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 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 std::vector<Constant *> overallConstantExprElts(NumberKernels); 524 for (size_t i = 0; i < NumberKernels; i++) { 525 LDSVariableReplacement Replacement = KernelToReplacement[kernels[i]]; 526 overallConstantExprElts[i] = getAddressesOfVariablesInKernel( 527 Ctx, Variables, Replacement.LDSVarsToConstantGEP); 528 } 529 530 Constant *init = 531 ConstantArray::get(AllKernelsOffsetsType, overallConstantExprElts); 532 533 return new GlobalVariable( 534 M, AllKernelsOffsetsType, true, GlobalValue::InternalLinkage, init, 535 "llvm.amdgcn.lds.offset.table", nullptr, GlobalValue::NotThreadLocal, 536 AMDGPUAS::CONSTANT_ADDRESS); 537 } 538 539 void replaceUseWithTableLookup(Module &M, IRBuilder<> &Builder, 540 GlobalVariable *LookupTable, 541 GlobalVariable *GV, Use &U, 542 Value *OptionalIndex) { 543 // Table is a constant array of the same length as OrderedKernels 544 LLVMContext &Ctx = M.getContext(); 545 Type *I32 = Type::getInt32Ty(Ctx); 546 auto *I = cast<Instruction>(U.getUser()); 547 548 Value *tableKernelIndex = getTableLookupKernelIndex(M, I->getFunction()); 549 550 if (auto *Phi = dyn_cast<PHINode>(I)) { 551 BasicBlock *BB = Phi->getIncomingBlock(U); 552 Builder.SetInsertPoint(&(*(BB->getFirstInsertionPt()))); 553 } else { 554 Builder.SetInsertPoint(I); 555 } 556 557 SmallVector<Value *, 3> GEPIdx = { 558 ConstantInt::get(I32, 0), 559 tableKernelIndex, 560 }; 561 if (OptionalIndex) 562 GEPIdx.push_back(OptionalIndex); 563 564 Value *Address = Builder.CreateInBoundsGEP( 565 LookupTable->getValueType(), LookupTable, GEPIdx, GV->getName()); 566 567 Value *loaded = Builder.CreateLoad(I32, Address); 568 569 Value *replacement = 570 Builder.CreateIntToPtr(loaded, GV->getType(), GV->getName()); 571 572 U.set(replacement); 573 } 574 575 void replaceUsesInInstructionsWithTableLookup( 576 Module &M, ArrayRef<GlobalVariable *> ModuleScopeVariables, 577 GlobalVariable *LookupTable) { 578 579 LLVMContext &Ctx = M.getContext(); 580 IRBuilder<> Builder(Ctx); 581 Type *I32 = Type::getInt32Ty(Ctx); 582 583 for (size_t Index = 0; Index < ModuleScopeVariables.size(); Index++) { 584 auto *GV = ModuleScopeVariables[Index]; 585 586 for (Use &U : make_early_inc_range(GV->uses())) { 587 auto *I = dyn_cast<Instruction>(U.getUser()); 588 if (!I) 589 continue; 590 591 replaceUseWithTableLookup(M, Builder, LookupTable, GV, U, 592 ConstantInt::get(I32, Index)); 593 } 594 } 595 } 596 597 static DenseSet<Function *> kernelsThatIndirectlyAccessAnyOfPassedVariables( 598 Module &M, LDSUsesInfoTy &LDSUsesInfo, 599 DenseSet<GlobalVariable *> const &VariableSet) { 600 601 DenseSet<Function *> KernelSet; 602 603 if (VariableSet.empty()) 604 return KernelSet; 605 606 for (Function &Func : M.functions()) { 607 if (Func.isDeclaration() || !isKernelLDS(&Func)) 608 continue; 609 for (GlobalVariable *GV : LDSUsesInfo.indirect_access[&Func]) { 610 if (VariableSet.contains(GV)) { 611 KernelSet.insert(&Func); 612 break; 613 } 614 } 615 } 616 617 return KernelSet; 618 } 619 620 static GlobalVariable * 621 chooseBestVariableForModuleStrategy(const DataLayout &DL, 622 VariableFunctionMap &LDSVars) { 623 // Find the global variable with the most indirect uses from kernels 624 625 struct CandidateTy { 626 GlobalVariable *GV = nullptr; 627 size_t UserCount = 0; 628 size_t Size = 0; 629 630 CandidateTy() = default; 631 632 CandidateTy(GlobalVariable *GV, uint64_t UserCount, uint64_t AllocSize) 633 : GV(GV), UserCount(UserCount), Size(AllocSize) {} 634 635 bool operator<(const CandidateTy &Other) const { 636 // Fewer users makes module scope variable less attractive 637 if (UserCount < Other.UserCount) { 638 return true; 639 } 640 if (UserCount > Other.UserCount) { 641 return false; 642 } 643 644 // Bigger makes module scope variable less attractive 645 if (Size < Other.Size) { 646 return false; 647 } 648 649 if (Size > Other.Size) { 650 return true; 651 } 652 653 // Arbitrary but consistent 654 return GV->getName() < Other.GV->getName(); 655 } 656 }; 657 658 CandidateTy MostUsed; 659 660 for (auto &K : LDSVars) { 661 GlobalVariable *GV = K.first; 662 if (K.second.size() <= 1) { 663 // A variable reachable by only one kernel is best lowered with kernel 664 // strategy 665 continue; 666 } 667 CandidateTy Candidate( 668 GV, K.second.size(), 669 DL.getTypeAllocSize(GV->getValueType()).getFixedValue()); 670 if (MostUsed < Candidate) 671 MostUsed = Candidate; 672 } 673 674 return MostUsed.GV; 675 } 676 677 static void