1 //===-- AMDGPULowerModuleLDSPass.cpp ------------------------------*- C++ -*-=// 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 // This pass eliminates local data store, LDS, uses from non-kernel functions. 10 // LDS is contiguous memory allocated per kernel execution. 11 // 12 // Background. 13 // 14 // The programming model is global variables, or equivalently function local 15 // static variables, accessible from kernels or other functions. For uses from 16 // kernels this is straightforward - assign an integer to the kernel for the 17 // memory required by all the variables combined, allocate them within that. 18 // For uses from functions there are performance tradeoffs to choose between. 19 // 20 // This model means the GPU runtime can specify the amount of memory allocated. 21 // If this is more than the kernel assumed, the excess can be made available 22 // using a language specific feature, which IR represents as a variable with 23 // no initializer. This feature is referred to here as "Dynamic LDS" and is 24 // lowered slightly differently to the normal case. 25 // 26 // Consequences of this GPU feature: 27 // - memory is limited and exceeding it halts compilation 28 // - a global accessed by one kernel exists independent of other kernels 29 // - a global exists independent of simultaneous execution of the same kernel 30 // - the address of the global may be different from different kernels as they 31 // do not alias, which permits only allocating variables they use 32 // - if the address is allowed to differ, functions need help to find it 33 // 34 // Uses from kernels are implemented here by grouping them in a per-kernel 35 // struct instance. This duplicates the variables, accurately modelling their 36 // aliasing properties relative to a single global representation. It also 37 // permits control over alignment via padding. 38 // 39 // Uses from functions are more complicated and the primary purpose of this 40 // IR pass. Several different lowering are chosen between to meet requirements 41 // to avoid allocating any LDS where it is not necessary, as that impacts 42 // occupancy and may fail the compilation, while not imposing overhead on a 43 // feature whose primary advantage over global memory is performance. The basic 44 // design goal is to avoid one kernel imposing overhead on another. 45 // 46 // Implementation. 47 // 48 // LDS variables with constant annotation or non-undef initializer are passed 49 // through unchanged for simplification or error diagnostics in later passes. 50 // Non-undef initializers are not yet implemented for LDS. 51 // 52 // LDS variables that are always allocated at the same address can be found 53 // by lookup at that address. Otherwise runtime information/cost is required. 54 // 55 // The simplest strategy possible is to group all LDS variables in a single 56 // struct and allocate that struct in every kernel such that the original 57 // variables are always at the same address. LDS is however a limited resource 58 // so this strategy is unusable in practice. It is not implemented here. 59 // 60 // Strategy | Precise allocation | Zero runtime cost | General purpose | 61 // --------+--------------------+-------------------+-----------------+ 62 // Module | No | Yes | Yes | 63 // Table | Yes | No | Yes | 64 // Kernel | Yes | Yes | No | 65 // Hybrid | Yes | Partial | Yes | 66 // 67 // "Module" spends LDS memory to save cycles. "Table" spends cycles and global 68 // memory to save LDS. "Kernel" is as fast as kernel allocation but only works 69 // for variables that are known reachable from a single kernel. "Hybrid" picks 70 // between all three. When forced to choose between LDS and cycles we minimise 71 // LDS use. 72 73 // The "module" lowering implemented here finds LDS variables which are used by 74 // non-kernel functions and creates a new struct with a field for each of those 75 // LDS variables. Variables that are only used from kernels are excluded. 76 // Kernels that do not use this struct are annoteated with the attribute 77 // amdgpu-elide-module-lds which allows the back end to elide the allocation. 78 // 79 // The "table" lowering implemented here has three components. 80 // First kernels are assigned a unique integer identifier which is available in 81 // functions it calls through the intrinsic amdgcn_lds_kernel_id. The integer 82 // is passed through a specific SGPR, thus works with indirect calls. 83 // Second, each kernel allocates LDS variables independent of other kernels and 84 // writes the addresses it chose for each variable into an array in consistent 85 // order. If the kernel does not allocate a given variable, it writes undef to 86 // the corresponding array location. These arrays are written to a constant 87 // table in the order matching the kernel unique integer identifier. 88 // Third, uses from non-kernel functions are replaced with a table lookup using 89 // the intrinsic function to find the address of the variable. 90 // 91 // "Kernel" lowering is only applicable for variables that are unambiguously 92 // reachable from exactly one kernel. For those cases, accesses to the variable 93 // can be lowered to ConstantExpr address of a struct instance specific to that 94 // one kernel. This is zero cost in space and in compute. It will raise a fatal 95 // error on any variable that might be reachable from multiple kernels and is 96 // thus most easily used as part of the hybrid lowering strategy. 97 // 98 // Hybrid lowering is a mixture of the above. It uses the zero cost kernel 99 // lowering where it can. It lowers the variable accessed by the greatest 100 // number of kernels using the module strategy as that is free for the first 101 // variable. Any futher variables that can be lowered with the module strategy 102 // without incurring LDS memory overhead are. The remaining ones are lowered 103 // via table. 104 // 105 // Consequences 106 // - No heuristics or user controlled magic numbers, hybrid is the right choice 107 // - Kernels that don't use functions (or have had them all inlined) are not 108 // affected by any lowering for kernels that do. 109 // - Kernels that don't make indirect function calls are not affected by those 110 // that do. 111 // - Variables which are used by lots of kernels, e.g. those injected by a 112 // language runtime in most kernels, are expected to have no overhead 113 // - Implementations that instantiate templates per-kernel where those templates 114 // use LDS are expected to hit the "Kernel" lowering strategy 115 // - The runtime properties impose a cost in compiler implementation complexity 116 // 117 // Dynamic LDS implementation 118 // Dynamic LDS is lowered similarly to the "table" strategy above and uses the 119 // same intrinsic to identify which kernel is at the root of the dynamic call 120 // graph. This relies on the specified behaviour that all dynamic LDS variables 121 // alias one another, i.e. are at the same address, with respect to a given 122 // kernel. Therefore this pass creates new dynamic LDS variables for each kernel 123 // that allocates any dynamic LDS and builds a table of addresses out of those. 124 // The AMDGPUPromoteAlloca pass skips kernels that use dynamic LDS. 125 // The corresponding optimisation for "kernel" lowering where the table lookup 126 // is elided is not implemented. 127 // 128 // 129 // Implementation notes / limitations 130 // A single LDS global variable represents an instance per kernel that can reach 131 // said variables. This pass essentially specialises said variables per kernel. 