llvm/lib/Target/AMDGPU/SIAnnotateControlFlow.cpp

   1 //===- SIAnnotateControlFlow.cpp ------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 /// \file
  10 /// Annotates the control flow with hardware specific intrinsics.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "AMDGPU.h"
  15 #include "GCNSubtarget.h"
  16 #include "llvm/Analysis/LegacyDivergenceAnalysis.h"
  17 #include "llvm/Analysis/LoopInfo.h"
  18 #include "llvm/CodeGen/TargetPassConfig.h"
  19 #include "llvm/IR/BasicBlock.h"
  20 #include "llvm/IR/Constants.h"
  21 #include "llvm/IR/Dominators.h"
  22 #include "llvm/IR/IntrinsicsAMDGPU.h"
  23 #include "llvm/InitializePasses.h"
  24 #include "llvm/Target/TargetMachine.h"
  25 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
  26 #include "llvm/Transforms/Utils/Local.h"
  27
  28 using namespace llvm;
  29
  30 #define DEBUG_TYPE "si-annotate-control-flow"
  31
  32 namespace {
  33
  34 // Complex types used in this pass
  35 using StackEntry = std::pair<BasicBlock *, Value *>;
  36 using StackVector = SmallVector<StackEntry, 16>;
  37
  38 class SIAnnotateControlFlow : public FunctionPass {
  39   LegacyDivergenceAnalysis *DA;
  40
  41   Type *Boolean;
  42   Type *Void;
  43   Type *IntMask;
  44   Type *ReturnStruct;
  45
  46   ConstantInt *BoolTrue;
  47   ConstantInt *BoolFalse;
  48   UndefValue *BoolUndef;
  49   Constant *IntMaskZero;
  50
  51   Function *If;
  52   Function *Else;
  53   Function *IfBreak;
  54   Function *Loop;
  55   Function *EndCf;
  56
  57   DominatorTree *DT;
  58   StackVector Stack;
  59
  60   LoopInfo *LI;
  61
  62   void initialize(Module &M, const GCNSubtarget &ST);
  63
  64   bool isUniform(BranchInst *T);
  65
  66   bool isTopOfStack(BasicBlock *BB);
  67
  68   Value *popSaved();
  69
  70   void push(BasicBlock *BB, Value *Saved);
  71
  72   bool isElse(PHINode *Phi);
  73
  74   bool hasKill(const BasicBlock *BB);
  75
  76   void eraseIfUnused(PHINode *Phi);
  77
  78   void openIf(BranchInst *Term);
  79
  80   void insertElse(BranchInst *Term);
  81
  82   Value *
  83   handleLoopCondition(Value *Cond, PHINode *Broken, llvm::Loop *L,
  84                       BranchInst *Term);
  85
  86   void handleLoop(BranchInst *Term);
  87
  88   void closeControlFlow(BasicBlock *BB);
  89
  90 public:
  91   static char ID;
  92
  93   SIAnnotateControlFlow() : FunctionPass(ID) {}
  94
  95   bool runOnFunction(Function &F) override;
  96
  97   StringRef getPassName() const override { return "SI annotate control flow"; }
  98
  99   void getAnalysisUsage(AnalysisUsage &AU) const override {
 100     AU.addRequired<LoopInfoWrapperPass>();
 101     AU.addRequired<DominatorTreeWrapperPass>();
 102     AU.addRequired<LegacyDivergenceAnalysis>();
 103     AU.addPreserved<LoopInfoWrapperPass>();
 104     AU.addPreserved<DominatorTreeWrapperPass>();
 105     AU.addRequired<TargetPassConfig>();
 106     FunctionPass::getAnalysisUsage(AU);
 107   }
 108 };
 109
 110 } // end anonymous namespace
 111
 112 INITIALIZE_PASS_BEGIN(SIAnnotateControlFlow, DEBUG_TYPE,
 113                       "Annotate SI Control Flow", false, false)