recordLDSAbsoluteAddress(Module *M, GlobalVariable *GV, 678 uint32_t Address) { 679 // Write the specified address into metadata where it can be retrieved by 680 // the assembler. Format is a half open range, [Address Address+1) 681 LLVMContext &Ctx = M->getContext(); 682 auto *IntTy = 683 M->getDataLayout().getIntPtrType(Ctx, AMDGPUAS::LOCAL_ADDRESS); 684 auto *MinC = ConstantAsMetadata::get(ConstantInt::get(IntTy, Address)); 685 auto *MaxC = ConstantAsMetadata::get(ConstantInt::get(IntTy, Address + 1)); 686 GV->setMetadata(LLVMContext::MD_absolute_symbol, 687 MDNode::get(Ctx, {MinC, MaxC})); 688 } 689 690 DenseMap<Function *, Value *> tableKernelIndexCache; 691 Value *getTableLookupKernelIndex(Module &M, Function *F) { 692 // Accesses from a function use the amdgcn_lds_kernel_id intrinsic which 693 // lowers to a read from a live in register. Emit it once in the entry 694 // block to spare deduplicating it later. 695 if (tableKernelIndexCache.count(F) == 0) { 696 LLVMContext &Ctx = M.getContext(); 697 IRBuilder<> Builder(Ctx); 698 FunctionType *FTy = FunctionType::get(Type::getInt32Ty(Ctx), {}); 699 Function *Decl = 700 Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_lds_kernel_id, {}); 701 702 BasicBlock::iterator it = 703 F->getEntryBlock().getFirstNonPHIOrDbgOrAlloca(); 704 Instruction &i = *it; 705 Builder.SetInsertPoint(&i); 706 707 tableKernelIndexCache[F] = Builder.CreateCall(FTy, Decl, {}); 708 } 709 710 return tableKernelIndexCache[F]; 711 } 712 713 static std::vector<Function *> assignLDSKernelIDToEachKernel( 714 Module *M, DenseSet<Function *> const &KernelsThatAllocateTableLDS, 715 DenseSet<Function *> const &KernelsThatIndirectlyAllocateDynamicLDS) { 716 // Associate kernels in the set with an arbirary but reproducible order and 717 // annotate them with that order in metadata. This metadata is recognised by 718 // the backend and lowered to a SGPR which can be read from using 719 // amdgcn_lds_kernel_id. 720 721 std::vector<Function *> OrderedKernels; 722 if (!KernelsThatAllocateTableLDS.empty() || 723 !KernelsThatIndirectlyAllocateDynamicLDS.empty()) { 724 725 for (Function &Func : M->functions()) { 726 if (Func.isDeclaration()) 727 continue; 728 if (!isKernelLDS(&Func)) 729 continue; 730 731 if (KernelsThatAllocateTableLDS.contains(&Func) || 732 KernelsThatIndirectlyAllocateDynamicLDS.contains(&Func)) { 733 assert(Func.hasName()); // else fatal error earlier 734 OrderedKernels.push_back(&Func); 735 } 736 } 737 738 // Put them in an arbitrary but reproducible order 739 OrderedKernels = sortByName(std::move(OrderedKernels)); 740 741 // Annotate the kernels with their order in this vector 742 LLVMContext &Ctx = M->getContext(); 743 IRBuilder<> Builder(Ctx); 744 745 if (OrderedKernels.size() > UINT32_MAX) { 746 // 32 bit keeps it in one SGPR. > 2**32 kernels won't fit on the GPU 747 report_fatal_error("Unimplemented LDS lowering for > 2**32 kernels"); 748 } 749 750 for (size_t i = 0; i < OrderedKernels.size(); i++) { 751 Metadata *AttrMDArgs[1] = { 752 ConstantAsMetadata::get(Builder.getInt32(i)), 753 }; 754 OrderedKernels[i]->setMetadata("llvm.amdgcn.lds.kernel.id", 755 MDNode::get(Ctx, AttrMDArgs)); 756 } 757 } 758 return OrderedKernels; 759 } 760 761 static void partitionVariablesIntoIndirectStrategies( 762 Module &M, LDSUsesInfoTy const &LDSUsesInfo, 763 VariableFunctionMap &LDSToKernelsThatNeedToAccessItIndirectly, 764 DenseSet<GlobalVariable *> &ModuleScopeVariables, 765 DenseSet<GlobalVariable *> &TableLookupVariables, 766 DenseSet<GlobalVariable *> &KernelAccessVariables, 767 DenseSet<GlobalVariable *> &DynamicVariables) { 768 769 GlobalVariable *HybridModuleRoot = 770 LoweringKindLoc != LoweringKind::hybrid 771 ? nullptr 772 : chooseBestVariableForModuleStrategy( 773 M.getDataLayout(), LDSToKernelsThatNeedToAccessItIndirectly); 774 775 DenseSet<Function *> const EmptySet; 776 DenseSet<Function *> const &HybridModuleRootKernels = 777 HybridModuleRoot 778 ? LDSToKernelsThatNeedToAccessItIndirectly[HybridModuleRoot] 779 : EmptySet; 780 781 for (auto &K : LDSToKernelsThatNeedToAccessItIndirectly) { 782 // Each iteration of this loop assigns exactly one global variable to 783 // exactly one of the implementation strategies. 