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 // 77 // The "table" lowering implemented here has three components. 78 // First kernels are assigned a unique integer identifier which is available in 79 // functions it calls through the intrinsic amdgcn_lds_kernel_id. The integer 80 // is passed through a specific SGPR, thus works with indirect calls. 81 // Second, each kernel allocates LDS variables independent of other kernels and 82 // writes the addresses it chose for each variable into an array in consistent 83 // order. If the kernel does not allocate a given variable, it writes undef to 84 // the corresponding array location. These arrays are written to a constant 85 // table in the order matching the kernel unique integer identifier. 86 // Third, uses from non-kernel functions are replaced with a table lookup using 87 // the intrinsic function to find the address of the variable. 88 // 89 // "Kernel" lowering is only applicable for variables that are unambiguously 90 // reachable from exactly one kernel. For those cases, accesses to the variable 91 // can be lowered to ConstantExpr address of a struct instance specific to that 92 // one kernel. This is zero cost in space and in compute. It will raise a fatal 93 // error on any variable that might be reachable from multiple kernels and is 94 // thus most easily used as part of the hybrid lowering strategy. 95 // 96 // Hybrid lowering is a mixture of the above. It uses the zero cost kernel 97 // lowering where it can. It lowers the variable accessed by the greatest 98 // number of kernels using the module strategy as that is free for the first 99 // variable. Any futher variables that can be lowered with the module strategy 100 // without incurring LDS memory overhead are. The remaining ones are lowered 101 // via table. 102 // 103 // Consequences 104 // - No heuristics or user controlled magic numbers, hybrid is the right choice 105 // - Kernels that don't use functions (or have had them all inlined) are not 106 // affected by any lowering for kernels that do. 107 // - Kernels that don't make indirect function calls are not affected by those 108 // that do. 109 // - Variables which are used by lots of kernels, e.g. those injected by a 110 // language runtime in most kernels, are expected to have no overhead 111 // - Implementations that instantiate templates per-kernel where those templates 112 // use LDS are expected to hit the "Kernel" lowering strategy 113 // - The runtime properties impose a cost in compiler implementation complexity 114 // 115 // Dynamic LDS implementation 116 // Dynamic LDS is lowered similarly to the "table" strategy above and uses the 117 // same intrinsic to identify which kernel is at the root of the dynamic call 118 // graph. This relies on the specified behaviour that all dynamic LDS variables 119 // alias one another, i.e. are at the same address, with respect to a given 120 // kernel. Therefore this pass creates new dynamic LDS variables for each kernel 121 // that allocates any dynamic LDS and builds a table of addresses out of those. 122 // The AMDGPUPromoteAlloca pass skips kernels that use dynamic LDS. 123 // The corresponding optimisation for "kernel" lowering where the table lookup 124 // is elided is not implemented. 125 // 126 // 127 // Implementation notes / limitations 128 // A single LDS global variable represents an instance per kernel that can reach 129 // said variables. This pass essentially specialises said variables per kernel. 130 // Handling ConstantExpr during the pass complicated this significantly so now 131 // all ConstantExpr uses of LDS variables are expanded to instructions. This 132 // may need amending when implementing non-undef initialisers. 133 // 134 // Lowering is split between this IR pass and the back end. This pass chooses 135 // where given variables should be allocated and marks them with metadata, 136 // MD_absolute_symbol. The backend places the variables in coincidentally the 137 // same location and raises a fatal error if something has gone awry. This works 138 // in practice because the only pass between this one and the backend that 139 // changes LDS is PromoteAlloca and the changes it makes do not conflict. 140 // 141 // Addresses are written to constant global arrays based on the same metadata. 142 // 143 // The backend lowers LDS variables in the order of traversal of the function. 144 // This is at odds with the deterministic layout required. The workaround is to 145 // allocate the fixed-address variables immediately upon starting the function 146 // where they can be placed as intended. This requires a means of mapping from 147 // the function to the variables that it allocates. For the module scope lds, 148 // this is via metadata indicating whether the variable is not required. If a 149 // pass deletes that metadata, a fatal error on disagreement with the absolute 150 // symbol metadata will occur. For kernel scope and dynamic, this is by _name_ 151 // correspondence between the function and the variable. It requires the 152 // kernel to have a name (which is only a limitation for tests in practice) and 153 // for nothing to rename the corresponding symbols. This is a hazard if the pass 154 // is run multiple times during debugging. Alternative schemes considered all 155 // involve bespoke metadata. 156 // 157 // If the name correspondence can be replaced, multiple distinct kernels that 158 // have the same memory layout can map to the same kernel id (as the address 159 // itself is handled by the absolute symbol metadata) and that will allow more 160 // uses of the "kernel" style faster lowering and reduce the size of the lookup 161 // tables. 162 // 163 // There is a test that checks this does not fire for a graphics shader. This 164 // lowering is expected to work for graphics if the isKernel test is changed. 165 // 166 // The current markUsedByKernel is sufficient for PromoteAlloca but is elided 167 // before codegen. Replacing this with an equivalent intrinsic which lasts until 168 // shortly after the machine function lowering of LDS would help break the name 169 // mapping. The other part needed is probably to amend PromoteAlloca to embed 170 // the LDS variables it creates in the same struct created here. That avoids the 171 // current hazard where a PromoteAlloca LDS variable might be allocated before 172 // the kernel scope (and thus error on the address check). Given a new invariant 173 // that no LDS variables exist outside of the structs managed here, and an 174 // intrinsic that lasts until after the LDS frame lowering, it should be 175 // possible to drop the name mapping and fold equivalent memory layouts. 