132 // Handling ConstantExpr during the pass complicated this significantly so now 133 // all ConstantExpr uses of LDS variables are expanded to instructions. This 134 // may need amending when implementing non-undef initialisers. 135 // 136 // Lowering is split between this IR pass and the back end. This pass chooses 137 // where given variables should be allocated and marks them with metadata, 138 // MD_absolute_symbol. The backend places the variables in coincidentally the 139 // same location and raises a fatal error if something has gone awry. This works 140 // in practice because the only pass between this one and the backend that 141 // changes LDS is PromoteAlloca and the changes it makes do not conflict. 142 // 143 // Addresses are written to constant global arrays based on the same metadata. 144 // 145 // The backend lowers LDS variables in the order of traversal of the function. 146 // This is at odds with the deterministic layout required. The workaround is to 147 // allocate the fixed-address variables immediately upon starting the function 148 // where they can be placed as intended. This requires a means of mapping from 149 // the function to the variables that it allocates. For the module scope lds, 150 // this is via metadata indicating whether the variable is not required. If a 151 // pass deletes that metadata, a fatal error on disagreement with the absolute 152 // symbol metadata will occur. For kernel scope and dynamic, this is by _name_ 153 // correspondence between the function and the variable. It requires the 154 // kernel to have a name (which is only a limitation for tests in practice) and 155 // for nothing to rename the corresponding symbols. This is a hazard if the pass 156 // is run multiple times during debugging. Alternative schemes considered all 157 // involve bespoke metadata. 158 // 159 // If the name correspondence can be replaced, multiple distinct kernels that 160 // have the same memory layout can map to the same kernel id (as the address 161 // itself is handled by the absolute symbol metadata) and that will allow more 162 // uses of the "kernel" style faster lowering and reduce the size of the lookup 163 // tables. 164 // 165 // There is a test that checks this does not fire for a graphics shader. This 166 // lowering is expected to work for graphics if the isKernel test is changed. 167 // 168 // The current markUsedByKernel is sufficient for PromoteAlloca but is elided 169 // before codegen. Replacing this with an equivalent intrinsic which lasts until 170 // shortly after the machine function lowering of LDS would help break the name 171 // mapping. The other part needed is probably to amend PromoteAlloca to embed 172 // the LDS variables it creates in the same struct created here. That avoids the 173 // current hazard where a PromoteAlloca LDS variable might be allocated before 174 // the kernel scope (and thus error on the address check). Given a new invariant 175 // that no LDS variables exist outside of the structs managed here, and an 176 // intrinsic that lasts until after the LDS frame lowering, it should be 177 // possible to drop the name mapping and fold equivalent memory layouts. 178 // 179 //===----------------------------------------------------------------------===// 180 181 #include "AMDGPU.h" 182 #include "Utils/AMDGPUBaseInfo.h" 183 #include "Utils/AMDGPUMemoryUtils.h" 184 #include "llvm/ADT/BitVector.h" 185 #include "llvm/ADT/DenseMap.h" 186 #include "llvm/ADT/DenseSet.h" 187 #include "llvm/ADT/STLExtras.h" 188 #include "llvm/ADT/SetOperations.h" 189 #include "llvm/ADT/SetVector.h" 190 #include "llvm/Analysis/CallGraph.h" 191 #include "llvm/IR/Constants.h" 192 #include "llvm/IR/DerivedTypes.h" 193 #include "llvm/IR/IRBuilder.h" 194 #include "llvm/IR/InlineAsm.h" 195 #include "llvm/IR/Instructions.h" 196 #include "llvm/IR/IntrinsicsAMDGPU.h" 197 #include "llvm/IR/MDBuilder.h" 198 #include "llvm/IR/ReplaceConstant.h" 199 #include "llvm/InitializePasses.h" 200 #include "llvm/Pass.h" 201 #include "llvm/Support/CommandLine.h" 202 #include "llvm/Support/Debug.h" 203 #include "llvm/Support/OptimizedStructLayout.h" 204 #include "llvm/Transforms/Utils/BasicBlockUtils.h" 205 #include "llvm/Transforms/Utils/ModuleUtils.h" 206 207 #include <tuple> 208 #include <vector> 209 210 #include <cstdio> 211 212 #define DEBUG_TYPE "amdgpu-lower-module-lds" 213 214 using namespace llvm; 215 216 namespace { 217 218 cl::opt<bool> SuperAlignLDSGlobals( 219 "amdgpu-super-align-lds-globals", 220 cl::desc("Increase alignment of LDS if it is not on align boundary"), 221 cl::init(true), cl::Hidden); 222 223 enum class LoweringKind { module, table, kernel, hybrid }; 224 cl::opt<LoweringKind> LoweringKindLoc( 225 "amdgpu-lower-module-lds-strategy", 226 cl::desc("Specify lowering strategy for function LDS access:"), cl::Hidden, 227 cl::init(LoweringKind::hybrid), 228 cl::values( 229 clEnumValN(LoweringKind::table, "table", "Lower via table lookup"), 230 clEnumValN(LoweringKind::module, "module", "Lower via module struct"), 231 clEnumValN( 232 LoweringKind::kernel, "kernel", 233 "Lower variables reachable from one kernel, otherwise abort"), 234 clEnumValN(LoweringKind::hybrid, "hybrid", 235 "Lower via mixture of above strategies"))); 236 237 bool isKernelLDS(const Function *F) { 238 // Some weirdness here. AMDGPU::isKernelCC does not call into 239 // AMDGPU::isKernel with the calling conv, it instead calls into 240 // isModuleEntryFunction which returns true for more calling conventions 241 // than AMDGPU::isKernel does. There's a FIXME on AMDGPU::isKernel. 242 // There's also a test that checks that the LDS lowering does not hit on 243 // a graphics shader, denoted amdgpu_ps, so stay with the limited case. 244 // Putting LDS in the name of the function to draw attention to this. 245 return AMDGPU::isKernel(F->getCallingConv()); 246 } 247 248 template <typename T> std::vector<T> sortByName(std::vector<T> &&V) { 249 llvm::sort(V.begin(), V.end(), [](const auto *L, const auto *R) { 250 return L->getName() < R->getName(); 251 }); 252 return {std::move(V)}; 253 } 254 255 class AMDGPULowerModuleLDS : public ModulePass { 256 257 static void 258 removeLocalVarsFromUsedLists(Module &M, 259 const DenseSet<GlobalVariable *> &LocalVars) { 260 // The verifier rejects used lists containing an inttoptr of a constant 261 // so remove the variables from these lists before replaceAllUsesWith 262 SmallPtrSet<Constant *, 8> LocalVarsSet; 263 for (GlobalVariable *LocalVar : LocalVars) 264 LocalVarsSet.insert(cast<Constant>(LocalVar->stripPointerCasts())); 265 266 removeFromUsedLists( 267 M, [&LocalVarsSet](Constant *C) { return LocalVarsSet.count(C); }); 268 269 for (GlobalVariable *LocalVar : LocalVars) 270 LocalVar->removeDeadConstantUsers(); 271 } 272 273 static void markUsedByKernel(IRBuilder<> &Builder, Function *Func, 274 GlobalVariable *SGV) { 275 // The llvm.amdgcn.module.lds instance is implicitly used by all kernels 276 // that might call a function which accesses a field within it. This is 277 // presently approximated to 'all kernels' if there are any such functions 278 // in the module. This implicit use is redefined as an explicit use here so 279 // that later passes, specifically PromoteAlloca, account for the required 280 // memory without any knowledge of this transform. 