1//===-- AMDGPULowerModuleLDSPass.cpp ------------------------------*- C++ -*-=//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This pass eliminates local data store, LDS, uses from non-kernel functions.
10// LDS is contiguous memory allocated per kernel execution.
11//
12// Background.
13//
14// The programming model is global variables, or equivalently function local
15// static variables, accessible from kernels or other functions. For uses from
16// kernels this is straightforward - assign an integer to the kernel for the
17// memory required by all the variables combined, allocate them within that.
18// For uses from functions there are performance tradeoffs to choose between.
19//
20// This model means the GPU runtime can specify the amount of memory allocated.
21// If this is more than the kernel assumed, the excess can be made available
22// using a language specific feature, which IR represents as a variable with
23// no initializer. This feature is referred to here as "Dynamic LDS" and is
24// lowered slightly differently to the normal case.
25//
26// Consequences of this GPU feature:
27// - memory is limited and exceeding it halts compilation
28// - a global accessed by one kernel exists independent of other kernels
29// - a global exists independent of simultaneous execution of the same kernel
30// - the address of the global may be different from different kernels as they
31// do not alias, which permits only allocating variables they use
32// - if the address is allowed to differ, functions need help to find it
33//
34// Uses from kernels are implemented here by grouping them in a per-kernel
35// struct instance. This duplicates the variables, accurately modelling their
36// aliasing properties relative to a single global representation. It also
37// permits control over alignment via padding.
38//
39// Uses from functions are more complicated and the primary purpose of this
40// IR pass. Several different lowering are chosen between to meet requirements
41// to avoid allocating any LDS where it is not necessary, as that impacts
42// occupancy and may fail the compilation, while not imposing overhead on a
43// feature whose primary advantage over global memory is performance. The basic
44// design goal is to avoid one kernel imposing overhead on another.
45//
46// Implementation.
47//
48// LDS variables with constant annotation or non-undef initializer are passed
49// through unchanged for simplification or error diagnostics in later passes.
50// Non-undef initializers are not yet implemented for LDS.
51//
52// LDS variables that are always allocated at the same address can be found
53// by lookup at that address. Otherwise runtime information/cost is required.
54//
55// The simplest strategy possible is to group all LDS variables in a single
56// struct and allocate that struct in every kernel such that the original
57// variables are always at the same address. LDS is however a limited resource
58// so this strategy is unusable in practice. It is not implemented here.
59//
60// Strategy | Precise allocation | Zero runtime cost | General purpose |
61// --------+--------------------+-------------------+-----------------+
62// Module | No | Yes | Yes |
63// Table | Yes | No | Yes |
64// Kernel | Yes | Yes | No |
65// Hybrid | Yes | Partial | Yes |
66//
67// "Module" spends LDS memory to save cycles. "Table" spends cycles and global
68// memory to save LDS. "Kernel" is as fast as kernel allocation but only works
69// for variables that are known reachable from a single kernel. "Hybrid" picks
70// between all three. When forced to choose between LDS and cycles we minimise
71// LDS use.
72
73// The "module" lowering implemented here finds LDS variables which are used by
74// non-kernel functions and creates a new struct with a field for each of those
75// LDS variables. Variables that are only used from kernels are excluded.
76//
77// The "table" lowering implemented here has three components.
78// First kernels are assigned a unique integer identifier which is available in
79// functions it calls through the intrinsic amdgcn_lds_kernel_id. The integer
80// is passed through a specific SGPR, thus works with indirect calls.
81// Second, each kernel allocates LDS variables independent of other kernels and
82// writes the addresses it chose for each variable into an array in consistent
83// order. If the kernel does not allocate a given variable, it writes undef to
84// the corresponding array location. These arrays are written to a constant
85// table in the order matching the kernel unique integer identifier.
86// Third, uses from non-kernel functions are replaced with a table lookup using
87// the intrinsic function to find the address of the variable.
88//
89// "Kernel" lowering is only applicable for variables that are unambiguously
90// reachable from exactly one kernel. For those cases, accesses to the variable
91// can be lowered to ConstantExpr address of a struct instance specific to that
92// one kernel. This is zero cost in space and in compute. It will raise a fatal
93// error on any variable that might be reachable from multiple kernels and is
94// thus most easily used as part of the hybrid lowering strategy.
95//
96// Hybrid lowering is a mixture of the above. It uses the zero cost kernel
97// lowering where it can. It lowers the variable accessed by the greatest
98// number of kernels using the module strategy as that is free for the first
99// variable. Any futher variables that can be lowered with the module strategy
100// without incurring LDS memory overhead are. The remaining ones are lowered
101// via table.
102//
103// Consequences
104// - No heuristics or user controlled magic numbers, hybrid is the right choice
105// - Kernels that don't use functions (or have had them all inlined) are not
106// affected by any lowering for kernels that do.
107// - Kernels that don't make indirect function calls are not affected by those
108// that do.
109// - Variables which are used by lots of kernels, e.g. those injected by a
110// language runtime in most kernels, are expected to have no overhead
111// - Implementations that instantiate templates per-kernel where those templates
112// use LDS are expected to hit the "Kernel" lowering strategy
113// - The runtime properties impose a cost in compiler implementation complexity
114//
115// Dynamic LDS implementation
116// Dynamic LDS is lowered similarly to the "table" strategy above and uses the
117// same intrinsic to identify which kernel is at the root of the dynamic call
118// graph. This relies on the specified behaviour that all dynamic LDS variables
119// alias one another, i.e. are at the same address, with respect to a given
120// kernel. Therefore this pass creates new dynamic LDS variables for each kernel
121// that allocates any dynamic LDS and builds a table of addresses out of those.
122// The AMDGPUPromoteAlloca pass skips kernels that use dynamic LDS.
123// The corresponding optimisation for "kernel" lowering where the table lookup
124// is elided is not implemented.
