1 //===-- AMDGPULowerModuleLDSPass.cpp ------------------------------*- C++ -*-=// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // This pass eliminates local data store, LDS, uses from non-kernel functions. 10 // LDS is contiguous memory allocated per kernel execution. 11 // 12 // Background. 13 // 14 // The programming model is global variables, or equivalently function local 15 // static variables, accessible from kernels or other functions. For uses from 16 // kernels this is straightforward - assign an integer to the kernel for the 17 // memory required by all the variables combined, allocate them within that. 18 // For uses from functions there are performance tradeoffs to choose between. 19 // 20 // This model means the GPU runtime can specify the amount of memory allocated. 21 // If this is more than the kernel assumed, the excess can be made available 22 // using a language specific feature, which IR represents as a variable with 23 // no initializer. This feature is referred to here as "Dynamic LDS" and is 24 // lowered slightly differently to the normal case. 25 // 26 // Consequences of this GPU feature: 27 // - memory is limited and exceeding it halts compilation 28 // - a global accessed by one kernel exists independent of other kernels 29 // - a global exists independent of simultaneous execution of the same kernel 30 // - the address of the global may be different from different kernels as they 31 // do not alias, which permits only allocating variables they use 32 // - if the address is allowed to differ, functions need help to find it 33 // 34 // Uses from kernels are implemented here by grouping them in a per-kernel 35 // struct instance. This duplicates the variables, accurately modelling their 36 // aliasing properties relative to a single global representation. It also 37 // permits control over alignment via padding. 38 // 39 // Uses from functions are more complicated and the primary purpose of this 40 // IR pass. Several different lowering are chosen between to meet requirements 41 // to avoid allocating any LDS where it is not necessary, as that impacts 42 // occupancy and may fail the compilation, while not imposing overhead on a 43 // feature whose primary advantage over global memory is performance. The basic 44 // design goal is to avoid one kernel imposing overhead on another. 45 // 46 // Implementation. 47 // 48 // LDS variables with constant annotation or non-undef initializer are passed 49 // through unchanged for simplification or error diagnostics in later passes. 50 // Non-undef initializers are not yet implemented for LDS. 51 // 52 // LDS variables that are always allocated at the same address can be found 53 // by lookup at that address. Otherwise runtime information/cost is required. 54 // 55 // The simplest strategy possible is to group all LDS variables in a single 56 // struct and allocate that struct in every kernel such that the original 57 // variables are always at the same address. LDS is however a limited resource 58 // so this strategy is unusable in practice. It is not implemented here. 59 // 60 // Strategy | Precise allocation | Zero runtime cost | General purpose | 61 // --------+--------------------+-------------------+-----------------+ 62 // Module | No | Yes | Yes | 63 // Table | Yes | No | Yes | 64 // Kernel | Yes | Yes | No | 65 // Hybrid | Yes | Partial | Yes | 66 // 67 // "Module" spends LDS memory to save cycles. "Table" spends cycles and global 68 // memory to save LDS. "Kernel" is as fast as kernel allocation but only works 69 // for variables that are known reachable from a single kernel. "Hybrid" picks 70 // between all three. When forced to choose between LDS and cycles we minimise 71 // LDS use. 72 73 // The "module" lowering implemented here finds LDS variables which are used by 74 // non-kernel functions and creates a new struct with a field for each of those 75 // LDS variables. Variables that are only used from kernels are excluded. 76 // Kernels that do not use this struct are annoteated with the attribute 77 // amdgpu-elide-module-lds which allows the back end to elide the allocation. 78 // 79 // The "table" lowering implemented here has three components. 80 // First kernels are assigned a unique integer identifier which is available in 81 // functions it calls through the intrinsic amdgcn_lds_kernel_id. The integer 82 // is passed through a specific SGPR, thus works with indirect calls. 83 // Second, each kernel allocates LDS variables independent of other kernels and 84 // writes the addresses it chose for each variable into an array in consistent 85 // order. If the kernel does not allocate a given variable, it writes undef to 86 // the corresponding array location. These arrays are written to a constant 87 // table in the order matching the kernel unique integer identifier. 88 // Third, uses from non-kernel functions are replaced with a table lookup using 89 // the intrinsic function to find the address of the variable. 90 // 91 // "Kernel" lowering is only applicable for variables that are unambiguously 92 // reachable from exactly one kernel. For those cases, accesses to the variable 93 // can be lowered to ConstantExpr address of a struct instance specific to that 94 // one kernel. This is zero cost in space and in compute. It will raise a fatal 95 // error on any variable that might be reachable from multiple kernels and is 96 // thus most easily used as part of the hybrid lowering strategy. 97 // 98 // Hybrid lowering is a mixture of the above. It uses the zero cost kernel 99 // lowering where it can. It lowers the variable accessed by the greatest 100 // number of kernels using the module strategy as that is free for the first 101 // variable. Any futher variables that can be lowered with the module strategy 102 // without incurring LDS memory overhead are. The remaining ones are lowered 103 // via table. 104 // 105 // Consequences 106 // - No heuristics or user controlled magic numbers, hybrid is the right choice 107 // - Kernels that don't use functions (or have had them all inlined) are not 108 // affected by any lowering for kernels that do. 109 // - Kernels that don't make indirect function calls are not affected by those 110 // that do. 111 // - Variables which are used by lots of kernels, e.g. those injected by a 112 // language runtime in most kernels, are expected to have no overhead 113 // - Implementations that instantiate templates per-kernel where those templates 114 // use LDS are expected to hit the "Kernel" lowering strategy 115 // - The runtime properties impose a cost in compiler implementation complexity 116 // 117 // Dynamic LDS implementation 118 // Dynamic LDS is lowered similarly to the "table" strategy above and uses the 119 // same intrinsic to identify which kernel is at the root of the dynamic call 120 // graph. This relies on the specified behaviour that all dynamic LDS variables 121 // alias one another, i.e. are at the same address, with respect to a given 122 // kernel. Therefore this pass creates new dynamic LDS variables for each kernel 123 // that allocates any dynamic LDS and builds a table of addresses out of those. 124 // The AMDGPUPromoteAlloca pass skips kernels that use dynamic LDS. 125 // The corresponding optimisation for "kernel" lowering where the table lookup 126 // is elided is not implemented. 127 // 128 // 129 // Implementation notes / limitations 130 // A single LDS global variable represents an instance per kernel that can reach 131 // said variables. This pass essentially specialises said variables per kernel. 