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/Dominators.h"
18#include "llvm/IR/Constants.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
25using namespace llvm;
26
27namespace {
28
29// Complex types used in this pass
30typedef std::pair<BasicBlock *, Value *> StackEntry;
31typedef SmallVector<StackEntry, 16> StackVector;
32
33// Intrinsic names the control flow is annotated with
34static const char *const IfIntrinsic = "llvm.SI.if";
35static const char *const ElseIntrinsic = "llvm.SI.else";
36static const char *const BreakIntrinsic = "llvm.SI.break";
37static const char *const IfBreakIntrinsic = "llvm.SI.if.break";
38static const char *const ElseBreakIntrinsic = "llvm.SI.else.break";
39static const char *const LoopIntrinsic = "llvm.SI.loop";
40static const char *const EndCfIntrinsic = "llvm.SI.end.cf";
41
42class SIAnnotateControlFlow : public FunctionPass {
43
44  static char ID;
45
46  Type *Boolean;
47  Type *Void;
48  Type *Int64;
49  Type *ReturnStruct;
50
51  ConstantInt *BoolTrue;
52  ConstantInt *BoolFalse;
53  UndefValue *BoolUndef;
54  Constant *Int64Zero;
55
56  Constant *If;
57  Constant *Else;
58  Constant *Break;
59  Constant *IfBreak;
60  Constant *ElseBreak;
61  Constant *Loop;
62  Constant *EndCf;
63
64  DominatorTree *DT;
65  StackVector Stack;
66  SSAUpdater PhiInserter;
67
68  bool isTopOfStack(BasicBlock *BB);
69
70  Value *popSaved();
71
72  void push(BasicBlock *BB, Value *Saved);
73
74  bool isElse(PHINode *Phi);
75
76  void eraseIfUnused(PHINode *Phi);
77
78  void openIf(BranchInst *Term);
79
80  void insertElse(BranchInst *Term);
81
82  void handleLoopCondition(Value *Cond);
83
84  void handleLoop(BranchInst *Term);
85
86  void closeControlFlow(BasicBlock *BB);
87
88public:
89  SIAnnotateControlFlow():
90    FunctionPass(ID) { }
91
92  virtual bool doInitialization(Module &M);
93
94  virtual bool runOnFunction(Function &F);
95
96  virtual const char *getPassName() const {
97    return "SI annotate control flow";
98  }
99
100  virtual void getAnalysisUsage(AnalysisUsage &AU) const {
101    AU.addRequired<DominatorTree>();
102    AU.addPreserved<DominatorTree>();
103    FunctionPass::getAnalysisUsage(AU);
104  }
105
106};
107
108} // end anonymous namespace
109
110char SIAnnotateControlFlow::ID = 0;
111
112/// \brief Initialize all the types and constants used in the pass
113bool SIAnnotateControlFlow::doInitialization(Module &M) {
114  LLVMContext &Context = M.getContext();
115
116  Void = Type::getVoidTy(Context);
117  Boolean = Type::getInt1Ty(Context);
118  Int64 = Type::getInt64Ty(Context);
119  ReturnStruct = StructType::get(Boolean, Int64, (Type *)0);
120
121  BoolTrue = ConstantInt::getTrue(Context);
122  BoolFalse = ConstantInt::getFalse(Context);
123  BoolUndef = UndefValue::get(Boolean);
124  Int64Zero = ConstantInt::get(Int64, 0);
125
126  If = M.getOrInsertFunction(
127    IfIntrinsic, ReturnStruct, Boolean, (Type *)0);
128
129  Else = M.getOrInsertFunction(
130    ElseIntrinsic, ReturnStruct, Int64, (Type *)0);
131
132  Break = M.getOrInsertFunction(
133    BreakIntrinsic, Int64, Int64, (Type *)0);
134
135  IfBreak = M.getOrInsertFunction(
136    IfBreakIntrinsic, Int64, Boolean, Int64, (Type *)0);
137
138  ElseBreak = M.getOrInsertFunction(
139    ElseBreakIntrinsic, Int64, Int64, Int64, (Type *)0);
140
141  Loop = M.getOrInsertFunction(
142    LoopIntrinsic, Boolean, Int64, (Type *)0);
143
144  EndCf = M.getOrInsertFunction(
145    EndCfIntrinsic, Void, Int64, (Type *)0);
146
147  return false;
148}
149
150/// \brief Is BB the last block saved on the stack ?