784 785 GlobalVariable *GV = K.first; 786 assert(AMDGPU::isLDSVariableToLower(*GV)); 787 assert(K.second.size() != 0); 788 789 if (AMDGPU::isDynamicLDS(*GV)) { 790 DynamicVariables.insert(GV); 791 continue; 792 } 793 794 switch (LoweringKindLoc) { 795 case LoweringKind::module: 796 ModuleScopeVariables.insert(GV); 797 break; 798 799 case LoweringKind::table: 800 TableLookupVariables.insert(GV); 801 break; 802 803 case LoweringKind::kernel: 804 if (K.second.size() == 1) { 805 KernelAccessVariables.insert(GV); 806 } else { 807 report_fatal_error( 808 "cannot lower LDS '" + GV->getName() + 809 "' to kernel access as it is reachable from multiple kernels"); 810 } 811 break; 812 813 case LoweringKind::hybrid: { 814 if (GV == HybridModuleRoot) { 815 assert(K.second.size() != 1); 816 ModuleScopeVariables.insert(GV); 817 } else if (K.second.size() == 1) { 818 KernelAccessVariables.insert(GV); 819 } else if (set_is_subset(K.second, HybridModuleRootKernels)) { 820 ModuleScopeVariables.insert(GV); 821 } else { 822 TableLookupVariables.insert(GV); 823 } 824 break; 825 } 826 } 827 } 828 829 // All LDS variables accessed indirectly have now been partitioned into 830 // the distinct lowering strategies. 831 assert(ModuleScopeVariables.size() + TableLookupVariables.size() + 832 KernelAccessVariables.size() + DynamicVariables.size() == 833 LDSToKernelsThatNeedToAccessItIndirectly.size()); 834 } 835 836 static GlobalVariable *lowerModuleScopeStructVariables( 837 Module &M, DenseSet<GlobalVariable *> const &ModuleScopeVariables, 838 DenseSet<Function *> const &KernelsThatAllocateModuleLDS) { 839 // Create a struct to hold the ModuleScopeVariables 840 // Replace all uses of those variables from non-kernel functions with the 841 // new struct instance Replace only the uses from kernel functions that will 842 // allocate this instance. That is a space optimisation - kernels that use a 843 // subset of the module scope struct and do not need to allocate it for 844 // indirect calls will only allocate the subset they use (they do so as part 845 // of the per-kernel lowering). 846 if (ModuleScopeVariables.empty()) { 847 return nullptr; 848 } 849 850 LLVMContext &Ctx = M.getContext(); 851 852 LDSVariableReplacement ModuleScopeReplacement = 853 createLDSVariableReplacement(M, "llvm.amdgcn.module.lds", 854 ModuleScopeVariables); 855 856 appendToCompilerUsed(M, {static_cast<GlobalValue *>( 857 ConstantExpr::getPointerBitCastOrAddrSpaceCast( 858 cast<Constant>(ModuleScopeReplacement.SGV), 859 Type::getInt8PtrTy(Ctx)))}); 860 861 // module.lds will be allocated at zero in any kernel that allocates it 862 recordLDSAbsoluteAddress(&M, ModuleScopeReplacement.SGV, 0); 863 864 // historic 865 removeLocalVarsFromUsedLists(M, ModuleScopeVariables); 866 867 // Replace all uses of module scope variable from non-kernel functions 868 replaceLDSVariablesWithStruct( 869 M, ModuleScopeVariables, ModuleScopeReplacement, [&](Use &U) { 870 Instruction *I = dyn_cast<Instruction>(U.getUser()); 871 if (!I) { 872 return false; 873 } 874 Function *F = I->getFunction(); 875 return !isKernelLDS(F); 876 }); 877 878 // Replace uses of module scope variable from kernel functions that 879 // allocate the module scope variable, otherwise leave them unchanged 880 // Record on each kernel whether the module scope global is used by it 881 882 IRBuilder<> Builder(Ctx); 883 884 for (Function &Func : M.functions()) { 885 if (Func.isDeclaration() || !isKernelLDS(&Func)) 886 continue; 887 888 if (KernelsThatAllocateModuleLDS.contains(&Func)) { 889 replaceLDSVariablesWithStruct( 890 M, ModuleScopeVariables, ModuleScopeReplacement, [&](Use &U) { 891 Instruction *I = dyn_cast<Instruction>(U.getUser()); 892 if (!I) { 893 return false; 894 } 895 Function *F = I->getFunction(); 896 return F == &Func; 897 }); 898 899 markUsedByKernel(Builder, &Func, ModuleScopeReplacement.SGV); 900 901 } else { 902 markElideModuleLDS(Func); 903 } 904 } 905 906 return ModuleScopeReplacement.SGV; 907 } 908 909 static DenseMap<Function *, LDSVariableReplacement> 910 lowerKernelScopeStructVariables( 911 Module &M, LDSUsesInfoTy &LDSUsesInfo, 912 DenseSet<GlobalVariable *> const &ModuleScopeVariables, 913 DenseSet<Function *> const &KernelsThatAllocateModuleLDS, 914 GlobalVariable *MaybeModuleScopeStruct) { 915 916 // Create a struct for each kernel for the non-module-scope variables. 917 918 DenseMap<Function *, LDSVariableReplacement> KernelToReplacement; 919 for (Function &Func : M.functions()) { 920 if (Func.isDeclaration() || !isKernelLDS(&Func)) 921 continue; 922 923 DenseSet<GlobalVariable *> KernelUsedVariables; 924 // Allocating variables that are used directly in this struct to get 925 // alignment aware allocation and predictable frame size. 926 for (auto &v : LDSUsesInfo.direct_access[&Func]) { 927 if (!AMDGPU::isDynamicLDS(*v)) { 928 KernelUsedVariables.insert(v); 929 } 930 } 931 932 // Allocating variables that are accessed indirectly so that a lookup of 933 // this struct instance can find them from nested functions. 