lib/Target/AMDGPU/SIAnnotateControlFlow.cpp

   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/ADT/STLExtras.h"
  18 #include "llvm/ADT/SmallVector.h"
  19 #include "llvm/Analysis/LegacyDivergenceAnalysis.h"
  20 #include "llvm/Analysis/LoopInfo.h"
  21 #include "llvm/Transforms/Utils/Local.h"
  22 #include "llvm/IR/BasicBlock.h"
  23 #include "llvm/IR/CFG.h"
  24 #include "llvm/IR/Constant.h"
  25 #include "llvm/IR/Constants.h"
  26 #include "llvm/IR/DerivedTypes.h"
  27 #include "llvm/IR/Dominators.h"
  28 #include "llvm/IR/Function.h"
  29 #include "llvm/IR/Instruction.h"
  30 #include "llvm/IR/Instructions.h"
  31 #include "llvm/IR/Intrinsics.h"
  32 #include "llvm/IR/Module.h"
  33 #include "llvm/IR/Type.h"
  34 #include "llvm/IR/ValueHandle.h"
  35 #include "llvm/Pass.h"
  36 #include "llvm/Support/Casting.h"
  37 #include "llvm/Support/Debug.h"
  38 #include "llvm/Support/ErrorHandling.h"
  39 #include "llvm/Support/raw_ostream.h"
  40 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
  41 #include <cassert>
  42 #include <utility>
  43
  44 using namespace llvm;
  45
  46 #define DEBUG_TYPE "si-annotate-control-flow"
  47
  48 namespace {
  49
  50 // Complex types used in this pass
  51 using StackEntry = std::pair<BasicBlock *, Value *>;
  52 using StackVector = SmallVector<StackEntry, 16>;
  53
  54 class SIAnnotateControlFlow : public FunctionPass {
  55   LegacyDivergenceAnalysis *DA;
  56
  57   Type *Boolean;
  58   Type *Void;
  59   Type *Int64;
  60   Type *ReturnStruct;
  61
  62   ConstantInt *BoolTrue;
  63   ConstantInt *BoolFalse;
  64   UndefValue *BoolUndef;
  65   Constant *Int64Zero;
  66
  67   Function *If;
  68   Function *Else;
  69   Function *Break;
  70   Function *IfBreak;
  71   Function *ElseBreak;
  72   Function *Loop;
  73   Function *EndCf;
  74
  75   DominatorTree *DT;
  76   StackVector Stack;
  77
  78   LoopInfo *LI;
  79
  80   bool isUniform(BranchInst *T);
  81
  82   bool isTopOfStack(BasicBlock *BB);
  83
  84   Value *popSaved();
  85
  86   void push(BasicBlock *BB, Value *Saved);
  87
  88   bool isElse(PHINode *Phi);
  89
  90   void eraseIfUnused(PHINode *Phi);
  91
  92   void openIf(BranchInst *Term);
  93
  94   void insertElse(BranchInst *Term);
  95
  96   Value *
  97   handleLoopCondition(Value *Cond, PHINode *Broken, llvm::Loop *L,
  98                       BranchInst *Term,
  99                       SmallVectorImpl<WeakTrackingVH> &LoopPhiConditions);
 100
 101   void handleLoop(BranchInst *Term);
 102
 103   void closeControlFlow(BasicBlock *BB);
 104
 105 public:
 106   static char ID;
 107
 108   SIAnnotateControlFlow() : FunctionPass(ID) {}
 109
 110   bool doInitialization(Module &M) override;
 111
 112   bool runOnFunction(Function &F) override;
 113
 114   StringRef getPassName() const override { return "SI annotate control flow"; }
 115
 116   void getAnalysisUsage(AnalysisUsage &AU) const override {
 117     AU.addRequired<LoopInfoWrapperPass>();
 118     AU.addRequired<DominatorTreeWrapperPass>();
 119     AU.addRequired<LegacyDivergenceAnalysis>();
 120     AU.addPreserved<DominatorTreeWrapperPass>();
 121     FunctionPass::getAnalysisUsage(AU);
 122   }
 123 };
 124
 125 } // end anonymous namespace
 126
 127 INITIALIZE_PASS_BEGIN(SIAnnotateControlFlow, DEBUG_TYPE,
 128                       "Annotate SI Control Flow", false, false)
 129 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
 130 INITIALIZE_PASS_DEPENDENCY(LegacyDivergenceAnalysis)
 131 INITIALIZE_PASS_END(SIAnnotateControlFlow, DEBUG_TYPE,
 132                     "Annotate SI Control Flow", false, false)
 133
 134 char SIAnnotateControlFlow::ID = 0;
 135
 136 /// Initialize all the types and constants used in the pass
 137 bool SIAnnotateControlFlow::doInitialization(Module &M) {
 138   LLVMContext &Context = M.getContext();
 139
 140   Void = Type::getVoidTy(Context);
 141   Boolean = Type::getInt1Ty(Context);
 142   Int64 = Type::getInt64Ty(Context);
 143   ReturnStruct = StructType::get(Boolean, Int64);
 144
 145   BoolTrue = ConstantInt::getTrue(Context);
 146   BoolFalse = ConstantInt::getFalse(Context);
 147   BoolUndef = UndefValue::get(Boolean);
 148   Int64Zero = ConstantInt::get(Int64, 0);
 149
 150   If = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_if);
 151   Else = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_else);
 152   Break = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_break);
 153   IfBreak = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_if_break);
 154   ElseBreak = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_else_break);
 155   Loop = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_loop);
 156   EndCf = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_end_cf);
 157   return false;
 158 }
 159
 160 /// Is the branch condition uniform or did the StructurizeCFG pass
 161 /// consider it as such?