132 // Handling ConstantExpr during the pass complicated this significantly so now 133 // all ConstantExpr uses of LDS variables are expanded to instructions. This 134 // may need amending when implementing non-undef initialisers. 135 // 136 // Lowering is split between this IR pass and the back end. This pass chooses 137 // where given variables should be allocated and marks them with metadata, 138 // MD_absolute_symbol. The backend places the variables in coincidentally the 139 // same location and raises a fatal error if something has gone awry. This works 140 // in practice because the only pass between this one and the backend that 141 // changes LDS is PromoteAlloca and the changes it makes do not conflict. 142 // 143 // Addresses are written to constant global arrays based on the same metadata. 144 // 145 // The backend lowers LDS variables in the order of traversal of the function. 146 // This is at odds with the deterministic layout required. The workaround is to 147 // allocate the fixed-address variables immediately upon starting the function 148 // where they can be placed as intended. This requires a means of mapping from 149 // the function to the variables that it allocates. For the module scope lds, 150 // this is via metadata indicating whether the variable is not required. If a 151 // pass deletes that metadata, a fatal error on disagreement with the absolute 152 // symbol metadata will occur. For kernel scope and dynamic, this is by _name_ 153 // correspondence between the function and the variable. It requires the 154 // kernel to have a name (which is only a limitation for tests in practice) and 155 // for nothing to rename the corresponding symbols. This is a hazard if the pass 156 // is run multiple times during debugging. Alternative schemes considered all 157 // involve bespoke metadata. 158 // 159 // If the name correspondence can be replaced, multiple distinct kernels that 160 // have the same memory layout can map to the same kernel id (as the address 161 // itself is handled by the absolute symbol metadata) and that will allow more 162 // uses of the "kernel" style faster lowering and reduce the size of the lookup 163 // tables. 164 // 165 // There is a test that checks this does not fire for a graphics shader. This 166 // lowering is expected to work for graphics if the isKernel test is changed. 167 // 168 // The current markUsedByKernel is sufficient for PromoteAlloca but is elided 169 // before codegen. Replacing this with an equivalent intrinsic which lasts until 170 // shortly after the machine function lowering of LDS would help break the name 171 // mapping. The other part needed is probably to amend PromoteAlloca to embed 172 // the LDS variables it creates in the same struct created here. That avoids the 173 // current hazard where a PromoteAlloca LDS variable might be allocated before 174 // the kernel scope (and thus error on the address check). Given a new invariant 175 // that no LDS variables exist outside of the structs managed here, and an 176 // intrinsic that lasts until after the LDS frame lowering, it should be 177 // possible to drop the name mapping and fold equivalent memory layouts. 178 // 179 //===----------------------------------------------------------------------===// 180 181 #include "AMDGPU.h" 182 #include "Utils/AMDGPUBaseInfo.h" 183 #include "Utils/AMDGPUMemoryUtils.h" 184 #include "llvm/ADT/BitVector.h" 185 #include "llvm/ADT/DenseMap.h" 186 #include "llvm/ADT/DenseSet.h" 187 #include "llvm/ADT/STLExtras.h" 188 #include "llvm/ADT/SetOperations.h" 189 #include "llvm/ADT/SetVector.h" 190 #include "llvm/Analysis/CallGraph.h" 191 #include "llvm/IR/Constants.h" 192 #include "llvm/IR/DerivedTypes.h" 193 #include "llvm/IR/IRBuilder.h" 194 #include "llvm/IR/InlineAsm.h" 195 #include "llvm/IR/Instructions.h" 196 #include "llvm/IR/IntrinsicsAMDGPU.h" 197 #include "llvm/IR/MDBuilder.h" 198 #include "llvm/IR/ReplaceConstant.h" 199 #include "llvm/InitializePasses.h" 200 #include "llvm/Pass.h" 201 #include "llvm/Support/CommandLine.h" 202 #include "llvm/Support/Debug.h" 203 #include "llvm/Support/OptimizedStructLayout.h" 204 #include "llvm/Transforms/Utils/BasicBlockUtils.h" 205 #include "llvm/Transforms/Utils/ModuleUtils.h" 206 207 #include <tuple> 208 #include <vector> 209 210 #include <cstdio> 211 212 #define DEBUG_TYPE "amdgpu-lower-module-lds" 213 214 using namespace llvm; 215 216 namespace { 217 218 cl::opt<bool> SuperAlignLDSGlobals( 219 "amdgpu-super-align-lds-globals", 220 cl::desc("Increase alignment of LDS if it is not on align boundary"), 221 cl::init(true), cl::Hidden); 222 223 enum class LoweringKind { module, table, kernel, hybrid }; 224 cl::opt<LoweringKind> LoweringKindLoc( 225 "amdgpu-lower-module-lds-strategy", 226 cl::desc("Specify lowering strategy for function LDS access:"), cl::Hidden, 227 cl::init(LoweringKind::hybrid), 228 cl::values( 229 clEnumValN(LoweringKind::table, "table", "Lower via table lookup"), 230 clEnumValN(LoweringKind::module, "module", "Lower via module struct"), 231 clEnumValN( 232 LoweringKind::kernel, "kernel", 233 "Lower variables reachable from one kernel, otherwise abort"), 234 clEnumValN(LoweringKind::hybrid, "hybrid", 235 "Lower via mixture of above strategies"))); 236 237 bool isKernelLDS(const Function *F) { 238 // Some weirdness here. AMDGPU::isKernelCC does not call into 239 // AMDGPU::isKernel with the calling conv, it instead calls into 240 // isModuleEntryFunction which returns true for more calling conventions 241 // than AMDGPU::isKernel does. There's a FIXME on AMDGPU::isKernel. 242 // There's also a test that checks that the LDS lowering does not hit on 243 // a graphics shader, denoted amdgpu_ps, so stay with the limited case. 244 // Putting LDS in the name of the function to draw attention to this. 245 return AMDGPU::isKernel(F->getCallingConv()); 246 } 247 248 template <typename T> std::vector<T> sortByName(std::vector<T> &&V) { 249 llvm::sort(V.begin(), V.end(), [](const auto *L, const auto *R) { 250 return L->getName() < R->getName(); 251 }); 252 return {std::move(V)}; 253 } 254 255 class AMDGPULowerModuleLDS : public ModulePass { 256 257 static void 258 removeLocalVarsFromUsedLists(Module &M, 259 const DenseSet<GlobalVariable *> &LocalVars) { 260 // The verifier rejects used lists containing an inttoptr of a constant 261 // so remove the variables from these lists before replaceAllUsesWith 262 SmallPtrSet<Constant *, 8> LocalVarsSet; 263 for (GlobalVariable *LocalVar : LocalVars) 264 LocalVarsSet.insert(cast<Constant>(LocalVar->stripPointerCasts())); 265 266 removeFromUsedLists( 267 M, [&LocalVarsSet](Constant *C) { return LocalVarsSet.count(C); }); 268 269 for (GlobalVariable *LocalVar : LocalVars) 270 LocalVar->removeDeadConstantUsers(); 271 } 272 273 static void markUsedByKernel(IRBuilder<> &Builder, Function *Func, 274 GlobalVariable *SGV) { 275 // The llvm.amdgcn.module.lds instance is implicitly used by all kernels 276 // that might call a function which accesses a field within it. This is 277 // presently approximated to 'all kernels' if there are any such functions 278 // in the module. This implicit use is redefined as an explicit use here so 279 // that later passes, specifically PromoteAlloca, account for the required 280 // memory without any knowledge of this transform. 