934 for (auto &v : LDSUsesInfo.indirect_access[&Func]) { 935 if (!AMDGPU::isDynamicLDS(*v)) { 936 KernelUsedVariables.insert(v); 937 } 938 } 939 940 // Variables allocated in module lds must all resolve to that struct, 941 // not to the per-kernel instance. 942 if (KernelsThatAllocateModuleLDS.contains(&Func)) { 943 for (GlobalVariable *v : ModuleScopeVariables) { 944 KernelUsedVariables.erase(v); 945 } 946 } 947 948 if (KernelUsedVariables.empty()) { 949 // Either used no LDS, or the LDS it used was all in the module struct 950 // or dynamically sized 951 continue; 952 } 953 954 // The association between kernel function and LDS struct is done by 955 // symbol name, which only works if the function in question has a 956 // name This is not expected to be a problem in practice as kernels 957 // are called by name making anonymous ones (which are named by the 958 // backend) difficult to use. This does mean that llvm test cases need 959 // to name the kernels. 960 if (!Func.hasName()) { 961 report_fatal_error("Anonymous kernels cannot use LDS variables"); 962 } 963 964 std::string VarName = 965 (Twine("llvm.amdgcn.kernel.") + Func.getName() + ".lds").str(); 966 967 auto Replacement = 968 createLDSVariableReplacement(M, VarName, KernelUsedVariables); 969 970 // remove preserves existing codegen 971 removeLocalVarsFromUsedLists(M, KernelUsedVariables); 972 KernelToReplacement[&Func] = Replacement; 973 974 // Rewrite uses within kernel to the new struct 975 replaceLDSVariablesWithStruct( 976 M, KernelUsedVariables, Replacement, [&Func](Use &U) { 977 Instruction *I = dyn_cast<Instruction>(U.getUser()); 978 return I && I->getFunction() == &Func; 979 }); 980 } 981 return KernelToReplacement; 982 } 983 984 static GlobalVariable * 985 buildRepresentativeDynamicLDSInstance(Module &M, LDSUsesInfoTy &LDSUsesInfo, 986 Function *func) { 987 // Create a dynamic lds variable with a name associated with the passed 988 // function that has the maximum alignment of any dynamic lds variable 989 // reachable from this kernel. Dynamic LDS is allocated after the static LDS 990 // allocation, possibly after alignment padding. The representative variable 991 // created here has the maximum alignment of any other dynamic variable 992 // reachable by that kernel. All dynamic LDS variables are allocated at the 993 // same address in each kernel in order to provide the documented aliasing 994 // semantics. Setting the alignment here allows this IR pass to accurately 995 // predict the exact constant at which it will be allocated. 996 997 assert(isKernelLDS(func)); 998 999 LLVMContext &Ctx = M.getContext(); 1000 const DataLayout &DL = M.getDataLayout(); 1001 Align MaxDynamicAlignment(1); 1002 1003 auto UpdateMaxAlignment = [&MaxDynamicAlignment, &DL](GlobalVariable *GV) { 1004 if (AMDGPU::isDynamicLDS(*GV)) { 1005 MaxDynamicAlignment = 1006 std::max(MaxDynamicAlignment, AMDGPU::getAlign(DL, GV)); 1007 } 1008 }; 1009 1010 for (GlobalVariable *GV : LDSUsesInfo.indirect_access[func]) { 1011 UpdateMaxAlignment(GV); 1012 } 1013 1014 for (GlobalVariable *GV : LDSUsesInfo.direct_access[func]) { 1015 UpdateMaxAlignment(GV); 1016 } 1017 1018 assert(func->hasName()); // Checked by caller 1019 auto emptyCharArray = ArrayType::get(Type::getInt8Ty(Ctx), 0); 1020 GlobalVariable *N = new GlobalVariable( 1021 M, emptyCharArray, false, GlobalValue::ExternalLinkage, nullptr, 1022 Twine("llvm.amdgcn." + func->getName() + ".dynlds"), nullptr, GlobalValue::NotThreadLocal, AMDGPUAS::LOCAL_ADDRESS, 1023 false); 1024 N->setAlignment(MaxDynamicAlignment); 1025 1026 assert(AMDGPU::isDynamicLDS(*N)); 1027 return N; 1028 } 1029 1030 DenseMap<Function *, GlobalVariable *> lowerDynamicLDSVariables( 1031 Module &M, LDSUsesInfoTy &LDSUsesInfo, 1032 DenseSet<Function *> const &KernelsThatIndirectlyAllocateDynamicLDS, 1033 DenseSet<GlobalVariable *> const &DynamicVariables, 1034 std::vector<Function *> const &OrderedKernels) { 1035 DenseMap<Function *, GlobalVariable *> KernelToCreatedDynamicLDS; 1036 if (!KernelsThatIndirectlyAllocateDynamicLDS.empty()) { 1037 LLVMContext &Ctx = M.getContext(); 1038 IRBuilder<> Builder(Ctx); 1039 Type *I32 = Type::getInt32Ty(Ctx); 1040 1041 std::vector<Constant *> newDynamicLDS; 1042 1043 // Table is built in the same order as OrderedKernels 1044 for (auto &func : OrderedKernels) { 1045 1046 if (KernelsThatIndirectlyAllocateDynamicLDS.contains(func)) { 1047 