151bool SIAnnotateControlFlow::isTopOfStack(BasicBlock *BB) {
152  return !Stack.empty() && Stack.back().first == BB;
153}
154
155/// \brief Pop the last saved value from the control flow stack
156Value *SIAnnotateControlFlow::popSaved() {
157  return Stack.pop_back_val().second;
158}
159
160/// \brief Push a BB and saved value to the control flow stack
161void SIAnnotateControlFlow::push(BasicBlock *BB, Value *Saved) {
162  Stack.push_back(std::make_pair(BB, Saved));
163}
164
165/// \brief Can the condition represented by this PHI node treated like
166/// an "Else" block?
167bool SIAnnotateControlFlow::isElse(PHINode *Phi) {
168  BasicBlock *IDom = DT->getNode(Phi->getParent())->getIDom()->getBlock();
169  for (unsigned i = 0, e = Phi->getNumIncomingValues(); i != e; ++i) {
170    if (Phi->getIncomingBlock(i) == IDom) {
171
172      if (Phi->getIncomingValue(i) != BoolTrue)
173        return false;
174
175    } else {
176      if (Phi->getIncomingValue(i) != BoolFalse)
177        return false;
178
179    }
180  }
181  return true;
182}
183
184// \brief Erase "Phi" if it is not used any more
185void SIAnnotateControlFlow::eraseIfUnused(PHINode *Phi) {
186  if (!Phi->hasNUsesOrMore(1))
187    Phi->eraseFromParent();
188}
189
190/// \brief Open a new "If" block
191void SIAnnotateControlFlow::openIf(BranchInst *Term) {
192  Value *Ret = CallInst::Create(If, Term->getCondition(), "", Term);
193  Term->setCondition(ExtractValueInst::Create(Ret, 0, "", Term));
194  push(Term->getSuccessor(1), ExtractValueInst::Create(Ret, 1, "", Term));
195}
196
197/// \brief Close the last "If" block and open a new "Else" block
198void SIAnnotateControlFlow::insertElse(BranchInst *Term) {
199  Value *Ret = CallInst::Create(Else, popSaved(), "", Term);
200  Term->setCondition(ExtractValueInst::Create(Ret, 0, "", Term));
201  push(Term->getSuccessor(1), ExtractValueInst::Create(Ret, 1, "", Term));
202}
203
204/// \brief Recursively handle the condition leading to a loop
205void SIAnnotateControlFlow::handleLoopCondition(Value *Cond) {
206  if (PHINode *Phi = dyn_cast<PHINode>(Cond)) {
207
208    // Handle all non constant incoming values first
209    for (unsigned i = 0, e = Phi->getNumIncomingValues(); i != e; ++i) {
210      Value *Incoming = Phi->getIncomingValue(i);
211      if (isa<ConstantInt>(Incoming))
212        continue;
213
214      Phi->setIncomingValue(i, BoolFalse);
215      handleLoopCondition(Incoming);
216    }
217
218    BasicBlock *Parent = Phi->getParent();
219    BasicBlock *IDom = DT->getNode(Parent)->getIDom()->getBlock();
220
221    for (unsigned i = 0, e = Phi->getNumIncomingValues(); i != e; ++i) {
222
223      Value *Incoming = Phi->getIncomingValue(i);
224      if (Incoming != BoolTrue)
225        continue;
226
227      BasicBlock *From = Phi->getIncomingBlock(i);
228      if (From == IDom) {
229        CallInst *OldEnd = dyn_cast<CallInst>(Parent->getFirstInsertionPt());
230        if (OldEnd && OldEnd->getCalledFunction() == EndCf) {
231          Value *Args[] = {
232            OldEnd->getArgOperand(0),
233            PhiInserter.GetValueAtEndOfBlock(Parent)
234          };