125//
126//
127// Implementation notes / limitations
128// A single LDS global variable represents an instance per kernel that can reach
129// said variables. This pass essentially specialises said variables per kernel.
130// Handling ConstantExpr during the pass complicated this significantly so now
131// all ConstantExpr uses of LDS variables are expanded to instructions. This
132// may need amending when implementing non-undef initialisers.
133//
134// Lowering is split between this IR pass and the back end. This pass chooses
135// where given variables should be allocated and marks them with metadata,
136// MD_absolute_symbol. The backend places the variables in coincidentally the
137// same location and raises a fatal error if something has gone awry. This works
138// in practice because the only pass between this one and the backend that
139// changes LDS is PromoteAlloca and the changes it makes do not conflict.
140//
141// Addresses are written to constant global arrays based on the same metadata.
142//
143// The backend lowers LDS variables in the order of traversal of the function.
144// This is at odds with the deterministic layout required. The workaround is to
145// allocate the fixed-address variables immediately upon starting the function
146// where they can be placed as intended. This requires a means of mapping from
147// the function to the variables that it allocates. For the module scope lds,
148// this is via metadata indicating whether the variable is not required. If a
149// pass deletes that metadata, a fatal error on disagreement with the absolute
150// symbol metadata will occur. For kernel scope and dynamic, this is by _name_
151// correspondence between the function and the variable. It requires the
152// kernel to have a name (which is only a limitation for tests in practice) and
153// for nothing to rename the corresponding symbols. This is a hazard if the pass
154// is run multiple times during debugging. Alternative schemes considered all
155// involve bespoke metadata.
156//
157// If the name correspondence can be replaced, multiple distinct kernels that
158// have the same memory layout can map to the same kernel id (as the address
159// itself is handled by the absolute symbol metadata) and that will allow more
160// uses of the "kernel" style faster lowering and reduce the size of the lookup
161// tables.
162//
163// There is a test that checks this does not fire for a graphics shader. This
164// lowering is expected to work for graphics if the isKernel test is changed.
165//
166// The current markUsedByKernel is sufficient for PromoteAlloca but is elided
167// before codegen. Replacing this with an equivalent intrinsic which lasts until
168// shortly after the machine function lowering of LDS would help break the name
169// mapping. The other part needed is probably to amend PromoteAlloca to embed
170// the LDS variables it creates in the same struct created here. That avoids the
171// current hazard where a PromoteAlloca LDS variable might be allocated before
172// the kernel scope (and thus error on the address check). Given a new invariant
173// that no LDS variables exist outside of the structs managed here, and an
174// intrinsic that lasts until after the LDS frame lowering, it should be
175// possible to drop the name mapping and fold equivalent memory layouts.
176//
177//===----------------------------------------------------------------------===//
178
179#include "AMDGPU.h"
180#include "AMDGPUTargetMachine.h"
181#include "Utils/AMDGPUBaseInfo.h"
182#include "Utils/AMDGPUMemoryUtils.h"
183#include "llvm/ADT/BitVector.h"
184#include "llvm/ADT/DenseMap.h"
185#include "llvm/ADT/DenseSet.h"
186#include "llvm/ADT/STLExtras.h"
187#include "llvm/ADT/SetOperations.h"
188#include "llvm/Analysis/CallGraph.h"
189#include "llvm/CodeGen/TargetPassConfig.h"
190#include "llvm/IR/Constants.h"
191#include "llvm/IR/DerivedTypes.h"
192#include "llvm/IR/IRBuilder.h"
193#include "llvm/IR/InlineAsm.h"
194#include "llvm/IR/Instructions.h"
195#include "llvm/IR/IntrinsicsAMDGPU.h"
196#include "llvm/IR/MDBuilder.h"
197#include "llvm/IR/ReplaceConstant.h"
198#include "llvm/InitializePasses.h"
199#include "llvm/Pass.h"
200#include "llvm/Support/CommandLine.h"
201#include "llvm/Support/Debug.h"
202#include "llvm/Support/Format.h"
203#include "llvm/Support/OptimizedStructLayout.h"
204#include "llvm/Support/raw_ostream.h"
205#include "llvm/Transforms/Utils/BasicBlockUtils.h"
206#include "llvm/Transforms/Utils/ModuleUtils.h"
207
208#include <vector>
209
210#include <cstdio>
211
212#define DEBUG_TYPE "amdgpu-lower-module-lds"
213
214using namespace llvm;
215using namespace AMDGPU;
216
217namespace {
218
219cl::opt<bool> SuperAlignLDSGlobals(
220 "amdgpu-super-align-lds-globals",
221 cl::desc("Increase alignment of LDS if it is not on align boundary"),
222 cl::init(Val: true), cl::Hidden);
223
224enum class LoweringKind { module, table, kernel, hybrid };
225cl::opt<LoweringKind> LoweringKindLoc(
226 "amdgpu-lower-module-lds-strategy",
227 cl::desc("Specify lowering strategy for function LDS access:"), cl::Hidden,
228 cl::init(Val: LoweringKind::hybrid),
229 cl::values(
230 clEnumValN(LoweringKind::table, "table", "Lower via table lookup"),
231 clEnumValN(LoweringKind::module, "module", "Lower via module struct"),
232 clEnumValN(
233 LoweringKind::kernel, "kernel",
234 "Lower variables reachable from one kernel, otherwise abort"),
235 clEnumValN(LoweringKind::hybrid, "hybrid",
236 "Lower via mixture of above strategies")));
237
238template <typename T> std::vector<T> sortByName(std::vector<T> &&V) {
239 llvm::sort(V.begin(), V.end(), [](const auto *L, const auto *R) {
240 return L->getName() < R->getName();
241 });
242 return {std::move(V)};
243}
244
245class AMDGPULowerModuleLDS {
246 const AMDGPUTargetMachine &TM;
247
248 static void
249 removeLocalVarsFromUsedLists(Module &M,
250 const DenseSet<GlobalVariable *> &LocalVars) {
251 // The verifier rejects used lists containing an inttoptr of a constant
252 // so remove the variables from these lists before replaceAllUsesWith
253 SmallPtrSet<Constant *, 8> LocalVarsSet;
254 for (GlobalVariable *LocalVar : LocalVars)
255 LocalVarsSet.insert(Ptr: cast<Constant>(Val: LocalVar->stripPointerCasts()));
256
257 removeFromUsedLists(
258 M, ShouldRemove: [&LocalVarsSet](Constant *C) { return LocalVarsSet.count(Ptr: C); });
259
260 for (GlobalVariable *LocalVar : LocalVars)
261 LocalVar->removeDeadConstantUsers();
262 }
263
264 static void markUsedByKernel(Function *Func, GlobalVariable *SGV) {
265 // The llvm.amdgcn.module.lds instance is implicitly used by all kernels
266 // that might call a function which accesses a field within it. This is
267 // presently approximated to 'all kernels' if there are any such functions
268 // in the module. This implicit use is redefined as an explicit use here so
269 // that later passes, specifically PromoteAlloca, account for the required
270 // memory without any knowledge of this transform.