281 282 // An operand bundle on llvm.donothing works because the call instruction 283 // survives until after the last pass that needs to account for LDS. It is 284 // better than inline asm as the latter survives until the end of codegen. A 285 // totally robust solution would be a function with the same semantics as 286 // llvm.donothing that takes a pointer to the instance and is lowered to a 287 // no-op after LDS is allocated, but that is not presently necessary. 288 289 // This intrinsic is eliminated shortly before instruction selection. It 290 // does not suffice to indicate to ISel that a given global which is not 291 // immediately used by the kernel must still be allocated by it. An 292 // equivalent target specific intrinsic which lasts until immediately after 293 // codegen would suffice for that, but one would still need to ensure that 294 // the variables are allocated in the anticpated order. 295 296 LLVMContext &Ctx = Func->getContext(); 297 298 Builder.SetInsertPoint(Func->getEntryBlock().getFirstNonPHI()); 299 300 FunctionType *FTy = FunctionType::get(Type::getVoidTy(Ctx), {}); 301 302 Function *Decl = 303 Intrinsic::getDeclaration(Func->getParent(), Intrinsic::donothing, {}); 304 305 Value *UseInstance[1] = {Builder.CreateInBoundsGEP( 306 SGV->getValueType(), SGV, ConstantInt::get(Type::getInt32Ty(Ctx), 0))}; 307 308 Builder.CreateCall(FTy, Decl, {}, 309 {OperandBundleDefT<Value *>("ExplicitUse", UseInstance)}, 310 ""); 311 } 312 313 static bool eliminateConstantExprUsesOfLDSFromAllInstructions(Module &M) { 314 // Constants are uniqued within LLVM. A ConstantExpr referring to a LDS 315 // global may have uses from multiple different functions as a result. 316 // This pass specialises LDS variables with respect to the kernel that 317 // allocates them. 318 319 // This is semantically equivalent to (the unimplemented as slow): 320 // for (auto &F : M.functions()) 321 // for (auto &BB : F) 322 // for (auto &I : BB) 323 // for (Use &Op : I.operands()) 324 // if (constantExprUsesLDS(Op)) 325 // replaceConstantExprInFunction(I, Op); 326 327 SmallVector<Constant *> LDSGlobals; 328 for (auto &GV : M.globals()) 329 if (AMDGPU::isLDSVariableToLower(GV)) 330 LDSGlobals.push_back(&GV); 331 332 return convertUsersOfConstantsToInstructions(LDSGlobals); 333 } 334 335 public: 336 static char ID; 337 338 AMDGPULowerModuleLDS() : ModulePass(ID) { 339 initializeAMDGPULowerModuleLDSPass(*PassRegistry::getPassRegistry()); 340 } 341 342 using FunctionVariableMap = DenseMap<Function *, DenseSet<GlobalVariable *>>; 343 344 using VariableFunctionMap = DenseMap<GlobalVariable *, DenseSet<Function *>>; 345 346 static void getUsesOfLDSByFunction(CallGraph const &CG, Module &M, 347 FunctionVariableMap &kernels, 348 FunctionVariableMap &functions) { 349 350 // Get uses from the current function, excluding uses by called functions 351 // Two output variables to avoid walking the globals list twice 352 for (auto &GV : M.globals()) { 353 if (!AMDGPU::isLDSVariableToLower(GV)) { 354 continue; 355 } 356 357 for (User *V : GV.users()) { 358 if (auto *I = dyn_cast<Instruction>(V)) { 359 Function *F = I->getFunction(); 360 if (isKernelLDS(F)) { 361 kernels[F].insert(&GV); 362 } else { 363 functions[F].insert(&GV); 364 } 365 } 366 } 367 } 368 } 369 370 struct LDSUsesInfoTy { 371 FunctionVariableMap direct_access; 372 FunctionVariableMap indirect_access; 373 }; 374 375 static LDSUsesInfoTy getTransitiveUsesOfLDS(CallGraph const &CG, Module &M) { 376 377 FunctionVariableMap direct_map_kernel; 378 FunctionVariableMap direct_map_function; 379 getUsesOfLDSByFunction(CG, M, direct_map_kernel, direct_map_function); 380 381 // Collect variables that are used by functions whose address has escaped 382 DenseSet<GlobalVariable *> VariablesReachableThroughFunctionPointer; 383 for (Function &F : M.functions()) { 384 if (!isKernelLDS(&F)) 385 if (F.hasAddressTaken(nullptr, 386 /* IgnoreCallbackUses */ false, 387 /* IgnoreAssumeLikeCalls */ false, 388 /* IgnoreLLVMUsed */ true, 389 /* IgnoreArcAttachedCall */ false)) { 390 set_union(VariablesReachableThroughFunctionPointer, 391 direct_map_function[&F]); 392 } 393 } 394 395 auto functionMakesUnknownCall = [&](const Function *F) -> bool { 396 assert(!F->isDeclaration()); 397 for (const CallGraphNode::CallRecord &R : *CG[F]) { 398 if (!R.second->getFunction()) { 399 return true; 400 } 401 } 402 return false; 403 }; 404 405 // Work out which variables are reachable through function calls 406 FunctionVariableMap transitive_map_function = direct_map_function; 407 408 // If the function makes any unknown call, assume the worst case that it can 409 // access all variables accessed by functions whose address escaped 410 for (Function &F : M.functions()) { 411 if (!F.isDeclaration() && functionMakesUnknownCall(&F)) { 412 if (!isKernelLDS(&F)) { 413 set_union(transitive_map_function[&F], 414 VariablesReachableThroughFunctionPointer); 415 } 416 } 417 } 418 419 // Direct implementation of collecting all variables reachable from each 420 // function 421 for (Function &Func : M.functions()) { 422 if (Func.isDeclaration() || isKernelLDS(&Func)) 423 continue; 424 425 DenseSet<Function *> seen; // catches cycles 426 SmallVector<Function *, 4> wip{&Func}; 427 428 while (!wip.empty()) { 429 Function *F = wip.pop_back_val(); 430 431 // Can accelerate this by referring to transitive map for functions that 432 // have already been computed, with more care than this 433 set_union(transitive_map_function[&Func], direct_map_function[F]); 434 435 for (const CallGraphNode::CallRecord &R : *CG[F]) { 436 Function *ith = R.second->getFunction(); 437 if (ith) { 438 if (!seen.contains(ith)) { 439 seen.insert(ith); 440 wip.push_back(ith); 441 } 442 } 443 } 444 } 445 } 446 447 // direct_map_kernel lists which variables are used by the kernel 448 // find the variables which are used through a function call 449 FunctionVariableMap indirect_map_kernel; 450 451 for (Function &Func : M.functions()) { 452 if (Func.isDeclaration() || !isKernelLDS(&Func)) 453 continue; 454 455 for (const CallGraphNode::CallRecord &R : *CG[&Func]) { 456 Function *ith = R.second->getFunction(); 457 if (ith) { 458 set_union(indirect_map_kernel[&Func], transitive_map_function[ith]); 459 } else { 460 set_union(indirect_map_kernel[&Func], 461 VariablesReachableThroughFunctionPointer); 462 } 463 } 464 } 465 466 return {std::move(direct_map_kernel), std::move(indirect_map_kernel)}; 467 } 468 469 struct LDSVariableReplacement { 470 GlobalVariable *SGV = nullptr; 471 DenseMap<GlobalVariable *, Constant *> LDSVarsToConstantGEP; 472 }; 473 474 // remap from lds global to a constantexpr gep to where it has been moved to 475 // for each kernel 476 // an array with an element for each kernel containing where the corresponding 477 // variable was remapped to 478 479 static Constant *getAddressesOfVariablesInKernel( 480 LLVMContext &Ctx, ArrayRef<GlobalVariable *> Variables, 481 const DenseMap<GlobalVariable *, Constant *> &LDSVarsToConstantGEP) { 482 // Create a ConstantArray containing the address of each Variable within the 483 // kernel corresponding to LDSVarsToConstantGEP, or poison if that kernel 484 // does not allocate it 485 // TODO: Drop the ptrtoint conversion 486 487 Type *I32 = Type::getInt32Ty(Ctx); 488 489 ArrayType *KernelOffsetsType = ArrayType::get(I32, Variables.size()); 490 491 SmallVector<Constant *> Elements; 492 for (size_t i = 0; i < Variables.size(); i++) { 493 GlobalVariable *GV = Variables[i]; 494 auto ConstantGepIt = LDSVarsToConstantGEP.find(GV); 495 if (ConstantGepIt != LDSVarsToConstantGEP.end()) { 