assert(isKernelLDS(func)); 1048 if (!func->hasName()) { 1049 report_fatal_error("Anonymous kernels cannot use LDS variables"); 1050 } 1051 1052 GlobalVariable *N = 1053 buildRepresentativeDynamicLDSInstance(M, LDSUsesInfo, func); 1054 1055 KernelToCreatedDynamicLDS[func] = N; 1056 1057 markUsedByKernel(Builder, func, N); 1058 1059 auto emptyCharArray = ArrayType::get(Type::getInt8Ty(Ctx), 0); 1060 auto GEP = ConstantExpr::getGetElementPtr( 1061 emptyCharArray, N, ConstantInt::get(I32, 0), true); 1062 newDynamicLDS.push_back(ConstantExpr::getPtrToInt(GEP, I32)); 1063 } else { 1064 newDynamicLDS.push_back(PoisonValue::get(I32)); 1065 } 1066 } 1067 assert(OrderedKernels.size() == newDynamicLDS.size()); 1068 1069 ArrayType *t = ArrayType::get(I32, newDynamicLDS.size()); 1070 Constant *init = ConstantArray::get(t, newDynamicLDS); 1071 GlobalVariable *table = new GlobalVariable( 1072 M, t, true, GlobalValue::InternalLinkage, init, 1073 "llvm.amdgcn.dynlds.offset.table", nullptr, 1074 GlobalValue::NotThreadLocal, AMDGPUAS::CONSTANT_ADDRESS); 1075 1076 for (GlobalVariable *GV : DynamicVariables) { 1077 for (Use &U : make_early_inc_range(GV->uses())) { 1078 auto *I = dyn_cast<Instruction>(U.getUser()); 1079 if (!I) 1080 continue; 1081 if (isKernelLDS(I->getFunction())) 1082 continue; 1083 1084 replaceUseWithTableLookup(M, Builder, table, GV, U, nullptr); 1085 } 1086 } 1087 } 1088 return KernelToCreatedDynamicLDS; 1089 } 1090 1091 static bool canElideModuleLDS(const Function &F) { 1092 return F.hasFnAttribute("amdgpu-elide-module-lds"); 1093 } 1094 1095 static void markElideModuleLDS(Function &F) { 1096 F.addFnAttr("amdgpu-elide-module-lds"); 1097 } 1098 1099 bool runOnModule(Module &M) override { 1100 CallGraph CG = CallGraph(M); 1101 bool Changed = superAlignLDSGlobals(M); 1102 1103 Changed |= eliminateConstantExprUsesOfLDSFromAllInstructions(M); 1104 1105 Changed = true; // todo: narrow this down 1106 1107 // For each kernel, what variables does it access directly or through 1108 // callees 1109 LDSUsesInfoTy LDSUsesInfo = getTransitiveUsesOfLDS(CG, M); 1110 1111 // For each variable accessed through callees, which kernels access it 1112 VariableFunctionMap LDSToKernelsThatNeedToAccessItIndirectly; 1113 for (auto &K : LDSUsesInfo.indirect_access) { 1114 Function *F = K.first; 1115 assert(isKernelLDS(F)); 1116 for (GlobalVariable *GV : K.second) { 1117 LDSToKernelsThatNeedToAccessItIndirectly[GV].insert(F); 1118 } 1119 } 1120 1121 // Partition variables accessed indirectly into the different strategies 1122 DenseSet<GlobalVariable *> ModuleScopeVariables; 1123 DenseSet<GlobalVariable *> TableLookupVariables; 1124 DenseSet<GlobalVariable *> KernelAccessVariables; 1125 DenseSet<GlobalVariable *> DynamicVariables; 1126 partitionVariablesIntoIndirectStrategies( 1127 M, LDSUsesInfo, LDSToKernelsThatNeedToAccessItIndirectly, 1128 ModuleScopeVariables, TableLookupVariables, KernelAccessVariables, 1129 DynamicVariables); 1130 1131 // If the kernel accesses a variable that is going to be stored in the 1132 // module instance through a call then that kernel needs to allocate the 1133 // module instance 1134 const DenseSet<Function *> KernelsThatAllocateModuleLDS = 1135 kernelsThatIndirectlyAccessAnyOfPassedVariables(M, LDSUsesInfo, 1136 ModuleScopeVariables); 1137 const DenseSet<Function *> KernelsThatAllocateTableLDS = 1138 kernelsThatIndirectlyAccessAnyOfPassedVariables(M, LDSUsesInfo, 1139 TableLookupVariables); 1140 1141 const DenseSet<Function *> KernelsThatIndirectlyAllocateDynamicLDS = 1142 kernelsThatIndirectlyAccessAnyOfPassedVariables(M, LDSUsesInfo, 1143 DynamicVariables); 1144 1145 GlobalVariable *MaybeModuleScopeStruct = lowerModuleScopeStructVariables( 1146 M, ModuleScopeVariables, KernelsThatAllocateModuleLDS); 1147 1148 DenseMap<Function *, LDSVariableReplacement> KernelToReplacement = 1149 lowerKernelScopeStructVariables(M, LDSUsesInfo, ModuleScopeVariables, 1150 KernelsThatAllocateModuleLDS, 1151 MaybeModuleScopeStruct); 1152 1153 // Lower zero cost accesses to the kernel instances just created 1154 for (auto &GV : KernelAccessVariables) { 1155 auto &funcs = LDSToKernelsThatNeedToAccessItIndirectly[GV]; 1156 assert(funcs.size() == 1); // Only one kernel can access it 1157 LDSVariableReplacement Replacement = 1158 KernelToReplacement[*(funcs.begin())]; 1159 1160 DenseSet<GlobalVariable *> Vec; 1161 Vec.insert(GV); 1162 1163 // TODO: Looks like a latent bug, Replacement may not be marked 1164 // UsedByKernel here 1165 replaceLDSVariablesWithStruct(M, Vec, Replacement, [](Use &U) { 