281 282 // An operand bundle on llvm.donothing works because the call instruction 283 // survives until after the last pass that needs to account for LDS. It is 284 // better than inline asm as the latter survives until the end of codegen. A 285 // totally robust solution would be a function with the same semantics as 286 // llvm.donothing that takes a pointer to the instance and is lowered to a 287 // no-op after LDS is allocated, but that is not presently necessary. 288 289 // This intrinsic is eliminated shortly before instruction selection. It 290 // does not suffice to indicate to ISel that a given global which is not 291 // immediately used by the kernel must still be allocated by it. An 292 // equivalent target specific intrinsic which lasts until immediately after 293 // codegen would suffice for that, but one would still need to ensure that 294 // the variables are allocated in the anticpated order. 295 296 LLVMContext &Ctx = Func->getContext(); 297 298 Builder.SetInsertPoint(Func->getEntryBlock().getFirstNonPHI()); 299 300 FunctionType *FTy = FunctionType::get(Type::getVoidTy(Ctx), {}); 301 302 Function *Decl = 303 Intrinsic::getDeclaration(Func->getParent(), Intrinsic::donothing, {}); 304 305 Value *UseInstance[1] = {Builder.CreateInBoundsGEP( 306 SGV->getValueType(), SGV, ConstantInt::get(Type::getInt32Ty(Ctx), 0))}; 307 308 Builder.CreateCall(FTy, Decl, {}, 309 {OperandBundleDefT<Value *>("ExplicitUse", UseInstance)}, 310 ""); 311 } 312 313 static bool eliminateConstantExprUsesOfLDSFromAllInstructions(Module &M) { 314 // Constants are uniqued within LLVM. A ConstantExpr referring to a LDS 315 // global may have uses from multiple different functions as a result. 316 // This pass specialises LDS variables with respect to the kernel that 317 // allocates them. 318 319 // This is semantically equivalent to (the unimplemented as slow): 320 // for (auto &F : M.functions()) 321 // for (auto &BB : F) 322 // for (auto &I : BB) 323 // for (Use &Op : I.operands()) 324 // if (constantExprUsesLDS(Op)) 325 // replaceConstantExprInFunction(I, Op); 326 327 SmallVector<Constant *> LDSGlobals; 328 for (auto &GV : M.globals()) 329 if (AMDGPU::isLDSVariableToLower(GV)) 330 LDSGlobals.push_back(&GV); 331 332 return convertUsersOfConstantsToInstructions(LDSGlobals); 333 } 334 335 public: 336 static char ID; 337 338 AMDGPULowerModuleLDS() : ModulePass(ID) { 339 initializeAMDGPULowerModuleLDSPass(*PassRegistry::getPassRegistry()); 340 } 341 342 using FunctionVariableMap = DenseMap<Function *, DenseSet<GlobalVariable *>>; 343 344 using VariableFunctionMap = DenseMap<GlobalVariable *, DenseSet<Function *>>; 345 346 static void getUsesOfLDSByFunction(CallGraph const &CG, Module &M, 347 FunctionVariableMap &kernels, 348 FunctionVariableMap &functions) { 349 350 // Get uses from the current function, excluding uses by called functions 351 // Two output variables to avoid walking the globals list twice 352 for (auto &GV : M.globals()) { 353 if (!AMDGPU::isLDSVariableToLower(GV)) { 354 continue; 355 } 356 357 if (GV.isAbsoluteSymbolRef()) { 358 report_fatal_error( 359 "LDS variables with absolute addresses are unimplemented."); 360 } 361 362 for (User *V : GV.users()) { 363 if (auto *I = dyn_cast<Instruction>(V)) { 364 Function *F = I->getFunction(); 365 if (isKernelLDS(F)) { 366 kernels[F].insert(&GV); 367 } else { 368 functions[F].insert(&GV); 369 } 370 } 371 } 372 } 373 } 374 375 struct LDSUsesInfoTy { 376 FunctionVariableMap direct_access; 377 FunctionVariableMap indirect_access; 378 }; 379 380 static LDSUsesInfoTy getTransitiveUsesOfLDS(CallGraph const &CG, Module &M) { 381 382 FunctionVariableMap direct_map_kernel; 383 FunctionVariableMap direct_map_function; 384 getUsesOfLDSByFunction(CG, M, direct_map_kernel, direct_map_function); 385 386 // Collect variables that are used by functions whose address has escaped 387 DenseSet<GlobalVariable *> VariablesReachableThroughFunctionPointer; 388 for (Function &F : M.functions()) { 389 if (!isKernelLDS(&F)) 390 if (F.hasAddressTaken(nullptr, 391 /* IgnoreCallbackUses */ false, 392 /* IgnoreAssumeLikeCalls */ false, 393 /* IgnoreLLVMUsed */ true, 394 /* IgnoreArcAttachedCall */ false)) { 395 set_union(VariablesReachableThroughFunctionPointer, 396 direct_map_function[&F]); 397 } 398 } 399 400 auto functionMakesUnknownCall = [&](const Function *F) -> bool { 401 assert(!F->isDeclaration()); 402 for (const CallGraphNode::CallRecord &R : *CG[F]) { 403 if (!R.second->getFunction()) { 404 return true; 405 } 406 } 407 return false; 408 }; 409 410 // Work out which variables are reachable through function calls 411 FunctionVariableMap transitive_map_function = direct_map_function; 412 413 // If the function makes any unknown call, assume the worst case that it can 414 // access all variables accessed by functions whose address escaped 415 for (Function &F : M.functions()) { 416 if (!F.isDeclaration() && functionMakesUnknownCall(&F)) { 417 if (!isKernelLDS(&F)) { 418 set_union(transitive_map_function[&F], 419 VariablesReachableThroughFunctionPointer); 420 } 421 } 422 } 423 424 // Direct implementation of collecting all variables reachable from each 425 // function 426 for (Function &Func : M.functions()) { 427 if (Func.isDeclaration() || isKernelLDS(&Func)) 428 continue; 429 430 DenseSet<Function *> seen; // catches cycles 431 SmallVector<Function *, 4> wip{&Func}; 432 433 while (!wip.empty()) { 434 Function *F = wip.pop_back_val(); 435 436 // Can accelerate this by referring to transitive map for functions that 437 // have already been computed, with more care than this 438 set_union(transitive_map_function[&Func], direct_map_function[F]); 439 440 for (const CallGraphNode::CallRecord &R : *CG[F]) { 441 Function *ith = R.second->getFunction(); 442 if (ith) { 443 if (!seen.contains(ith)) { 444 seen.insert(ith); 445 wip.push_back(ith); 446 } 447 } 448 } 449 } 450 } 451 452 // direct_map_kernel lists which variables are used by the kernel 453 // find the variables which are used through a function call 454 FunctionVariableMap indirect_map_kernel; 455 456 for (Function &Func : M.functions()) { 457 if (Func.isDeclaration() || !isKernelLDS(&Func)) 458 continue; 459 460 for (const CallGraphNode::CallRecord &R : *CG[&Func]) { 461 Function *ith = R.second->getFunction(); 462 if (ith) { 463 set_union(indirect_map_kernel[&Func], transitive_map_function[ith]); 464 } else { 465 set_union(indirect_map_kernel[&Func], 466 VariablesReachableThroughFunctionPointer); 467 } 468 } 469 } 470 471 return {std::move(direct_map_kernel), std::move(indirect_map_kernel)}; 472 } 473 474 struct LDSVariableReplacement { 475 GlobalVariable *SGV = nullptr; 476 DenseMap<GlobalVariable *, Constant *> LDSVarsToConstantGEP; 477 }; 478 479 // remap from lds global to a constantexpr gep to where it has been moved to 480 // for each kernel 481 // an array with an element for each kernel containing where the corresponding 482 // variable was remapped to 483 484 static Constant *getAddressesOfVariablesInKernel( 485 LLVMContext &Ctx, ArrayRef<GlobalVariable *> Variables, 486 const DenseMap<GlobalVariable *, Constant *> &LDSVarsToConstantGEP) { 487 // Create a ConstantArray containing the address of each Variable within the 488 // kernel corresponding to LDSVarsToConstantGEP, or poison if that kernel 489 // does not allocate it 490 // TODO: Drop the ptrtoint conversion 491 492 Type *I32 = Type::getInt32Ty(Ctx); 493 494 ArrayType *KernelOffsetsType = ArrayType::get(I32, Variables.size()); 495 496 SmallVector<Constant *> Elements; 497 for (size_t i = 0; i < Variables.size(); i++) { 498 GlobalVariable *GV = Variables[i]; 499 auto ConstantGepIt = LDSVarsToConstantGEP.find(GV); 500 if (ConstantGepIt != LDSVarsToConstantGEP.end()) { 501 auto elt = ConstantExpr::getPtrToInt(ConstantGepIt->second, I32); 502 Elements.push_back(elt); 503 } else { 504 Elements.push_back(PoisonValue::get(I32)); 505 } 506 } 507 return ConstantArray::get(KernelOffsetsType, Elements); 508 } 509 510 static GlobalVariable *buildLookupTable( 511 Module &M, ArrayRef<GlobalVariable *> Variables, 512 ArrayRef<Function *> kernels, 513 DenseMap<Function *, LDSVariableReplacement> &KernelToReplacement) { 514 if (Variables.empty()) { 515 return nullptr; 516 } 517 LLVMContext &Ctx = M.getContext(); 518 519 const size_t NumberVariables = Variables.size(); 520 const size_t NumberKernels = kernels.size(); 521 522 ArrayType *KernelOffsetsType = 523 ArrayType::get(Type::getInt32Ty(Ctx), NumberVariables); 524 525 ArrayType *AllKernelsOffsetsType = 526 ArrayType::get(KernelOffsetsType, NumberKernels); 527 528 Constant *Missing = PoisonValue::get(KernelOffsetsType); 529 std::vector<Constant *> overallConstantExprElts(NumberKernels); 530 for (size_t i = 0; i < NumberKernels; i++) { 531 auto Replacement = KernelToReplacement.find(kernels[i]); 532 overallConstantExprElts[i] = 533 (Replacement == KernelToReplacement.end()) 534 ? Missing 535 : getAddressesOfVariablesInKernel( 536 Ctx, Variables, Replacement->second.LDSVarsToConstantGEP); 537 } 538 539 Constant *init = 540 ConstantArray::get(AllKernelsOffsetsType, overallConstantExprElts); 541 542 return new GlobalVariable( 543 M, AllKernelsOffsetsType, true, GlobalValue::InternalLinkage, init, 544 "llvm.amdgcn.lds.offset.table", nullptr, GlobalValue::NotThreadLocal, 545 AMDGPUAS::CONSTANT_ADDRESS); 546 } 547 548 void replaceUseWithTableLookup(Module &M, IRBuilder<> &Builder, 549 GlobalVariable *LookupTable, 550 GlobalVariable *GV, Use &U, 551 Value *OptionalIndex) { 552 // Table is a constant array of the same length as OrderedKernels 553 LLVMContext &Ctx = M.getContext(); 554 Type *I32 = Type::getInt32Ty(Ctx); 555 auto *I = cast<Instruction>(U.getUser()); 556 557 Value *tableKernelIndex = getTableLookupKernelIndex(M, I->getFunction()); 558 559 if (auto *Phi = dyn_cast<PHINode>(I)) { 560 BasicBlock *BB = Phi->getIncomingBlock(U); 561 Builder.SetInsertPoint(&(*(BB->getFirstInsertionPt()))); 562 } else { 563 Builder.SetInsertPoint(I); 564 } 565 566 SmallVector<Value *, 3> GEPIdx = { 567 ConstantInt::get(I32, 0), 568 tableKernelIndex, 569 }; 570 if (OptionalIndex) 571 GEPIdx.push_back(OptionalIndex); 572 573 Value *Address = Builder.CreateInBoundsGEP( 574 LookupTable->getValueType(), LookupTable, GEPIdx, GV->getName()); 575 576 Value *loaded = Builder.CreateLoad(I32, Address); 577 578 Value *replacement = 579 Builder.CreateIntToPtr(loaded, GV->getType(), GV->getName()); 580 581 U.set(replacement); 582 } 583 584 void replaceUsesInInstructionsWithTableLookup( 585 Module &M, ArrayRef<GlobalVariable *> ModuleScopeVariables, 586 GlobalVariable *LookupTable) { 587 588 LLVMContext &Ctx = M.getContext(); 589 IRBuilder<> Builder(Ctx); 590 Type *I32 = Type::getInt32Ty(Ctx); 591 592 for (size_t Index = 0; Index < ModuleScopeVariables.size(); Index++) { 593 auto *GV = ModuleScopeVariables[Index]; 594 595 for (Use &U : make_early_inc_range(GV->uses())) { 596 auto *I = dyn_cast<Instruction>(U.getUser()); 597 if (!I) 598 continue; 599 600 replaceUseWithTableLookup(M, Builder, LookupTable, GV, U, 601 ConstantInt::get(I32, Index)); 602 } 603 } 604 } 605 606 static DenseSet<Function *> kernelsThatIndirectlyAccessAnyOfPassedVariables( 607 Module &M, LDSUsesInfoTy &LDSUsesInfo, 608 DenseSet<GlobalVariable *> const &VariableSet) { 609 610 DenseSet<Function *> KernelSet; 611 612 if (VariableSet.empty()) 613 return KernelSet; 614 615 for (Function &Func : M.functions()) { 616 if (Func.isDeclaration() || !isKernelLDS(&Func)) 617 continue; 618 for (GlobalVariable *GV : LDSUsesInfo.indirect_access[&Func]) { 619 if (VariableSet.contains(GV)) { 620 KernelSet.insert(&Func); 621 break; 622 } 623 } 624 } 625 626 return KernelSet; 627 } 628 629 static GlobalVariable * 630 chooseBestVariableForModuleStrategy(const DataLayout &DL, 631 VariableFunctionMap &LDSVars) { 632 // Find the global variable with the most indirect uses from kernels 633 634 struct CandidateTy { 635 GlobalVariable *GV = nullptr; 636 size_t UserCount = 0; 637 size_t Size = 0; 638 639 CandidateTy() = default; 640 641 CandidateTy(GlobalVariable *GV, uint64_t UserCount, uint64_t AllocSize) 642 : GV(GV), UserCount(UserCount), Size(AllocSize) {} 643 644 bool operator<(const CandidateTy &Other) const { 645 // Fewer users makes module scope variable less attractive 646 if (UserCount < Other.UserCount) { 647 return true; 648 } 649 if (UserCount > Other.UserCount) { 650 return false; 651 } 652 653 // Bigger makes module scope variable less attractive 654 if (Size < Other.Size) { 655 return false; 656 } 657 658 if (Size > Other.Size) { 659 return true; 660 } 661 662 // Arbitrary but consistent 663 return GV->getName() < Other.GV->getName(); 664 } 665 }; 666 667 CandidateTy MostUsed; 668 669 for (auto &K : LDSVars) { 670 GlobalVariable *GV = K.first; 671 if (K.second.size() <= 1) { 672 // A variable reachable by only one kernel is best lowered with kernel 673 // strategy 674 continue; 675 } 676 CandidateTy Candidate( 677 GV, K.second.size(), 678 DL.getTypeAllocSize(GV->getValueType()).getFixedValue()); 679 if (MostUsed < Candidate) 680 MostUsed = Candidate; 681 } 682 683 return MostUsed.GV; 684 } 685 686 static void recordLDSAbsoluteAddress(Module *M, GlobalVariable *GV, 687 uint32_t Address) { 688 // Write the specified address into metadata where it can be retrieved by 689 // the assembler. Format is a half open range, [Address Address+1) 690 LLVMContext &Ctx = M->getContext(); 691 auto *IntTy = 692 M->getDataLayout().getIntPtrType(Ctx, AMDGPUAS::LOCAL_ADDRESS); 693 auto *MinC = ConstantAsMetadata::get(ConstantInt::get(IntTy, Address)); 694 auto *MaxC = ConstantAsMetadata::get(ConstantInt::get(IntTy, Address + 1)); 695 GV->setMetadata(LLVMContext::MD_absolute_symbol, 696 MDNode::get(Ctx, {MinC, MaxC})); 697 } 698 699 DenseMap<Function *, Value *> tableKernelIndexCache; 700 Value *getTableLookupKernelIndex(Module &M, Function *F) { 701 // Accesses from a function use the amdgcn_lds_kernel_id intrinsic which 702 // lowers to a read from a live in register. Emit it once in the entry 703 // block to spare deduplicating it later. 