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 "AMDGPUSubtarget.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/CodeGen/TargetPassConfig.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 "llvm/Transforms/Utils/Local.h"
  42 #include <cassert>
  43 #include <utility>
  44
  45 using namespace llvm;
  46
  47 #define DEBUG_TYPE "si-annotate-control-flow"
  48
  49 namespace {
  50
  51 // Complex types used in this pass
  52 using StackEntry = std::pair<BasicBlock *, Value *>;
  53 using StackVector = SmallVector<StackEntry, 16>;
  54
  55 class SIAnnotateControlFlow : public FunctionPass {
  56   LegacyDivergenceAnalysis *DA;
  57
  58   Type *Boolean;
  59   Type *Void;
  60   Type *IntMask;
  61   Type *ReturnStruct;
  62
  63   ConstantInt *BoolTrue;
  64   ConstantInt *BoolFalse;
  65   UndefValue *BoolUndef;
  66   Constant *IntMaskZero;
  67
  68   Function *If;
  69   Function *Else;
  70   Function *IfBreak;
  71   Function *Loop;
  72   Function *EndCf;
  73
  74   DominatorTree *DT;
  75   StackVector Stack;
  76
  77   LoopInfo *LI;
  78
  79   void initialize(Module &M, const GCNSubtarget &ST);
  80
  81   bool isUniform(BranchInst *T);
  82
  83   bool isTopOfStack(BasicBlock *BB);
  84
  85   Value *popSaved();
  86
  87   void push(BasicBlock *BB, Value *Saved);
  88
  89   bool isElse(PHINode *Phi);
  90
  91   void eraseIfUnused(PHINode *Phi);
  92
  93   void openIf(BranchInst *Term);
  94
  95   void insertElse(BranchInst *Term);
  96
  97   Value *
  98   handleLoopCondition(Value *Cond, PHINode *Broken, llvm::Loop *L,
  99                       BranchInst *Term);
 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 runOnFunction(Function &F) override;
 111
 112   StringRef getPassName() const override { return "SI annotate control flow"; }
 113
 114   void getAnalysisUsage(AnalysisUsage &AU) const override {
 115     AU.addRequired<LoopInfoWrapperPass>();
 116     AU.addRequired<DominatorTreeWrapperPass>();
 117     AU.addRequired<LegacyDivergenceAnalysis>();
 118     AU.addPreserved<DominatorTreeWrapperPass>();
 119     AU.addRequired<TargetPassConfig>();
 120     FunctionPass::getAnalysisUsage(AU);
 121   }
 122 };
 123
 124 } // end anonymous namespace
 125
 126 INITIALIZE_PASS_BEGIN(SIAnnotateControlFlow, DEBUG_TYPE,
 127                       "Annotate SI Control Flow", false, false)
 128 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
 129 INITIALIZE_PASS_DEPENDENCY(LegacyDivergenceAnalysis)
 130 INITIALIZE_PASS_DEPENDENCY(TargetPassConfig)
 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 void SIAnnotateControlFlow::initialize(Module &M, const GCNSubtarget &ST) {
 138   LLVMContext &Context = M.getContext();
 139
 140   Void = Type::getVoidTy(Context);
 141   Boolean = Type::getInt1Ty(Context);
 142   IntMask = ST.isWave32() ? Type::getInt32Ty(Context)
 143                            : Type::getInt64Ty(Context);
 144   ReturnStruct = StructType::get(Boolean, IntMask);
 145
 146   BoolTrue = ConstantInt::getTrue(Context);
 147   BoolFalse = ConstantInt::getFalse(Context);
 148   BoolUndef = UndefValue::get(Boolean);
 149   IntMaskZero = ConstantInt::get(IntMask, 0);
 150
 151   If = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_if, { IntMask });
 152   Else = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_else,
 153                                    { IntMask, IntMask });
 154   IfBreak = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_if_break,
 155                                       { IntMask, IntMask });
 156   Loop = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_loop, { IntMask });
 157   EndCf = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_end_cf, { IntMask });
 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) ||
 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   if (Instruction *Inst = dyn_cast<Instruction>(Cond)) {
 232     BasicBlock *Parent = Inst->getParent();
 233     Instruction *Insert;
 234     if (L->contains(Inst)) {
 235       Insert = Parent->getTerminator();
 236     } else {
 237       Insert = L->getHeader()->getFirstNonPHIOrDbgOrLifetime();
 238     }
 239
 240     Value *Args[] = { Cond, Broken };
 241     return CallInst::Create(IfBreak, Args, "", Insert);
 242   }
 243
 244   // Insert IfBreak in the loop header TERM for constant COND other than true.