1166 return isa<Instruction>(U.getUser()); 1167 }); 1168 } 1169 1170 // The ith element of this vector is kernel id i 1171 std::vector<Function *> OrderedKernels = 1172 assignLDSKernelIDToEachKernel(&M, KernelsThatAllocateTableLDS, 1173 KernelsThatIndirectlyAllocateDynamicLDS); 1174 1175 if (!KernelsThatAllocateTableLDS.empty()) { 1176 LLVMContext &Ctx = M.getContext(); 1177 IRBuilder<> Builder(Ctx); 1178 1179 for (size_t i = 0; i < OrderedKernels.size(); i++) { 1180 markUsedByKernel(Builder, OrderedKernels[i], 1181 KernelToReplacement[OrderedKernels[i]].SGV); 1182 } 1183 1184 // The order must be consistent between lookup table and accesses to 1185 // lookup table 1186 auto TableLookupVariablesOrdered = sortByName(std::vector( 1187 TableLookupVariables.begin(), TableLookupVariables.end())); 1188 1189 GlobalVariable *LookupTable = buildLookupTable( 1190 M, TableLookupVariablesOrdered, OrderedKernels, KernelToReplacement); 1191 replaceUsesInInstructionsWithTableLookup(M, TableLookupVariablesOrdered, 1192 LookupTable); 1193 } 1194 1195 DenseMap<Function *, GlobalVariable *> KernelToCreatedDynamicLDS = 1196 lowerDynamicLDSVariables(M, LDSUsesInfo, 1197 KernelsThatIndirectlyAllocateDynamicLDS, 1198 DynamicVariables, OrderedKernels); 1199 1200 // All kernel frames have been allocated. Calculate and record the 1201 // addresses. 1202 1203 { 1204 const DataLayout &DL = M.getDataLayout(); 1205 1206 for (Function &Func : M.functions()) { 1207 if (Func.isDeclaration() || !isKernelLDS(&Func)) 1208 continue; 1209 1210 // All three of these are optional. The first variable is allocated at 1211 // zero. They are allocated by allocateKnownAddressLDSGlobal in the 1212 // following order: 1213 //{ 1214 // module.lds 1215 // alignment padding 1216 // kernel instance 1217 // alignment padding 1218 // dynamic lds variables 1219 //} 1220 1221 const bool AllocateModuleScopeStruct = 1222 MaybeModuleScopeStruct && !canElideModuleLDS(Func); 1223 1224 auto Replacement = KernelToReplacement.find(&Func); 1225 const bool AllocateKernelScopeStruct = 1226 Replacement != KernelToReplacement.end(); 1227 1228 const bool AllocateDynamicVariable = 1229 KernelToCreatedDynamicLDS.contains(&Func); 1230 1231 uint32_t Offset = 0; 1232 1233 if (AllocateModuleScopeStruct) { 1234 // Allocated at zero, recorded once on construction, not once per 1235 // kernel 1236 Offset += DL.getTypeAllocSize(MaybeModuleScopeStruct->getValueType()); 1237 } 1238 1239 if (AllocateKernelScopeStruct) { 1240 GlobalVariable *KernelStruct = Replacement->second.SGV; 1241 1242 Offset = alignTo(Offset, AMDGPU::getAlign(DL, KernelStruct)); 1243 1244 recordLDSAbsoluteAddress(&M, KernelStruct, Offset); 1245 1246 Offset += DL.getTypeAllocSize(KernelStruct->getValueType()); 1247 1248 } 1249 1250 if (AllocateDynamicVariable) { 1251 GlobalVariable *DynamicVariable = KernelToCreatedDynamicLDS[&Func]; 1252 1253 Offset = alignTo(Offset, AMDGPU::getAlign(DL, DynamicVariable)); 1254 1255 recordLDSAbsoluteAddress(&M, DynamicVariable, Offset); 1256 } 1257 } 1258 } 1259 1260 for (auto &GV : make_early_inc_range(M.globals())) 1261 if (AMDGPU::isLDSVariableToLower(GV)) { 1262 // probably want to remove from used lists 1263 GV.removeDeadConstantUsers(); 1264 if (GV.use_empty()) 1265 GV.eraseFromParent(); 1266 } 1267 1268 return Changed; 1269 } 1270 1271 private: 1272 // Increase the alignment of LDS globals if necessary to maximise the chance 1273 // that we can use aligned LDS instructions to access them. 1274 static bool superAlignLDSGlobals(Module &M) { 1275 const DataLayout &DL = M.getDataLayout(); 1276 bool Changed = false; 1277 if (!SuperAlignLDSGlobals) { 1278 return Changed; 1279 } 1280 1281 for (auto &GV : M.globals()) { 1282 if (GV.getType()->getPointerAddressSpace() != AMDGPUAS::LOCAL_ADDRESS) { 1283 // Only changing alignment of LDS variables 1284 continue; 1285 } 1286 if (!GV.hasInitializer()) { 1287 // cuda/hip extern __shared__ variable, leave alignment alone 1288 continue; 1289 } 1290 1291 Align Alignment = AMDGPU::getAlign(DL, &GV); 1292 TypeSize GVSize = DL.getTypeAllocSize(GV.getValueType()); 1293 1294 if (GVSize > 8) { 1295 // We might want to use a b96 or b128 load/store 1296 Alignment = std::max(Alignment, Align(16)); 1297 } else if (GVSize > 4) { 1298 // We might want to use a b64 load/store 1299 Alignment = std::max(Alignment, Align(8)); 1300 } else if (GVSize > 2) { 1301 // We might want to use a b32 load/store 1302 Alignment = std::max(Alignment, Align(4)); 1303 } else if (GVSize > 1) { 1304 // We might want to use a b16 load/store 1305 Alignment = std::max(Alignment, Align(2)); 1306 } 1307 1308 if (Alignment != AMDGPU::getAlign(DL, &GV)) { 1309 Changed = true; 1310 GV.setAlignment(Alignment); 1311 } 1312 } 1313 return Changed; 1314 } 1315 1316 static LDSVariableReplacement createLDSVariableReplacement( 1317 Module &M, std::string VarName, 1318 DenseSet<GlobalVariable *> const &LDSVarsToTransform) { 1319 // Create a struct instance containing LDSVarsToTransform and map from those 1320 // variables to ConstantExprGEP 1321 // Variables may be introduced to meet alignment requirements. No aliasing 1322 // metadata is useful for these as they have no uses. Erased before return. 