704 if (tableKernelIndexCache.count(F) == 0) { 705 LLVMContext &Ctx = M.getContext(); 706 IRBuilder<> Builder(Ctx); 707 FunctionType *FTy = FunctionType::get(Type::getInt32Ty(Ctx), {}); 708 Function *Decl = 709 Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_lds_kernel_id, {}); 710 711 BasicBlock::iterator it = 712 F->getEntryBlock().getFirstNonPHIOrDbgOrAlloca(); 713 Instruction &i = *it; 714 Builder.SetInsertPoint(&i); 715 716 tableKernelIndexCache[F] = Builder.CreateCall(FTy, Decl, {}); 717 } 718 719 return tableKernelIndexCache[F]; 720 } 721 722 static std::vector<Function *> assignLDSKernelIDToEachKernel( 723 Module *M, DenseSet<Function *> const &KernelsThatAllocateTableLDS, 724 DenseSet<Function *> const &KernelsThatIndirectlyAllocateDynamicLDS) { 725 // Associate kernels in the set with an arbirary but reproducible order and 726 // annotate them with that order in metadata. This metadata is recognised by 727 // the backend and lowered to a SGPR which can be read from using 728 // amdgcn_lds_kernel_id. 729 730 std::vector<Function *> OrderedKernels; 731 if (!KernelsThatAllocateTableLDS.empty() || 732 !KernelsThatIndirectlyAllocateDynamicLDS.empty()) { 733 734 for (Function &Func : M->functions()) { 735 if (Func.isDeclaration()) 736 continue; 737 if (!isKernelLDS(&Func)) 738 continue; 739 740 if (KernelsThatAllocateTableLDS.contains(&Func) || 741 KernelsThatIndirectlyAllocateDynamicLDS.contains(&Func)) { 742 assert(Func.hasName()); // else fatal error earlier 743 OrderedKernels.push_back(&Func); 744 } 745 } 746 747 // Put them in an arbitrary but reproducible order 748 OrderedKernels = sortByName(std::move(OrderedKernels)); 749 750 // Annotate the kernels with their order in this vector 751 LLVMContext &Ctx = M->getContext(); 752 IRBuilder<> Builder(Ctx); 753 754 if (OrderedKernels.size() > UINT32_MAX) { 755 // 32 bit keeps it in one SGPR. > 2**32 kernels won't fit on the GPU 756 report_fatal_error("Unimplemented LDS lowering for > 2**32 kernels"); 757 } 758 759 for (size_t i = 0; i < OrderedKernels.size(); i++) { 760 Metadata *AttrMDArgs[1] = { 761 ConstantAsMetadata::get(Builder.getInt32(i)), 762 }; 763 OrderedKernels[i]->setMetadata("llvm.amdgcn.lds.kernel.id", 764 MDNode::get(Ctx, AttrMDArgs)); 765 } 766 } 767 return OrderedKernels; 768 } 769 770 static void partitionVariablesIntoIndirectStrategies( 771 Module &M, LDSUsesInfoTy const &LDSUsesInfo, 772 VariableFunctionMap &LDSToKernelsThatNeedToAccessItIndirectly, 773 DenseSet<GlobalVariable *> &ModuleScopeVariables, 774 DenseSet<GlobalVariable *> &TableLookupVariables, 775 DenseSet<GlobalVariable *> &KernelAccessVariables, 776 DenseSet<GlobalVariable *> &DynamicVariables) { 777 778 GlobalVariable *HybridModuleRoot = 779 LoweringKindLoc != LoweringKind::hybrid 780 ? nullptr 781 : chooseBestVariableForModuleStrategy( 782 M.getDataLayout(), LDSToKernelsThatNeedToAccessItIndirectly); 783 784 DenseSet<Function *> const EmptySet; 785 DenseSet<Function *> const &HybridModuleRootKernels = 786 HybridModuleRoot 787 ? LDSToKernelsThatNeedToAccessItIndirectly[HybridModuleRoot] 788 : EmptySet; 789 790 for (auto &K : LDSToKernelsThatNeedToAccessItIndirectly) { 791 // Each iteration of this loop assigns exactly one global variable to 792 // exactly one of the implementation strategies. 793 794 GlobalVariable *GV = K.first; 795 assert(AMDGPU::isLDSVariableToLower(*GV)); 796 assert(K.second.size() != 0); 797 798 if (AMDGPU::isDynamicLDS(*GV)) { 799 DynamicVariables.insert(GV); 800 continue; 801 } 802 803 switch (LoweringKindLoc) { 804 case LoweringKind::module: 805 ModuleScopeVariables.insert(GV); 806 break; 807 808 case LoweringKind::table: 809 TableLookupVariables.insert(GV); 810 break; 811 812 case LoweringKind::kernel: 813 if (K.second.size() == 1) { 814 KernelAccessVariables.insert(GV); 815 } else { 816 report_fatal_error( 817 "cannot lower LDS '" + GV->getName() + 818 "' to kernel access as it is reachable from multiple kernels"); 819 } 820 break; 821 822 case LoweringKind::hybrid: { 823 if (GV == HybridModuleRoot) { 824 assert(K.second.size() != 1); 825 ModuleScopeVariables.insert(GV); 826 } else if (K.second.size() == 1) { 827 KernelAccessVariables.insert(GV); 828 } else if (set_is_subset(K.second, HybridModuleRootKernels)) { 829 ModuleScopeVariables.insert(GV); 830 } else { 831 TableLookupVariables.insert(GV); 832 } 833 break; 834 } 835 } 836 } 837 838 // All LDS variables accessed indirectly have now been partitioned into 839 // the distinct lowering strategies. 840 assert(ModuleScopeVariables.size() + TableLookupVariables.size() + 841 KernelAccessVariables.size() + DynamicVariables.size() == 842 LDSToKernelsThatNeedToAccessItIndirectly.size()); 843 } 844 845 static GlobalVariable *lowerModuleScopeStructVariables( 846 Module &M, DenseSet<GlobalVariable *> const &ModuleScopeVariables, 847 DenseSet<Function *> const &KernelsThatAllocateModuleLDS) { 848 // Create a struct to hold the ModuleScopeVariables 849 // Replace all uses of those variables from non-kernel functions with the 850 // new struct instance Replace only the uses from kernel functions that will 851 // allocate this instance. That is a space optimisation - kernels that use a 852 // subset of the module scope struct and do not need to allocate it for 853 // indirect calls will only allocate the subset they use (they do so as part 854 // of the per-kernel lowering). 855 if (ModuleScopeVariables.empty()) { 856 return nullptr; 857 } 858 859 LLVMContext &Ctx = M.getContext(); 860 861 LDSVariableReplacement ModuleScopeReplacement = 862 createLDSVariableReplacement(M, "llvm.amdgcn.module.lds", 863 ModuleScopeVariables); 864 865 appendToCompilerUsed(M, {static_cast<GlobalValue *>( 866 ConstantExpr::getPointerBitCastOrAddrSpaceCast( 867 cast<Constant>(ModuleScopeReplacement.SGV), 868 Type::getInt8PtrTy(Ctx)))}); 869 870 // module.lds will be allocated at zero in any kernel that allocates it 871 recordLDSAbsoluteAddress(&M, ModuleScopeReplacement.SGV, 0); 872 873 // historic 874 removeLocalVarsFromUsedLists(M, ModuleScopeVariables); 875 876 // Replace all uses of module scope variable from non-kernel functions 877 replaceLDSVariablesWithStruct( 878 M, ModuleScopeVariables, ModuleScopeReplacement, [&](Use &U) { 879 Instruction *I = dyn_cast<Instruction>(U.getUser()); 880 if (!I) { 881 return false; 882 } 883 Function *F = I->getFunction(); 884 return !isKernelLDS(F); 885 }); 886 887 // Replace uses of module scope variable from kernel functions that 888 // allocate the module scope variable, otherwise leave them unchanged 889 // Record on each kernel whether the module scope global is used by it 890 891 IRBuilder<> Builder(Ctx); 892 893 for (Function &Func : M.functions()) { 894 if (Func.isDeclaration() || !isKernelLDS(&Func)) 895 continue; 896 897 if (KernelsThatAllocateModuleLDS.contains(&Func)) { 898 replaceLDSVariablesWithStruct( 899 M, ModuleScopeVariables, ModuleScopeReplacement, [&](Use &U) { 900 Instruction *I = dyn_cast<Instruction>(U.getUser()); 901 if (!I) { 902 return false; 903 } 904 Function *F = I->getFunction(); 905 return F == &Func; 906 }); 907 908 markUsedByKernel(Builder, &Func, ModuleScopeReplacement.SGV); 909 910 } else { 911 markElideModuleLDS(Func); 912 } 913 } 914 915 return ModuleScopeReplacement.SGV; 916 } 917 918 static DenseMap<Function *, LDSVariableReplacement> 919 lowerKernelScopeStructVariables( 920 Module &M, LDSUsesInfoTy &LDSUsesInfo, 921 DenseSet<GlobalVariable *> const &ModuleScopeVariables, 922 DenseSet<Function *> const &KernelsThatAllocateModuleLDS, 923 GlobalVariable *MaybeModuleScopeStruct) { 924 925 // Create a struct for each kernel for the non-module-scope variables. 926 927 IRBuilder<> Builder(M.getContext()); 928 DenseMap<Function *, LDSVariableReplacement> KernelToReplacement; 929 for (Function &Func : M.functions()) { 930 if (Func.isDeclaration() || !isKernelLDS(&Func)) 931 continue; 932 933 DenseSet<GlobalVariable *> KernelUsedVariables; 934 // Allocating variables that are used directly in this struct to get 935 // alignment aware allocation and predictable frame size. 936 for (auto &v : LDSUsesInfo.direct_access[&Func]) { 937 if (!AMDGPU::isDynamicLDS(*v)) { 938 KernelUsedVariables.insert(v); 939 } 940 } 941 942 // Allocating variables that are accessed indirectly so that a lookup of 943 // this struct instance can find them from nested functions. 944 for (auto &v : LDSUsesInfo.indirect_access[&Func]) { 945 if (!AMDGPU::isDynamicLDS(*v)) { 946 KernelUsedVariables.insert(v); 947 } 948 } 949 950 // Variables allocated in module lds must all resolve to that struct, 951 // not to the per-kernel instance. 