176 // 177 //===----------------------------------------------------------------------===// 178 179 #include "AMDGPU.h" 180 #include "AMDGPUTargetMachine.h" 181 #include "Utils/AMDGPUBaseInfo.h" 182 #include "Utils/AMDGPUMemoryUtils.h" 183 #include "llvm/ADT/BitVector.h" 184 #include "llvm/ADT/DenseMap.h" 185 #include "llvm/ADT/DenseSet.h" 186 #include "llvm/ADT/STLExtras.h" 187 #include "llvm/ADT/SetOperations.h" 188 #include "llvm/Analysis/CallGraph.h" 189 #include "llvm/CodeGen/TargetPassConfig.h" 190 #include "llvm/IR/Constants.h" 191 #include "llvm/IR/DerivedTypes.h" 192 #include "llvm/IR/IRBuilder.h" 193 #include "llvm/IR/InlineAsm.h" 194 #include "llvm/IR/Instructions.h" 195 #include "llvm/IR/IntrinsicsAMDGPU.h" 196 #include "llvm/IR/MDBuilder.h" 197 #include "llvm/IR/ReplaceConstant.h" 198 #include "llvm/InitializePasses.h" 199 #include "llvm/Pass.h" 200 #include "llvm/Support/CommandLine.h" 201 #include "llvm/Support/Debug.h" 202 #include "llvm/Support/Format.h" 203 #include "llvm/Support/OptimizedStructLayout.h" 204 #include "llvm/Support/raw_ostream.h" 205 #include "llvm/Transforms/Utils/BasicBlockUtils.h" 206 #include "llvm/Transforms/Utils/ModuleUtils.h" 207 208 #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 { 256 const AMDGPUTargetMachine &TM; 257 258 static void 259 removeLocalVarsFromUsedLists(Module &M, 260 const DenseSet<GlobalVariable *> &LocalVars) { 261 // The verifier rejects used lists containing an inttoptr of a constant 262 // so remove the variables from these lists before replaceAllUsesWith 263 SmallPtrSet<Constant *, 8> LocalVarsSet; 264 for (GlobalVariable *LocalVar : LocalVars) 265 LocalVarsSet.insert(cast<Constant>(LocalVar->stripPointerCasts())); 266 267 removeFromUsedLists( 268 M, [&LocalVarsSet](Constant *C) { return LocalVarsSet.count(C); }); 269 270 for (GlobalVariable *LocalVar : LocalVars) 271 LocalVar->removeDeadConstantUsers(); 272 } 273 274 static void markUsedByKernel(Function *Func, 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 BasicBlock *Entry = &Func->getEntryBlock(); 296 IRBuilder<> Builder(Entry, Entry->getFirstNonPHIIt()); 297 298 Function *Decl = 299 Intrinsic::getDeclaration(Func->getParent(), Intrinsic::donothing, {}); 300 301 Value *UseInstance[1] = { 302 Builder.CreateConstInBoundsGEP1_32(SGV->getValueType(), SGV, 0)}; 303 304 Builder.CreateCall( 305 Decl, {}, {OperandBundleDefT<Value *>("ExplicitUse", UseInstance)}); 306 } 307 308 static bool eliminateConstantExprUsesOfLDSFromAllInstructions(Module &M) { 309 // Constants are uniqued within LLVM. A ConstantExpr referring to a LDS 310 // global may have uses from multiple different functions as a result. 311 // This pass specialises LDS variables with respect to the kernel that 312 // allocates them. 313 314 // This is semantically equivalent to (the unimplemented as slow): 315 // for (auto &F : M.functions()) 316 // for (auto &BB : F) 317 // for (auto &I : BB) 318 // for (Use &Op : I.operands()) 319 // if (constantExprUsesLDS(Op)) 320 // replaceConstantExprInFunction(I, Op); 321 322 SmallVector<Constant *> LDSGlobals; 323 for (auto &GV : M.globals()) 324 if (AMDGPU::isLDSVariableToLower(GV)) 325 LDSGlobals.push_back(&GV); 326 327 return convertUsersOfConstantsToInstructions(LDSGlobals); 328 } 329 330 public: 331 AMDGPULowerModuleLDS(const AMDGPUTargetMachine &TM_) : TM(TM_) {} 332 333 using FunctionVariableMap = DenseMap<Function *, DenseSet<GlobalVariable *>>; 334 335 using VariableFunctionMap = DenseMap<GlobalVariable *, DenseSet<Function *>>; 336 337 static void getUsesOfLDSByFunction(CallGraph const &CG, Module &M, 338 FunctionVariableMap &kernels, 339 FunctionVariableMap &functions) { 340 341 // Get uses from the current function, excluding uses by called functions 342 // Two output variables to avoid walking the globals list twice 343 std::optional<bool> HasAbsoluteGVs; 344 for (auto &GV : M.globals()) { 345 if (!AMDGPU::isLDSVariableToLower(GV)) { 346 continue; 347 } 348 349 // Check if the module is consistent: either all GVs are absolute (happens 350 // when we run the pass more than once), or none are. 351 const bool IsAbsolute = GV.isAbsoluteSymbolRef(); 352 if (HasAbsoluteGVs.has_value()) { 353 if (*HasAbsoluteGVs != IsAbsolute) { 354 report_fatal_error( 355 "Module cannot mix absolute and non-absolute LDS GVs"); 356 } 357 } else 358 HasAbsoluteGVs = IsAbsolute; 359 360 if (IsAbsolute) 361 continue; 362 363 for (User *V : GV.users()) { 364 if (auto *I = dyn_cast<Instruction>(V)) { 365 Function *F = I->getFunction(); 366 if (isKernelLDS(F)) { 367 kernels[F].insert(&GV); 368 } else { 369 functions[F].insert(&GV); 370 } 371 } 372 } 373 } 374 } 375 376 struct LDSUsesInfoTy { 377 FunctionVariableMap direct_access; 378 FunctionVariableMap indirect_access; 379 }; 380 381 static LDSUsesInfoTy getTransitiveUsesOfLDS(CallGraph const &CG, Module &M) { 382 383 FunctionVariableMap direct_map_kernel; 384 FunctionVariableMap direct_map_function; 385 getUsesOfLDSByFunction(CG, M, direct_map_kernel, direct_map_function); 386 387 // Collect variables that are used by functions whose address has escaped 388 DenseSet<GlobalVariable *> VariablesReachableThroughFunctionPointer; 389 for (Function &F : M.functions()) { 390 if (!isKernelLDS(&F)) 391 if (F.hasAddressTaken(nullptr, 392 /* IgnoreCallbackUses */ false, 393 /* IgnoreAssumeLikeCalls */ false, 394 /* IgnoreLLVMUsed */ true, 395 /* IgnoreArcAttachedCall */ false)) { 396 set_union(VariablesReachableThroughFunctionPointer, 397 direct_map_function[&F]); 398 } 399 } 400 401 auto functionMakesUnknownCall = [&](const Function *F) -> bool { 402 assert(!F->isDeclaration()); 403 for (const CallGraphNode::CallRecord &R : *CG[F]) { 404 if (!R.second->getFunction()) { 405 return true; 406 } 407 } 408 return false; 409 }; 410 411 // Work out which variables are reachable through function calls 412 FunctionVariableMap transitive_map_function = direct_map_function; 413 414 // If the function makes any unknown call, assume the worst case that it can 415 // access all variables accessed by functions whose address escaped 416 for (Function &F : M.functions()) { 417 if (!F.isDeclaration() && functionMakesUnknownCall(&F)) { 418 if (!isKernelLDS(&F)) { 419 set_union(transitive_map_function[&F], 420 VariablesReachableThroughFunctionPointer); 421 } 422 } 423 } 424 425 // Direct implementation of collecting all variables reachable from each 426 // function 427 for (Function &Func : M.functions()) { 428 if (Func.isDeclaration() || isKernelLDS(&Func)) 429 continue; 430 431 DenseSet<Function *> seen; // catches cycles 432 SmallVector<Function *, 4> wip{&Func}; 433 434 while (!wip.empty()) { 435 Function *F = wip.pop_back_val(); 436 437 // Can accelerate this by referring to transitive map for functions that 438 // have already been computed, with more care than this 439 set_union(transitive_map_function[&Func], direct_map_function[F]); 440 441 for (const CallGraphNode::CallRecord &R : *CG[F]) { 442 Function *ith = R.second->getFunction(); 443 if (ith) { 444 if (!seen.contains(ith)) { 445 seen.insert(ith); 446 wip.push_back(ith); 447 } 448 } 449 } 450 } 451 } 452 453 // direct_map_kernel lists which variables are used by the kernel 454 // find the variables which are used through a function call 455 FunctionVariableMap