235          Value *Ret = CallInst::Create(ElseBreak, Args, "", OldEnd);
236          PhiInserter.AddAvailableValue(Parent, Ret);
237          continue;
238        }
239      }
240
241      TerminatorInst *Insert = From->getTerminator();
242      Value *Arg = PhiInserter.GetValueAtEndOfBlock(From);
243      Value *Ret = CallInst::Create(Break, Arg, "", Insert);
244      PhiInserter.AddAvailableValue(From, Ret);
245    }
246    eraseIfUnused(Phi);
247
248  } else if (Instruction *Inst = dyn_cast<Instruction>(Cond)) {
249    BasicBlock *Parent = Inst->getParent();
250    TerminatorInst *Insert = Parent->getTerminator();
251    Value *Args[] = { Cond, PhiInserter.GetValueAtEndOfBlock(Parent) };
252    Value *Ret = CallInst::Create(IfBreak, Args, "", Insert);
253    PhiInserter.AddAvailableValue(Parent, Ret);
254
255  } else {
256    assert(0 && "Unhandled loop condition!");
257  }
258}
259
260/// \brief Handle a back edge (loop)
261void SIAnnotateControlFlow::handleLoop(BranchInst *Term) {
262  BasicBlock *Target = Term->getSuccessor(1);
263  PHINode *Broken = PHINode::Create(Int64, 0, "", &Target->front());
264
265  PhiInserter.Initialize(Int64, "");
266  PhiInserter.AddAvailableValue(Target, Broken);
267
268  Value *Cond = Term->getCondition();
269  Term->setCondition(BoolTrue);
270  handleLoopCondition(Cond);
271
272  BasicBlock *BB = Term->getParent();
273  Value *Arg = PhiInserter.GetValueAtEndOfBlock(BB);
274  for (pred_iterator PI = pred_begin(Target), PE = pred_end(Target);
275       PI != PE; ++PI) {
276
277    Broken->addIncoming(*PI == BB ? Arg : Int64Zero, *PI);
278  }
279
280  Term->setCondition(CallInst::Create(Loop, Arg, "", Term));
281  push(Term->getSuccessor(0), Arg);
282}
283
284/// \brief Close the last opened control flow
285void SIAnnotateControlFlow::closeControlFlow(BasicBlock *BB) {
286  CallInst::Create(EndCf, popSaved(), "", BB->getFirstInsertionPt());
287}
288
289/// \brief Annotate the control flow with intrinsics so the backend can
290/// recognize if/then/else and loops.
291bool SIAnnotateControlFlow::runOnFunction(Function &F) {
292  DT = &getAnalysis<DominatorTree>();
293
294  for (df_iterator<BasicBlock *> I = df_begin(&F.getEntryBlock()),
295       E = df_end(&F.getEntryBlock()); I != E; ++I) {
296
297    BranchInst *Term = dyn_cast<BranchInst>((*I)->getTerminator());
298
299    if (!Term || Term->isUnconditional()) {
300      if (isTopOfStack(*I))
301        closeControlFlow(*I);
302      continue;
303    }
304
305    if (I.nodeVisited(Term->getSuccessor(1))) {
306      if (isTopOfStack(*I))
307        closeControlFlow(*I);
308      handleLoop(Term);
309      continue;
310    }
311
312    if (isTopOfStack(*I)) {
313      PHINode *Phi = dyn_cast<PHINode>(Term->getCondition());
314      if (Phi && Phi->getParent() == *I && isElse(Phi)) {
315        insertElse(Term);
316        eraseIfUnused(Phi);
317        continue;
318      }
319      closeControlFlow(*I);
320    }
321    openIf(Term);
322  }
323
324  assert(Stack.empty());
325  return true;
326}
327
328/// \brief Create the annotation pass
329FunctionPass *llvm::createSIAnnotateControlFlowPass() {
330  return new SIAnnotateControlFlow();
331}
332