 114 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
 115 INITIALIZE_PASS_DEPENDENCY(LegacyDivergenceAnalysis)
 116 INITIALIZE_PASS_DEPENDENCY(TargetPassConfig)
 117 INITIALIZE_PASS_END(SIAnnotateControlFlow, DEBUG_TYPE,
 118                     "Annotate SI Control Flow", false, false)
 119
 120 char SIAnnotateControlFlow::ID = 0;
 121
 122 /// Initialize all the types and constants used in the pass
 123 void SIAnnotateControlFlow::initialize(Module &M, const GCNSubtarget &ST) {
 124   LLVMContext &Context = M.getContext();
 125
 126   Void = Type::getVoidTy(Context);
 127   Boolean = Type::getInt1Ty(Context);
 128   IntMask = ST.isWave32() ? Type::getInt32Ty(Context)
 129                            : Type::getInt64Ty(Context);
 130   ReturnStruct = StructType::get(Boolean, IntMask);
 131
 132   BoolTrue = ConstantInt::getTrue(Context);
 133   BoolFalse = ConstantInt::getFalse(Context);
 134   BoolUndef = UndefValue::get(Boolean);
 135   IntMaskZero = ConstantInt::get(IntMask, 0);
 136
 137   If = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_if, { IntMask });
 138   Else = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_else,
 139                                    { IntMask, IntMask });
 140   IfBreak = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_if_break,
 141                                       { IntMask });
 142   Loop = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_loop, { IntMask });
 143   EndCf = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_end_cf, { IntMask });
 144 }
 145
 146 /// Is the branch condition uniform or did the StructurizeCFG pass
 147 /// consider it as such?
 148 bool SIAnnotateControlFlow::isUniform(BranchInst *T) {
 149   return DA->isUniform(T) ||
 150          T->getMetadata("structurizecfg.uniform") != nullptr;
 151 }
 152
 153 /// Is BB the last block saved on the stack ?
 154 bool SIAnnotateControlFlow::isTopOfStack(BasicBlock *BB) {
 155   return !Stack.empty() && Stack.back().first == BB;
 156 }
 157
 158 /// Pop the last saved value from the control flow stack
 159 Value *SIAnnotateControlFlow::popSaved() {
 160   return Stack.pop_back_val().second;
 161 }
 162
 163 /// Push a BB and saved value to the control flow stack
 164 void SIAnnotateControlFlow::push(BasicBlock *BB, Value *Saved) {
 165   Stack.push_back(std::make_pair(BB, Saved));
 166 }
 167
 168 /// Can the condition represented by this PHI node treated like
 169 /// an "Else" block?
 170 bool SIAnnotateControlFlow::isElse(PHINode *Phi) {
 171   BasicBlock *IDom = DT->getNode(Phi->getParent())->getIDom()->getBlock();
 172   for (unsigned i = 0, e = Phi->getNumIncomingValues(); i != e; ++i) {
 173     if (Phi->getIncomingBlock(i) == IDom) {
 174
 175       if (Phi->getIncomingValue(i) != BoolTrue)
 176         return false;
 177
 178     } else {
 179       if (Phi->getIncomingValue(i) != BoolFalse)
 180         return false;
 181
 182     }
 183   }
 184   return true;
 185 }
 186
 187 bool SIAnnotateControlFlow::hasKill(const BasicBlock *BB) {
 188   for (const Instruction &I : *BB) {
 189     if (const CallInst *CI = dyn_cast<CallInst>(&I))
 190       if (CI->getIntrinsicID() == Intrinsic::amdgcn_kill)