indirect_map_kernel; 456 457 for (Function &Func : M.functions()) { 458 if (Func.isDeclaration() || !isKernelLDS(&Func)) 459 continue; 460 461 for (const CallGraphNode::CallRecord &R : *CG[&Func]) { 462 Function *ith = R.second->getFunction(); 463 if (ith) { 464 set_union(indirect_map_kernel[&Func], transitive_map_function[ith]); 465 } else { 466 set_union(indirect_map_kernel[&Func], 467 VariablesReachableThroughFunctionPointer); 468 } 469 } 470 } 471 472 return {std::move(direct_map_kernel), std::move(indirect_map_kernel)}; 473 } 474 475 struct LDSVariableReplacement { 476 GlobalVariable *SGV = nullptr; 477 DenseMap<GlobalVariable *, Constant *> LDSVarsToConstantGEP; 478 }; 479 480 // remap from lds global to a constantexpr gep to where it has been moved to 481 // for each kernel 482 // an array with an element for each kernel containing where the corresponding 483 // variable was remapped to 484 485 static Constant *getAddressesOfVariablesInKernel( 486 LLVMContext &Ctx, ArrayRef<GlobalVariable *> Variables, 487 const DenseMap<GlobalVariable *, Constant *> &LDSVarsToConstantGEP) { 488 // Create a ConstantArray containing the address of each Variable within the 489 // kernel corresponding to LDSVarsToConstantGEP, or poison if that kernel 490 // does not allocate it 491 // TODO: Drop the ptrtoint conversion 492 493 Type *I32 = Type::getInt32Ty(Ctx); 494 495 ArrayType *KernelOffsetsType = ArrayType::get(I32, Variables.size()); 496 497 SmallVector<Constant *> Elements; 498 for (size_t i = 0; i < Variables.size(); i++) { 499 GlobalVariable *GV = Variables[i]; 500 auto ConstantGepIt = LDSVarsToConstantGEP.find(GV); 501 if (ConstantGepIt != LDSVarsToConstantGEP.end()) { 502 auto elt = ConstantExpr::getPtrToInt(ConstantGepIt->second, I32); 503 Elements.push_back(elt); 504 } else { 505 Elements.push_back(PoisonValue::get(I32)); 506 } 507 } 508 return ConstantArray::get(KernelOffsetsType, Elements); 509 } 510 511 static GlobalVariable *buildLookupTable( 512 Module &M, ArrayRef<GlobalVariable *> Variables, 513 ArrayRef<Function *> kernels, 514 DenseMap<Function *, LDSVariableReplacement> &KernelToReplacement) { 515 if (Variables.empty()) { 516 return nullptr; 517 } 518 LLVMContext &Ctx = M.getContext(); 519 520 const size_t NumberVariables = Variables.size(); 521 const size_t NumberKernels = kernels.size(); 522 523 ArrayType *KernelOffsetsType = 524 ArrayType::get(Type::getInt32Ty(Ctx), NumberVariables); 525 526 ArrayType *AllKernelsOffsetsType = 527 ArrayType::get(KernelOffsetsType, NumberKernels); 528 529 Constant *Missing = PoisonValue::get(KernelOffsetsType); 530 std::vector<Constant *> overallConstantExprElts(NumberKernels); 531 for (size_t i = 0; i < NumberKernels; i++) { 532 auto Replacement = KernelToReplacement.find(kernels[i]); 533 overallConstantExprElts[i] = 534 (Replacement == KernelToReplacement.end()) 535 ? Missing 536 : getAddressesOfVariablesInKernel( 537 Ctx, Variables, Replacement->second.LDSVarsToConstantGEP); 538 } 539 540 Constant *init = 541 ConstantArray::get(AllKernelsOffsetsType, overallConstantExprElts); 542 543 return new GlobalVariable( 544 M, AllKernelsOffsetsType, true, GlobalValue::InternalLinkage, init, 545 "llvm.amdgcn.lds.offset.table", nullptr, GlobalValue::NotThreadLocal, 546 AMDGPUAS::CONSTANT_ADDRESS); 547 } 548 549 void replaceUseWithTableLookup(Module &M, IRBuilder<> &Builder, 550 GlobalVariable *LookupTable, 551 GlobalVariable *GV, Use &U, 552 Value *OptionalIndex) { 553 // Table is a constant array of the same length as OrderedKernels 554 LLVMContext &Ctx = M.getContext(); 555 Type *I32 = Type::getInt32Ty(Ctx); 556 auto *I = cast<Instruction>(U.getUser()); 557 558 Value *tableKernelIndex = getTableLookupKernelIndex(M, I->getFunction()); 559 560 if (auto *Phi = dyn_cast<PHINode>(I)) { 561 BasicBlock *BB = Phi->getIncomingBlock(U); 562 Builder.SetInsertPoint(&(*(BB->getFirstInsertionPt()))); 563 } else { 564 Builder.SetInsertPoint(I); 565 } 566 567 SmallVector<Value *, 3> GEPIdx = { 568 ConstantInt::get(I32, 0), 569 tableKernelIndex, 570 }; 571 if (OptionalIndex) 572 GEPIdx.push_back(OptionalIndex); 573 574 Value *Address = Builder.CreateInBoundsGEP( 575 LookupTable->getValueType(), LookupTable, GEPIdx, GV->getName()); 576 577 Value *loaded = Builder.CreateLoad(I32, Address); 578 579 Value *replacement = 580 Builder.CreateIntToPtr(loaded, GV->getType(), GV->getName()); 581 582 U.set(replacement); 583 } 584 585 void replaceUsesInInstructionsWithTableLookup( 586 Module &M, ArrayRef<GlobalVariable *> ModuleScopeVariables, 587 GlobalVariable *LookupTable) { 588 589 LLVMContext &Ctx = M.getContext(); 590 IRBuilder<> Builder(Ctx); 591 Type *I32 = Type::getInt32Ty(Ctx); 592 593 for (size_t Index = 0; Index < ModuleScopeVariables.size(); Index++) { 594 auto *GV = ModuleScopeVariables[Index]; 595 596 for (Use &U : make_early_inc_range(GV->uses())) { 597 auto *I = dyn_cast<Instruction>(U.getUser()); 598 if (!I) 599 continue; 600 601 replaceUseWithTableLookup(M, Builder, LookupTable, GV, U, 602 ConstantInt::get(I32, Index)); 603 } 604 } 605 } 606 607 static DenseSet<Function *> kernelsThatIndirectlyAccessAnyOfPassedVariables( 608 Module &M, LDSUsesInfoTy &LDSUsesInfo, 609 DenseSet<GlobalVariable *> const &VariableSet) { 610 611 DenseSet<Function *> KernelSet; 612 613 if (VariableSet.empty()) 614 return KernelSet; 615 616 for (Function &Func : M.functions()) { 617 if (Func.isDeclaration() || !isKernelLDS(&Func)) 618 continue; 619 for (GlobalVariable *GV : LDSUsesInfo.indirect_access[&Func]) { 620 if (VariableSet.contains(GV)) { 621 KernelSet.insert(&Func); 622 break; 623 } 624 } 625 } 626 627 return KernelSet; 628 } 629 630 static GlobalVariable * 631 chooseBestVariableForModuleStrategy(const DataLayout &DL, 632 VariableFunctionMap &LDSVars) { 633 // Find the global variable with the most indirect uses from kernels 634 635 struct CandidateTy { 636 GlobalVariable *GV = nullptr; 637 size_t UserCount = 0; 638 size_t Size = 0; 639 640 CandidateTy() = default; 641 642 CandidateTy(GlobalVariable *GV, uint64_t UserCount, uint64_t AllocSize) 643 : GV(GV), UserCount(UserCount), Size(AllocSize) {} 644 645 bool operator<(const CandidateTy &Other) const { 646 // Fewer users makes module scope variable less attractive 647 if (UserCount < Other.UserCount) { 648 return true; 649 } 650 if (UserCount > Other.UserCount) { 651 return false; 652 } 653 654 // Bigger makes module scope variable less attractive 655 if (Size < Other.Size) { 656 return false; 657 } 658 659 if (Size > Other.Size) { 660 return true; 661 } 662 663 // Arbitrary but consistent 664 return GV->getName() < Other.GV->getName(); 665 } 666 }; 667 668 CandidateTy MostUsed; 669 670 for (auto &K : LDSVars) { 671 GlobalVariable *GV = K.first; 672 if (K.second.size() <= 1) { 673 // A variable reachable by only one kernel is best lowered with kernel 674 // strategy 675 continue; 676 } 677 CandidateTy Candidate( 678 GV, K.second.size(), 679 DL.getTypeAllocSize(GV->getValueType()).getFixedValue()); 