271
272 // An operand bundle on llvm.donothing works because the call instruction
273 // survives until after the last pass that needs to account for LDS. It is
274 // better than inline asm as the latter survives until the end of codegen. A
275 // totally robust solution would be a function with the same semantics as
276 // llvm.donothing that takes a pointer to the instance and is lowered to a
277 // no-op after LDS is allocated, but that is not presently necessary.
278
279 // This intrinsic is eliminated shortly before instruction selection. It
280 // does not suffice to indicate to ISel that a given global which is not
281 // immediately used by the kernel must still be allocated by it. An
282 // equivalent target specific intrinsic which lasts until immediately after
283 // codegen would suffice for that, but one would still need to ensure that
284 // the variables are allocated in the anticipated order.
285 BasicBlock *Entry = &Func->getEntryBlock();
286 IRBuilder<> Builder(Entry, Entry->getFirstNonPHIIt());
287
288 Function *Decl =
289 Intrinsic::getDeclaration(M: Func->getParent(), id: Intrinsic::donothing, Tys: {});
290
291 Value *UseInstance[1] = {
292 Builder.CreateConstInBoundsGEP1_32(Ty: SGV->getValueType(), Ptr: SGV, Idx0: 0)};
293
294 Builder.CreateCall(
295 Callee: Decl, Args: {}, OpBundles: {OperandBundleDefT<Value *>("ExplicitUse", UseInstance)});
296 }
297
298public:
299 AMDGPULowerModuleLDS(const AMDGPUTargetMachine &TM_) : TM(TM_) {}
300
301 struct LDSVariableReplacement {
302 GlobalVariable *SGV = nullptr;
303 DenseMap<GlobalVariable *, Constant *> LDSVarsToConstantGEP;
304 };
305
306 // remap from lds global to a constantexpr gep to where it has been moved to
307 // for each kernel
308 // an array with an element for each kernel containing where the corresponding
309 // variable was remapped to
310
311 static Constant *getAddressesOfVariablesInKernel(
312 LLVMContext &Ctx, ArrayRef<GlobalVariable *> Variables,
313 const DenseMap<GlobalVariable *, Constant *> &LDSVarsToConstantGEP) {
314 // Create a ConstantArray containing the address of each Variable within the
315 // kernel corresponding to LDSVarsToConstantGEP, or poison if that kernel
316 // does not allocate it
317 // TODO: Drop the ptrtoint conversion
318
319 Type *I32 = Type::getInt32Ty(C&: Ctx);
320
321 ArrayType *KernelOffsetsType = ArrayType::get(ElementType: I32, NumElements: Variables.size());
322
323 SmallVector<Constant *> Elements;
324 for (GlobalVariable *GV : Variables) {
325 auto ConstantGepIt = LDSVarsToConstantGEP.find(Val: GV);
326 if (ConstantGepIt != LDSVarsToConstantGEP.end()) {
327 auto elt = ConstantExpr::getPtrToInt(C: ConstantGepIt->second, Ty: I32);
328 Elements.push_back(Elt: elt);
329 } else {
330 Elements.push_back(Elt: PoisonValue::get(T: I32));
331 }
332 }
333 return ConstantArray::get(T: KernelOffsetsType, V: Elements);
334 }
335
336 static GlobalVariable *buildLookupTable(
337 Module &M, ArrayRef<GlobalVariable *> Variables,
338 ArrayRef<Function *> kernels,
339 DenseMap<Function *, LDSVariableReplacement> &KernelToReplacement) {
340 if (Variables.empty()) {
341 return nullptr;
342 }
343 LLVMContext &Ctx = M.getContext();
344
345 const size_t NumberVariables = Variables.size();
346 const size_t NumberKernels = kernels.size();
347
348 ArrayType *KernelOffsetsType =
349 ArrayType::get(ElementType: Type::getInt32Ty(C&: Ctx), NumElements: NumberVariables);
350
351 ArrayType *AllKernelsOffsetsType =
352 ArrayType::get(ElementType: KernelOffsetsType, NumElements: NumberKernels);
353
354 Constant *Missing = PoisonValue::get(T: KernelOffsetsType);
355 std::vector<Constant *> overallConstantExprElts(NumberKernels);
356 for (size_t i = 0; i < NumberKernels; i++) {
357 auto Replacement = KernelToReplacement.find(Val: kernels[i]);
358 overallConstantExprElts[i] =
359 (Replacement == KernelToReplacement.end())
360 ? Missing
361 : getAddressesOfVariablesInKernel(
362 Ctx, Variables, LDSVarsToConstantGEP: Replacement->second.LDSVarsToConstantGEP);
363 }
364
365 Constant *init =
366 ConstantArray::get(T: AllKernelsOffsetsType, V: overallConstantExprElts);
367
368 return new GlobalVariable(
369 M, AllKernelsOffsetsType, true, GlobalValue::InternalLinkage, init,
370 "llvm.amdgcn.lds.offset.table", nullptr, GlobalValue::NotThreadLocal,
371 AMDGPUAS::CONSTANT_ADDRESS);
372 }
373
374 void replaceUseWithTableLookup(Module &M, IRBuilder<> &Builder,
375 GlobalVariable *LookupTable,
376 GlobalVariable *GV, Use &U,
377 Value *OptionalIndex) {
378 // Table is a constant array of the same length as OrderedKernels
379 LLVMContext &Ctx = M.getContext();