 162 bool SIAnnotateControlFlow::isUniform(BranchInst *T) {
 163   return DA->isUniform(T->getCondition()) ||
 164          T->getMetadata("structurizecfg.uniform") != nullptr;
 165 }
 166
 167 /// Is BB the last block saved on the stack ?
 168 bool SIAnnotateControlFlow::isTopOfStack(BasicBlock *BB) {
 169   return !Stack.empty() && Stack.back().first == BB;
 170 }
 171
 172 /// Pop the last saved value from the control flow stack
 173 Value *SIAnnotateControlFlow::popSaved() {
 174   return Stack.pop_back_val().second;
 175 }
 176
 177 /// Push a BB and saved value to the control flow stack
 178 void SIAnnotateControlFlow::push(BasicBlock *BB, Value *Saved) {
 179   Stack.push_back(std::make_pair(BB, Saved));
 180 }
 181
 182 /// Can the condition represented by this PHI node treated like
 183 /// an "Else" block?
 184 bool SIAnnotateControlFlow::isElse(PHINode *Phi) {
 185   BasicBlock *IDom = DT->getNode(Phi->getParent())->getIDom()->getBlock();
 186   for (unsigned i = 0, e = Phi->getNumIncomingValues(); i != e; ++i) {
 187     if (Phi->getIncomingBlock(i) == IDom) {
 188
 189       if (Phi->getIncomingValue(i) != BoolTrue)
 190         return false;
 191
 192     } else {
 193       if (Phi->getIncomingValue(i) != BoolFalse)
 194         return false;
 195
 196     }
 197   }
 198   return true;
 199 }
 200
 201 // Erase "Phi" if it is not used any more
 202 void SIAnnotateControlFlow::eraseIfUnused(PHINode *Phi) {
 203   if (RecursivelyDeleteDeadPHINode(Phi)) {
 204     LLVM_DEBUG(dbgs() << "Erased unused condition phi\n");
 205   }
 206 }
 207
 208 /// Open a new "If" block
 209 void SIAnnotateControlFlow::openIf(BranchInst *Term) {
 210   if (isUniform(Term))
 211     return;
 212
 213   Value *Ret = CallInst::Create(If, Term->getCondition(), "", Term);
 214   Term->setCondition(ExtractValueInst::Create(Ret, 0, "", Term));
 215   push(Term->getSuccessor(1), ExtractValueInst::Create(Ret, 1, "", Term));
 216 }
 217
 218 /// Close the last "If" block and open a new "Else" block
 219 void SIAnnotateControlFlow::insertElse(BranchInst *Term) {
 220   if (isUniform(Term)) {
 221     return;
 222   }
 223   Value *Ret = CallInst::Create(Else, popSaved(), "", Term);
 224   Term->setCondition(ExtractValueInst::Create(Ret, 0, "", Term));
 225   push(Term->getSuccessor(1), ExtractValueInst::Create(Ret, 1, "", Term));
 226 }
 227
 228 /// Recursively handle the condition leading to a loop
 229 Value *SIAnnotateControlFlow::handleLoopCondition(
 230     Value *Cond, PHINode *Broken, llvm::Loop *L, BranchInst *Term,
 231     SmallVectorImpl<WeakTrackingVH> &LoopPhiConditions) {
 232   // Only search through PHI nodes which are inside the loop.  If we try this
 233   // with PHI nodes that are outside of the loop, we end up inserting new PHI
 234   // nodes outside of the loop which depend on values defined inside the loop.
