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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/IR/Constants.h"
18 #include "llvm/IR/Dominators.h"
19 #include "llvm/IR/Instructions.h"
20 #include "llvm/IR/Module.h"
21 #include "llvm/Pass.h"
22 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
23 #include "llvm/Transforms/Utils/SSAUpdater.h"
24 
25 using namespace llvm;
26 
27 #define DEBUG_TYPE "si-annotate-control-flow"
28 
29 namespace {
30 
31 // Complex types used in this pass
32 typedef std::pair<BasicBlock *, Value *> StackEntry;
33 typedef SmallVector<StackEntry, 16> StackVector;
34 
35 // Intrinsic names the control flow is annotated with
36 static const char *const IfIntrinsic = "llvm.SI.if";
37 static const char *const ElseIntrinsic = "llvm.SI.else";
38 static const char *const BreakIntrinsic = "llvm.SI.break";
39 static const char *const IfBreakIntrinsic = "llvm.SI.if.break";
40 static const char *const ElseBreakIntrinsic = "llvm.SI.else.break";
41 static const char *const LoopIntrinsic = "llvm.SI.loop";
42 static const char *const EndCfIntrinsic = "llvm.SI.end.cf";
43 
44 class SIAnnotateControlFlow : public FunctionPass {
45 
46   static char ID;
47 
48   Type *Boolean;
49   Type *Void;
50   Type *Int64;
51   Type *ReturnStruct;
52 
53   ConstantInt *BoolTrue;
54   ConstantInt *BoolFalse;
55   UndefValue *BoolUndef;
56   Constant *Int64Zero;
57 
58   Constant *If;
59   Constant *Else;
60   Constant *Break;
61   Constant *IfBreak;
62   Constant *ElseBreak;
63   Constant *Loop;
64   Constant *EndCf;
65 
66   DominatorTree *DT;
67   StackVector Stack;
68 
69   bool isTopOfStack(BasicBlock *BB);
70 
71   Value *popSaved();
72 
73   void push(BasicBlock *BB, Value *Saved);
74 
75   bool isElse(PHINode *Phi);
76 
77   void eraseIfUnused(PHINode *Phi);
78 
79   void openIf(BranchInst *Term);
80 
81   void insertElse(BranchInst *Term);
82 
83   Value *handleLoopCondition(Value *Cond, PHINode *Broken);
84 
85   void handleLoop(BranchInst *Term);
86 
87   void closeControlFlow(BasicBlock *BB);
88 
89 public:
SIAnnotateControlFlow()90   SIAnnotateControlFlow():
91     FunctionPass(ID) { }
92 
93   bool doInitialization(Module &M) override;
94 
95   bool runOnFunction(Function &F) override;
96 
getPassName() const97   const char *getPassName() const override {
98     return "SI annotate control flow";
99   }
100 
getAnalysisUsage(AnalysisUsage & AU) const101   void getAnalysisUsage(AnalysisUsage &AU) const override {
102     AU.addRequired<DominatorTreeWrapperPass>();
103     AU.addPreserved<DominatorTreeWrapperPass>();
104     FunctionPass::getAnalysisUsage(AU);
105   }
106 
107 };
108 
109 } // end anonymous namespace
110 
111 char SIAnnotateControlFlow::ID = 0;
112 
113 /// \brief Initialize all the types and constants used in the pass
doInitialization(Module & M)114 bool SIAnnotateControlFlow::doInitialization(Module &M) {
115   LLVMContext &Context = M.getContext();
116 
117   Void = Type::getVoidTy(Context);
118   Boolean = Type::getInt1Ty(Context);
119   Int64 = Type::getInt64Ty(Context);
120   ReturnStruct = StructType::get(Boolean, Int64, (Type *)nullptr);
121 
122   BoolTrue = ConstantInt::getTrue(Context);
123   BoolFalse = ConstantInt::getFalse(Context);
124   BoolUndef = UndefValue::get(Boolean);
125   Int64Zero = ConstantInt::get(Int64, 0);
126 
127   If = M.getOrInsertFunction(
128     IfIntrinsic, ReturnStruct, Boolean, (Type *)nullptr);
129 
130   Else = M.getOrInsertFunction(
131     ElseIntrinsic, ReturnStruct, Int64, (Type *)nullptr);
132 
133   Break = M.getOrInsertFunction(
134     BreakIntrinsic, Int64, Int64, (Type *)nullptr);
135 
136   IfBreak = M.getOrInsertFunction(
137     IfBreakIntrinsic, Int64, Boolean, Int64, (Type *)nullptr);
138 
139   ElseBreak = M.getOrInsertFunction(
140     ElseBreakIntrinsic, Int64, Int64, Int64, (Type *)nullptr);
141 
142   Loop = M.getOrInsertFunction(
143     LoopIntrinsic, Boolean, Int64, (Type *)nullptr);
144 
145   EndCf = M.getOrInsertFunction(
146     EndCfIntrinsic, Void, Int64, (Type *)nullptr);
147 
148   return false;
149 }
150 
151 /// \brief Is BB the last block saved on the stack ?