380 Type *I32 = Type::getInt32Ty(C&: Ctx);
381 auto *I = cast<Instruction>(Val: U.getUser());
382
383 Value *tableKernelIndex = getTableLookupKernelIndex(M, F: I->getFunction());
384
385 if (auto *Phi = dyn_cast<PHINode>(Val: I)) {
386 BasicBlock *BB = Phi->getIncomingBlock(U);
387 Builder.SetInsertPoint(&(*(BB->getFirstInsertionPt())));
388 } else {
389 Builder.SetInsertPoint(I);
390 }
391
392 SmallVector<Value *, 3> GEPIdx = {
393 ConstantInt::get(Ty: I32, V: 0),
394 tableKernelIndex,
395 };
396 if (OptionalIndex)
397 GEPIdx.push_back(Elt: OptionalIndex);
398
399 Value *Address = Builder.CreateInBoundsGEP(
400 Ty: LookupTable->getValueType(), Ptr: LookupTable, IdxList: GEPIdx, Name: GV->getName());
401
402 Value *loaded = Builder.CreateLoad(Ty: I32, Ptr: Address);
403
404 Value *replacement =
405 Builder.CreateIntToPtr(V: loaded, DestTy: GV->getType(), Name: GV->getName());
406
407 U.set(replacement);
408 }
409
410 void replaceUsesInInstructionsWithTableLookup(
411 Module &M, ArrayRef<GlobalVariable *> ModuleScopeVariables,
412 GlobalVariable *LookupTable) {
413
414 LLVMContext &Ctx = M.getContext();
415 IRBuilder<> Builder(Ctx);
416 Type *I32 = Type::getInt32Ty(C&: Ctx);
417
418 for (size_t Index = 0; Index < ModuleScopeVariables.size(); Index++) {
419 auto *GV = ModuleScopeVariables[Index];
420
421 for (Use &U : make_early_inc_range(Range: GV->uses())) {
422 auto *I = dyn_cast<Instruction>(Val: U.getUser());
423 if (!I)
424 continue;
425
426 replaceUseWithTableLookup(M, Builder, LookupTable, GV, U,
427 OptionalIndex: ConstantInt::get(Ty: I32, V: Index));
428 }
429 }
430 }
431
432 static DenseSet<Function *> kernelsThatIndirectlyAccessAnyOfPassedVariables(
433 Module &M, LDSUsesInfoTy &LDSUsesInfo,
434 DenseSet<GlobalVariable *> const &VariableSet) {
435
436 DenseSet<Function *> KernelSet;
437
438 if (VariableSet.empty())
439 return KernelSet;
440
441 for (Function &Func : M.functions()) {
442 if (Func.isDeclaration() || !isKernelLDS(F: &Func))
443 continue;
444 for (GlobalVariable *GV : LDSUsesInfo.indirect_access[&Func]) {
445 if (VariableSet.contains(V: GV)) {
446 KernelSet.insert(V: &Func);
447 break;
448 }
449 }
450 }
451
452 return KernelSet;
453 }
454
455 static GlobalVariable *
456 chooseBestVariableForModuleStrategy(const DataLayout &DL,
457 VariableFunctionMap &LDSVars) {
458 // Find the global variable with the most indirect uses from kernels
459
460 struct CandidateTy {
461 GlobalVariable *GV = nullptr;
462 size_t UserCount = 0;
463 size_t Size = 0;
464
465 CandidateTy() = default;
466
467 CandidateTy(GlobalVariable *GV, uint64_t UserCount, uint64_t AllocSize)
468 : GV(GV), UserCount(UserCount), Size(AllocSize) {}
469
470 bool operator<(const CandidateTy &Other) const {
471 // Fewer users makes module scope variable less attractive
472 if (UserCount < Other.UserCount) {
473 return true;
474 }
475 if (UserCount > Other.UserCount) {
476 return false;
477 }
478
479 // Bigger makes module scope variable less attractive
480 if (Size < Other.Size) {
481 return false;
482 }
483
484 if (Size > Other.Size) {
485 return true;
486 }
487
488 // Arbitrary but consistent
489 return GV->getName() < Other.GV->getName();
490 }
491 };
492
493 CandidateTy MostUsed;
494
495 for (auto &K : LDSVars) {
496 GlobalVariable *GV = K.first;
497 if (K.second.size() <= 1) {
498 // A variable reachable by only one kernel is best lowered with kernel
499 // strategy
500 continue;
501 }
502 CandidateTy Candidate(
503 GV, K.second.size(),
504 DL.getTypeAllocSize(Ty: GV->getValueType()).getFixedValue());
505 if (MostUsed < Candidate)
506 MostUsed = Candidate;
507 }
508
509 return MostUsed.GV;
510 }
511
512 static void recordLDSAbsoluteAddress(Module *M, GlobalVariable *GV,
513 uint32_t Address) {
514 // Write the specified address into metadata where it can be retrieved by
515 // the assembler. Format is a half open range, [Address Address+1)
516 LLVMContext &Ctx = M->getContext();
517 auto *IntTy =
518 M->getDataLayout().getIntPtrType(C&: Ctx, AddressSpace: AMDGPUAS::LOCAL_ADDRESS);
519 auto *MinC = ConstantAsMetadata::get(C: ConstantInt::get(Ty: IntTy, V: Address));
520 auto *MaxC = ConstantAsMetadata::get(C: ConstantInt::get(Ty: IntTy, V: Address + 1));
521 GV->setMetadata(KindID: LLVMContext::MD_absolute_symbol,
522 Node: MDNode::get(Context&: Ctx, MDs: {MinC, MaxC}));
523 }
524
525 DenseMap<Function *, Value *> tableKernelIndexCache;
526 Value *getTableLookupKernelIndex(Module &M, Function *F) {
527 // Accesses from a function use the amdgcn_lds_kernel_id intrinsic which
528 // lowers to a read from a live in register. Emit it once in the entry
529 // block to spare deduplicating it later.
