAnnotateControlFlowPass() {
363 return new SIAnnotateControlFlow();
364 }
365