 191         return true;
 192   }
 193   return false;
 194 }
 195
 196 // Erase "Phi" if it is not used any more
 197 void SIAnnotateControlFlow::eraseIfUnused(PHINode *Phi) {
 198   if (RecursivelyDeleteDeadPHINode(Phi)) {
 199     LLVM_DEBUG(dbgs() << "Erased unused condition phi\n");
 200   }
 201 }
 202
 203 /// Open a new "If" block
 204 void SIAnnotateControlFlow::openIf(BranchInst *Term) {
 205   if (isUniform(Term))
 206     return;
 207
 208   Value *Ret = CallInst::Create(If, Term->getCondition(), "", Term);
 209   Term->setCondition(ExtractValueInst::Create(Ret, 0, "", Term));
 210   push(Term->getSuccessor(1), ExtractValueInst::Create(Ret, 1, "", Term));
 211 }
 212
 213 /// Close the last "If" block and open a new "Else" block
 214 void SIAnnotateControlFlow::insertElse(BranchInst *Term) {
 215   if (isUniform(Term)) {
 216     return;
 217   }
 218   Value *Ret = CallInst::Create(Else, popSaved(), "", Term);
 219   Term->setCondition(ExtractValueInst::Create(Ret, 0, "", Term));
 220   push(Term->getSuccessor(1), ExtractValueInst::Create(Ret, 1, "", Term));
 221 }
 222
 223 /// Recursively handle the condition leading to a loop
 224 Value *SIAnnotateControlFlow::handleLoopCondition(
 225     Value *Cond, PHINode *Broken, llvm::Loop *L, BranchInst *Term) {
 226   if (Instruction *Inst = dyn_cast<Instruction>(Cond)) {
 227     BasicBlock *Parent = Inst->getParent();
 228     Instruction *Insert;
 229     if (L->contains(Inst)) {
 230       Insert = Parent->getTerminator();
 231     } else {
 232       Insert = L->getHeader()->getFirstNonPHIOrDbgOrLifetime();
 233     }
 234
 235     Value *Args[] = { Cond, Broken };
 236     return CallInst::Create(IfBreak, Args, "", Insert);
 237   }
 238
 239   // Insert IfBreak in the loop header TERM for constant COND other than true.
 240   if (isa<Constant>(Cond)) {
 241     Instruction *Insert = Cond == BoolTrue ?
 242       Term : L->getHeader()->getTerminator();
 243
 244     Value *Args[] = { Cond, Broken };
 245     return CallInst::Create(IfBreak, Args, "", Insert);
 246   }
 247
 248   llvm_unreachable("Unhandled loop condition!");
 249 }
 250
 251 /// Handle a back edge (loop)
 252 void SIAnnotateControlFlow::handleLoop(BranchInst *Term) {
 253   if (isUniform(Term))
 254     return;
 255
 256   BasicBlock *BB = Term->getParent();
 257   llvm::Loop *L = LI->getLoopFor(BB);
 258   if (!L)
 259     return;
 260
 261   BasicBlock *Target = Term->getSuccessor(1);
 262   PHINode *Broken = PHINode::Create(IntMask, 0, "phi.broken", &Target->front());
 263
 264   Value *Cond = Term->getCondition();
 265   Term->setCondition(BoolTrue);
 266   Value *Arg = handleLoopCondition(Cond, Broken, L, Term);
 267
 268   for (BasicBlock *Pred : predecessors(Target)) {
 269     Value *PHIValue = IntMaskZero;
 270     if (Pred == BB) // Remember the value of the previous iteration.
 271       PHIValue = Arg;
 272     // If the backedge from Pred to Target could be executed before the exit
 273     // of the loop at BB, it should not reset or change "Broken", which keeps
 274     // track of the number of threads exited the loop at BB.