496 auto elt = ConstantExpr::getPtrToInt(ConstantGepIt->second, I32); 497 Elements.push_back(elt); 498 } else { 499 Elements.push_back(PoisonValue::get(I32)); 500 } 501 } 502 return ConstantArray::get(KernelOffsetsType, Elements); 503 } 504 505 static GlobalVariable *buildLookupTable( 506 Module &M, ArrayRef<GlobalVariable *> Variables, 507 ArrayRef<Function *> kernels, 508 DenseMap<Function *, LDSVariableReplacement> &KernelToReplacement) { 509 if (Variables.empty()) { 510 return nullptr; 511 } 512 LLVMContext &Ctx = M.getContext(); 513 514 const size_t NumberVariables = Variables.size(); 515 const size_t NumberKernels = kernels.size(); 516 517 ArrayType *KernelOffsetsType = 518 ArrayType::get(Type::getInt32Ty(Ctx), NumberVariables); 519 520 ArrayType *AllKernelsOffsetsType = 521 ArrayType::get(KernelOffsetsType, NumberKernels); 522 523 Constant *Missing = PoisonValue::get(KernelOffsetsType); 524 std::vector<Constant *> overallConstantExprElts(NumberKernels); 525 for (size_t i = 0; i < NumberKernels; i++) { 526 auto Replacement = KernelToReplacement.find(kernels[i]); 527 overallConstantExprElts[i] = 528 (Replacement == KernelToReplacement.end()) 529 ? Missing 530 : getAddressesOfVariablesInKernel( 531 Ctx, Variables, Replacement->second.LDSVarsToConstantGEP); 532 } 533 534 Constant *init = 535 ConstantArray::get(AllKernelsOffsetsType, overallConstantExprElts); 536 537 return new GlobalVariable( 538 M, AllKernelsOffsetsType, true, GlobalValue::InternalLinkage, init, 539 "llvm.amdgcn.lds.offset.table", nullptr, GlobalValue::NotThreadLocal, 540 AMDGPUAS::CONSTANT_ADDRESS); 541 } 542 543 void replaceUseWithTableLookup(Module &M, IRBuilder<> &Builder, 544 GlobalVariable *LookupTable, 545 GlobalVariable *GV, Use &U, 546 Value *OptionalIndex) { 547 // Table is a constant array of the same length as OrderedKernels 548 LLVMContext &Ctx = M.getContext(); 549 Type *I32 = Type::getInt32Ty(Ctx); 550 auto *I = cast<Instruction>(U.getUser()); 551 552 Value *tableKernelIndex = getTableLookupKernelIndex(M, I->getFunction()); 553 554 if (auto *Phi = dyn_cast<PHINode>(I)) { 555 BasicBlock *BB = Phi->getIncomingBlock(U); 556 Builder.SetInsertPoint(&(*(BB->getFirstInsertionPt()))); 557 } else { 558 Builder.SetInsertPoint(I); 559 } 560 561 SmallVector<Value *, 3> GEPIdx = { 562 ConstantInt::get(I32, 0), 563 tableKernelIndex, 564 }; 565 if (OptionalIndex) 566 GEPIdx.push_back(OptionalIndex); 567 568 Value *Address = Builder.CreateInBoundsGEP( 569 LookupTable->getValueType(), LookupTable, GEPIdx, GV->getName()); 570 571 Value *loaded = Builder.CreateLoad(I32, Address); 572 573 Value *replacement = 574 Builder.CreateIntToPtr(loaded, GV->getType(), GV->getName()); 575 576 U.set(replacement); 577 } 578 579 void replaceUsesInInstructionsWithTableLookup( 580 Module &M, ArrayRef<GlobalVariable *> ModuleScopeVariables, 581 GlobalVariable *LookupTable) { 582 583 LLVMContext &Ctx = M.getContext(); 584 IRBuilder<> Builder(Ctx); 585 Type *I32 = Type::getInt32Ty(Ctx); 586 587 for (size_t Index = 0; Index < ModuleScopeVariables.size(); Index++) { 588 auto *GV = ModuleScopeVariables[Index]; 589 590 for (Use &U : make_early_inc_range(GV->uses())) { 591 auto *I = dyn_cast<Instruction>(U.getUser()); 592 if (!I) 593 continue; 594 595 replaceUseWithTableLookup(M, Builder, LookupTable, GV, U, 596 ConstantInt::get(I32, Index)); 597 } 598 } 599 } 600 601 static DenseSet<Function *> kernelsThatIndirectlyAccessAnyOfPassedVariables( 602 Module &M, LDSUsesInfoTy &LDSUsesInfo, 603 DenseSet<GlobalVariable *> const &VariableSet) { 604 605 DenseSet<Function *> KernelSet; 606 607 if (VariableSet.empty()) 608 return KernelSet; 609 610 for (Function &Func : M.functions()) { 611 if (Func.isDeclaration() || !isKernelLDS(&Func)) 612 continue; 613 for (GlobalVariable *GV : LDSUsesInfo.indirect_access[&Func]) { 614 if (VariableSet.contains(GV)) { 615 KernelSet.insert(&Func); 616 break; 617 } 618 } 619 } 620 621 return KernelSet; 622 } 623 624 static GlobalVariable * 625 chooseBestVariableForModuleStrategy(const DataLayout &DL, 626 VariableFunctionMap &LDSVars) { 627 // Find the global variable with the most indirect uses from kernels 628 629 struct CandidateTy { 630 GlobalVariable *GV = nullptr; 631 size_t UserCount = 0; 632 size_t Size = 0; 633 634 CandidateTy() = default; 635 636 CandidateTy(GlobalVariable *GV, uint64_t UserCount, uint64_t AllocSize) 637 : GV(GV), UserCount(UserCount), Size(AllocSize) {} 638 639 bool operator<(const CandidateTy &Other) const { 640 // Fewer users makes module scope variable less attractive 641 if (UserCount < Other.UserCount) { 642 return true; 643 } 644 if (UserCount > Other.UserCount) { 645 return false; 646 } 647 648 // Bigger makes module scope variable less attractive 649 if (Size < Other.Size) { 650 return false; 651 } 652 653 if (Size > Other.Size) { 654 return true; 655 } 656 657 // Arbitrary but consistent 658 return GV->getName() < Other.GV->getName(); 659 } 660 }; 661 662 CandidateTy MostUsed; 663 664 for (auto &K : LDSVars) { 665 GlobalVariable *GV = K.first; 666 if (K.second.size() <= 1) { 667 // A variable reachable by only one kernel is best lowered with kernel 668 // strategy 669 continue; 670 } 671 CandidateTy Candidate( 672 GV, K.second.size(), 673 DL.getTypeAllocSize(GV->getValueType()).getFixedValue()); 674 if (MostUsed < Candidate) 675 MostUsed = Candidate; 676 } 677 678 return MostUsed.GV; 679 } 680 681 static void recordLDSAbsoluteAddress(Module *M, GlobalVariable *GV, 682 uint32_t Address) { 683 // Write the specified address into metadata where it can be retrieved by 684 // the assembler. Format is a half open range, [Address Address+1) 685 LLVMContext &Ctx = M->getContext(); 686 auto *IntTy = 687 M->getDataLayout().getIntPtrType(Ctx, AMDGPUAS::LOCAL_ADDRESS); 688 auto *MinC = ConstantAsMetadata::get(ConstantInt::get(IntTy, Address)); 689 auto *MaxC = ConstantAsMetadata::get(ConstantInt::get(IntTy, Address + 1)); 690 GV->setMetadata(LLVMContext::MD_absolute_symbol, 691 MDNode::get(Ctx, {MinC, MaxC})); 692 } 693 694 DenseMap<Function *, Value *> tableKernelIndexCache; 695 Value *getTableLookupKernelIndex(Module &M, Function *F) { 696 // Accesses from a function use the amdgcn_lds_kernel_id intrinsic which 697 // lowers to a read from a live in register. Emit it once in the entry 698 // block to spare deduplicating it later. 699 if (tableKernelIndexCache.count(F) == 0) { 700 LLVMContext &Ctx = M.getContext(); 701 IRBuilder<> Builder(Ctx); 702 FunctionType *FTy = FunctionType::get(Type::getInt32Ty(Ctx), {}); 703 Function *Decl = 704 Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_lds_kernel_id, {}); 705 706 BasicBlock::iterator it = 707 F->getEntryBlock().getFirstNonPHIOrDbgOrAlloca(); 708 Instruction &i = *it; 709 Builder.SetInsertPoint(&i); 710 711 tableKernelIndexCache[F] = Builder.CreateCall(FTy, Decl, {}); 712 } 713 714 return tableKernelIndexCache[F]; 715 } 716 717 static std::vector<Function *> assignLDSKernelIDToEachKernel( 718 Module *M, DenseSet<Function *> const &KernelsThatAllocateTableLDS, 719 DenseSet<Function *> const &KernelsThatIndirectlyAllocateDynamicLDS) { 720 // Associate kernels in the set with an arbirary but reproducible order and 721 // annotate them with that order in metadata. This metadata is recognised by 722 // the backend and lowered to a SGPR which can be read from using 723 // amdgcn_lds_kernel_id. 724 725 std::vector<Function *> OrderedKernels; 726 if (!KernelsThatAllocateTableLDS.empty() || 727 !KernelsThatIndirectlyAllocateDynamicLDS.empty()) { 