680 if (MostUsed < Candidate) 681 MostUsed = Candidate; 682 } 683 684 return MostUsed.GV; 685 } 686 687 static void recordLDSAbsoluteAddress(Module *M, GlobalVariable *GV, 688 uint32_t Address) { 689 // Write the specified address into metadata where it can be retrieved by 690 // the assembler. Format is a half open range, [Address Address+1) 691 LLVMContext &Ctx = M->getContext(); 692 auto *IntTy = 693 M->getDataLayout().getIntPtrType(Ctx, AMDGPUAS::LOCAL_ADDRESS); 694 auto *MinC = ConstantAsMetadata::get(ConstantInt::get(IntTy, Address)); 695 auto *MaxC = ConstantAsMetadata::get(ConstantInt::get(IntTy, Address + 1)); 696 GV->setMetadata(LLVMContext::MD_absolute_symbol, 697 MDNode::get(Ctx, {MinC, MaxC})); 698 } 699 700 DenseMap<Function *, Value *> tableKernelIndexCache; 701 Value *getTableLookupKernelIndex(Module &M, Function *F) { 702 // Accesses from a function use the amdgcn_lds_kernel_id intrinsic which 703 // lowers to a read from a live in register. Emit it once in the entry 704 // block to spare deduplicating it later. 705 auto [It, Inserted] = tableKernelIndexCache.try_emplace(F); 706 if (Inserted) { 707 Function *Decl = 708 Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_lds_kernel_id, {}); 709 710 auto InsertAt = F->getEntryBlock().getFirstNonPHIOrDbgOrAlloca(); 711 IRBuilder<> Builder(&*InsertAt); 712 713 It->second = Builder.CreateCall(Decl, {}); 714 } 715 716 return It->second; 717 } 718 719 static std::vector<Function *> assignLDSKernelIDToEachKernel( 720 Module *M, DenseSet<Function *> const &KernelsThatAllocateTableLDS, 721 DenseSet<Function *> const &KernelsThatIndirectlyAllocateDynamicLDS) { 722 // Associate kernels in the set with an arbirary but reproducible order and 723 // annotate them with that order in metadata. This metadata is recognised by 724 // the backend and lowered to a SGPR which can be read from using 725 // amdgcn_lds_kernel_id. 726 727 std::vector<Function *> OrderedKernels; 728 if (!KernelsThatAllocateTableLDS.empty() || 729 !KernelsThatIndirectlyAllocateDynamicLDS.empty()) { 730 731 for (Function &Func : M->functions()) { 732 if (Func.isDeclaration()) 733 continue; 734 if (!isKernelLDS(&Func)) 735 continue; 736 737 if (KernelsThatAllocateTableLDS.contains(&Func) || 738 KernelsThatIndirectlyAllocateDynamicLDS.contains(&Func)) { 739 assert(Func.hasName()); // else fatal error earlier 740 OrderedKernels.push_back(&Func); 741 } 742 } 743 744 // Put them in an arbitrary but reproducible order 745 OrderedKernels = sortByName(std::move(OrderedKernels)); 746 747 // Annotate the kernels with their order in this vector 748 LLVMContext &Ctx = M->getContext(); 749 IRBuilder<> Builder(Ctx); 750 751 if (OrderedKernels.size() > UINT32_MAX) { 752 // 32 bit keeps it in one SGPR. > 2**32 kernels won't fit on the GPU 753 report_fatal_error("Unimplemented LDS lowering for > 2**32 kernels"); 754 } 755 756 for (size_t i = 0; i < OrderedKernels.size(); i++) { 757 Metadata *AttrMDArgs[1] = { 758 ConstantAsMetadata::get(Builder.getInt32(i)), 759 }; 760 OrderedKernels[i]->setMetadata("llvm.amdgcn.lds.kernel.id", 761 MDNode::get(Ctx, AttrMDArgs)); 762 } 763 } 764 return OrderedKernels; 765 } 766 767 static void partitionVariablesIntoIndirectStrategies( 768 Module &M, LDSUsesInfoTy const &LDSUsesInfo, 769 VariableFunctionMap &LDSToKernelsThatNeedToAccessItIndirectly, 770 DenseSet<GlobalVariable *> &ModuleScopeVariables, 771 DenseSet<GlobalVariable *> &TableLookupVariables, 772 DenseSet<GlobalVariable *> &KernelAccessVariables, 773 DenseSet<GlobalVariable *> &DynamicVariables) { 774 775 GlobalVariable *HybridModuleRoot = 776 LoweringKindLoc != LoweringKind::hybrid 777 ? nullptr 778 : chooseBestVariableForModuleStrategy( 779 M.getDataLayout(), LDSToKernelsThatNeedToAccessItIndirectly); 780 781 DenseSet<Function *> const EmptySet; 782 DenseSet<Function *> const &HybridModuleRootKernels = 783 HybridModuleRoot 784 ? LDSToKernelsThatNeedToAccessItIndirectly[HybridModuleRoot] 785 : EmptySet; 786 787 for (auto &K : LDSToKernelsThatNeedToAccessItIndirectly) { 788 // Each iteration of this loop assigns exactly one global variable to 789 // exactly one of the implementation strategies. 790 791 GlobalVariable *GV = K.first; 792 assert(AMDGPU::isLDSVariableToLower(*GV)); 793 assert(K.second.size() != 0); 794 795 if (AMDGPU::isDynamicLDS(*GV)) { 796 DynamicVariables.insert(GV); 797 continue; 798 } 799 800 switch (LoweringKindLoc) { 801 case LoweringKind::module: 802 ModuleScopeVariables.insert(GV); 803 break; 804 805 case LoweringKind::table: 806 TableLookupVariables.insert(GV); 807 break; 808 809 case LoweringKind::kernel: 810 if (K.second.size() == 1) { 811 KernelAccessVariables.insert(GV); 812 } else { 813 report_fatal_error( 814 "cannot lower LDS '" + GV->getName() + 815 "' to kernel access as it is reachable from multiple kernels"); 816 } 817 break; 818 819 case LoweringKind::hybrid: { 820 if (GV == HybridModuleRoot) { 821 assert(K.second.size() != 1); 822 ModuleScopeVariables.insert(GV); 823 } else if (K.second.size() == 1) { 824 KernelAccessVariables.insert(GV); 825 } else if (set_is_subset(K.second, HybridModuleRootKernels)) { 826 ModuleScopeVariables.insert(GV); 827 } else { 828 TableLookupVariables.insert(GV); 829 } 830 break; 831 } 832 } 833 } 834 835 // All LDS variables accessed indirectly have now been partitioned into 836 // the distinct lowering strategies. 837 assert(ModuleScopeVariables.size() + TableLookupVariables.size() + 838 KernelAccessVariables.size() + DynamicVariables.size() == 839 LDSToKernelsThatNeedToAccessItIndirectly.size()); 840 } 841 842 static GlobalVariable *lowerModuleScopeStructVariables( 843 Module &M, DenseSet<GlobalVariable *> const &ModuleScopeVariables, 844 DenseSet<Function *> const &KernelsThatAllocateModuleLDS) { 845 // Create a struct to hold the ModuleScopeVariables 846 // Replace all uses of those variables from non-kernel functions with the 847 // new struct instance Replace only the uses from kernel functions that will 848 // allocate this instance. That is a space optimisation - kernels that use a 849 // subset of the module scope struct and do not need to allocate it for 850 // indirect calls will only allocate the subset they use (they do so as part 851 // of the per-kernel lowering). 