530 auto [It, Inserted] = tableKernelIndexCache.try_emplace(Key: F);
531 if (Inserted) {
532 Function *Decl =
533 Intrinsic::getDeclaration(M: &M, id: Intrinsic::amdgcn_lds_kernel_id, Tys: {});
534
535 auto InsertAt = F->getEntryBlock().getFirstNonPHIOrDbgOrAlloca();
536 IRBuilder<> Builder(&*InsertAt);
537
538 It->second = Builder.CreateCall(Callee: Decl, Args: {});
539 }
540
541 return It->second;
542 }
543
544 static std::vector<Function *> assignLDSKernelIDToEachKernel(
545 Module *M, DenseSet<Function *> const &KernelsThatAllocateTableLDS,
546 DenseSet<Function *> const &KernelsThatIndirectlyAllocateDynamicLDS) {
547 // Associate kernels in the set with an arbitrary but reproducible order and
548 // annotate them with that order in metadata. This metadata is recognised by
549 // the backend and lowered to a SGPR which can be read from using
550 // amdgcn_lds_kernel_id.
551
552 std::vector<Function *> OrderedKernels;
553 if (!KernelsThatAllocateTableLDS.empty() ||
554 !KernelsThatIndirectlyAllocateDynamicLDS.empty()) {
555
556 for (Function &Func : M->functions()) {
557 if (Func.isDeclaration())
558 continue;
559 if (!isKernelLDS(F: &Func))
560 continue;
561
562 if (KernelsThatAllocateTableLDS.contains(V: &Func) ||
563 KernelsThatIndirectlyAllocateDynamicLDS.contains(V: &Func)) {
564 assert(Func.hasName()); // else fatal error earlier
565 OrderedKernels.push_back(x: &Func);
566 }
567 }
568
569 // Put them in an arbitrary but reproducible order
570 OrderedKernels = sortByName(V: std::move(OrderedKernels));
571
572 // Annotate the kernels with their order in this vector
573 LLVMContext &Ctx = M->getContext();
574 IRBuilder<> Builder(Ctx);
575
576 if (OrderedKernels.size() > UINT32_MAX) {
577 // 32 bit keeps it in one SGPR. > 2**32 kernels won't fit on the GPU
578 report_fatal_error(reason: "Unimplemented LDS lowering for > 2**32 kernels");
579 }
580
581 for (size_t i = 0; i < OrderedKernels.size(); i++) {
582 Metadata *AttrMDArgs[1] = {
583 ConstantAsMetadata::get(C: Builder.getInt32(C: i)),
584 };
585 OrderedKernels[i]->setMetadata(Kind: "llvm.amdgcn.lds.kernel.id",
586 Node: MDNode::get(Context&: Ctx, MDs: AttrMDArgs));
587 }
588 }
589 return OrderedKernels;
590 }
591
592 static void partitionVariablesIntoIndirectStrategies(
593 Module &M, LDSUsesInfoTy const &LDSUsesInfo,
594 VariableFunctionMap &LDSToKernelsThatNeedToAccessItIndirectly,
595 DenseSet<GlobalVariable *> &ModuleScopeVariables,
596 DenseSet<GlobalVariable *> &TableLookupVariables,
597 DenseSet<GlobalVariable *> &KernelAccessVariables,
598 DenseSet<GlobalVariable *> &DynamicVariables) {
599
600 GlobalVariable *HybridModuleRoot =
601 LoweringKindLoc != LoweringKind::hybrid
602 ? nullptr
603 : chooseBestVariableForModuleStrategy(
604 DL: M.getDataLayout(), LDSVars&: LDSToKernelsThatNeedToAccessItIndirectly);
605
606 DenseSet<Function *> const EmptySet;
607 DenseSet<Function *> const &HybridModuleRootKernels =
608 HybridModuleRoot
609 ? LDSToKernelsThatNeedToAccessItIndirectly[HybridModuleRoot]
610 : EmptySet;
611
612 for (auto &K : LDSToKernelsThatNeedToAccessItIndirectly) {
613 // Each iteration of this loop assigns exactly one global variable to
614 // exactly one of the implementation strategies.
615
616 GlobalVariable *GV = K.first;
617 assert(AMDGPU::isLDSVariableToLower(*GV));
618 assert(K.second.size() != 0);
619
620 if (AMDGPU::isDynamicLDS(GV: *GV)) {
621 DynamicVariables.insert(V: GV);
622 continue;
623 }
624
625 switch (LoweringKindLoc) {
626 case LoweringKind::module:
627 ModuleScopeVariables.insert(V: GV);
628 break;
629
630 case LoweringKind::table:
631 TableLookupVariables.insert(V: GV);
632 break;
633
634 case LoweringKind::kernel:
635 if (K.second.size() == 1) {
636 KernelAccessVariables.insert(V: GV);
637 } else {
638 report_fatal_error(
639 reason: "cannot lower LDS '" + GV->getName() +
640 "' to kernel access as it is reachable from multiple kernels");
641 }
642 break;
643
644 case LoweringKind::hybrid: {
645 if (GV == HybridModuleRoot) {
646 assert(K.second.size() != 1);
647 ModuleScopeVariables.insert(V: GV);
648 } else if (K.second.size() == 1) {
649 KernelAccessVariables.insert(V: GV);
650 } else if (set_is_subset(S1: K.second, S2: HybridModuleRootKernels)) {
651 ModuleScopeVariables.insert(V: GV);
652 } else {
653 TableLookupVariables.insert(V: GV);
654 }
655 break;
656 }
657 }
658 }
659
660 // All LDS variables accessed indirectly have now been partitioned into
661 // the distinct lowering strategies.
