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.amdgcn.if";
38 static const char *const ElseIntrinsic = "llvm.amdgcn.else";
39 static const char *const BreakIntrinsic = "llvm.amdgcn.break";
40 static const char *const IfBreakIntrinsic = "llvm.amdgcn.if.break";
41 static const char *const ElseBreakIntrinsic = "llvm.amdgcn.else.break";
42 static const char *const LoopIntrinsic = "llvm.amdgcn.loop";
43 static const char *const EndCfIntrinsic = "llvm.amdgcn.end.cf";
44 
45 class SIAnnotateControlFlow : public FunctionPass {
46 
47   Type *Boolean;
48   Type *Void;
49   Type *Int64;
50   Type *ReturnStruct;
51 
52   ConstantInt *BoolTrue;
53   ConstantInt *BoolFalse;
54   UndefValue *BoolUndef;
55   Constant *Int64Zero;
56 
57   Constant *If;
58   Constant *Else;
59   Constant *Break;
60   Constant *IfBreak;
61   Constant *ElseBreak;
62   Constant *Loop;
63   Constant *EndCf;
64 
65   DominatorTree *DT;
66   StackVector Stack;
67 
68   LoopInfo *LI;
69 
70   bool isTopOfStack(BasicBlock *BB);
71 
72   Value *popSaved();
73 
74   void push(BasicBlock *BB, Value *Saved);
75 
76   bool isElse(PHINode *Phi);
77 
78   void eraseIfUnused(PHINode *Phi);
79 
80   void openIf(BranchInst *Term);
81 
82   void insertElse(BranchInst *Term);
83 
84   Value *handleLoopCondition(Value *Cond, PHINode *Broken, llvm::Loop *L);
85 
86   void handleLoop(BranchInst *Term);
87 
88   void closeControlFlow(BasicBlock *BB);
89 
90 public:
91   static char ID;
92 
93   SIAnnotateControlFlow():
94     FunctionPass(ID) { }
95 
96   bool doInitialization(Module &M) override;
97 
98   bool runOnFunction(Function &F) override;
99 
100   const char *getPassName() const override {
101     return "SI annotate control flow";
102   }
103 
104   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 INITIALIZE_PASS_BEGIN(SIAnnotateControlFlow, DEBUG_TYPE,
116                       "Annotate SI Control Flow", false, false)
117 INITIALIZE_PASS_END(SIAnnotateControlFlow, DEBUG_TYPE,
118                     "Annotate SI Control Flow", false, false)
119 
120 char SIAnnotateControlFlow::ID = 0;
121 
122 /// \brief Initialize all the types and constants used in the pass
123 bool SIAnnotateControlFlow::doInitialization(Module &M) {
124   LLVMContext &Context = M.getContext();
125 
126   Void = Type::getVoidTy(Context);
127   Boolean = Type::getInt1Ty(Context);
128   Int64 = Type::getInt64Ty(Context);
129   ReturnStruct = StructType::get(Boolean, Int64, (Type *)nullptr);
130 
131   BoolTrue = ConstantInt::getTrue(Context);
132   BoolFalse = ConstantInt::getFalse(Context);
133   BoolUndef = UndefValue::get(Boolean);
134   Int64Zero = ConstantInt::get(Int64, 0);
135 
136   If = M.getOrInsertFunction(
137     IfIntrinsic, ReturnStruct, Boolean, (Type *)nullptr);
138 
139   Else = M.getOrInsertFunction(
140     ElseIntrinsic, ReturnStruct, Int64, (Type *)nullptr);
141 
142   Break = M.getOrInsertFunction(
143     BreakIntrinsic, Int64, Int64, (Type *)nullptr);
144 
145   IfBreak = M.getOrInsertFunction(
146     IfBreakIntrinsic, Int64, Boolean, Int64, (Type *)nullptr);
147 
148   ElseBreak = M.getOrInsertFunction(
149     ElseBreakIntrinsic, Int64, Int64, Int64, (Type *)nullptr);
150 
151   Loop = M.getOrInsertFunction(
152     LoopIntrinsic, Boolean, Int64, (Type *)nullptr);
153 
154   EndCf = M.getOrInsertFunction(
155     EndCfIntrinsic, Void, Int64, (Type *)nullptr);
156 
157   return false;
158 }
159 
160 /// \brief Is BB the last block saved on the stack ?