852 if (ModuleScopeVariables.empty()) { 853 return nullptr; 854 } 855 856 LLVMContext &Ctx = M.getContext(); 857 858 LDSVariableReplacement ModuleScopeReplacement = 859 createLDSVariableReplacement(M, "llvm.amdgcn.module.lds", 860 ModuleScopeVariables); 861 862 appendToCompilerUsed(M, {static_cast<GlobalValue *>( 863 ConstantExpr::getPointerBitCastOrAddrSpaceCast( 864 cast<Constant>(ModuleScopeReplacement.SGV), 865 PointerType::getUnqual(Ctx)))}); 866 867 // module.lds will be allocated at zero in any kernel that allocates it 868 recordLDSAbsoluteAddress(&M, ModuleScopeReplacement.SGV, 0); 869 870 // historic 871 removeLocalVarsFromUsedLists(M, ModuleScopeVariables); 872 873 // Replace all uses of module scope variable from non-kernel functions 874 replaceLDSVariablesWithStruct( 875 M, ModuleScopeVariables, ModuleScopeReplacement, [&](Use &U) { 876 Instruction *I = dyn_cast<Instruction>(U.getUser()); 877 if (!I) { 878 return false; 879 } 880 Function *F = I->getFunction(); 881 return !isKernelLDS(F); 882 }); 883 884 // Replace uses of module scope variable from kernel functions that 885 // allocate the module scope variable, otherwise leave them unchanged 886 // Record on each kernel whether the module scope global is used by it 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(&Func, ModuleScopeReplacement.SGV); 904 } 905 } 906 907 return ModuleScopeReplacement.SGV; 908 } 909 910 static DenseMap<Function *, LDSVariableReplacement> 911 lowerKernelScopeStructVariables( 912 Module &M, LDSUsesInfoTy &LDSUsesInfo, 913 DenseSet<GlobalVariable *> const &ModuleScopeVariables, 914 DenseSet<Function *> const &KernelsThatAllocateModuleLDS, 915 GlobalVariable *MaybeModuleScopeStruct) { 916 917 // Create a struct for each kernel for the non-module-scope variables. 918 919 DenseMap<Function *, LDSVariableReplacement> KernelToReplacement; 920 for (Function &Func : M.functions()) { 921 if (Func.isDeclaration() || !isKernelLDS(&Func)) 922 continue; 923 924 DenseSet<GlobalVariable *> KernelUsedVariables; 925 // Allocating variables that are used directly in this struct to get 926 // alignment aware allocation and predictable frame size. 927 for (auto &v : LDSUsesInfo.direct_access[&Func]) { 928 if (!AMDGPU::isDynamicLDS(*v)) { 929 KernelUsedVariables.insert(v); 930 } 931 } 932 933 // Allocating variables that are accessed indirectly so that a lookup of 934 // this struct instance can find them from nested functions. 935 for (auto &v : LDSUsesInfo.indirect_access[&Func]) { 936 if (!AMDGPU::isDynamicLDS(*v)) { 937 KernelUsedVariables.insert(v); 938 } 939 } 940 941 // Variables allocated in module lds must all resolve to that struct, 942 // not to the per-kernel instance. 943 if (KernelsThatAllocateModuleLDS.contains(&Func)) { 944 for (GlobalVariable *v : ModuleScopeVariables) { 945 KernelUsedVariables.erase(v); 946 } 947 } 948 949 if (KernelUsedVariables.empty()) { 950 // Either used no LDS, or the LDS it used was all in the module struct 951 // or dynamically sized 952 continue; 953 } 954 955 // The association between kernel function and LDS struct is done by 956 // symbol name, which only works if the function in question has a 957 // name This is not expected to be a problem in practice as kernels 958 // are called by name making anonymous ones (which are named by the 959 // backend) difficult to use. This does mean that llvm test cases need 960 // to name the kernels. 961 if (!Func.hasName()) { 962 report_fatal_error("Anonymous kernels cannot use LDS variables"); 963 } 964 965 std::string VarName = 966 (Twine("llvm.amdgcn.kernel.") + Func.getName() + ".lds").str(); 967 968 auto Replacement = 969 createLDSVariableReplacement(M, VarName, KernelUsedVariables); 970 971 // If any indirect uses, create a direct use to ensure allocation 972 // TODO: Simpler to unconditionally mark used but that regresses 973 // codegen in test/CodeGen/AMDGPU/noclobber-barrier.ll 974 auto Accesses = LDSUsesInfo.indirect_access.find(&Func); 975 if ((Accesses != LDSUsesInfo.indirect_access.end()) && 976 !Accesses->second.empty()) 977 markUsedByKernel(&Func, Replacement.SGV); 978 979 // remove preserves existing codegen 980 removeLocalVarsFromUsedLists(M, KernelUsedVariables); 981 KernelToReplacement[&Func] = Replacement; 982 983 // Rewrite uses within kernel to the new struct 984 replaceLDSVariablesWithStruct( 985 M, KernelUsedVariables, Replacement, [&Func](Use &U) { 986 Instruction *I = dyn_cast<Instruction>(U.getUser()); 987 return I && I->getFunction() == &Func; 988 }); 989 } 990 return KernelToReplacement; 991 } 992 993 static GlobalVariable * 994 buildRepresentativeDynamicLDSInstance(Module &M, LDSUsesInfoTy &LDSUsesInfo, 995 Function *func) { 996 // Create a dynamic lds variable with a name associated with the passed 997 // function that has the maximum alignment of any dynamic lds variable 998 // reachable from this kernel. Dynamic LDS is allocated after the static LDS 999 // allocation, possibly after alignment padding. The representative variable 1000 // created here has the maximum alignment of any other dynamic variable 1001 // reachable by that kernel. All dynamic LDS variables are allocated at the 1002 // same address in each kernel in order to provide the documented aliasing 1003 // semantics. Setting the alignment here allows this IR pass to accurately 1004 // predict the exact constant at which it will be allocated. 1005 1006 assert(isKernelLDS(func)); 1007 1008 LLVMContext &Ctx = M.getContext(); 1009 const DataLayout &DL = M.getDataLayout(); 1010 Align MaxDynamicAlignment(1); 1011 1012 auto UpdateMaxAlignment = [&MaxDynamicAlignment, &DL](GlobalVariable *GV) { 1013 if (AMDGPU::isDynamicLDS(*GV)) { 1014 MaxDynamicAlignment = 1015 std::max(MaxDynamicAlignment, AMDGPU::getAlign(DL, GV)); 1016 } 1017 }; 1018 1019 for (GlobalVariable *GV : LDSUsesInfo.indirect_access[func]) { 1020 UpdateMaxAlignment(GV); 1021 } 1022 1023 for (GlobalVariable *GV : LDSUsesInfo.direct_access[func]) { 1024 UpdateMaxAlignment(GV); 1025 } 1026 1027 assert(func->hasName()); // Checked by caller 1028 auto emptyCharArray = ArrayType::get(Type::getInt8Ty(Ctx), 0); 1029 GlobalVariable *N = new GlobalVariable( 1030 M, emptyCharArray, false, GlobalValue::ExternalLinkage, nullptr, 1031 Twine("llvm.amdgcn." + func->getName() + ".dynlds"), nullptr, GlobalValue::NotThreadLocal, AMDGPUAS::LOCAL_ADDRESS, 1032 false); 1033 N->setAlignment(MaxDynamicAlignment); 1034 1035 assert(AMDGPU::isDynamicLDS(*N)); 1036 return N; 1037 } 1038 1039 /// Strip "amdgpu-no-lds-kernel-id" from any functions where we may have 1040 /// introduced its use. If AMDGPUAttributor ran prior to the pass, we inferred 1041 /// the lack of llvm.amdgcn.lds.kernel.id calls. 1042 void removeNoLdsKernelIdFromReachable(CallGraph &CG, Function *KernelRoot) { 1043 KernelRoot->removeFnAttr("amdgpu-no-lds-kernel-id"); 1044 1045 SmallVector<Function *> Tmp({CG[KernelRoot]->getFunction()}); 1046 if (!Tmp.back()) 1047 return; 1048 1049 SmallPtrSet<Function *, 8> Visited; 1050 bool SeenUnknownCall = false; 1051 1052 do { 1053 Function *F = Tmp.pop_back_val(); 1054 1055 for (auto &N : *CG[F]) { 1056 if (!N.second) 1057 continue; 1058 1059 Function *Callee = N.second->getFunction(); 1060 if (!Callee) { 1061 if (!SeenUnknownCall) { 1062 SeenUnknownCall = true; 1063 1064 // If we see any indirect calls, assume nothing about potential 1065 // targets. 1066 // TODO: This could be refined to possible LDS global users. 