1323 1324 LLVMContext &Ctx = M.getContext(); 1325 const DataLayout &DL = M.getDataLayout(); 1326 assert(!LDSVarsToTransform.empty()); 1327 1328 SmallVector<OptimizedStructLayoutField, 8> LayoutFields; 1329 LayoutFields.reserve(LDSVarsToTransform.size()); 1330 { 1331 // The order of fields in this struct depends on the order of 1332 // varables in the argument which varies when changing how they 1333 // are identified, leading to spurious test breakage. 1334 auto Sorted = sortByName( 1335 std::vector(LDSVarsToTransform.begin(), LDSVarsToTransform.end())); 1336 1337 for (GlobalVariable *GV : Sorted) { 1338 OptimizedStructLayoutField F(GV, 1339 DL.getTypeAllocSize(GV->getValueType()), 1340 AMDGPU::getAlign(DL, GV)); 1341 LayoutFields.emplace_back(F); 1342 } 1343 } 1344 1345 performOptimizedStructLayout(LayoutFields); 1346 1347 std::vector<GlobalVariable *> LocalVars; 1348 BitVector IsPaddingField; 1349 LocalVars.reserve(LDSVarsToTransform.size()); // will be at least this large 1350 IsPaddingField.reserve(LDSVarsToTransform.size()); 1351 { 1352 uint64_t CurrentOffset = 0; 1353 for (size_t I = 0; I < LayoutFields.size(); I++) { 1354 GlobalVariable *FGV = static_cast<GlobalVariable *>( 1355 const_cast<void *>(LayoutFields[I].Id)); 1356 Align DataAlign = LayoutFields[I].Alignment; 1357 1358 uint64_t DataAlignV = DataAlign.value(); 1359 if (uint64_t Rem = CurrentOffset % DataAlignV) { 1360 uint64_t Padding = DataAlignV - Rem; 1361 1362 // Append an array of padding bytes to meet alignment requested 1363 // Note (o + (a - (o % a)) ) % a == 0 1364 // (offset + Padding ) % align == 0 1365 1366 Type *ATy = ArrayType::get(Type::getInt8Ty(Ctx), Padding); 1367 LocalVars.push_back(new GlobalVariable( 1368 M, ATy, false, GlobalValue::InternalLinkage, UndefValue::get(ATy), 1369 "", nullptr, GlobalValue::NotThreadLocal, AMDGPUAS::LOCAL_ADDRESS, 1370 false)); 1371 IsPaddingField.push_back(true); 1372 CurrentOffset += Padding; 1373 } 1374 1375 LocalVars.push_back(FGV); 1376 IsPaddingField.push_back(false); 1377 CurrentOffset += LayoutFields[I].Size; 1378 } 1379 } 1380 1381 std::vector<Type *> LocalVarTypes; 1382 LocalVarTypes.reserve(LocalVars.size()); 1383 std::transform( 1384 LocalVars.cbegin(), LocalVars.cend(), std::back_inserter(LocalVarTypes), 1385 [](const GlobalVariable *V) -> Type * { return V->getValueType(); }); 1386 1387 StructType *LDSTy = StructType::create(Ctx, LocalVarTypes, VarName + ".t"); 1388 1389 Align StructAlign = AMDGPU::getAlign(DL, LocalVars[0]); 1390 1391 GlobalVariable *SGV = new GlobalVariable( 1392 M, LDSTy, false, GlobalValue::InternalLinkage, UndefValue::get(LDSTy), 1393 VarName, nullptr, GlobalValue::NotThreadLocal, AMDGPUAS::LOCAL_ADDRESS, 1394 false); 1395 SGV->setAlignment(StructAlign); 1396 1397 DenseMap<GlobalVariable *, Constant *> Map; 1398 Type *I32 = Type::getInt32Ty(Ctx); 1399 for (size_t I = 0; I < LocalVars.size(); I++) { 1400 GlobalVariable *GV = LocalVars[I]; 1401 Constant *GEPIdx[] = {ConstantInt::get(I32, 0), ConstantInt::get(I32, I)}; 1402 Constant *GEP = ConstantExpr::getGetElementPtr(LDSTy, SGV, GEPIdx, true); 1403 if (IsPaddingField[I]) { 1404 assert(GV->use_empty()); 1405 GV->eraseFromParent(); 1406 } else { 1407 Map[GV] = GEP; 1408 } 1409 } 1410 assert(Map.size() == LDSVarsToTransform.size()); 1411 return {SGV, std::move(Map)}; 1412 } 1413 1414 template <typename PredicateTy> 1415 static void replaceLDSVariablesWithStruct( 1416 Module &M, DenseSet<GlobalVariable *> const &LDSVarsToTransformArg, 1417 const LDSVariableReplacement &Replacement, PredicateTy Predicate) { 1418 LLVMContext &Ctx = M.getContext(); 1419 const DataLayout &DL = M.getDataLayout(); 1420 1421 // A hack... we need to insert the aliasing info in a predictable order for 1422 // lit tests. Would like to have them in a stable order already, ideally the 1423 // same order they get allocated, which might mean an ordered set container 1424 std::vector<GlobalVariable *> LDSVarsToTransform = sortByName(std::vector( 1425 LDSVarsToTransformArg.begin(), LDSVarsToTransformArg.end())); 1426 1427 // Create alias.scope and their lists. Each field in the new structure 1428 // does not alias with all other fields. 