952 if (KernelsThatAllocateModuleLDS.contains(&Func)) { 953 for (GlobalVariable *v : ModuleScopeVariables) { 954 KernelUsedVariables.erase(v); 955 } 956 } 957 958 if (KernelUsedVariables.empty()) { 959 // Either used no LDS, or the LDS it used was all in the module struct 960 // or dynamically sized 961 continue; 962 } 963 964 // The association between kernel function and LDS struct is done by 965 // symbol name, which only works if the function in question has a 966 // name This is not expected to be a problem in practice as kernels 967 // are called by name making anonymous ones (which are named by the 968 // backend) difficult to use. This does mean that llvm test cases need 969 // to name the kernels. 970 if (!Func.hasName()) { 971 report_fatal_error("Anonymous kernels cannot use LDS variables"); 972 } 973 974 std::string VarName = 975 (Twine("llvm.amdgcn.kernel.") + Func.getName() + ".lds").str(); 976 977 auto Replacement = 978 createLDSVariableReplacement(M, VarName, KernelUsedVariables); 979 980 // If any indirect uses, create a direct use to ensure allocation 981 // TODO: Simpler to unconditionally mark used but that regresses 982 // codegen in test/CodeGen/AMDGPU/noclobber-barrier.ll 983 auto Accesses = LDSUsesInfo.indirect_access.find(&Func); 984 if ((Accesses != LDSUsesInfo.indirect_access.end()) && 985 !Accesses->second.empty()) 986 markUsedByKernel(Builder, &Func, Replacement.SGV); 987 988 // remove preserves existing codegen 989 removeLocalVarsFromUsedLists(M, KernelUsedVariables); 990 KernelToReplacement[&Func] = Replacement; 991 992 // Rewrite uses within kernel to the new struct 993 replaceLDSVariablesWithStruct( 994 M, KernelUsedVariables, Replacement, [&Func](Use &U) { 995 Instruction *I = dyn_cast<Instruction>(U.getUser()); 996 return I && I->getFunction() == &Func; 997 }); 998 } 999 return KernelToReplacement; 1000 } 1001 1002 static GlobalVariable * 1003 buildRepresentativeDynamicLDSInstance(Module &M, LDSUsesInfoTy &LDSUsesInfo, 1004 Function *func) { 1005 // Create a dynamic lds variable with a name associated with the passed 1006 // function that has the maximum alignment of any dynamic lds variable 1007 // reachable from this kernel. Dynamic LDS is allocated after the static LDS 1008 // allocation, possibly after alignment padding. The representative variable 1009 // created here has the maximum alignment of any other dynamic variable 1010 // reachable by that kernel. All dynamic LDS variables are allocated at the 1011 // same address in each kernel in order to provide the documented aliasing 1012 // semantics. Setting the alignment here allows this IR pass to accurately 1013 // predict the exact constant at which it will be allocated. 1014 1015 assert(isKernelLDS(func)); 1016 1017 LLVMContext &Ctx = M.getContext(); 1018 const DataLayout &DL = M.getDataLayout(); 1019 Align MaxDynamicAlignment(1); 1020 1021 auto UpdateMaxAlignment = [&MaxDynamicAlignment, &DL](GlobalVariable *GV) { 1022 if (AMDGPU::isDynamicLDS(*GV)) { 1023 MaxDynamicAlignment = 1024 std::max(MaxDynamicAlignment, AMDGPU::getAlign(DL, GV)); 1025 } 1026 }; 1027 1028 for (GlobalVariable *GV : LDSUsesInfo.indirect_access[func]) { 1029 UpdateMaxAlignment(GV); 1030 } 1031 1032 for (GlobalVariable *GV : LDSUsesInfo.direct_access[func]) { 1033 UpdateMaxAlignment(GV); 1034 } 1035 1036 assert(func->hasName()); // Checked by caller 1037 auto emptyCharArray = ArrayType::get(Type::getInt8Ty(Ctx), 0); 1038 GlobalVariable *N = new GlobalVariable( 1039 M, emptyCharArray, false, GlobalValue::ExternalLinkage, nullptr, 1040 Twine("llvm.amdgcn." + func->getName() + ".dynlds"), nullptr, GlobalValue::NotThreadLocal, AMDGPUAS::LOCAL_ADDRESS, 1041 false); 1042 N->setAlignment(MaxDynamicAlignment); 1043 1044 assert(AMDGPU::isDynamicLDS(*N)); 1045 return N; 1046 } 1047 1048 DenseMap<Function *, GlobalVariable *> lowerDynamicLDSVariables( 1049 Module &M, LDSUsesInfoTy &LDSUsesInfo, 1050 DenseSet<Function *> const &KernelsThatIndirectlyAllocateDynamicLDS, 1051 DenseSet<GlobalVariable *> const &DynamicVariables, 1052 std::vector<Function *> const &OrderedKernels) { 1053 DenseMap<Function *, GlobalVariable *> KernelToCreatedDynamicLDS; 1054 if (!KernelsThatIndirectlyAllocateDynamicLDS.empty()) { 1055 LLVMContext &Ctx = M.getContext(); 1056 IRBuilder<> Builder(Ctx); 1057 Type *I32 = Type::getInt32Ty(Ctx); 1058 1059 std::vector<Constant *> newDynamicLDS; 1060 1061 // Table is built in the same order as OrderedKernels 1062 for (auto &func : OrderedKernels) { 1063 1064 if (KernelsThatIndirectlyAllocateDynamicLDS.contains(func)) { 1065 assert(isKernelLDS(func)); 1066 if (!func->hasName()) { 1067 report_fatal_error("Anonymous kernels cannot use LDS variables"); 1068 } 1069 1070 GlobalVariable *N = 1071 buildRepresentativeDynamicLDSInstance(M, LDSUsesInfo, func); 1072 1073 KernelToCreatedDynamicLDS[func] = N; 1074 1075 markUsedByKernel(Builder, func, N); 1076 1077 auto emptyCharArray = ArrayType::get(Type::getInt8Ty(Ctx), 0); 1078 auto GEP = ConstantExpr::getGetElementPtr( 1079 emptyCharArray, N, ConstantInt::get(I32, 0), true); 1080 newDynamicLDS.push_back(ConstantExpr::getPtrToInt(GEP, I32)); 1081 } else { 1082 newDynamicLDS.push_back(PoisonValue::get(I32)); 1083 } 1084 } 1085 assert(OrderedKernels.size() == newDynamicLDS.size()); 1086 1087 ArrayType *t = ArrayType::get(I32, newDynamicLDS.size()); 1088 Constant *init = ConstantArray::get(t, newDynamicLDS); 1089 GlobalVariable *table = new GlobalVariable( 1090 M, t, true, GlobalValue::InternalLinkage, init, 1091 "llvm.amdgcn.dynlds.offset.table", nullptr, 1092 GlobalValue::NotThreadLocal, AMDGPUAS::CONSTANT_ADDRESS); 1093 1094 for (GlobalVariable *GV : DynamicVariables) { 1095 for (Use &U : make_early_inc_range(GV->uses())) { 1096 auto *I = dyn_cast<Instruction>(U.getUser()); 1097 if (!I) 1098 continue; 1099 if (isKernelLDS(I->getFunction())) 1100 continue; 1101 1102 replaceUseWithTableLookup(M, Builder, table, GV, U, nullptr); 1103 } 1104 } 1105 } 1106 return KernelToCreatedDynamicLDS; 1107 } 1108 1109 static bool canElideModuleLDS(const Function &F) { 1110 return F.hasFnAttribute("amdgpu-elide-module-lds"); 1111 } 1112 1113 static void markElideModuleLDS(Function &F) { 1114 F.addFnAttr("amdgpu-elide-module-lds"); 1115 } 1116 1117 bool runOnModule(Module &M) override { 1118 CallGraph CG = CallGraph(M); 1119 bool Changed = superAlignLDSGlobals(M); 1120 1121 Changed |= eliminateConstantExprUsesOfLDSFromAllInstructions(M); 1122 1123 Changed = true; // todo: narrow this down 1124 1125 // For each kernel, what variables does it access directly or through 1126 // callees 1127 LDSUsesInfoTy LDSUsesInfo = getTransitiveUsesOfLDS(CG, M); 1128 1129 // For each variable accessed through callees, which kernels access it 1130 VariableFunctionMap LDSToKernelsThatNeedToAccessItIndirectly; 1131 for (auto &K : LDSUsesInfo.indirect_access) { 1132 Function *F = K.first; 1133 assert(isKernelLDS(F)); 1134 for (GlobalVariable *GV : K.second) { 1135 LDSToKernelsThatNeedToAccessItIndirectly[GV].insert(F); 1136 } 1137 } 1138 1139 // Partition variables accessed indirectly into the different strategies 1140 DenseSet<GlobalVariable *> ModuleScopeVariables; 1141 DenseSet<GlobalVariable *> TableLookupVariables; 1142 DenseSet<GlobalVariable *> KernelAccessVariables; 1143 DenseSet<GlobalVariable *> DynamicVariables; 1144 partitionVariablesIntoIndirectStrategies( 1145 M, LDSUsesInfo, LDSToKernelsThatNeedToAccessItIndirectly, 1146 ModuleScopeVariables, TableLookupVariables, KernelAccessVariables, 1147 