isTopOfStack(BasicBlock * BB)152 bool SIAnnotateControlFlow::isTopOfStack(BasicBlock *BB) {
153   return !Stack.empty() && Stack.back().first == BB;
154 }
155 
156 /// \brief Pop the last saved value from the control flow stack
popSaved()157 Value *SIAnnotateControlFlow::popSaved() {
158   return Stack.pop_back_val().second;
159 }
160 
161 /// \brief Push a BB and saved value to the control flow stack
push(BasicBlock * BB,Value * Saved)162 void SIAnnotateControlFlow::push(BasicBlock *BB, Value *Saved) {
163   Stack.push_back(std::make_pair(BB, Saved));
164 }
165 
166 /// \brief Can the condition represented by this PHI node treated like
167 /// an "Else" block?
isElse(PHINode * Phi)168 bool SIAnnotateControlFlow::isElse(PHINode *Phi) {
169   BasicBlock *IDom = DT->getNode(Phi->getParent())->getIDom()->getBlock();
170   for (unsigned i = 0, e = Phi->getNumIncomingValues(); i != e; ++i) {
171     if (Phi->getIncomingBlock(i) == IDom) {
172 
173       if (Phi->getIncomingValue(i) != BoolTrue)
174         return false;
175 
176     } else {
177       if (Phi->getIncomingValue(i) != BoolFalse)
178         return false;
179 
180     }
181   }
182   return true;
183 }
184 
185 // \brief Erase "Phi" if it is not used any more
eraseIfUnused(PHINode * Phi)186 void SIAnnotateControlFlow::eraseIfUnused(PHINode *Phi) {
187   if (!Phi->hasNUsesOrMore(1))
188     Phi->eraseFromParent();
189 }
190 
191 /// \brief Open a new "If" block
openIf(BranchInst * Term)192 void SIAnnotateControlFlow::openIf(BranchInst *Term) {
193   Value *Ret = CallInst::Create(If, Term->getCondition(), "", Term);
194   Term->setCondition(ExtractValueInst::Create(Ret, 0, "", Term));
195   push(Term->getSuccessor(1), ExtractValueInst::Create(Ret, 1, "", Term));
196 }
197 
198 /// \brief Close the last "If" block and open a new "Else" block
insertElse(BranchInst * Term)199 void SIAnnotateControlFlow::insertElse(BranchInst *Term) {
200   Value *Ret = CallInst::Create(Else, popSaved(), "", Term);
201   Term->setCondition(ExtractValueInst::Create(Ret, 0, "", Term));
202   push(Term->getSuccessor(1), ExtractValueInst::Create(Ret, 1, "", Term));
203 }
204 
205 /// \brief Recursively handle the condition leading to a loop
handleLoopCondition(Value * Cond,PHINode * Broken)206 Value *SIAnnotateControlFlow::handleLoopCondition(Value *Cond, PHINode *Broken) {
207   if (PHINode *Phi = dyn_cast<PHINode>(Cond)) {
208     BasicBlock *Parent = Phi->getParent();
209     PHINode *NewPhi = PHINode::Create(Int64, 0, "", &Parent->front());
210     Value *Ret = NewPhi;
211 
212     // Handle all non-constant incoming values first
213     for (unsigned i = 0, e = Phi->getNumIncomingValues(); i != e; ++i) {
214       Value *Incoming = Phi->getIncomingValue(i);
215       BasicBlock *From = Phi->getIncomingBlock(i);
216       if (isa<ConstantInt>(Incoming)) {
217         NewPhi->addIncoming(Broken, From);
218         continue;
219       }
220 
221       Phi->setIncomingValue(i, BoolFalse);
222       Value *PhiArg = handleLoopCondition(Incoming, Broken);
223       NewPhi->addIncoming(PhiArg, From);
224     }
225 
226     BasicBlock *IDom = DT->getNode(Parent)->getIDom()->getBlock();
227 
228     for (unsigned i = 0, e = Phi->getNumIncomingValues(); i != e; ++i) {
229 
230       Value *Incoming = Phi->getIncomingValue(i);
231       if (Incoming != BoolTrue)
232         continue;
233 