1067 for (auto &N : *CG.getExternalCallingNode()) { 1068 Function *PotentialCallee = N.second->getFunction(); 1069 if (!isKernelLDS(PotentialCallee)) 1070 PotentialCallee->removeFnAttr("amdgpu-no-lds-kernel-id"); 1071 } 1072 1073 continue; 1074 } 1075 } 1076 1077 Callee->removeFnAttr("amdgpu-no-lds-kernel-id"); 1078 if (Visited.insert(Callee).second) 1079 Tmp.push_back(Callee); 1080 } 1081 } while (!Tmp.empty()); 1082 } 1083 1084 DenseMap<Function *, GlobalVariable *> lowerDynamicLDSVariables( 1085 Module &M, LDSUsesInfoTy &LDSUsesInfo, 1086 DenseSet<Function *> const &KernelsThatIndirectlyAllocateDynamicLDS, 1087 DenseSet<GlobalVariable *> const &DynamicVariables, 1088 std::vector<Function *> const &OrderedKernels) { 1089 DenseMap<Function *, GlobalVariable *> KernelToCreatedDynamicLDS; 1090 if (!KernelsThatIndirectlyAllocateDynamicLDS.empty()) { 1091 LLVMContext &Ctx = M.getContext(); 1092 IRBuilder<> Builder(Ctx); 1093 Type *I32 = Type::getInt32Ty(Ctx); 1094 1095 std::vector<Constant *> newDynamicLDS; 1096 1097 // Table is built in the same order as OrderedKernels 1098 for (auto &func : OrderedKernels) { 1099 1100 if (KernelsThatIndirectlyAllocateDynamicLDS.contains(func)) { 1101 assert(isKernelLDS(func)); 1102 if (!func->hasName()) { 1103 report_fatal_error("Anonymous kernels cannot use LDS variables"); 1104 } 1105 1106 GlobalVariable *N = 1107 buildRepresentativeDynamicLDSInstance(M, LDSUsesInfo, func); 1108 1109 KernelToCreatedDynamicLDS[func] = N; 1110 1111 markUsedByKernel(func, N); 1112 1113 auto emptyCharArray = ArrayType::get(Type::getInt8Ty(Ctx), 0); 1114 auto GEP = ConstantExpr::getGetElementPtr( 1115 emptyCharArray, N, ConstantInt::get(I32, 0), true); 1116 newDynamicLDS.push_back(ConstantExpr::getPtrToInt(GEP, I32)); 1117 } else { 1118 newDynamicLDS.push_back(PoisonValue::get(I32)); 1119 } 1120 } 1121 assert(OrderedKernels.size() == newDynamicLDS.size()); 1122 1123 ArrayType *t = ArrayType::get(I32, newDynamicLDS.size()); 1124 Constant *init = ConstantArray::get(t, newDynamicLDS); 1125 GlobalVariable *table = new GlobalVariable( 1126 M, t, true, GlobalValue::InternalLinkage, init, 1127 "llvm.amdgcn.dynlds.offset.table", nullptr, 1128 GlobalValue::NotThreadLocal, AMDGPUAS::CONSTANT_ADDRESS); 1129 1130 for (GlobalVariable *GV : DynamicVariables) { 1131 for (Use &U : make_early_inc_range(GV->uses())) { 1132 auto *I = dyn_cast<Instruction>(U.getUser()); 1133 if (!I) 1134 continue; 1135 if (isKernelLDS(I->getFunction())) 1136 continue; 1137 1138 replaceUseWithTableLookup(M, Builder, table, GV, U, nullptr); 1139 } 1140 } 1141 } 1142 return KernelToCreatedDynamicLDS; 1143 } 1144 1145 bool runOnModule(Module &M) { 1146 CallGraph CG = CallGraph(M); 1147 bool Changed = superAlignLDSGlobals(M); 1148 1149 Changed |= eliminateConstantExprUsesOfLDSFromAllInstructions(M); 1150 1151 Changed = true; // todo: narrow this down 1152 1153 // For each kernel, what variables does it access directly or through 1154 // callees 1155 LDSUsesInfoTy LDSUsesInfo = getTransitiveUsesOfLDS(CG, M); 1156 1157 // For each variable accessed through callees, which kernels access it 1158 VariableFunctionMap LDSToKernelsThatNeedToAccessItIndirectly; 1159 for (auto &K : LDSUsesInfo.indirect_access) { 1160 Function *F = K.first; 1161 assert(isKernelLDS(F)); 1162 for (GlobalVariable *GV : K.second) { 1163 LDSToKernelsThatNeedToAccessItIndirectly[GV].insert(F); 1164 } 1165 } 1166 1167 // Partition variables accessed indirectly into the different strategies 1168 DenseSet<GlobalVariable *> ModuleScopeVariables; 1169 DenseSet<GlobalVariable *> TableLookupVariables; 1170 DenseSet<GlobalVariable *> KernelAccessVariables; 1171 DenseSet<GlobalVariable *> DynamicVariables; 1172 partitionVariablesIntoIndirectStrategies( 1173 M, LDSUsesInfo, LDSToKernelsThatNeedToAccessItIndirectly, 1174 ModuleScopeVariables, TableLookupVariables, KernelAccessVariables, 1175 DynamicVariables); 1176 1177 // If the kernel accesses a variable that is going to be stored in the 1178 // module instance through a call then that kernel needs to allocate the 1179 // module instance 1180 const DenseSet<Function *> KernelsThatAllocateModuleLDS = 1181 kernelsThatIndirectlyAccessAnyOfPassedVariables(M, LDSUsesInfo, 1182 ModuleScopeVariables); 1183 const DenseSet<Function *> KernelsThatAllocateTableLDS = 1184 kernelsThatIndirectlyAccessAnyOfPassedVariables(M, LDSUsesInfo, 1185 TableLookupVariables); 1186 1187 const DenseSet<Function *> KernelsThatIndirectlyAllocateDynamicLDS = 1188 kernelsThatIndirectlyAccessAnyOfPassedVariables(M, LDSUsesInfo, 1189 DynamicVariables); 1190 1191 GlobalVariable *MaybeModuleScopeStruct = lowerModuleScopeStructVariables( 1192 M, ModuleScopeVariables, KernelsThatAllocateModuleLDS); 1193 1194 DenseMap<Function *, LDSVariableReplacement> KernelToReplacement = 1195 lowerKernelScopeStructVariables(M, LDSUsesInfo, ModuleScopeVariables, 1196 KernelsThatAllocateModuleLDS, 1197 MaybeModuleScopeStruct); 1198 1199 // Lower zero cost accesses to the kernel instances just created 1200 for (auto &GV : KernelAccessVariables) { 1201 auto &funcs = LDSToKernelsThatNeedToAccessItIndirectly[GV]; 1202 assert(funcs.size() == 1); // Only one kernel can access it 1203 LDSVariableReplacement Replacement = 1204 KernelToReplacement[*(funcs.begin())]; 1205 1206 DenseSet<GlobalVariable *> Vec; 1207 Vec.insert(GV); 1208 1209 replaceLDSVariablesWithStruct(M, Vec, Replacement, [](Use &U) { 1210 return isa<Instruction>(U.getUser()); 1211 }); 1212 } 1213 1214 // The ith element of this vector is kernel id i 1215 std::vector<Function *> OrderedKernels = 1216 assignLDSKernelIDToEachKernel(&M, KernelsThatAllocateTableLDS, 1217 KernelsThatIndirectlyAllocateDynamicLDS); 1218 1219 if (!KernelsThatAllocateTableLDS.empty()) { 1220 LLVMContext &Ctx = M.getContext(); 1221 IRBuilder<> Builder(Ctx); 1222 1223 // The order must be consistent between lookup table and accesses to 1224 // lookup table 1225 auto TableLookupVariablesOrdered = 1226 sortByName(std::vector<GlobalVariable *>(TableLookupVariables.begin(), 1227 TableLookupVariables.end())); 1228 1229 GlobalVariable *LookupTable = buildLookupTable( 1230 M, TableLookupVariablesOrdered, OrderedKernels, KernelToReplacement); 1231 replaceUsesInInstructionsWithTableLookup(M, TableLookupVariablesOrdered, 1232 LookupTable); 1233 1234 // Strip amdgpu-no-lds-kernel-id from all functions reachable from the 1235 // kernel. We may have inferred this wasn't used prior to the pass. 1236 // 1237 // TODO: We could filter out subgraphs that do not access LDS globals. 1238 for (Function *F : KernelsThatAllocateTableLDS) 1239 removeNoLdsKernelIdFromReachable(CG, F); 1240 } 1241 1242 DenseMap<Function *, GlobalVariable *> KernelToCreatedDynamicLDS = 1243 lowerDynamicLDSVariables(M, LDSUsesInfo, 1244 KernelsThatIndirectlyAllocateDynamicLDS, 1245 DynamicVariables, OrderedKernels); 1246 1247 // All kernel frames have been allocated. Calculate and record the 1248 // addresses. 1249 { 1250 const DataLayout &DL = M.getDataLayout(); 1251 1252 for (Function &Func : M.functions()) { 1253 if (Func.isDeclaration() || !isKernelLDS(&Func)) 1254 continue; 1255 1256 // All three of these are optional. The first variable is allocated at 1257 // zero. They are allocated by AMDGPUMachineFunction as one block. 