DynamicVariables); 1148 1149 // If the kernel accesses a variable that is going to be stored in the 1150 // module instance through a call then that kernel needs to allocate the 1151 // module instance 1152 const DenseSet<Function *> KernelsThatAllocateModuleLDS = 1153 kernelsThatIndirectlyAccessAnyOfPassedVariables(M, LDSUsesInfo, 1154 ModuleScopeVariables); 1155 const DenseSet<Function *> KernelsThatAllocateTableLDS = 1156 kernelsThatIndirectlyAccessAnyOfPassedVariables(M, LDSUsesInfo, 1157 TableLookupVariables); 1158 1159 const DenseSet<Function *> KernelsThatIndirectlyAllocateDynamicLDS = 1160 kernelsThatIndirectlyAccessAnyOfPassedVariables(M, LDSUsesInfo, 1161 DynamicVariables); 1162 1163 GlobalVariable *MaybeModuleScopeStruct = lowerModuleScopeStructVariables( 1164 M, ModuleScopeVariables, KernelsThatAllocateModuleLDS); 1165 1166 DenseMap<Function *, LDSVariableReplacement> KernelToReplacement = 1167 lowerKernelScopeStructVariables(M, LDSUsesInfo, ModuleScopeVariables, 1168 KernelsThatAllocateModuleLDS, 1169 MaybeModuleScopeStruct); 1170 1171 // Lower zero cost accesses to the kernel instances just created 1172 for (auto &GV : KernelAccessVariables) { 1173 auto &funcs = LDSToKernelsThatNeedToAccessItIndirectly[GV]; 1174 assert(funcs.size() == 1); // Only one kernel can access it 1175 LDSVariableReplacement Replacement = 1176 KernelToReplacement[*(funcs.begin())]; 1177 1178 DenseSet<GlobalVariable *> Vec; 1179 Vec.insert(GV); 1180 1181 replaceLDSVariablesWithStruct(M, Vec, Replacement, [](Use &U) { 1182 return isa<Instruction>(U.getUser()); 1183 }); 1184 } 1185 1186 // The ith element of this vector is kernel id i 1187 std::vector<Function *> OrderedKernels = 1188 assignLDSKernelIDToEachKernel(&M, KernelsThatAllocateTableLDS, 1189 KernelsThatIndirectlyAllocateDynamicLDS); 1190 1191 if (!KernelsThatAllocateTableLDS.empty()) { 1192 LLVMContext &Ctx = M.getContext(); 1193 IRBuilder<> Builder(Ctx); 1194 1195 // The order must be consistent between lookup table and accesses to 1196 // lookup table 1197 auto TableLookupVariablesOrdered = 1198 sortByName(std::vector<GlobalVariable *>(TableLookupVariables.begin(), 1199 TableLookupVariables.end())); 1200 1201 GlobalVariable *LookupTable = buildLookupTable( 1202 M, TableLookupVariablesOrdered, OrderedKernels, KernelToReplacement); 1203 replaceUsesInInstructionsWithTableLookup(M, TableLookupVariablesOrdered, 1204 LookupTable); 1205 } 1206 1207 DenseMap<Function *, GlobalVariable *> KernelToCreatedDynamicLDS = 1208 lowerDynamicLDSVariables(M, LDSUsesInfo, 1209 KernelsThatIndirectlyAllocateDynamicLDS, 1210 DynamicVariables, OrderedKernels); 1211 1212 // All kernel frames have been allocated. Calculate and record the 1213 // addresses. 1214 1215 { 1216 const DataLayout &DL = M.getDataLayout(); 1217 1218 for (Function &Func : M.functions()) { 1219 if (Func.isDeclaration() || !isKernelLDS(&Func)) 1220 continue; 1221 1222 // All three of these are optional. The first variable is allocated at 1223 // zero. They are allocated by allocateKnownAddressLDSGlobal in the 1224 // following order: 1225 //{ 1226 // module.lds 1227 // alignment padding 1228 // kernel instance 1229 // alignment padding 1230 // dynamic lds variables 1231 //} 1232 1233 const bool AllocateModuleScopeStruct = 1234 MaybeModuleScopeStruct && !canElideModuleLDS(Func); 1235 1236 auto Replacement = KernelToReplacement.find(&Func); 1237 const bool AllocateKernelScopeStruct = 1238 Replacement != KernelToReplacement.end(); 1239 1240 const bool AllocateDynamicVariable = 1241 KernelToCreatedDynamicLDS.contains(&Func); 1242 1243 uint32_t Offset = 0; 1244 1245 if (AllocateModuleScopeStruct) { 1246 // Allocated at zero, recorded once on construction, not once per 1247 // kernel 1248 Offset += DL.getTypeAllocSize(MaybeModuleScopeStruct->getValueType()); 1249 } 1250 1251 if (AllocateKernelScopeStruct) { 1252 GlobalVariable *KernelStruct = Replacement->second.SGV; 1253 1254 Offset = alignTo(Offset, AMDGPU::getAlign(DL, KernelStruct)); 1255 1256 recordLDSAbsoluteAddress(&M, KernelStruct, Offset); 1257 1258 Offset += DL.getTypeAllocSize(KernelStruct->getValueType()); 1259 1260 } 1261 1262 if (AllocateDynamicVariable) { 1263 GlobalVariable *DynamicVariable = KernelToCreatedDynamicLDS[&Func]; 1264 1265 Offset = alignTo(Offset, AMDGPU::getAlign(DL, DynamicVariable)); 1266 1267 recordLDSAbsoluteAddress(&M, DynamicVariable, Offset); 1268 } 1269 } 1270 } 1271 1272 for (auto &GV : make_early_inc_range(M.globals())) 1273 if (AMDGPU::isLDSVariableToLower(GV)) { 1274 // probably want to remove from used lists 1275 GV.removeDeadConstantUsers(); 1276 if (GV.use_empty()) 1277 GV.eraseFromParent(); 1278 } 1279 1280 return Changed; 1281 } 1282 1283 private: 1284 // Increase the alignment of LDS globals if necessary to maximise the chance 1285 // that we can use aligned LDS instructions to access them. 1286 static bool superAlignLDSGlobals(Module &M) { 1287 const DataLayout &DL = M.getDataLayout(); 1288 bool Changed = false; 1289 if (!SuperAlignLDSGlobals) { 1290 return Changed; 1291 } 1292 1293 for (auto &GV : M.globals()) { 1294 if (GV.getType()->getPointerAddressSpace() != AMDGPUAS::LOCAL_ADDRESS) { 1295 // Only changing alignment of LDS variables 1296 continue; 1297 } 1298 if (!GV.hasInitializer()) { 1299 // cuda/hip extern __shared__ variable, leave alignment alone 1300 continue; 1301 } 1302 1303 Align Alignment = AMDGPU::getAlign(DL, &GV); 1304 TypeSize GVSize = DL.getTypeAllocSize(GV.getValueType()); 1305 1306 if (GVSize > 8) { 1307 // We might want to use a b96 or b128 load/store 1308 Alignment = std::max(Alignment, Align(16)); 1309 } else if (GVSize > 4) { 1310 // We might want to use a b64 load/store 1311 Alignment = std::max(Alignment, Align(8)); 1312 } else if (GVSize > 2) { 1313 // We might want to use a b32 load/store 1314 Alignment = std::max(Alignment, Align(4)); 1315 } else if (GVSize > 1) { 1316 // We might want to use a b16 load/store 1317 Alignment = std::max(Alignment, Align(2)); 1318 } 1319 1320 if (Alignment != AMDGPU::getAlign(DL, &GV)) { 1321 Changed = true; 1322 GV.setAlignment(Alignment); 1323 } 1324 } 1325 return Changed; 1326 } 1327 1328 static LDSVariableReplacement createLDSVariableReplacement( 1329 Module &M, std::string VarName, 1330 DenseSet<GlobalVariable *> const &LDSVarsToTransform) { 1331 // Create a struct instance containing LDSVarsToTransform and map from those 1332 // variables to ConstantExprGEP 1333 // Variables may be introduced to meet alignment requirements. No aliasing 1334 // metadata is useful for these as they have no uses. Erased before return. 1335 1336 LLVMContext &Ctx = M.getContext(); 1337 const DataLayout &DL = M.getDataLayout(); 1338 assert(!LDSVarsToTransform.empty()); 1339 1340 SmallVector<OptimizedStructLayoutField, 8> LayoutFields; 1341 LayoutFields.reserve(LDSVarsToTransform.size()); 1342 { 1343 // The order of fields in this struct depends on the order of 1344 // varables in the argument which varies when changing how they 1345 // are identified, leading to spurious test breakage. 