662 assert(ModuleScopeVariables.size() + TableLookupVariables.size() +
663 KernelAccessVariables.size() + DynamicVariables.size() ==
664 LDSToKernelsThatNeedToAccessItIndirectly.size());
665 }
666
667 static GlobalVariable *lowerModuleScopeStructVariables(
668 Module &M, DenseSet<GlobalVariable *> const &ModuleScopeVariables,
669 DenseSet<Function *> const &KernelsThatAllocateModuleLDS) {
670 // Create a struct to hold the ModuleScopeVariables
671 // Replace all uses of those variables from non-kernel functions with the
672 // new struct instance Replace only the uses from kernel functions that will
673 // allocate this instance. That is a space optimisation - kernels that use a
674 // subset of the module scope struct and do not need to allocate it for
675 // indirect calls will only allocate the subset they use (they do so as part
676 // of the per-kernel lowering).
677 if (ModuleScopeVariables.empty()) {
678 return nullptr;
679 }
680
681 LLVMContext &Ctx = M.getContext();
682
683 LDSVariableReplacement ModuleScopeReplacement =
684 createLDSVariableReplacement(M, VarName: "llvm.amdgcn.module.lds",
685 LDSVarsToTransform: ModuleScopeVariables);
686
687 appendToCompilerUsed(M, Values: {static_cast<GlobalValue *>(
688 ConstantExpr::getPointerBitCastOrAddrSpaceCast(
689 C: cast<Constant>(Val: ModuleScopeReplacement.SGV),
690 Ty: PointerType::getUnqual(C&: Ctx)))});
691
692 // module.lds will be allocated at zero in any kernel that allocates it
693 recordLDSAbsoluteAddress(M: &M, GV: ModuleScopeReplacement.SGV, Address: 0);
694
695 // historic
696 removeLocalVarsFromUsedLists(M, LocalVars: ModuleScopeVariables);
697
698 // Replace all uses of module scope variable from non-kernel functions
699 replaceLDSVariablesWithStruct(
700 M, LDSVarsToTransformArg: ModuleScopeVariables, Replacement: ModuleScopeReplacement, Predicate: [&](Use &U) {
701 Instruction *I = dyn_cast<Instruction>(Val: U.getUser());
702 if (!I) {
703 return false;
704 }
705 Function *F = I->getFunction();
706 return !isKernelLDS(F);
707 });
708
709 // Replace uses of module scope variable from kernel functions that
710 // allocate the module scope variable, otherwise leave them unchanged
711 // Record on each kernel whether the module scope global is used by it
712
713 for (Function &Func : M.functions()) {
714 if (Func.isDeclaration() || !isKernelLDS(F: &Func))
715 continue;
716
717 if (KernelsThatAllocateModuleLDS.contains(V: &Func)) {
718 replaceLDSVariablesWithStruct(
719 M, LDSVarsToTransformArg: ModuleScopeVariables, Replacement: ModuleScopeReplacement, Predicate: [&](Use &U) {
720 Instruction *I = dyn_cast<Instruction>(Val: U.getUser());
721 if (!I) {
722 return false;
723 }
724 Function *F = I->getFunction();
725 return F == &Func;
726 });
727
728 markUsedByKernel(Func: &Func, SGV: ModuleScopeReplacement.SGV);
729 }
730 }
731
732 return ModuleScopeReplacement.SGV;
733 }
734
735 static DenseMap<Function *, LDSVariableReplacement>
736 lowerKernelScopeStructVariables(
737 Module &M, LDSUsesInfoTy &LDSUsesInfo,
738 DenseSet<GlobalVariable *> const &ModuleScopeVariables,
739 DenseSet<Function *> const &KernelsThatAllocateModuleLDS,
740 GlobalVariable *MaybeModuleScopeStruct) {
741
742 // Create a struct for each kernel for the non-module-scope variables.
743
744 DenseMap<Function *, LDSVariableReplacement> KernelToReplacement;
745 for (Function &Func : M.functions()) {
746 if (Func.isDeclaration() || !isKernelLDS(F: &Func))
747 continue;
748
749 DenseSet<GlobalVariable *> KernelUsedVariables;
750 // Allocating variables that are used directly in this struct to get
751 // alignment aware allocation and predictable frame size.
752 for (auto &v : LDSUsesInfo.direct_access[&Func]) {
753 if (!AMDGPU::isDynamicLDS(GV: *v)) {
754 KernelUsedVariables.insert(V: v);
755 }
756 }
757
758 // Allocating variables that are accessed indirectly so that a lookup of
759 // this struct instance can find them from nested functions.
760 for (auto &v : LDSUsesInfo.indirect_access[&Func]) {
761 if (!AMDGPU::isDynamicLDS(GV: *v)) {
762 KernelUsedVariables.insert(V: v);
763 }
764 }
765
766 // Variables allocated in module lds must all resolve to that struct,
767 // not to the per-kernel instance.
