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 } 376