1429 SmallVector<MDNode *> AliasScopes; 1430 SmallVector<Metadata *> NoAliasList; 1431 const size_t NumberVars = LDSVarsToTransform.size(); 1432 if (NumberVars > 1) { 1433 MDBuilder MDB(Ctx); 1434 AliasScopes.reserve(NumberVars); 1435 MDNode *Domain = MDB.createAnonymousAliasScopeDomain(); 1436 for (size_t I = 0; I < NumberVars; I++) { 1437 MDNode *Scope = MDB.createAnonymousAliasScope(Domain); 1438 AliasScopes.push_back(Scope); 1439 } 1440 NoAliasList.append(&AliasScopes[1], AliasScopes.end()); 1441 } 1442 1443 // Replace uses of ith variable with a constantexpr to the corresponding 1444 // field of the instance that will be allocated by AMDGPUMachineFunction 1445 for (size_t I = 0; I < NumberVars; I++) { 1446 GlobalVariable *GV = LDSVarsToTransform[I]; 1447 Constant *GEP = Replacement.LDSVarsToConstantGEP[GV]; 1448 1449 GV->replaceUsesWithIf(GEP, Predicate); 1450 1451 APInt APOff(DL.getIndexTypeSizeInBits(GEP->getType()), 0); 1452 GEP->stripAndAccumulateInBoundsConstantOffsets(DL, APOff); 1453 uint64_t Offset = APOff.getZExtValue(); 1454 1455 Align A = 1456 commonAlignment(Replacement.SGV->getAlign().valueOrOne(), Offset); 1457 1458 if (I) 1459 NoAliasList[I - 1] = AliasScopes[I - 1]; 1460 MDNode *NoAlias = 1461 NoAliasList.empty() ? nullptr : MDNode::get(Ctx, NoAliasList); 1462 MDNode *AliasScope = 1463 AliasScopes.empty() ? nullptr : MDNode::get(Ctx, {AliasScopes[I]}); 1464 1465 refineUsesAlignmentAndAA(GEP, A, DL, AliasScope, NoAlias); 1466 } 1467 } 1468 1469 static void refineUsesAlignmentAndAA(Value *Ptr, Align A, 1470 const DataLayout &DL, MDNode *AliasScope, 1471 MDNode *NoAlias, unsigned MaxDepth = 5) { 1472 if (!MaxDepth || (A == 1 && !AliasScope)) 1473 return; 1474 1475 for (User *U : Ptr->users()) { 1476 if (auto *I = dyn_cast<Instruction>(U)) { 1477 if (AliasScope && I->mayReadOrWriteMemory()) { 1478 MDNode *AS = I->getMetadata(LLVMContext::MD_alias_scope); 1479 AS = (AS ? MDNode::getMostGenericAliasScope(AS, AliasScope) 1480 : AliasScope); 1481 I->setMetadata(LLVMContext::MD_alias_scope, AS); 1482 1483 MDNode *NA = I->getMetadata(LLVMContext::MD_noalias); 1484 NA = (NA ? MDNode::intersect(NA, NoAlias) : NoAlias); 1485 I->setMetadata(LLVMContext::MD_noalias, NA); 1486 } 1487 } 1488 1489 if (auto *LI = dyn_cast<LoadInst>(U)) { 1490 LI->setAlignment(std::max(A, LI->getAlign())); 1491 continue; 1492 } 1493 if (auto *SI = dyn_cast<StoreInst>(U)) { 1494 if (SI->getPointerOperand() == Ptr) 1495 SI->setAlignment(std::max(A, SI->getAlign())); 1496 continue; 1497 } 1498 if (auto *AI = dyn_cast<AtomicRMWInst>(U)) { 1499 // None of atomicrmw operations can work on pointers, but let's 1500 // check it anyway in case it will or we will process ConstantExpr. 1501 if (AI->getPointerOperand() == Ptr) 1502 AI->setAlignment(std::max(A, AI->getAlign())); 1503 continue; 1504 } 1505 if (auto *AI = dyn_cast<AtomicCmpXchgInst>(U)) { 1506 if (AI->getPointerOperand() == Ptr) 1507 AI->setAlignment(std::max(A, AI->getAlign())); 1508 continue; 1509 } 1510 if (auto *GEP = dyn_cast<GetElementPtrInst>(U)) { 1511 unsigned BitWidth = DL.getIndexTypeSizeInBits(GEP->getType()); 1512 APInt Off(BitWidth, 0); 1513 if (GEP->getPointerOperand() == Ptr) { 1514 Align GA; 1515 if (GEP->accumulateConstantOffset(DL, Off)) 1516 GA = commonAlignment(A, Off.getLimitedValue()); 1517 refineUsesAlignmentAndAA(GEP, GA, DL, AliasScope, NoAlias, 1518 MaxDepth - 1); 1519 } 1520 continue; 1521 } 1522 if (auto *I = dyn_cast<Instruction>(U)) { 1523 if (I->getOpcode() == Instruction::BitCast || 1524 I->getOpcode() == Instruction::AddrSpaceCast) 1525 refineUsesAlignmentAndAA(I, A, DL, AliasScope, NoAlias, MaxDepth - 1); 1526 } 1527 } 1528 } 1529 }; 1530 1531 } // namespace 1532 char AMDGPULowerModuleLDS::ID = 0; 1533 1534 char &llvm::AMDGPULowerModuleLDSID = AMDGPULowerModuleLDS::ID; 1535 1536 INITIALIZE_PASS(AMDGPULowerModuleLDS, DEBUG_TYPE, 1537 "Lower uses of LDS variables from non-kernel functions", false, 1538 false) 1539 1540 ModulePass *llvm::createAMDGPULowerModuleLDSPass() { 1541 return new AMDGPULowerModuleLDS(); 1542 } 1543 1544 PreservedAnalyses AMDGPULowerModuleLDSPass::run(Module &M, 1545 ModuleAnalysisManager &) { 1546 return AMDGPULowerModuleLDS().runOnModule(M) ? PreservedAnalyses::none() 1547 : PreservedAnalyses::all(); 1548 } 1549