 235   // This will break the module with
 236   // 'Instruction does not dominate all users!' errors.
 237   PHINode *Phi = nullptr;
 238   if ((Phi = dyn_cast<PHINode>(Cond)) && L->contains(Phi)) {
 239     BasicBlock *Parent = Phi->getParent();
 240     PHINode *NewPhi = PHINode::Create(Int64, 0, "loop.phi", &Parent->front());
 241     Value *Ret = NewPhi;
 242
 243     // Handle all non-constant incoming values first
 244     for (unsigned i = 0, e = Phi->getNumIncomingValues(); i != e; ++i) {
 245       Value *Incoming = Phi->getIncomingValue(i);
 246       BasicBlock *From = Phi->getIncomingBlock(i);
 247       if (isa<ConstantInt>(Incoming)) {
 248         NewPhi->addIncoming(Broken, From);
 249         continue;
 250       }
 251
 252       Phi->setIncomingValue(i, BoolFalse);
 253       Value *PhiArg = handleLoopCondition(Incoming, Broken, L,
 254                                           Term, LoopPhiConditions);
 255       NewPhi->addIncoming(PhiArg, From);
 256     }
 257
 258     BasicBlock *IDom = DT->getNode(Parent)->getIDom()->getBlock();
 259
 260     for (unsigned i = 0, e = Phi->getNumIncomingValues(); i != e; ++i) {
 261       Value *Incoming = Phi->getIncomingValue(i);
 262       if (Incoming != BoolTrue)
 263         continue;
 264
 265       BasicBlock *From = Phi->getIncomingBlock(i);
 266       if (From == IDom) {
 267         // We're in the following situation:
 268         //   IDom/From
 269         //      |   \
 270         //      |   If-block
 271         //      |   /
 272         //     Parent
 273         // where we want to break out of the loop if the If-block is not taken.
 274         // Due to the depth-first traversal, there should be an end.cf
 275         // intrinsic in Parent, and we insert an else.break before it.
 276         //
 277         // Note that the end.cf need not be the first non-phi instruction
 278         // of parent, particularly when we're dealing with a multi-level
 279         // break, but it should occur within a group of intrinsic calls
 280         // at the beginning of the block.
 281         CallInst *OldEnd = dyn_cast<CallInst>(Parent->getFirstInsertionPt());
 282         while (OldEnd && OldEnd->getCalledFunction() != EndCf)
 283           OldEnd = dyn_cast<CallInst>(OldEnd->getNextNode());
 284         if (OldEnd && OldEnd->getCalledFunction() == EndCf) {
 285           Value *Args[] = { OldEnd->getArgOperand(0), NewPhi };
 286           Ret = CallInst::Create(ElseBreak, Args, "", OldEnd);
 287           continue;
 288         }
 289       }
 290
 291       TerminatorInst *Insert = From->getTerminator();
 292       Value *PhiArg = CallInst::Create(Break, Broken, "", Insert);
 293       NewPhi->setIncomingValue(i, PhiArg);
 294     }
 295
 296     LoopPhiConditions.push_back(WeakTrackingVH(Phi));
 297     return Ret;
 298   }
 299
 300   if (Instruction *Inst = dyn_cast<Instruction>(Cond)) {
 301     BasicBlock *Parent = Inst->getParent();
 302     Instruction *Insert;
 303     if (L->contains(Inst)) {
 304       Insert = Parent->getTerminator();
 305     } else {
 306       Insert = L->getHeader()->getFirstNonPHIOrDbgOrLifetime();
 307     }
 308
 309     Value *Args[] = { Cond, Broken };
 310     return CallInst::Create(IfBreak, Args, "", Insert);
 311   }
 312
 313   // Insert IfBreak in the loop header TERM for constant COND other than true.