1258 // Layout: 1259 //{ 1260 // module.lds 1261 // alignment padding 1262 // kernel instance 1263 // alignment padding 1264 // dynamic lds variables 1265 //} 1266 1267 const bool AllocateModuleScopeStruct = 1268 MaybeModuleScopeStruct && 1269 KernelsThatAllocateModuleLDS.contains(&Func); 1270 1271 auto Replacement = KernelToReplacement.find(&Func); 1272 const bool AllocateKernelScopeStruct = 1273 Replacement != KernelToReplacement.end(); 1274 1275 const bool AllocateDynamicVariable = 1276 KernelToCreatedDynamicLDS.contains(&Func); 1277 1278 uint32_t Offset = 0; 1279 1280 if (AllocateModuleScopeStruct) { 1281 // Allocated at zero, recorded once on construction, not once per 1282 // kernel 1283 Offset += DL.getTypeAllocSize(MaybeModuleScopeStruct->getValueType()); 1284 } 1285 1286 if (AllocateKernelScopeStruct) { 1287 GlobalVariable *KernelStruct = Replacement->second.SGV; 1288 Offset = alignTo(Offset, AMDGPU::getAlign(DL, KernelStruct)); 1289 recordLDSAbsoluteAddress(&M, KernelStruct, Offset); 1290 Offset += DL.getTypeAllocSize(KernelStruct->getValueType()); 1291 } 1292 1293 // If there is dynamic allocation, the alignment needed is included in 1294 // the static frame size. There may be no reference to the dynamic 1295 // variable in the kernel itself, so without including it here, that 1296 // alignment padding could be missed. 1297 if (AllocateDynamicVariable) { 1298 GlobalVariable *DynamicVariable = KernelToCreatedDynamicLDS[&Func]; 1299 Offset = alignTo(Offset, AMDGPU::getAlign(DL, DynamicVariable)); 1300 recordLDSAbsoluteAddress(&M, DynamicVariable, Offset); 1301 } 1302 1303 if (Offset != 0) { 1304 (void)TM; // TODO: Account for target maximum LDS 1305 std::string Buffer; 1306 raw_string_ostream SS{Buffer}; 1307 SS << format("%u", Offset); 1308 1309 // Instead of explictly marking kernels that access dynamic variables 1310 // using special case metadata, annotate with min-lds == max-lds, i.e. 1311 // that there is no more space available for allocating more static 1312 // LDS variables. That is the right condition to prevent allocating 1313 // more variables which would collide with the addresses assigned to 1314 // dynamic variables. 1315 if (AllocateDynamicVariable) 1316 SS << format(",%u", Offset); 1317 1318 Func.addFnAttr("amdgpu-lds-size", Buffer); 1319 } 1320 } 1321 } 1322 1323 for (auto &GV : make_early_inc_range(M.globals())) 1324 if (AMDGPU::isLDSVariableToLower(GV)) { 1325 // probably want to remove from used lists 1326 GV.removeDeadConstantUsers(); 1327 if (GV.use_empty()) 1328 GV.eraseFromParent(); 1329 } 1330 1331 return Changed; 1332 } 1333 1334 private: 1335 // Increase the alignment of LDS globals if necessary to maximise the chance 1336 // that we can use aligned LDS instructions to access them. 1337 static bool superAlignLDSGlobals(Module &M) { 1338 const DataLayout &DL = M.getDataLayout(); 1339 bool Changed = false; 1340 if (!SuperAlignLDSGlobals) { 1341 return Changed; 1342 } 1343 1344 for (auto &GV : M.globals()) { 1345 if (GV.getType()->getPointerAddressSpace() != AMDGPUAS::LOCAL_ADDRESS) { 1346 // Only changing alignment of LDS variables 1347 continue; 1348 } 1349 if (!GV.hasInitializer()) { 1350 // cuda/hip extern __shared__ variable, leave alignment alone 1351 continue; 1352 } 1353 1354 Align Alignment = AMDGPU::getAlign(DL, &GV); 1355 TypeSize GVSize = DL.getTypeAllocSize(GV.getValueType()); 1356 1357 if (GVSize > 8) { 1358 // We might want to use a b96 or b128 load/store 1359 Alignment = std::max(Alignment, Align(16)); 1360 } else if (GVSize > 4) { 1361 // We might want to use a b64 load/store 1362 Alignment = std::max(Alignment, Align(8)); 1363 } else if (GVSize > 2) { 1364 // We might want to use a b32 load/store 1365 Alignment = std::max(Alignment, Align(4)); 1366 } else if (GVSize > 1) { 1367 // We might want to use a b16 load/store 1368 Alignment = std::max(Alignment, Align(2)); 1369 } 1370 1371 if (Alignment != AMDGPU::getAlign(DL, &GV)) { 1372 Changed = true; 1373 GV.setAlignment(Alignment); 1374 } 1375 } 1376 return Changed; 1377 } 1378 1379 static LDSVariableReplacement createLDSVariableReplacement( 1380 Module &M, std::string VarName, 1381 DenseSet<GlobalVariable *> const &LDSVarsToTransform) { 1382 // Create a struct instance containing LDSVarsToTransform and map from those 1383 // variables to ConstantExprGEP 1384 // Variables may be introduced to meet alignment requirements. No aliasing 1385 // metadata is useful for these as they have no uses. Erased before return. 1386 1387 LLVMContext &Ctx = M.getContext(); 1388 const DataLayout &DL = M.getDataLayout(); 1389 assert(!LDSVarsToTransform.empty()); 1390 1391 SmallVector<OptimizedStructLayoutField, 8> LayoutFields; 1392 LayoutFields.reserve(LDSVarsToTransform.size()); 1393 { 1394 // The order of fields in this struct depends on the order of 1395 // varables in the argument which varies when changing how they 1396 // are identified, leading to spurious test breakage. 1397 auto Sorted = sortByName(std::vector<GlobalVariable *>( 1398 LDSVarsToTransform.begin(), LDSVarsToTransform.end())); 1399 1400 for (GlobalVariable *GV : Sorted) { 1401 OptimizedStructLayoutField F(GV, 1402 DL.getTypeAllocSize(GV->getValueType()), 1403 AMDGPU::getAlign(DL, GV)); 1404 LayoutFields.emplace_back(F); 1405 } 1406 } 1407 1408 performOptimizedStructLayout(LayoutFields); 1409 1410 std::vector<GlobalVariable *> LocalVars; 1411 BitVector IsPaddingField; 1412 LocalVars.reserve(LDSVarsToTransform.size()); // will be at least this large 1413 IsPaddingField.reserve(LDSVarsToTransform.size()); 1414 { 1415 uint64_t CurrentOffset = 0; 1416 for (size_t I = 0; I < LayoutFields.size(); I++) { 1417 GlobalVariable *FGV = static_cast<GlobalVariable *>( 1418 const_cast<void *>(LayoutFields[I].Id)); 1419 Align DataAlign = LayoutFields[I].Alignment; 1420 1421 uint64_t DataAlignV = DataAlign.value(); 1422 if (uint64_t Rem = CurrentOffset % DataAlignV) { 1423 uint64_t Padding = DataAlignV - Rem; 1424 1425 // Append an array of padding bytes to meet alignment requested 1426 // Note (o + (a - (o % a)) ) % a == 0 1427 // (offset + Padding ) % align == 0 1428 1429 Type *ATy = ArrayType::get(Type::getInt8Ty(Ctx), Padding); 1430 LocalVars.push_back(new GlobalVariable( 1431 M, ATy, false, GlobalValue::InternalLinkage, 1432 PoisonValue::get(ATy), "", nullptr, GlobalValue::NotThreadLocal, 1433 AMDGPUAS::LOCAL_ADDRESS, false)); 1434 IsPaddingField.push_back(true); 1435 CurrentOffset += Padding; 1436 } 1437 1438 LocalVars.push_back(FGV); 1439 IsPaddingField.push_back(false); 1440 CurrentOffset += LayoutFields[I].Size; 1441 } 1442 } 1443 1444 std::vector<Type *> LocalVarTypes; 1445 LocalVarTypes.reserve(LocalVars.size()); 1446 std::transform( 1447 LocalVars.cbegin(), LocalVars.cend(), std::back_inserter(LocalVarTypes), 1448 [](const GlobalVariable *V) -> Type * { return V->getValueType(); }); 1449 1450 StructType *LDSTy = StructType::create(Ctx, LocalVarTypes, VarName + ".t"); 1451 1452 Align