161 bool SIAnnotateControlFlow::isTopOfStack(BasicBlock *BB) {
162   return !Stack.empty() && Stack.back().first == BB;
163 }
164 
165 /// \brief Pop the last saved value from the control flow stack
166 Value *SIAnnotateControlFlow::popSaved() {
167   return Stack.pop_back_val().second;
168 }
169 
170 /// \brief Push a BB and saved value to the control flow stack
171 void SIAnnotateControlFlow::push(BasicBlock *BB, Value *Saved) {
172   Stack.push_back(std::make_pair(BB, Saved));
173 }
174 
175 /// \brief Can the condition represented by this PHI node treated like
176 /// an "Else" block?
177 bool SIAnnotateControlFlow::isElse(PHINode *Phi) {
178   BasicBlock *IDom = DT->getNode(Phi->getParent())->getIDom()->getBlock();
179   for (unsigned i = 0, e = Phi->getNumIncomingValues(); i != e; ++i) {
180     if (Phi->getIncomingBlock(i) == IDom) {
181 
182       if (Phi->getIncomingValue(i) != BoolTrue)
183         return false;
184 
185     } else {
186       if (Phi->getIncomingValue(i) != BoolFalse)
187         return false;
188 
189     }
190   }
191   return true;
192 }
193 
194 // \brief Erase "Phi" if it is not used any more
195 void SIAnnotateControlFlow::eraseIfUnused(PHINode *Phi) {
196   if (!Phi->hasNUsesOrMore(1))
197     Phi->eraseFromParent();
198 }
199 
200 /// \brief Open a new "If" block
201 void SIAnnotateControlFlow::openIf(BranchInst *Term) {
202   Value *Ret = CallInst::Create(If, Term->getCondition(), "", Term);
203   Term->setCondition(ExtractValueInst::Create(Ret, 0, "", Term));
204   push(Term->getSuccessor(1), ExtractValueInst::Create(Ret, 1, "", Term));
205 }
206 
207 /// \brief Close the last "If" block and open a new "Else" block
208 void SIAnnotateControlFlow::insertElse(BranchInst *Term) {
209   Value *Ret = CallInst::Create(Else, popSaved(), "", Term);
210   Term->setCondition(ExtractValueInst::Create(Ret, 0, "", Term));
211   push(Term->getSuccessor(1), ExtractValueInst::Create(Ret, 1, "", Term));
212 }
213 
214 /// \brief Recursively handle the condition leading to a loop
215 Value *SIAnnotateControlFlow::handleLoopCondition(Value *Cond, PHINode *Broken,
216                                                   llvm::Loop *L) {
217 
218   // Only search through PHI nodes which are inside the loop.  If we try this
219   // with PHI nodes that are outside of the loop, we end up inserting new PHI
220   // nodes outside of the loop which depend on values defined inside the loop.
221   // This will break the module with
222   // 'Instruction does not dominate all users!' errors.
223   PHINode *Phi = nullptr;
224   if ((Phi = dyn_cast<PHINode>(Cond)) && L->contains(Phi)) {
225 
226     BasicBlock *Parent = Phi->getParent();
227     PHINode *NewPhi = PHINode::Create(Int64, 0, "", &Parent->front());
228     Value *Ret = NewPhi;
229 
230     // Handle all non-constant incoming values first
231     for (unsigned i = 0, e = Phi->getNumIncomingValues(); i != e; ++i) {
232       Value *Incoming = Phi->getIncomingValue(i);
233       BasicBlock *From = Phi->getIncomingBlock(i);
234       if (isa<ConstantInt>(Incoming)) {
235         NewPhi->addIncoming(Broken, From);
236         continue;
237       }
238 
239       Phi->setIncomingValue(i, BoolFalse);
240       Value *PhiArg = handleLoopCondition(Incoming, Broken, L);
241       NewPhi->addIncoming(PhiArg, From);
242     }
243 
244     BasicBlock *IDom = DT->getNode(Parent)->getIDom()->getBlock();
245 
246     for (unsigned i = 0, e = Phi->getNumIncomingValues(); i != e; ++i) {
247 
248       Value *Incoming = Phi->getIncomingValue(i);
249       if (Incoming != BoolTrue)
250         continue;
251 
252       BasicBlock *From = Phi->getIncomingBlock(i);
253       if (From == IDom) {
254         CallInst *OldEnd = dyn_cast<CallInst>(Parent->getFirstInsertionPt());
255         if (OldEnd && OldEnd->getCalledFunction() == EndCf) {
256           Value *Args[] = { OldEnd->getArgOperand(0), NewPhi };
