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