 275     else if (L->contains(Pred) && DT->dominates(Pred, BB))
 276       PHIValue = Broken;
 277     Broken->addIncoming(PHIValue, Pred);
 278   }
 279
 280   Term->setCondition(CallInst::Create(Loop, Arg, "", Term));
 281
 282   push(Term->getSuccessor(0), Arg);
 283 }
 284
 285 /// Close the last opened control flow
 286 void SIAnnotateControlFlow::closeControlFlow(BasicBlock *BB) {
 287   llvm::Loop *L = LI->getLoopFor(BB);
 288
 289   assert(Stack.back().first == BB);
 290
 291   if (L && L->getHeader() == BB) {
 292     // We can't insert an EndCF call into a loop header, because it will
 293     // get executed on every iteration of the loop, when it should be
 294     // executed only once before the loop.
 295     SmallVector <BasicBlock *, 8> Latches;
 296     L->getLoopLatches(Latches);
 297
 298     SmallVector<BasicBlock *, 2> Preds;
 299     for (BasicBlock *Pred : predecessors(BB)) {
 300       if (!is_contained(Latches, Pred))
 301         Preds.push_back(Pred);
 302     }
 303
 304     BB = SplitBlockPredecessors(BB, Preds, "endcf.split", DT, LI, nullptr,
 305                                 false);
 306   }
 307
 308   Value *Exec = popSaved();
 309   Instruction *FirstInsertionPt = &*BB->getFirstInsertionPt();
 310   if (!isa<UndefValue>(Exec) && !isa<UnreachableInst>(FirstInsertionPt)) {
 311     Instruction *ExecDef = cast<Instruction>(Exec);
 312     BasicBlock *DefBB = ExecDef->getParent();
 313     if (!DT->dominates(DefBB, BB)) {
 314       // Split edge to make Def dominate Use
 315       FirstInsertionPt = &*SplitEdge(DefBB, BB, DT, LI)->getFirstInsertionPt();
 316     }
 317     CallInst::Create(EndCf, Exec, "", FirstInsertionPt);
 318   }
 319 }
 320
 321 /// Annotate the control flow with intrinsics so the backend can
 322 /// recognize if/then/else and loops.
 323 bool SIAnnotateControlFlow::runOnFunction(Function &F) {
 324   DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
 325   LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
 326   DA = &getAnalysis<LegacyDivergenceAnalysis>();
 327   TargetPassConfig &TPC = getAnalysis<TargetPassConfig>();
 328   const TargetMachine &TM = TPC.getTM<TargetMachine>();
 329
 330   initialize(*F.getParent(), TM.getSubtarget<GCNSubtarget>(F));
 331   for (df_iterator<BasicBlock *> I = df_begin(&F.getEntryBlock()),
 332        E = df_end(&F.getEntryBlock()); I != E; ++I) {
 333     BasicBlock *BB = *I;
 334     BranchInst *Term = dyn_cast<BranchInst>(BB->getTerminator());
 335
 336     if (!Term || Term->isUnconditional()) {
 337       if (isTopOfStack(BB))
 338         closeControlFlow(BB);
 339
 340       continue;
 341     }
 342
 343     if (I.nodeVisited(Term->getSuccessor(1))) {
 344       if (isTopOfStack(BB))
 345         closeControlFlow(BB);
 346
 347       if (DT->dominates(Term->getSuccessor(1), BB))
 348         handleLoop(Term);
 349       continue;
 350     }
 351
 352     if (isTopOfStack(BB)) {
 353       PHINode *Phi = dyn_cast<PHINode>(Term->getCondition());
 354       if (Phi && Phi->getParent() == BB && isElse(Phi) && !hasKill(BB)) {
 355         insertElse(Term);
 356         eraseIfUnused(Phi);
 357         continue;
 358       }
 359
 360       closeControlFlow(BB);
 361     }
 362
 363     openIf(Term);
 364   }
 365
 366   if (!Stack.empty()) {
 367     // CFG was probably not structured.
 368     report_fatal_error("failed to annotate CFG");
 369   }
 370
 371   return true;
 372 }
 373
 374 /// Create the annotation pass
 375 FunctionPass *llvm::createSIAnnotateControlFlowPass() {
 376   return new SIAnnotateControlFlow();
 377 }