234       BasicBlock *From = Phi->getIncomingBlock(i);
235       if (From == IDom) {
236         CallInst *OldEnd = dyn_cast<CallInst>(Parent->getFirstInsertionPt());
237         if (OldEnd && OldEnd->getCalledFunction() == EndCf) {
238           Value *Args[] = { OldEnd->getArgOperand(0), NewPhi };
239           Ret = CallInst::Create(ElseBreak, Args, "", OldEnd);
240           continue;
241         }
242       }
243       TerminatorInst *Insert = From->getTerminator();
244       Value *PhiArg = CallInst::Create(Break, Broken, "", Insert);
245       NewPhi->setIncomingValue(i, PhiArg);
246     }
247     eraseIfUnused(Phi);
248     return Ret;
249 
250   } else if (Instruction *Inst = dyn_cast<Instruction>(Cond)) {
251     BasicBlock *Parent = Inst->getParent();
252     TerminatorInst *Insert = Parent->getTerminator();
253     Value *Args[] = { Cond, Broken };
254     return CallInst::Create(IfBreak, Args, "", Insert);
255 
256   } else {
257     llvm_unreachable("Unhandled loop condition!");
258   }
259   return 0;
260 }
261 
262 /// \brief Handle a back edge (loop)
handleLoop(BranchInst * Term)263 void SIAnnotateControlFlow::handleLoop(BranchInst *Term) {
264   BasicBlock *Target = Term->getSuccessor(1);
265   PHINode *Broken = PHINode::Create(Int64, 0, "", &Target->front());
266 
267   Value *Cond = Term->getCondition();
268   Term->setCondition(BoolTrue);
269   Value *Arg = handleLoopCondition(Cond, Broken);
270 
271   BasicBlock *BB = Term->getParent();
272   for (pred_iterator PI = pred_begin(Target), PE = pred_end(Target);
273        PI != PE; ++PI) {
274 
275     Broken->addIncoming(*PI == BB ? Arg : Int64Zero, *PI);
276   }
277 
278   Term->setCondition(CallInst::Create(Loop, Arg, "", Term));
279   push(Term->getSuccessor(0), Arg);
280 }
281 
282 /// \brief Close the last opened control flow
closeControlFlow(BasicBlock * BB)283 void SIAnnotateControlFlow::closeControlFlow(BasicBlock *BB) {
284   CallInst::Create(EndCf, popSaved(), "", BB->getFirstInsertionPt());
285 }
286 
287 /// \brief Annotate the control flow with intrinsics so the backend can
288 /// recognize if/then/else and loops.
runOnFunction(Function & F)289 bool SIAnnotateControlFlow::runOnFunction(Function &F) {
290   DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
291 
292   for (df_iterator<BasicBlock *> I = df_begin(&F.getEntryBlock()),
293        E = df_end(&F.getEntryBlock()); I != E; ++I) {
294 
295     BranchInst *Term = dyn_cast<BranchInst>((*I)->getTerminator());
296 
297     if (!Term || Term->isUnconditional()) {
298       if (isTopOfStack(*I))
299         closeControlFlow(*I);
300       continue;
301     }
302 
303     if (I.nodeVisited(Term->getSuccessor(1))) {
304       if (isTopOfStack(*I))
305         closeControlFlow(*I);
306       handleLoop(Term);
307       continue;
308     }
309 
310     if (isTopOfStack(*I)) {
311       PHINode *Phi = dyn_cast<PHINode>(Term->getCondition());
312       if (Phi && Phi->getParent() == *I && isElse(Phi)) {
313         insertElse(Term);
314         eraseIfUnused(Phi);
315         continue;
316       }
317       closeControlFlow(*I);
318     }
319     openIf(Term);
320   }
321 
322   assert(Stack.empty());
323   return true;
324 }
325 
326 /// \brief Create the annotation pass
createSIAnnotateControlFlowPass()327 FunctionPass *llvm::createSIAnnotateControlFlowPass() {
328   return new SIAnnotateControlFlow();
329 }
330