728 729 for (Function &Func : M->functions()) { 730 if (Func.isDeclaration()) 731 continue; 732 if (!isKernelLDS(&Func)) 733 continue; 734 735 if (KernelsThatAllocateTableLDS.contains(&Func) || 736 KernelsThatIndirectlyAllocateDynamicLDS.contains(&Func)) { 737 assert(Func.hasName()); // else fatal error earlier 738 OrderedKernels.push_back(&Func); 739 } 740 } 741 742 // Put them in an arbitrary but reproducible order 743 OrderedKernels = sortByName(std::move(OrderedKernels)); 744 745 // Annotate the kernels with their order in this vector 746 LLVMContext &Ctx = M->getContext(); 747 IRBuilder<> Builder(Ctx); 748 749 if (OrderedKernels.size() > UINT32_MAX) { 750 // 32 bit keeps it in one SGPR. > 2**32 kernels won't fit on the GPU 751 report_fatal_error("Unimplemented LDS lowering for > 2**32 kernels"); 752 } 753 754 for (size_t i = 0; i < OrderedKernels.size(); i++) { 755 Metadata *AttrMDArgs[1] = { 756 ConstantAsMetadata::get(Builder.getInt32(i)), 757 }; 758 OrderedKernels[i]->setMetadata("llvm.amdgcn.lds.kernel.id", 759 MDNode::get(Ctx, AttrMDArgs)); 760 } 761 } 762 return OrderedKernels; 763 } 764 765 static void partitionVariablesIntoIndirectStrategies( 766 Module &M, LDSUsesInfoTy const &LDSUsesInfo, 767 VariableFunctionMap &LDSToKernelsThatNeedToAccessItIndirectly, 768 DenseSet<GlobalVariable *> &ModuleScopeVariables, 769 DenseSet<GlobalVariable *> &TableLookupVariables, 770 DenseSet<GlobalVariable *> &KernelAccessVariables, 771 DenseSet<GlobalVariable *> &DynamicVariables) { 772 773 GlobalVariable *HybridModuleRoot = 774 LoweringKindLoc != LoweringKind::hybrid 775 ? nullptr 776 : chooseBestVariableForModuleStrategy( 777 M.getDataLayout(), LDSToKernelsThatNeedToAccessItIndirectly); 778 779 DenseSet<Function *> const EmptySet; 780 DenseSet<Function *> const &HybridModuleRootKernels = 781 HybridModuleRoot 782 ? LDSToKernelsThatNeedToAccessItIndirectly[HybridModuleRoot] 783 : EmptySet; 784 785 for (auto &K : LDSToKernelsThatNeedToAccessItIndirectly) { 786 // Each iteration of this loop assigns exactly one global variable to 787 // exactly one of the implementation strategies. 788 789 GlobalVariable *GV = K.first; 790 assert(AMDGPU::isLDSVariableToLower(*GV)); 791 assert(K.second.size() != 0); 792 793 if (AMDGPU::isDynamicLDS(*GV)) { 794 DynamicVariables.insert(GV); 795 continue; 796 } 797 798 switch (LoweringKindLoc) { 799 case LoweringKind::module: 800 ModuleScopeVariables.insert(GV); 801 break; 802 803 case LoweringKind::table: 804 TableLookupVariables.insert(GV); 805 break; 806 807 case LoweringKind::kernel: 808 if (K.second.size() == 1) { 809 KernelAccessVariables.insert(GV); 810 } else { 811 report_fatal_error( 812 "cannot lower LDS '" + GV->getName() + 813 "' to kernel access as it is reachable from multiple kernels"); 814 } 815 break; 816 817 case LoweringKind::hybrid: { 818 if (GV == HybridModuleRoot) { 819 assert(K.second.size() != 1); 820 ModuleScopeVariables.insert(GV); 821 } else if (K.second.size() == 1) { 822 KernelAccessVariables.insert(GV); 823 } else if (set_is_subset(K.second, HybridModuleRootKernels)) { 824 ModuleScopeVariables.insert(GV); 825 } else { 826 TableLookupVariables.insert(GV); 827 } 828 break; 829 } 830 } 831 } 832 833 // All LDS variables accessed indirectly have now been partitioned into 834 // the distinct lowering strategies. 835 assert(ModuleScopeVariables.size() + TableLookupVariables.size() + 836 KernelAccessVariables.size() + DynamicVariables.size() == 837 LDSToKernelsThatNeedToAccessItIndirectly.size()); 838 } 839 840 static GlobalVariable *lowerModuleScopeStructVariables( 841 Module &M, DenseSet<GlobalVariable *> const &ModuleScopeVariables, 842 DenseSet<Function *> const &KernelsThatAllocateModuleLDS) { 843 // Create a struct to hold the ModuleScopeVariables 844 // Replace all uses of those variables from non-kernel functions with the 845 // new struct instance Replace only the uses from kernel functions that will 846 // allocate this instance. That is a space optimisation - kernels that use a 847 // subset of the module scope struct and do not need to allocate it for 848 // indirect calls will only allocate the subset they use (they do so as part 849 // of the per-kernel lowering). 850 if (ModuleScopeVariables.empty()) { 851 return nullptr; 852 } 853 854 LLVMContext &Ctx = M.getContext(); 855 856 LDSVariableReplacement ModuleScopeReplacement = 857 createLDSVariableReplacement(M, "llvm.amdgcn.module.lds", 858 ModuleScopeVariables); 859 860 appendToCompilerUsed(M, {static_cast<GlobalValue *>( 861 ConstantExpr::getPointerBitCastOrAddrSpaceCast( 862 cast<Constant>(ModuleScopeReplacement.SGV), 863 Type::getInt8PtrTy(Ctx)))}); 864 865 // module.lds will be allocated at zero in any kernel that allocates it 866 recordLDSAbsoluteAddress(&M, ModuleScopeReplacement.SGV, 0); 867 868 // historic 869 removeLocalVarsFromUsedLists(M, ModuleScopeVariables); 870 871 // Replace all uses of module scope variable from non-kernel functions 872 replaceLDSVariablesWithStruct( 873 M, ModuleScopeVariables, ModuleScopeReplacement, [&](Use &U) { 874 Instruction *I = dyn_cast<Instruction>(U.getUser()); 875 if (!I) { 876 return false; 877 } 878 Function *F = I->getFunction(); 879 return !isKernelLDS(F); 880 }); 881 882 // Replace uses of module scope variable from kernel functions that 883 // allocate the module scope variable, otherwise leave them unchanged 884 // Record on each kernel whether the module scope global is used by it 885 886 IRBuilder<> Builder(Ctx); 887 888 for (Function &Func : M.functions()) { 889 if (Func.isDeclaration() || !isKernelLDS(&Func)) 890 continue; 891 892 if (KernelsThatAllocateModuleLDS.contains(&Func)) { 893 replaceLDSVariablesWithStruct( 894 M, ModuleScopeVariables, ModuleScopeReplacement, [&](Use &U) { 895 Instruction *I = dyn_cast<Instruction>(U.getUser()); 896 if (!I) { 897 return false; 898 } 899 Function *F = I->getFunction(); 900 return F == &Func; 901 }); 902 903 markUsedByKernel(Builder, &Func, ModuleScopeReplacement.SGV); 904 905 } else { 906 markElideModuleLDS(Func); 907 } 908 } 909 910 return ModuleScopeReplacement.SGV; 911 } 912 913 static DenseMap<Function *, LDSVariableReplacement> 914 lowerKernelScopeStructVariables( 915 Module &M, LDSUsesInfoTy &LDSUsesInfo, 916 DenseSet<GlobalVariable *> const &ModuleScopeVariables, 917 DenseSet<Function *> const &KernelsThatAllocateModuleLDS, 918 GlobalVariable *MaybeModuleScopeStruct) { 919 920 // Create a struct for each kernel for the non-module-scope variables. 921 922 IRBuilder<> Builder(M.getContext()); 923 DenseMap<Function *, LDSVariableReplacement> KernelToReplacement; 924 for (Function &Func : M.functions()) { 925 if (Func.isDeclaration() || !isKernelLDS(&Func)) 926 continue; 927 928 DenseSet<GlobalVariable *> KernelUsedVariables; 929 // Allocating variables that are used directly in this struct to get 930 // alignment aware allocation and predictable frame size. 931 for (auto &v : LDSUsesInfo.direct_access[&Func]) { 932 if (!AMDGPU::isDynamicLDS(*v)) { 933 KernelUsedVariables.insert(v); 934 } 935 } 936 937 // Allocating variables that are accessed indirectly so that a lookup of 938 // this struct instance can find them from nested functions. 939 for (auto &v : LDSUsesInfo.indirect_access[&Func]) { 940 if (!AMDGPU::isDynamicLDS(*v)) { 941 KernelUsedVariables.insert(v); 942 } 943 } 944 945 // Variables allocated in module lds must all resolve to that struct, 946 // not to the per-kernel instance. 