768 if (KernelsThatAllocateModuleLDS.contains(V: &Func)) {
769 for (GlobalVariable *v : ModuleScopeVariables) {
770 KernelUsedVariables.erase(V: v);
771 }
772 }
773
774 if (KernelUsedVariables.empty()) {
775 // Either used no LDS, or the LDS it used was all in the module struct
776 // or dynamically sized
777 continue;
778 }
779
780 // The association between kernel function and LDS struct is done by
781 // symbol name, which only works if the function in question has a
782 // name This is not expected to be a problem in practice as kernels
783 // are called by name making anonymous ones (which are named by the
784 // backend) difficult to use. This does mean that llvm test cases need
785 // to name the kernels.
786 if (!Func.hasName()) {
787 report_fatal_error(reason: "Anonymous kernels cannot use LDS variables");
788 }
789
790 std::string VarName =
791 (Twine("llvm.amdgcn.kernel.") + Func.getName() + ".lds").str();
792
793 auto Replacement =
794 createLDSVariableReplacement(M, VarName, LDSVarsToTransform: KernelUsedVariables);
795
796 // If any indirect uses, create a direct use to ensure allocation
797 // TODO: Simpler to unconditionally mark used but that regresses
798 // codegen in test/CodeGen/AMDGPU/noclobber-barrier.ll
799 auto Accesses = LDSUsesInfo.indirect_access.find(Val: &Func);
800 if ((Accesses != LDSUsesInfo.indirect_access.end()) &&
801 !Accesses->second.empty())
802 markUsedByKernel(Func: &Func, SGV: Replacement.SGV);
803
804 // remove preserves existing codegen
805 removeLocalVarsFromUsedLists(M, LocalVars: KernelUsedVariables);
806 KernelToReplacement[&Func] = Replacement;
807
808 // Rewrite uses within kernel to the new struct
809 replaceLDSVariablesWithStruct(
810 M, LDSVarsToTransformArg: KernelUsedVariables, Replacement, Predicate: [&Func](Use &U) {
811 Instruction *I = dyn_cast<Instruction>(Val: U.getUser());
812 return I && I->getFunction() == &Func;
813 });
814 }
815 return KernelToReplacement;
816 }
817
818 static GlobalVariable *
819 buildRepresentativeDynamicLDSInstance(Module &M, LDSUsesInfoTy &LDSUsesInfo,
820 Function *func) {
821 // Create a dynamic lds variable with a name associated with the passed
822 // function that has the maximum alignment of any dynamic lds variable
823 // reachable from this kernel. Dynamic LDS is allocated after the static LDS
824 // allocation, possibly after alignment padding. The representative variable
825 // created here has the maximum alignment of any other dynamic variable
826 // reachable by that kernel. All dynamic LDS variables are allocated at the
827 // same address in each kernel in order to provide the documented aliasing
828 // semantics. Setting the alignment here allows this IR pass to accurately
829 // predict the exact constant at which it will be allocated.
830
831 assert(isKernelLDS(func));
832
833 LLVMContext &Ctx = M.getContext();
834 const DataLayout &DL = M.getDataLayout();
835 Align MaxDynamicAlignment(1);
836
837 auto UpdateMaxAlignment = [&MaxDynamicAlignment, &DL](GlobalVariable *GV) {
838 if (AMDGPU::isDynamicLDS(GV: *GV)) {
839 MaxDynamicAlignment =
840 std::max(a: MaxDynamicAlignment, b: AMDGPU::getAlign(DL, GV));
841 }
842 };
843
844 for (GlobalVariable *GV : LDSUsesInfo.indirect_access[func]) {
845 UpdateMaxAlignment(GV);
846 }
847
848 for (GlobalVariable *GV : LDSUsesInfo.direct_access[func]) {
849 UpdateMaxAlignment(GV);
850 }
851
852 assert(func->hasName()); // Checked by caller
853 auto emptyCharArray = ArrayType::get(ElementType: Type::getInt8Ty(C&: Ctx), NumElements: 0);
854 GlobalVariable *N = new GlobalVariable(
855 M, emptyCharArray, false, GlobalValue::ExternalLinkage, nullptr,
856 Twine("llvm.amdgcn." + func->getName() + ".dynlds"), nullptr, GlobalValue::NotThreadLocal, AMDGPUAS::LOCAL_ADDRESS,
857 false);
858 N->setAlignment(MaxDynamicAlignment);
859
860 assert(AMDGPU::isDynamicLDS(*N));
861 return N;
862 }
863
864 DenseMap<Function *, GlobalVariable *> lowerDynamicLDSVariables(
865 Module &M, LDSUsesInfoTy &LDSUsesInfo,
866 DenseSet<Function *> const &KernelsThatIndirectlyAllocateDynamicLDS,
867 DenseSet<GlobalVariable *> const &DynamicVariables,
868 std::vector<Function *> const &OrderedKernels) {
869 DenseMap<Function *, GlobalVariable *> KernelToCreatedDynamicLDS;
870 if (!KernelsThatIndirectlyAllocateDynamicLDS.empty()) {
871 LLVMContext &Ctx = M.getContext();
872 IRBuilder<> Builder(Ctx);
873 Type *I32 = Type::getInt32Ty(C&: Ctx);
874
875 std::vector<Constant *> newDynamicLDS;
876
877 // Table is built in the same order as OrderedKernels
878 for (auto &func : OrderedKernels) {
879
880 if (KernelsThatIndirectlyAllocateDynamicLDS.contains(V: func)) {
881 assert(isKernelLDS(func));
882 if (!func->hasName()) {
883 report_fatal_error(reason: "Anonymous kernels cannot use LDS variables");
884 }
885
886 GlobalVariable *N =
887 buildRepresentativeDynamicLDSInstance(M, LDSUsesInfo, func);