 245   if (isa<Constant>(Cond)) {
 246     Instruction *Insert = Cond == BoolTrue ?
 247       Term : L->getHeader()->getTerminator();
 248
 249     Value *Args[] = { Cond, Broken };
 250     return CallInst::Create(IfBreak, Args, "", Insert);
 251   }
 252
 253   llvm_unreachable("Unhandled loop condition!");
 254 }
 255
 256 /// Handle a back edge (loop)
 257 void SIAnnotateControlFlow::handleLoop(BranchInst *Term) {
 258   if (isUniform(Term))
 259     return;
 260
 261   BasicBlock *BB = Term->getParent();
 262   llvm::Loop *L = LI->getLoopFor(BB);
 263   if (!L)
 264     return;
 265
 266   BasicBlock *Target = Term->getSuccessor(1);
 267   PHINode *Broken = PHINode::Create(IntMask, 0, "phi.broken", &Target->front());
 268
 269   Value *Cond = Term->getCondition();
 270   Term->setCondition(BoolTrue);
 271   Value *Arg = handleLoopCondition(Cond, Broken, L, Term);
 272
 273   for (BasicBlock *Pred : predecessors(Target)) {
 274     Value *PHIValue = IntMaskZero;
 275     if (Pred == BB) // Remember the value of the previous iteration.
 276       PHIValue = Arg;
 277     // If the backedge from Pred to Target could be executed before the exit
 278     // of the loop at BB, it should not reset or change "Broken", which keeps
 279     // track of the number of threads exited the loop at BB.
 280     else if (L->contains(Pred) && DT->dominates(Pred, BB))
 281       PHIValue = Broken;
 282     Broken->addIncoming(PHIValue, Pred);
 283   }
 284
 285   Term->setCondition(CallInst::Create(Loop, Arg, "", Term));
 286
 287   push(Term->getSuccessor(0), Arg);
 288 }
 289
 290 /// Close the last opened control flow
 291 void SIAnnotateControlFlow::closeControlFlow(BasicBlock *BB) {
 292   llvm::Loop *L = LI->getLoopFor(BB);
 293
 294   assert(Stack.back().first == BB);
 295
 296   if (L && L->getHeader() == BB) {
 297     // We can't insert an EndCF call into a loop header, because it will
 298     // get executed on every iteration of the loop, when it should be
 299     // executed only once before the loop.
 300     SmallVector <BasicBlock *, 8> Latches;
 301     L->getLoopLatches(Latches);
 302
 303     SmallVector<BasicBlock *, 2> Preds;
 304     for (BasicBlock *Pred : predecessors(BB)) {
 305       if (!is_contained(Latches, Pred))
 306         Preds.push_back(Pred);
 307     }
 308
 309     BB = SplitBlockPredecessors(BB, Preds, "endcf.split", DT, LI, nullptr,
 310                                 false);
 311   }
 312
 313   Value *Exec = popSaved();
 314   Instruction *FirstInsertionPt = &*BB->getFirstInsertionPt();
 315   if (!isa<UndefValue>(Exec) && !isa<UnreachableInst>(FirstInsertionPt))
 316     CallInst::Create(EndCf, Exec, "", FirstInsertionPt);
 317 }
 318
 319 /// Annotate the control flow with intrinsics so the backend can
 320 /// recognize if/then/else and loops.
 321 bool SIAnnotateControlFlow::runOnFunction(Function &F) {
 322   DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
 323   LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
 324   DA = &getAnalysis<LegacyDivergenceAnalysis>();
 325   TargetPassConfig &TPC = getAnalysis<TargetPassConfig>();
 326   const TargetMachine &TM = TPC.getTM<TargetMachine>();
 327
 328   initialize(*F.getParent(), TM.getSubtarget<GCNSubtarget>(F));
 329
 330   for (df_iterator<BasicBlock *> I = df_begin(&F.getEntryBlock()),
 331        E = df_end(&F.getEntryBlock()); I != E; ++I) {
 332     BasicBlock *BB = *I;
 333     BranchInst *Term = dyn_cast<BranchInst>(BB->getTerminator());
 334
 335     if (!Term || Term->isUnconditional()) {
 336       if (isTopOfStack(BB))
 337         closeControlFlow(BB);
 338
 339       continue;
 340     }
 341
 342     if (I.nodeVisited(Term->getSuccessor(1))) {
 343       if (isTopOfStack(BB))
 344         closeControlFlow(BB);
 345
 346       handleLoop(Term);
 347       continue;
 348     }
 349
 350     if (isTopOfStack(BB)) {
 351       PHINode *Phi = dyn_cast<PHINode>(Term->getCondition());
 352       if (Phi && Phi->getParent() == BB && isElse(Phi)) {
 353         insertElse(Term);
 354         eraseIfUnused(Phi);
 355         continue;
 356       }
 357
 358       closeControlFlow(BB);
 359     }
 360
 361     openIf(Term);
 362   }
 363
 364   if (!Stack.empty()) {
 365     // CFG was probably not structured.
 366     report_fatal_error("failed to annotate CFG");
 367   }
 368
 369   return true;
 370 }
 371
 372 /// Create the annotation pass
 373 FunctionPass *llvm::createSIAnnotateControlFlowPass() {
 374   return new SIAnnotateControlFlow();
 375 }