947 if (KernelsThatAllocateModuleLDS.contains(&Func)) { 948 for (GlobalVariable *v : ModuleScopeVariables) { 949 KernelUsedVariables.erase(v); 950 } 951 } 952 953 if (KernelUsedVariables.empty()) { 954 // Either used no LDS, or the LDS it used was all in the module struct 955 // or dynamically sized 956 continue; 957 } 958 959 // The association between kernel function and LDS struct is done by 960 // symbol name, which only works if the function in question has a 961 // name This is not expected to be a problem in practice as kernels 962 // are called by name making anonymous ones (which are named by the 963 // backend) difficult to use. This does mean that llvm test cases need 964 // to name the kernels. 965 if (!Func.hasName()) { 966 report_fatal_error("Anonymous kernels cannot use LDS variables"); 967 } 968 969 std::string VarName = 970 (Twine("llvm.amdgcn.kernel.") + Func.getName() + ".lds").str(); 971 972 auto Replacement = 973 createLDSVariableReplacement(M, VarName, KernelUsedVariables); 974 975 // If any indirect uses, create a direct use to ensure allocation 976 // TODO: Simpler to unconditionally mark used but that regresses 977 // codegen in test/CodeGen/AMDGPU/noclobber-barrier.ll 978 auto Accesses = LDSUsesInfo.indirect_access.find(&Func); 979 if ((Accesses != LDSUsesInfo.indirect_access.end()) && 980 !Accesses->second.empty()) 981 markUsedByKernel(Builder, &Func, Replacement.SGV); 982 983 // remove preserves existing codegen 984 removeLocalVarsFromUsedLists(M, KernelUsedVariables); 985 KernelToReplacement[&Func] = Replacement; 986 987 // Rewrite uses within kernel to the new struct 988 replaceLDSVariablesWithStruct( 989 M, KernelUsedVariables, Replacement, [&Func](Use &U) { 990 Instruction *I = dyn_cast<Instruction>(U.getUser()); 991 return I && I->getFunction() == &Func; 992 }); 993 } 994 return KernelToReplacement; 995 } 996 997 static GlobalVariable * 998 buildRepresentativeDynamicLDSInstance(Module &M, LDSUsesInfoTy &LDSUsesInfo, 999 Function *func) { 1000 // Create a dynamic lds variable with a name associated with the passed 1001 // function that has the maximum alignment of any dynamic lds variable 1002 // reachable from this kernel. Dynamic LDS is allocated after the static LDS 1003 // allocation, possibly after alignment padding. The representative variable 1004 // created here has the maximum alignment of any other dynamic variable 1005 // reachable by that kernel. All dynamic LDS variables are allocated at the 1006 // same address in each kernel in order to provide the documented aliasing 1007 // semantics. Setting the alignment here allows this IR pass to accurately 1008 // predict the exact constant at which it will be allocated. 1009 1010 assert(isKernelLDS(func)); 1011 1012 LLVMContext &Ctx = M.getContext(); 1013 const DataLayout &DL = M.getDataLayout(); 1014 Align MaxDynamicAlignment(1); 1015 1016 auto UpdateMaxAlignment = [&MaxDynamicAlignment, &DL](GlobalVariable *GV) { 1017 if (AMDGPU::isDynamicLDS(*GV)) { 1018 MaxDynamicAlignment = 1019 std::max(MaxDynamicAlignment, AMDGPU::getAlign(DL, GV)); 1020 } 1021 }; 1022 1023 for (GlobalVariable *GV : LDSUsesInfo.indirect_access[func]) { 1024 UpdateMaxAlignment(GV); 1025 } 1026 1027 for (GlobalVariable *GV : LDSUsesInfo.direct_access[func]) { 1028 UpdateMaxAlignment(GV); 1029 } 1030 1031 assert(func->hasName()); // Checked by caller 1032 auto emptyCharArray = ArrayType::get(Type::getInt8Ty(Ctx), 0); 1033 GlobalVariable *N = new GlobalVariable( 1034 M, emptyCharArray, false, GlobalValue::ExternalLinkage, nullptr, 1035 Twine("llvm.amdgcn." + func->getName() + ".dynlds"), nullptr, GlobalValue::NotThreadLocal, AMDGPUAS::LOCAL_ADDRESS, 1036 false); 1037 N->setAlignment(MaxDynamicAlignment); 1038 1039 assert(AMDGPU::isDynamicLDS(*N)); 1040 return N; 1041 } 1042 1043 DenseMap<Function *, GlobalVariable *> lowerDynamicLDSVariables( 1044 Module &M, LDSUsesInfoTy &LDSUsesInfo, 1045 DenseSet<Function *> const &KernelsThatIndirectlyAllocateDynamicLDS, 1046 DenseSet<GlobalVariable *> const &DynamicVariables, 1047 std::vector<Function *> const &OrderedKernels) { 1048 DenseMap<Function *, GlobalVariable *> KernelToCreatedDynamicLDS; 1049 if (!KernelsThatIndirectlyAllocateDynamicLDS.empty()) { 1050 LLVMContext &Ctx = M.getContext(); 1051 IRBuilder<> Builder(Ctx); 1052 Type *I32 = Type::getInt32Ty(Ctx); 1053 1054 std::vector<Constant *> newDynamicLDS; 1055 1056 // Table is built in the same order as OrderedKernels 1057 for (auto &func : OrderedKernels) { 1058 1059 if (KernelsThatIndirectlyAllocateDynamicLDS.contains(func)) { 1060 assert(isKernelLDS(func)); 1061 if (!func->hasName()) { 1062 report_fatal_error("Anonymous kernels cannot use LDS variables"); 1063 } 1064 1065 GlobalVariable *N = 1066 buildRepresentativeDynamicLDSInstance(M, LDSUsesInfo, func); 1067 1068 KernelToCreatedDynamicLDS[func] = N; 1069 1070 markUsedByKernel(Builder, func, N); 1071 1072 auto emptyCharArray = ArrayType::get(Type::getInt8Ty(Ctx), 0); 1073 auto GEP = ConstantExpr::getGetElementPtr( 1074 emptyCharArray, N, ConstantInt::get(I32, 0), true); 1075 newDynamicLDS.push_back(ConstantExpr::getPtrToInt(GEP, I32)); 1076 } else { 1077 newDynamicLDS.push_back(PoisonValue::get(I32)); 1078 } 1079 } 1080 assert(OrderedKernels.size() == newDynamicLDS.size()); 1081 1082 ArrayType *t = ArrayType::get(I32, newDynamicLDS.size()); 1083 Constant *init = ConstantArray::get(t, newDynamicLDS); 1084 GlobalVariable *table = new GlobalVariable( 1085 M, t, true, GlobalValue::InternalLinkage, init, 1086 "llvm.amdgcn.dynlds.offset.table", nullptr, 1087 GlobalValue::NotThreadLocal, AMDGPUAS::CONSTANT_ADDRESS); 1088 1089 for (GlobalVariable *GV : DynamicVariables) { 1090 for (Use &U : make_early_inc_range(GV->uses())) { 1091 auto *I = dyn_cast<Instruction>(U.getUser()); 1092 if (!I) 1093 continue; 1094 if (isKernelLDS(I->getFunction())) 1095 continue; 1096 1097 replaceUseWithTableLookup(M, Builder, table, GV, U, nullptr); 1098 } 1099 } 1100 } 1101 return KernelToCreatedDynamicLDS; 1102 } 1103 1104 static bool canElideModuleLDS(const Function &F) { 1105 return F.hasFnAttribute("amdgpu-elide-module-lds"); 1106 } 1107 1108 static void markElideModuleLDS(Function &F) { 1109 F.addFnAttr("amdgpu-elide-module-lds"); 1110 } 1111 1112 bool runOnModule(Module &M) override { 1113 CallGraph CG = CallGraph(M); 1114 bool Changed = superAlignLDSGlobals(M); 1115 1116 Changed |= eliminateConstantExprUsesOfLDSFromAllInstructions(M); 1117 1118 Changed = true; // todo: narrow this down 1119 1120 // For each kernel, what variables does it access directly or through 1121 // callees 1122 LDSUsesInfoTy LDSUsesInfo = getTransitiveUsesOfLDS(CG, M); 1123 1124 // For each variable accessed through callees, which kernels access it 1125 VariableFunctionMap LDSToKernelsThatNeedToAccessItIndirectly; 1126 for (auto &K : LDSUsesInfo.indirect_access) { 1127 Function *F = K.first; 1128 assert(isKernelLDS(F)); 1129 for (GlobalVariable *GV : K.second) { 1130 LDSToKernelsThatNeedToAccessItIndirectly[GV].insert(F); 1131 } 1132 } 1133 1134 // Partition variables accessed indirectly into the different strategies 1135 DenseSet<GlobalVariable *> ModuleScopeVariables; 1136 DenseSet<GlobalVariable *> TableLookupVariables; 1137 DenseSet<GlobalVariable *> KernelAccessVariables; 1138 DenseSet<GlobalVariable *> DynamicVariables; 1139 partitionVariablesIntoIndirectStrategies( 1140 M, LDSUsesInfo, LDSToKernelsThatNeedToAccessItIndirectly, 1141 ModuleScopeVariables, TableLookupVariables, KernelAccessVariables, 1142 DynamicVariables); 1143 1144 // If the