1346 auto Sorted = sortByName(std::vector<GlobalVariable *>( 1347 LDSVarsToTransform.begin(), LDSVarsToTransform.end())); 1348 1349 for (GlobalVariable *GV : Sorted) { 1350 OptimizedStructLayoutField F(GV, 1351 DL.getTypeAllocSize(GV->getValueType()), 1352 AMDGPU::getAlign(DL, GV)); 1353 LayoutFields.emplace_back(F); 1354 } 1355 } 1356 1357 performOptimizedStructLayout(LayoutFields); 1358 1359 std::vector<GlobalVariable *> LocalVars; 1360 BitVector IsPaddingField; 1361 LocalVars.reserve(LDSVarsToTransform.size()); // will be at least this large 1362 IsPaddingField.reserve(LDSVarsToTransform.size()); 1363 { 1364 uint64_t CurrentOffset = 0; 1365 for (size_t I = 0; I < LayoutFields.size(); I++) { 1366 GlobalVariable *FGV = static_cast<GlobalVariable *>( 1367 const_cast<void *>(LayoutFields[I].Id)); 1368 Align DataAlign = LayoutFields[I].Alignment; 1369 1370 uint64_t DataAlignV = DataAlign.value(); 1371 if (uint64_t Rem = CurrentOffset % DataAlignV) { 1372 uint64_t Padding = DataAlignV - Rem; 1373 1374 // Append an array of padding bytes to meet alignment requested 1375 // Note (o + (a - (o % a)) ) % a == 0 1376 // (offset + Padding ) % align == 0 1377 1378 Type *ATy = ArrayType::get(Type::getInt8Ty(Ctx), Padding); 1379 LocalVars.push_back(new GlobalVariable( 1380 M, ATy, false, GlobalValue::InternalLinkage, UndefValue::get(ATy), 1381 "", nullptr, GlobalValue::NotThreadLocal, AMDGPUAS::LOCAL_ADDRESS, 1382 false)); 1383 IsPaddingField.push_back(true); 1384 CurrentOffset += Padding; 1385 } 1386 1387 LocalVars.push_back(FGV); 1388 IsPaddingField.push_back(false); 1389 CurrentOffset += LayoutFields[I].Size; 1390 } 1391 } 1392 1393 std::vector<Type *> LocalVarTypes; 1394 LocalVarTypes.reserve(LocalVars.size()); 1395 std::transform( 1396 LocalVars.cbegin(), LocalVars.cend(), std::back_inserter(LocalVarTypes), 1397 [](const GlobalVariable *V) -> Type * { return V->getValueType(); }); 1398 1399 StructType *LDSTy = StructType::create(Ctx, LocalVarTypes, VarName + ".t"); 1400 1401 Align StructAlign = AMDGPU::getAlign(DL, LocalVars[0]); 1402 1403 GlobalVariable *SGV = new GlobalVariable( 1404 M, LDSTy, false, GlobalValue::InternalLinkage, UndefValue::get(LDSTy), 1405 VarName, nullptr, GlobalValue::NotThreadLocal, AMDGPUAS::LOCAL_ADDRESS, 1406 false); 1407 SGV->setAlignment(StructAlign); 1408 1409 DenseMap<GlobalVariable *, Constant *> Map; 1410 Type *I32 = Type::getInt32Ty(Ctx); 1411 for (size_t I = 0; I < LocalVars.size(); I++) { 1412 GlobalVariable *GV = LocalVars[I]; 1413 Constant *GEPIdx[] = {ConstantInt::get(I32, 0), ConstantInt::get(I32, I)}; 1414 Constant *GEP = ConstantExpr::getGetElementPtr(LDSTy, SGV, GEPIdx, true); 1415 if (IsPaddingField[I]) { 1416 assert(GV->use_empty()); 1417 GV->eraseFromParent(); 1418 } else { 1419 Map[GV] = GEP; 1420 } 1421 } 1422 assert(Map.size() == LDSVarsToTransform.size()); 1423 return {SGV, std::move(Map)}; 1424 } 1425 1426 template <typename PredicateTy> 1427 static void replaceLDSVariablesWithStruct( 1428 Module &M, DenseSet<GlobalVariable *> const &LDSVarsToTransformArg, 1429 const LDSVariableReplacement &Replacement, PredicateTy Predicate) { 1430 LLVMContext &Ctx = M.getContext(); 1431 const DataLayout &DL = M.getDataLayout(); 1432 1433 // A hack... we need to insert the aliasing info in a predictable order for 1434 // lit tests. Would like to have them in a stable order already, ideally the 1435 // same order they get allocated, which might mean an ordered set container 1436 auto LDSVarsToTransform = sortByName(std::vector<GlobalVariable *>( 1437 LDSVarsToTransformArg.begin(), LDSVarsToTransformArg.end())); 1438 1439 // Create alias.scope and their lists. Each field in the new structure 1440 // does not alias with all other fields. 1441 SmallVector<MDNode *> AliasScopes; 1442 SmallVector<Metadata *> NoAliasList; 1443 const size_t NumberVars = LDSVarsToTransform.size(); 1444 if (NumberVars > 1) { 1445 MDBuilder MDB(Ctx); 1446 AliasScopes.reserve(NumberVars); 1447 MDNode *Domain = MDB.createAnonymousAliasScopeDomain(); 1448 for (size_t I = 0; I < NumberVars; I++) { 1449 MDNode *Scope = MDB.createAnonymousAliasScope(Domain); 1450 AliasScopes.push_back(Scope); 1451 } 1452 NoAliasList.append(&AliasScopes[1], AliasScopes.end()); 1453 } 1454 1455 // Replace uses of ith variable with a constantexpr to the corresponding 1456 // field of the instance that will be allocated by AMDGPUMachineFunction 1457 for (size_t I = 0; I < NumberVars; I++) { 1458 GlobalVariable *GV = LDSVarsToTransform[I]; 1459 Constant *GEP = Replacement.LDSVarsToConstantGEP.at(GV); 1460 1461 GV->replaceUsesWithIf(GEP, Predicate); 1462 1463 APInt APOff(DL.getIndexTypeSizeInBits(GEP->getType()), 0); 1464 GEP->stripAndAccumulateInBoundsConstantOffsets(DL, APOff); 1465 uint64_t Offset = APOff.getZExtValue(); 1466 1467 Align A = 1468 commonAlignment(Replacement.SGV->getAlign().valueOrOne(), Offset); 1469 1470 if (I) 1471 NoAliasList[I - 1] = AliasScopes[I - 1]; 1472 MDNode *NoAlias = 1473 NoAliasList.empty() ? nullptr : MDNode::get(Ctx, NoAliasList); 1474 MDNode *AliasScope = 1475 AliasScopes.empty() ? nullptr : MDNode::get(Ctx, {AliasScopes[I]}); 1476 1477 refineUsesAlignmentAndAA(GEP, A, DL, AliasScope, NoAlias); 1478 } 1479 } 1480 1481 static void refineUsesAlignmentAndAA(Value *Ptr, Align A, 1482 const DataLayout &DL, MDNode *AliasScope, 1483 MDNode *NoAlias, unsigned MaxDepth = 5) { 1484 if (!MaxDepth || (A == 1 && !AliasScope)) 1485 return; 1486 1487 for (User *U : Ptr->users()) { 1488 if (auto *I = dyn_cast<Instruction>(U)) { 1489 if (AliasScope && I->mayReadOrWriteMemory()) { 1490 MDNode *AS = I->getMetadata(LLVMContext::MD_alias_scope); 1491 AS = (AS ? MDNode::getMostGenericAliasScope(AS, AliasScope) 1492 : AliasScope); 1493 I->setMetadata(LLVMContext::MD_alias_scope, AS); 1494 1495 MDNode *NA = I->getMetadata(LLVMContext::MD_noalias); 1496 NA = (NA ? MDNode::intersect(NA, NoAlias) : NoAlias); 1497 I->setMetadata(LLVMContext::MD_noalias, NA); 1498 } 1499 } 1500 1501 if (auto *LI = dyn_cast<LoadInst>(U)) { 1502 LI->setAlignment(std::max(A, LI->getAlign())); 1503 continue; 1504 } 1505 if (auto *SI = dyn_cast<StoreInst>(U)) { 1506 if (SI->getPointerOperand() == Ptr) 1507 SI->setAlignment(std::max(A, SI->getAlign())); 1508 continue; 1509 } 1510 if (auto *AI = dyn_cast<AtomicRMWInst>(U)) { 1511 // None of atomicrmw operations can work on pointers, but let's 1512 // check it anyway in case it will or we will process ConstantExpr. 1513 if (AI->getPointerOperand() == Ptr) 1514 AI->setAlignment(std::max(A, AI->getAlign())); 1515 continue; 1516 } 1517 if (auto *AI = dyn_cast<AtomicCmpXchgInst>(U)) { 1518 if (AI->getPointerOperand() == Ptr) 1519 AI->setAlignment(std::max(A, AI->getAlign())); 1520 continue; 1521 } 1522 if (auto *GEP = dyn_cast<GetElementPtrInst>(U)) { 1523 unsigned BitWidth = DL.getIndexTypeSizeInBits(GEP->getType()); 1524 APInt Off(BitWidth, 0); 1525 if (GEP->getPointerOperand() == Ptr) { 1526 Align GA; 1527 if (GEP->accumulateConstantOffset(DL, Off)) 1528 GA = commonAlignment(A, Off.getLimitedValue()); 1529 refineUsesAlignmentAndAA(GEP, GA, DL, AliasScope, NoAlias, 1530 MaxDepth - 1); 1531 } 1532 continue; 1533 } 1534 if (auto *I = dyn_cast<Instruction>(U)) { 1535 if (I->getOpcode() == Instruction::BitCast || 1536 I->getOpcode() == Instruction::AddrSpaceCast) 1537 refineUsesAlignmentAndAA(I, A, DL, AliasScope, NoAlias, MaxDepth - 1); 1538 } 1539 } 1540 } 1541 }; 1542 1543 } // namespace 1544 char AMDGPULowerModuleLDS::ID = 0; 1545 1546 char &llvm::AMDGPULowerModuleLDSID = AMDGPULowerModuleLDS::ID; 1547 1548 INITIALIZE_PASS(AMDGPULowerModuleLDS, DEBUG_TYPE, 1549 "Lower uses of LDS variables from non-kernel functions", false, 1550 false) 1551 1552 ModulePass *llvm::createAMDGPULowerModuleLDSPass() { 1553 return new AMDGPULowerModuleLDS(); 1554 } 1555 1556 PreservedAnalyses AMDGPULowerModuleLDSPass::run(Module &M, 1557 ModuleAnalysisManager &) { 1558 return AMDGPULowerModuleLDS().runOnModule(M) ? PreservedAnalyses::none() 1559 : PreservedAnalyses::all(); 1560 } 1561