 314   if (isa<Constant>(Cond)) {
 315     Instruction *Insert = Cond == BoolTrue ?
 316       Term : L->getHeader()->getTerminator();
 317
 318     Value *Args[] = { Cond, Broken };
 319     return CallInst::Create(IfBreak, Args, "", Insert);
 320   }
 321
 322   llvm_unreachable("Unhandled loop condition!");
 323 }
 324
 325 /// Handle a back edge (loop)
 326 void SIAnnotateControlFlow::handleLoop(BranchInst *Term) {
 327   if (isUniform(Term))
 328     return;
 329
 330   BasicBlock *BB = Term->getParent();
 331   llvm::Loop *L = LI->getLoopFor(BB);
 332   if (!L)
 333     return;
 334
 335   BasicBlock *Target = Term->getSuccessor(1);
 336   PHINode *Broken = PHINode::Create(Int64, 0, "phi.broken", &Target->front());
 337
 338   SmallVector<WeakTrackingVH, 8> LoopPhiConditions;
 339   Value *Cond = Term->getCondition();
 340   Term->setCondition(BoolTrue);
 341   Value *Arg = handleLoopCondition(Cond, Broken, L, Term, LoopPhiConditions);
 342
 343   for (BasicBlock *Pred : predecessors(Target))
 344     Broken->addIncoming(Pred == BB ? Arg : Int64Zero, Pred);
 345
 346   Term->setCondition(CallInst::Create(Loop, Arg, "", Term));
 347
 348   for (WeakTrackingVH Val : llvm::reverse(LoopPhiConditions)) {
 349     if (PHINode *Cond = cast_or_null<PHINode>(Val))
 350       eraseIfUnused(Cond);
 351   }
 352
 353   push(Term->getSuccessor(0), Arg);
 354 }
 355
 356 /// Close the last opened control flow
 357 void SIAnnotateControlFlow::closeControlFlow(BasicBlock *BB) {
 358   llvm::Loop *L = LI->getLoopFor(BB);
 359
 360   assert(Stack.back().first == BB);
 361
 362   if (L && L->getHeader() == BB) {
 363     // We can't insert an EndCF call into a loop header, because it will
 364     // get executed on every iteration of the loop, when it should be
 365     // executed only once before the loop.
 366     SmallVector <BasicBlock *, 8> Latches;
 367     L->getLoopLatches(Latches);
 368
 369     SmallVector<BasicBlock *, 2> Preds;
 370     for (BasicBlock *Pred : predecessors(BB)) {
 371       if (!is_contained(Latches, Pred))
 372         Preds.push_back(Pred);
 373     }
 374
 375     BB = SplitBlockPredecessors(BB, Preds, "endcf.split", DT, LI, nullptr,
 376                                 false);
 377   }
 378
 379   Value *Exec = popSaved();
 380   Instruction *FirstInsertionPt = &*BB->getFirstInsertionPt();
 381   if (!isa<UndefValue>(Exec) && !isa<UnreachableInst>(FirstInsertionPt))
 382     CallInst::Create(EndCf, Exec, "", FirstInsertionPt);
 383 }
 384
 385 /// Annotate the control flow with intrinsics so the backend can
 386 /// recognize if/then/else and loops.
 387 bool SIAnnotateControlFlow::runOnFunction(Function &F) {
 388   DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
 389   LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
 390   DA = &getAnalysis<LegacyDivergenceAnalysis>();
 391
 392   for (df_iterator<BasicBlock *> I = df_begin(&F.getEntryBlock()),
 393        E = df_end(&F.getEntryBlock()); I != E; ++I) {
 394     BasicBlock *BB = *I;
 395     BranchInst *Term = dyn_cast<BranchInst>(BB->getTerminator());
 396
 397     if (!Term || Term->isUnconditional()) {
 398       if (isTopOfStack(BB))
 399         closeControlFlow(BB);
 400
 401       continue;
 402     }
 403
 404     if (I.nodeVisited(Term->getSuccessor(1))) {
 405       if (isTopOfStack(BB))
 406         closeControlFlow(BB);
 407
 408       handleLoop(Term);
 409       continue;
 410     }
 411
 412     if (isTopOfStack(BB)) {
 413       PHINode *Phi = dyn_cast<PHINode>(Term->getCondition());
 414       if (Phi && Phi->getParent() == BB && isElse(Phi)) {
 415         insertElse(Term);
 416         eraseIfUnused(Phi);
 417         continue;
 418       }
 419
 420       closeControlFlow(BB);
 421     }
 422
 423     openIf(Term);
 424   }
 425
 426   if (!Stack.empty()) {
 427     // CFG was probably not structured.
 428     report_fatal_error("failed to annotate CFG");
 429   }
 430
 431   return true;
 432 }
 433
 434 /// Create the annotation pass
 435 FunctionPass *llvm::createSIAnnotateControlFlowPass() {
 436   return new SIAnnotateControlFlow();
 437 }