StructAlign = AMDGPU::getAlign(DL, LocalVars[0]); 1453 1454 GlobalVariable *SGV = new GlobalVariable( 1455 M, LDSTy, false, GlobalValue::InternalLinkage, PoisonValue::get(LDSTy), 1456 VarName, nullptr, GlobalValue::NotThreadLocal, AMDGPUAS::LOCAL_ADDRESS, 1457 false); 1458 SGV->setAlignment(StructAlign); 1459 1460 DenseMap<GlobalVariable *, Constant *> Map; 1461 Type *I32 = Type::getInt32Ty(Ctx); 1462 for (size_t I = 0; I < LocalVars.size(); I++) { 1463 GlobalVariable *GV = LocalVars[I]; 1464 Constant *GEPIdx[] = {ConstantInt::get(I32, 0), ConstantInt::get(I32, I)}; 1465 Constant *GEP = ConstantExpr::getGetElementPtr(LDSTy, SGV, GEPIdx, true); 1466 if (IsPaddingField[I]) { 1467 assert(GV->use_empty()); 1468 GV->eraseFromParent(); 1469 } else { 1470 Map[GV] = GEP; 1471 } 1472 } 1473 assert(Map.size() == LDSVarsToTransform.size()); 1474 return {SGV, std::move(Map)}; 1475 } 1476 1477 template <typename PredicateTy> 1478 static void replaceLDSVariablesWithStruct( 1479 Module &M, DenseSet<GlobalVariable *> const &LDSVarsToTransformArg, 1480 const LDSVariableReplacement &Replacement, PredicateTy Predicate) { 1481 LLVMContext &Ctx = M.getContext(); 1482 const DataLayout &DL = M.getDataLayout(); 1483 1484 // A hack... we need to insert the aliasing info in a predictable order for 1485 // lit tests. Would like to have them in a stable order already, ideally the 1486 // same order they get allocated, which might mean an ordered set container 1487 auto LDSVarsToTransform = sortByName(std::vector<GlobalVariable *>( 1488 LDSVarsToTransformArg.begin(), LDSVarsToTransformArg.end())); 1489 1490 // Create alias.scope and their lists. Each field in the new structure 1491 // does not alias with all other fields. 1492 SmallVector<MDNode *> AliasScopes; 1493 SmallVector<Metadata *> NoAliasList; 1494 const size_t NumberVars = LDSVarsToTransform.size(); 1495 if (NumberVars > 1) { 1496 MDBuilder MDB(Ctx); 1497 AliasScopes.reserve(NumberVars); 1498 MDNode *Domain = MDB.createAnonymousAliasScopeDomain(); 1499 for (size_t I = 0; I < NumberVars; I++) { 1500 MDNode *Scope = MDB.createAnonymousAliasScope(Domain); 1501 AliasScopes.push_back(Scope); 1502 } 1503 NoAliasList.append(&AliasScopes[1], AliasScopes.end()); 1504 } 1505 1506 // Replace uses of ith variable with a constantexpr to the corresponding 1507 // field of the instance that will be allocated by AMDGPUMachineFunction 1508 for (size_t I = 0; I < NumberVars; I++) { 1509 GlobalVariable *GV = LDSVarsToTransform[I]; 1510 Constant *GEP = Replacement.LDSVarsToConstantGEP.at(GV); 1511 1512 GV->replaceUsesWithIf(GEP, Predicate); 1513 1514 APInt APOff(DL.getIndexTypeSizeInBits(GEP->getType()), 0); 1515 GEP->stripAndAccumulateInBoundsConstantOffsets(DL, APOff); 1516 uint64_t Offset = APOff.getZExtValue(); 1517 1518 Align A = 1519 commonAlignment(Replacement.SGV->getAlign().valueOrOne(), Offset); 1520 1521 if (I) 1522 NoAliasList[I - 1] = AliasScopes[I - 1]; 1523 MDNode *NoAlias = 1524 NoAliasList.empty() ? nullptr : MDNode::get(Ctx, NoAliasList); 1525 MDNode *AliasScope = 1526 AliasScopes.empty() ? nullptr : MDNode::get(Ctx, {AliasScopes[I]}); 1527 1528 refineUsesAlignmentAndAA(GEP, A, DL, AliasScope, NoAlias); 1529 } 1530 } 1531 1532 static void refineUsesAlignmentAndAA(Value *Ptr, Align A, 1533 const DataLayout &DL, MDNode *AliasScope, 1534 MDNode *NoAlias, unsigned MaxDepth = 5) { 1535 if (!MaxDepth || (A == 1 && !AliasScope)) 1536 return; 1537 1538 for (User *U : Ptr->users()) { 1539 if (auto *I = dyn_cast<Instruction>(U)) { 1540 if (AliasScope && I->mayReadOrWriteMemory()) { 1541 MDNode *AS = I->getMetadata(LLVMContext::MD_alias_scope); 1542 AS = (AS ? MDNode::getMostGenericAliasScope(AS, AliasScope) 1543 : AliasScope); 1544 I->setMetadata(LLVMContext::MD_alias_scope, AS); 1545 1546 MDNode *NA = I->getMetadata(LLVMContext::MD_noalias); 1547 NA = (NA ? MDNode::intersect(NA, NoAlias) : NoAlias); 1548 I->setMetadata(LLVMContext::MD_noalias, NA); 1549 } 1550 } 1551 1552 if (auto *LI = dyn_cast<LoadInst>(U)) { 1553 LI->setAlignment(std::max(A, LI->getAlign())); 1554 continue; 1555 } 1556 if (auto *SI = dyn_cast<StoreInst>(U)) { 1557 if (SI->getPointerOperand() == Ptr) 1558 SI->setAlignment(std::max(A, SI->getAlign())); 1559 continue; 1560 } 1561 if (auto *AI = dyn_cast<AtomicRMWInst>(U)) { 1562 // None of atomicrmw operations can work on pointers, but let's 1563 // check it anyway in case it will or we will process ConstantExpr. 1564 if (AI->getPointerOperand() == Ptr) 1565 AI->setAlignment(std::max(A, AI->getAlign())); 1566 continue; 1567 } 1568 if (auto *AI = dyn_cast<AtomicCmpXchgInst>(U)) { 1569 if (AI->getPointerOperand() == Ptr) 1570 AI->setAlignment(std::max(A, AI->getAlign())); 1571 continue; 1572 } 1573 if (auto *GEP = dyn_cast<GetElementPtrInst>(U)) { 1574 unsigned BitWidth = DL.getIndexTypeSizeInBits(GEP->getType()); 1575 APInt Off(BitWidth, 0); 1576 if (GEP->getPointerOperand() == Ptr) { 1577 Align GA; 1578 if (GEP->accumulateConstantOffset(DL, Off)) 1579 GA = commonAlignment(A, Off.getLimitedValue()); 1580 refineUsesAlignmentAndAA(GEP, GA, DL, AliasScope, NoAlias, 1581 MaxDepth - 1); 1582 } 1583 continue; 1584 } 1585 if (auto *I = dyn_cast<Instruction>(U)) { 1586 if (I->getOpcode() == Instruction::BitCast || 1587 I->getOpcode() == Instruction::AddrSpaceCast) 1588 refineUsesAlignmentAndAA(I, A, DL, AliasScope, NoAlias, MaxDepth - 1); 1589 } 1590 } 1591 } 1592 }; 1593 1594 class AMDGPULowerModuleLDSLegacy : public ModulePass { 1595 public: 1596 const AMDGPUTargetMachine *TM; 1597 static char ID; 1598 1599 AMDGPULowerModuleLDSLegacy(const AMDGPUTargetMachine *TM_ = nullptr) 1600 : ModulePass(ID), TM(TM_) { 1601 initializeAMDGPULowerModuleLDSLegacyPass(*PassRegistry::getPassRegistry()); 1602 } 1603 1604 void getAnalysisUsage(AnalysisUsage &AU) const override { 1605 if (!TM) 1606 AU.addRequired<TargetPassConfig>(); 1607 } 1608 1609 bool runOnModule(Module &M) override { 1610 if (!TM) { 1611 auto &TPC = getAnalysis<TargetPassConfig>(); 1612 TM = &TPC.getTM<AMDGPUTargetMachine>(); 1613 } 1614 1615 return AMDGPULowerModuleLDS(*TM).runOnModule(M); 1616 } 1617 }; 1618 1619 } // namespace 1620 char AMDGPULowerModuleLDSLegacy::ID = 0; 1621 1622 char &llvm::AMDGPULowerModuleLDSLegacyPassID = AMDGPULowerModuleLDSLegacy::ID; 1623 1624 INITIALIZE_PASS_BEGIN(AMDGPULowerModuleLDSLegacy, DEBUG_TYPE, 1625 "Lower uses of LDS variables from non-kernel functions", 1626 false, false) 1627 INITIALIZE_PASS_DEPENDENCY(TargetPassConfig) 1628 INITIALIZE_PASS_END(AMDGPULowerModuleLDSLegacy, DEBUG_TYPE, 1629 "Lower uses of LDS variables from non-kernel functions", 1630 false, false) 1631 1632 ModulePass * 1633 llvm::createAMDGPULowerModuleLDSLegacyPass(const AMDGPUTargetMachine *TM) { 1634 return new AMDGPULowerModuleLDSLegacy(TM); 1635 } 1636 1637 PreservedAnalyses AMDGPULowerModuleLDSPass::run(Module &M, 1638 ModuleAnalysisManager &) { 1639 return AMDGPULowerModuleLDS(TM).runOnModule(M) ? PreservedAnalyses::none() 1640 : PreservedAnalyses::all(); 1641 } 1642