kernel accesses a variable that is going to be stored in the 1145 // module instance through a call then that kernel needs to allocate the 1146 // module instance 1147 const DenseSet<Function *> KernelsThatAllocateModuleLDS = 1148 kernelsThatIndirectlyAccessAnyOfPassedVariables(M, LDSUsesInfo, 1149 ModuleScopeVariables); 1150 const DenseSet<Function *> KernelsThatAllocateTableLDS = 1151 kernelsThatIndirectlyAccessAnyOfPassedVariables(M, LDSUsesInfo, 1152 TableLookupVariables); 1153 1154 const DenseSet<Function *> KernelsThatIndirectlyAllocateDynamicLDS = 1155 kernelsThatIndirectlyAccessAnyOfPassedVariables(M, LDSUsesInfo, 1156 DynamicVariables); 1157 1158 GlobalVariable *MaybeModuleScopeStruct = lowerModuleScopeStructVariables( 1159 M, ModuleScopeVariables, KernelsThatAllocateModuleLDS); 1160 1161 DenseMap<Function *, LDSVariableReplacement> KernelToReplacement = 1162 lowerKernelScopeStructVariables(M, LDSUsesInfo, ModuleScopeVariables, 1163 KernelsThatAllocateModuleLDS, 1164 MaybeModuleScopeStruct); 1165 1166 // Lower zero cost accesses to the kernel instances just created 1167 for (auto &GV : KernelAccessVariables) { 1168 auto &funcs = LDSToKernelsThatNeedToAccessItIndirectly[GV]; 1169 assert(funcs.size() == 1); // Only one kernel can access it 1170 LDSVariableReplacement Replacement = 1171 KernelToReplacement[*(funcs.begin())]; 1172 1173 DenseSet<GlobalVariable *> Vec; 1174 Vec.insert(GV); 1175 1176 replaceLDSVariablesWithStruct(M, Vec, Replacement, [](Use &U) { 1177 return isa<Instruction>(U.getUser()); 1178 }); 1179 } 1180 1181 // The ith element of this vector is kernel id i 1182 std::vector<Function *> OrderedKernels = 1183 assignLDSKernelIDToEachKernel(&M, KernelsThatAllocateTableLDS, 1184 KernelsThatIndirectlyAllocateDynamicLDS); 1185 1186 if (!KernelsThatAllocateTableLDS.empty()) { 1187 LLVMContext &Ctx = M.getContext(); 1188 IRBuilder<> Builder(Ctx); 1189 1190 // The order must be consistent between lookup table and accesses to 1191 // lookup table 1192 auto TableLookupVariablesOrdered = 1193 sortByName(std::vector<GlobalVariable *>(TableLookupVariables.begin(), 1194 TableLookupVariables.end())); 1195 1196 GlobalVariable *LookupTable = buildLookupTable( 1197 M, TableLookupVariablesOrdered, OrderedKernels, KernelToReplacement); 1198 replaceUsesInInstructionsWithTableLookup(M, TableLookupVariablesOrdered, 1199 LookupTable); 1200 } 1201 1202 DenseMap<Function *, GlobalVariable *> KernelToCreatedDynamicLDS = 1203 lowerDynamicLDSVariables(M, LDSUsesInfo, 1204 KernelsThatIndirectlyAllocateDynamicLDS, 1205 DynamicVariables, OrderedKernels); 1206 1207 // All kernel frames have been allocated. Calculate and record the 1208 // addresses. 1209 1210 { 1211 const DataLayout &DL = M.getDataLayout(); 1212 1213 for (Function &Func : M.functions()) { 1214 if (Func.isDeclaration() || !isKernelLDS(&Func)) 1215 continue; 1216 1217 // All three of these are optional. The first variable is allocated at 1218 // zero. They are allocated by allocateKnownAddressLDSGlobal in the 1219 // following order: 1220 //{ 1221 // module.lds 1222 // alignment padding 1223 // kernel instance 1224 // alignment padding 1225 // dynamic lds variables 1226 //} 1227 1228 const bool AllocateModuleScopeStruct = 1229 MaybeModuleScopeStruct && !canElideModuleLDS(Func); 1230 1231 auto Replacement = KernelToReplacement.find(&Func); 1232 const bool AllocateKernelScopeStruct = 1233 Replacement != KernelToReplacement.end(); 1234 1235 const bool AllocateDynamicVariable = 1236 KernelToCreatedDynamicLDS.contains(&Func); 1237 1238 uint32_t Offset = 0; 1239 1240 if (AllocateModuleScopeStruct) { 1241 // Allocated at zero, recorded once on construction, not once per 1242 // kernel 1243 Offset += DL.getTypeAllocSize(MaybeModuleScopeStruct->getValueType()); 1244 } 1245 1246 if (AllocateKernelScopeStruct) { 1247 GlobalVariable *KernelStruct = Replacement->second.SGV; 1248 1249 Offset = alignTo(Offset, AMDGPU::getAlign(DL, KernelStruct)); 1250 1251 recordLDSAbsoluteAddress(&M, KernelStruct, Offset); 1252 1253 Offset += DL.getTypeAllocSize(KernelStruct->getValueType()); 1254 1255 } 1256 1257 if (AllocateDynamicVariable) { 1258 GlobalVariable *DynamicVariable = KernelToCreatedDynamicLDS[&Func]; 1259 1260 Offset = alignTo(Offset, AMDGPU::getAlign(DL, DynamicVariable)); 1261 1262 recordLDSAbsoluteAddress(&M, DynamicVariable, Offset); 1263 } 1264 } 1265 } 1266 1267 for (auto &GV : make_early_inc_range(M.globals())) 1268 if (AMDGPU::isLDSVariableToLower(GV)) { 1269 // probably want to remove from used lists 1270 GV.removeDeadConstantUsers(); 1271 if (GV.use_empty()) 1272 GV.eraseFromParent(); 1273 } 1274 1275 return Changed; 1276 } 1277 1278 private: 1279 // Increase the alignment of LDS globals if necessary to maximise the chance 1280 // that we can use aligned LDS instructions to access them. 1281 static bool superAlignLDSGlobals(Module &M) { 1282 const DataLayout &DL = M.getDataLayout(); 1283 bool Changed = false; 1284 if (!SuperAlignLDSGlobals) { 1285 return Changed; 1286 } 1287 1288 for (auto &GV : M.globals()) { 1289 if (GV.getType()->getPointerAddressSpace() != AMDGPUAS::LOCAL_ADDRESS) { 1290 // Only changing alignment of LDS variables 1291 continue; 1292 } 1293 if (!GV.hasInitializer()) { 1294 // cuda/hip extern __shared__ variable, leave alignment alone 1295 continue; 1296 } 1297 1298 Align Alignment = AMDGPU::getAlign(DL, &GV); 1299 TypeSize GVSize = DL.getTypeAllocSize(GV.getValueType()); 1300 1301 if (GVSize > 8) { 1302 // We might want to use a b96 or b128 load/store 1303 Alignment = std::max(Alignment, Align(16)); 1304 } else if (GVSize > 4) { 1305 // We might want to use a b64 load/store 1306 Alignment = std::max(Alignment, Align(8)); 1307 } else if (GVSize > 2) { 1308 // We might want to use a b32 load/store 1309 Alignment = std::max(Alignment, Align(4)); 1310 } else if (GVSize > 1) { 1311 // We might want to use a b16 load/store 1312 Alignment = std::max(Alignment, Align(2)); 1313 } 1314 1315 if (Alignment != AMDGPU::getAlign(DL, &GV)) { 1316 Changed = true; 1317 GV.setAlignment(Alignment); 1318 } 1319 } 1320 return Changed; 1321 } 1322 1323 static LDSVariableReplacement createLDSVariableReplacement( 1324 Module &M, std::string VarName, 1325 DenseSet<GlobalVariable *> const &LDSVarsToTransform) { 1326 // Create a struct instance containing LDSVarsToTransform and map from those 1327 // variables to ConstantExprGEP 1328 // Variables may be introduced to meet alignment requirements. No aliasing 1329 // metadata is useful for these as they have no uses. Erased before return. 1330 1331 LLVMContext &Ctx = M.getContext(); 1332 const DataLayout &DL = M.getDataLayout(); 1333 assert(!LDSVarsToTransform.empty()); 1334 1335 SmallVector<OptimizedStructLayoutField, 8> LayoutFields; 1336 LayoutFields.reserve(LDSVarsToTransform.size()); 1337 { 1338 // The order of fields in this struct depends on the order of 1339 // varables in the argument which varies when changing how they 1340 // are identified, leading to spurious test breakage. 