257           Ret = CallInst::Create(ElseBreak, Args, "", OldEnd);
258           continue;
259         }
260       }
261       TerminatorInst *Insert = From->getTerminator();
262       Value *PhiArg = CallInst::Create(Break, Broken, "", Insert);
263       NewPhi->setIncomingValue(i, PhiArg);
264     }
265     eraseIfUnused(Phi);
266     return Ret;
267 
268   } else if (Instruction *Inst = dyn_cast<Instruction>(Cond)) {
269     BasicBlock *Parent = Inst->getParent();
270     Instruction *Insert;
271     if (L->contains(Inst)) {
272       Insert = Parent->getTerminator();
273     } else {
274       Insert = L->getHeader()->getFirstNonPHIOrDbgOrLifetime();
275     }
276     Value *Args[] = { Cond, Broken };
277     return CallInst::Create(IfBreak, Args, "", Insert);
278 
279   } else {
280     llvm_unreachable("Unhandled loop condition!");
281   }
282   return 0;
283 }
284 
285 /// \brief Handle a back edge (loop)
286 void SIAnnotateControlFlow::handleLoop(BranchInst *Term) {
287   BasicBlock *BB = Term->getParent();
288   llvm::Loop *L = LI->getLoopFor(BB);
289   BasicBlock *Target = Term->getSuccessor(1);
290   PHINode *Broken = PHINode::Create(Int64, 0, "", &Target->front());
291 
292   Value *Cond = Term->getCondition();
293   Term->setCondition(BoolTrue);
294   Value *Arg = handleLoopCondition(Cond, Broken, L);
295 
296   for (pred_iterator PI = pred_begin(Target), PE = pred_end(Target);
297        PI != PE; ++PI) {
298 
299     Broken->addIncoming(*PI == BB ? Arg : Int64Zero, *PI);
300   }
301 
302   Term->setCondition(CallInst::Create(Loop, Arg, "", Term));
303   push(Term->getSuccessor(0), Arg);
304 }/// \brief Close the last opened control flow
305 void SIAnnotateControlFlow::closeControlFlow(BasicBlock *BB) {
306   llvm::Loop *L = LI->getLoopFor(BB);
307 
308   if (L && L->getHeader() == BB) {
309     // We can't insert an EndCF call into a loop header, because it will
310     // get executed on every iteration of the loop, when it should be
311     // executed only once before the loop.
312     SmallVector <BasicBlock*, 8> Latches;
313     L->getLoopLatches(Latches);
314 
315     std::vector<BasicBlock*> Preds;
316     for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB); PI != PE; ++PI) {
317       if (std::find(Latches.begin(), Latches.end(), *PI) == Latches.end())
318         Preds.push_back(*PI);
319     }
320     BB = llvm::SplitBlockPredecessors(BB, Preds, "endcf.split", DT, LI, false);
321   }
322 
323   CallInst::Create(EndCf, popSaved(), "", &*BB->getFirstInsertionPt());
324 }
325 
326 /// \brief Annotate the control flow with intrinsics so the backend can
327 /// recognize if/then/else and loops.
328 bool SIAnnotateControlFlow::runOnFunction(Function &F) {
329   DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
330   LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
331 
332   for (df_iterator<BasicBlock *> I = df_begin(&F.getEntryBlock()),
333        E = df_end(&F.getEntryBlock()); I != E; ++I) {
334 
335     BranchInst *Term = dyn_cast<BranchInst>((*I)->getTerminator());
336 
337     if (!Term || Term->isUnconditional()) {
338       if (isTopOfStack(*I))
339         closeControlFlow(*I);
340       continue;
341     }
342 
343     if (I.nodeVisited(Term->getSuccessor(1))) {
344       if (isTopOfStack(*I))
345         closeControlFlow(*I);
346       handleLoop(Term);
347       continue;
348     }
349 
350     if (isTopOfStack(*I)) {
351       PHINode *Phi = dyn_cast<PHINode>(Term->getCondition());
352       if (Phi && Phi->getParent() == *I && isElse(Phi)) {
353         insertElse(Term);
354         eraseIfUnused(Phi);
355         continue;
356       }
357       closeControlFlow(*I);
358     }
359     openIf(Term);
360   }
361 
362   assert(Stack.empty());
363   return true;
364 }
365 
366 /// \brief Create the annotation pass
367 FunctionPass *llvm::createSIAnnotateControlFlowPass() {
368   return new SIAnnotateControlFlow();
369 }
370