1341 auto Sorted = sortByName(std::vector<GlobalVariable *>( 1342 LDSVarsToTransform.begin(), LDSVarsToTransform.end())); 1343 1344 for (GlobalVariable *GV : Sorted) { 1345 OptimizedStructLayoutField F(GV, 1346 DL.getTypeAllocSize(GV->getValueType()), 1347 AMDGPU::getAlign(DL, GV)); 1348 LayoutFields.emplace_back(F); 1349 } 1350 } 1351 1352 performOptimizedStructLayout(LayoutFields); 1353 1354 std::vector<GlobalVariable *> LocalVars; 1355 BitVector IsPaddingField; 1356 LocalVars.reserve(LDSVarsToTransform.size()); // will be at least this large 1357 IsPaddingField.reserve(LDSVarsToTransform.size()); 1358 { 1359 uint64_t CurrentOffset = 0; 1360 for (size_t I = 0; I < LayoutFields.size(); I++) { 1361 GlobalVariable *FGV = static_cast<GlobalVariable *>( 1362 const_cast<void *>(LayoutFields[I].Id)); 1363 Align DataAlign = LayoutFields[I].Alignment; 1364 1365 uint64_t DataAlignV = DataAlign.value(); 1366 if (uint64_t Rem = CurrentOffset % DataAlignV) { 1367 uint64_t Padding = DataAlignV - Rem; 1368 1369 // Append an array of padding bytes to meet alignment requested 1370 // Note (o + (a - (o % a)) ) % a == 0 1371 // (offset + Padding ) % align == 0 1372 1373 Type *ATy = ArrayType::get(Type::getInt8Ty(Ctx), Padding); 1374 LocalVars.push_back(new GlobalVariable( 1375 M, ATy, false, GlobalValue::InternalLinkage, UndefValue::get(ATy), 1376 "", nullptr, GlobalValue::NotThreadLocal, AMDGPUAS::LOCAL_ADDRESS, 1377 false)); 1378 IsPaddingField.push_back(true); 1379 CurrentOffset += Padding; 1380 } 1381 1382 LocalVars.push_back(FGV); 1383 IsPaddingField.push_back(false); 1384 CurrentOffset += LayoutFields[I].Size; 1385 } 1386 } 1387 1388 std::vector<Type *> LocalVarTypes; 1389 LocalVarTypes.reserve(LocalVars.size()); 1390 std::transform( 1391 LocalVars.cbegin(), LocalVars.cend(), std::back_inserter(LocalVarTypes), 1392 [](const GlobalVariable *V) -> Type * { return V->getValueType(); }); 1393 1394 StructType *LDSTy = StructType::create(Ctx, LocalVarTypes, VarName + ".t"); 1395 1396 Align StructAlign = AMDGPU::getAlign(DL, LocalVars[0]); 1397 1398 GlobalVariable *SGV = new GlobalVariable( 1399 M, LDSTy, false, GlobalValue::InternalLinkage, UndefValue::get(LDSTy), 1400 VarName, nullptr, GlobalValue::NotThreadLocal, AMDGPUAS::LOCAL_ADDRESS, 1401 false); 1402 SGV->setAlignment(StructAlign); 1403 1404 DenseMap<GlobalVariable *, Constant *> Map; 1405 Type *I32 = Type::getInt32Ty(Ctx); 1406 for (size_t I = 0; I < LocalVars.size(); I++) { 1407 GlobalVariable *GV = LocalVars[I]; 1408 Constant *GEPIdx[] = {ConstantInt::get(I32, 0), ConstantInt::get(I32, I)}; 1409 Constant *GEP = ConstantExpr::getGetElementPtr(LDSTy, SGV, GEPIdx, true); 1410 if (IsPaddingField[I]) { 1411 assert(GV->use_empty()); 1412 GV->eraseFromParent(); 1413 } else { 1414 Map[GV] = GEP; 1415 } 1416 } 1417 assert(Map.size() == LDSVarsToTransform.size()); 1418 return {SGV, std::move(Map)}; 1419 } 1420 1421 template <typename PredicateTy> 1422 static void replaceLDSVariablesWithStruct( 1423 Module &M, DenseSet<GlobalVariable *> const &LDSVarsToTransformArg, 1424 const LDSVariableReplacement &Replacement, PredicateTy Predicate) { 1425 LLVMContext &Ctx = M.getContext(); 1426 const DataLayout &DL = M.getDataLayout(); 1427 1428 // A hack... we need to insert the aliasing info in a predictable order for 1429 // lit tests. Would like to have them in a stable order already, ideally the 1430 // same order they get allocated, which might mean an ordered set container 1431 auto LDSVarsToTransform = sortByName(std::vector<GlobalVariable *>( 1432 LDSVarsToTransformArg.begin(), LDSVarsToTransformArg.end())); 1433 1434 // Create alias.scope and their lists. Each field in the new structure 1435 // does not alias with all other fields. 1436 SmallVector<MDNode *> AliasScopes; 1437 SmallVector<Metadata *> NoAliasList; 1438 const size_t NumberVars = LDSVarsToTransform.size(); 1439 if (NumberVars > 1) { 1440 MDBuilder MDB(Ctx); 1441 AliasScopes.reserve(NumberVars); 1442 MDNode *Domain = MDB.createAnonymousAliasScopeDomain(); 1443 for (size_t I = 0; I < NumberVars; I++) { 1444 MDNode *Scope = MDB.createAnonymousAliasScope(Domain); 1445 AliasScopes.push_back(Scope); 1446 } 1447 NoAliasList.append(&AliasScopes[1], AliasScopes.end()); 1448 } 1449 1450 // Replace uses of ith variable with a constantexpr to the corresponding 1451 // field of the instance that will be allocated by AMDGPUMachineFunction 1452 for (size_t I = 0; I < NumberVars; I++) { 1453 GlobalVariable *GV = LDSVarsToTransform[I]; 1454 Constant *GEP = Replacement.LDSVarsToConstantGEP.at(GV); 1455 1456 GV->replaceUsesWithIf(GEP, Predicate); 1457 1458 APInt APOff(DL.getIndexTypeSizeInBits(GEP->getType()), 0); 1459 GEP->stripAndAccumulateInBoundsConstantOffsets(DL, APOff); 1460 uint64_t Offset = APOff.getZExtValue(); 1461 1462 Align A = 1463 commonAlignment(Replacement.SGV->getAlign().valueOrOne(), Offset); 1464 1465 if (I) 1466 NoAliasList[I - 1] = AliasScopes[I - 1]; 1467 MDNode *NoAlias = 1468 NoAliasList.empty() ? nullptr : MDNode::get(Ctx, NoAliasList); 1469 MDNode *AliasScope = 1470 AliasScopes.empty() ? nullptr : MDNode::get(Ctx, {AliasScopes[I]}); 1471 1472 refineUsesAlignmentAndAA(GEP, A, DL, AliasScope, NoAlias); 1473 } 1474 } 1475 1476 static void refineUsesAlignmentAndAA(Value *Ptr, Align A, 1477 const DataLayout &DL, MDNode *AliasScope, 1478 MDNode *NoAlias, unsigned MaxDepth = 5) { 1479 if (!MaxDepth || (A == 1 && !AliasScope)) 1480 return; 1481 1482 for (User *U : Ptr->users()) { 1483 if (auto *I = dyn_cast<Instruction>(U)) { 1484 if (AliasScope && I->mayReadOrWriteMemory()) { 1485 MDNode *AS = I->getMetadata(LLVMContext::MD_alias_scope); 1486 AS = (AS ? MDNode::getMostGenericAliasScope(AS, AliasScope) 1487 : AliasScope); 1488 I->setMetadata(LLVMContext::MD_alias_scope, AS); 1489 1490 MDNode *NA = I->getMetadata(LLVMContext::MD_noalias); 1491 NA = (NA ? MDNode::intersect(NA, NoAlias) : NoAlias); 1492 I->setMetadata(LLVMContext::MD_noalias, NA); 1493 } 1494 } 1495 1496 if (auto *LI = dyn_cast<LoadInst>(U)) { 1497 LI->setAlignment(std::max(A, LI->getAlign())); 1498 continue; 1499 } 1500 if (auto *SI = dyn_cast<StoreInst>(U)) { 1501 if (SI->getPointerOperand() == Ptr) 1502 SI->setAlignment(std::max(A, SI->getAlign())); 1503 continue; 1504 } 1505 if (auto *AI = dyn_cast<AtomicRMWInst>(U)) { 1506 // None of atomicrmw operations can work on pointers, but let's 1507 // check it anyway in case it will or we will process ConstantExpr. 1508 if (AI->getPointerOperand() == Ptr) 1509 AI->setAlignment(std::max(A, AI->getAlign())); 1510 continue; 1511 } 1512 if (auto *AI = dyn_cast<AtomicCmpXchgInst>(U)) { 1513 if (AI->getPointerOperand() == Ptr) 1514 AI->setAlignment(std::max(A, AI->getAlign())); 1515 continue; 1516 } 1517 if (auto *GEP = dyn_cast<GetElementPtrInst>(U)) { 1518 unsigned BitWidth = DL.getIndexTypeSizeInBits(GEP->getType()); 1519 APInt Off(BitWidth, 0); 1520 if (GEP->getPointerOperand() == Ptr) { 1521 Align GA; 1522 if (GEP->accumulateConstantOffset(DL, Off)) 1523 GA = commonAlignment(A, Off.getLimitedValue()); 1524 refineUsesAlignmentAndAA(GEP, GA, DL, AliasScope, NoAlias, 1525 MaxDepth - 1); 1526 } 1527 continue; 1528 } 1529 if (auto *I = dyn_cast<Instruction>(U)) { 1530 if (I->getOpcode() == Instruction::BitCast || 1531 I->getOpcode() == Instruction::AddrSpaceCast) 1532 refineUsesAlignmentAndAA(I, A, DL, AliasScope, NoAlias, MaxDepth - 1); 1533 } 1534 } 1535 } 1536 }; 1537 1538 } // namespace 1539 char AMDGPULowerModuleLDS::ID = 0; 1540 1541 char &llvm::AMDGPULowerModuleLDSID = AMDGPULowerModuleLDS::ID; 1542 1543 INITIALIZE_PASS(AMDGPULowerModuleLDS, DEBUG_TYPE, 1544 "Lower uses of LDS variables from non-kernel functions", false, 1545 false) 1546 1547 ModulePass *llvm::createAMDGPULowerModuleLDSPass() { 1548 return new AMDGPULowerModuleLDS(); 1549 } 1550 1551 PreservedAnalyses AMDGPULowerModuleLDSPass::run(Module &M, 1552 ModuleAnalysisManager &) { 1553 return AMDGPULowerModuleLDS().runOnModule(M) ? PreservedAnalyses::none() 1554 : PreservedAnalyses::all(); 1555 } 1556