888
889 KernelToCreatedDynamicLDS[func] = N;
890
891 markUsedByKernel(Func: func, SGV: N);
892
893 auto emptyCharArray = ArrayType::get(ElementType: Type::getInt8Ty(C&: Ctx), NumElements: 0);
894 auto GEP = ConstantExpr::getGetElementPtr(
895 Ty: emptyCharArray, C: N, Idx: ConstantInt::get(Ty: I32, V: 0), NW: true);
896 newDynamicLDS.push_back(x: ConstantExpr::getPtrToInt(C: GEP, Ty: I32));
897 } else {
898 newDynamicLDS.push_back(x: PoisonValue::get(T: I32));
899 }
900 }
901 assert(OrderedKernels.size() == newDynamicLDS.size());
902
903 ArrayType *t = ArrayType::get(ElementType: I32, NumElements: newDynamicLDS.size());
904 Constant *init = ConstantArray::get(T: t, V: newDynamicLDS);
905 GlobalVariable *table = new GlobalVariable(
906 M, t, true, GlobalValue::InternalLinkage, init,
907 "llvm.amdgcn.dynlds.offset.table", nullptr,
908 GlobalValue::NotThreadLocal, AMDGPUAS::CONSTANT_ADDRESS);
909
910 for (GlobalVariable *GV : DynamicVariables) {
911 for (Use &U : make_early_inc_range(Range: GV->uses())) {
912 auto *I = dyn_cast<Instruction>(Val: U.getUser());
913 if (!I)
914 continue;
915 if (isKernelLDS(F: I->getFunction()))
916 continue;
917
918 replaceUseWithTableLookup(M, Builder, LookupTable: table, GV, U, OptionalIndex: nullptr);
919 }
920 }
921 }
922 return KernelToCreatedDynamicLDS;
923 }
924
925 bool runOnModule(Module &M) {
926 CallGraph CG = CallGraph(M);
927 bool Changed = superAlignLDSGlobals(M);
928
929 Changed |= eliminateConstantExprUsesOfLDSFromAllInstructions(M);
930
931 Changed = true; // todo: narrow this down
932
933 // For each kernel, what variables does it access directly or through
934 // callees
935 LDSUsesInfoTy LDSUsesInfo = getTransitiveUsesOfLDS(CG, M);
936
937 // For each variable accessed through callees, which kernels access it
938 VariableFunctionMap LDSToKernelsThatNeedToAccessItIndirectly;
939 for (auto &K : LDSUsesInfo.indirect_access) {
940 Function *F = K.first;
941 assert(isKernelLDS(F));
942 for (GlobalVariable *GV : K.second) {
943 LDSToKernelsThatNeedToAccessItIndirectly[GV].insert(V: F);
944 }
945 }
946
947 // Partition variables accessed indirectly into the different strategies
948 DenseSet<GlobalVariable *> ModuleScopeVariables;
949 DenseSet<GlobalVariable *> TableLookupVariables;
950 DenseSet<GlobalVariable *> KernelAccessVariables;
951 DenseSet<GlobalVariable *> DynamicVariables;
952 partitionVariablesIntoIndirectStrategies(
953 M, LDSUsesInfo, LDSToKernelsThatNeedToAccessItIndirectly,
954 ModuleScopeVariables, TableLookupVariables, KernelAccessVariables,
955 DynamicVariables);
956
957 // If the kernel accesses a variable that is going to be stored in the
958 // module instance through a call then that kernel needs to allocate the
959 // module instance
960 const DenseSet<Function *> KernelsThatAllocateModuleLDS =
961 kernelsThatIndirectlyAccessAnyOfPassedVariables(M, LDSUsesInfo,
962 VariableSet: ModuleScopeVariables);
963 const DenseSet<Function *> KernelsThatAllocateTableLDS =
964 kernelsThatIndirectlyAccessAnyOfPassedVariables(M, LDSUsesInfo,
965 VariableSet: TableLookupVariables);
966
967 const DenseSet<Function *> KernelsThatIndirectlyAllocateDynamicLDS =
968 kernelsThatIndirectlyAccessAnyOfPassedVariables(M, LDSUsesInfo,
969 VariableSet: DynamicVariables);
970
971 GlobalVariable *MaybeModuleScopeStruct = lowerModuleScopeStructVariables(
972 M, ModuleScopeVariables, KernelsThatAllocateModuleLDS);
973
974 DenseMap<Function *, LDSVariableReplacement> KernelToReplacement =
975 lowerKernelScopeStructVariables(M, LDSUsesInfo, ModuleScopeVariables,
976 KernelsThatAllocateModuleLDS,
977 MaybeModuleScopeStruct);
978
979 // Lower zero cost accesses to the kernel instances just created
980 for (auto &GV : KernelAccessVariables) {
981 auto &funcs = LDSToKernelsThatNeedToAccessItIndirectly[GV];
982 assert(funcs.size() == 1); // Only one kernel can access it
983 LDSVariableReplacement Replacement =
984 KernelToReplacement[*(funcs.begin())];
985
986 DenseSet<GlobalVariable *> Vec;
987 Vec.insert(V: GV);
988
989 replaceLDSVariablesWithStruct(M, LDSVarsToTransformArg: Vec, Replacement, Predicate: [](Use &U) {
990 return isa<Instruction>(Val: U.getUser());
991 });
992 }
993
994 // The ith element of this vector is kernel id i
995 std::vector<Function *> OrderedKernels =
996 assignLDSKernelIDToEachKernel(M: &M, KernelsThatAllocateTableLDS,
997 KernelsThatIndirectlyAllocateDynamicLDS);
998
999 if (!KernelsThatAllocateTableLDS.empty()) {
1000 LLVMContext &Ctx = M.getContext();
1001 IRBuilder<> Builder(Ctx);
1002
1003 // The order must be consistent between lookup table and accesses to
1004 // lookup table
1005 auto TableLookupVariablesOrdered =
1006 sortByName(V: std::vector<GlobalVariable *>(TableLookupVariables.begin(),
1007 TableLookupVariables.end()));
1008
1009 GlobalVariable *LookupTable = buildLookupTable(
1010 M, Variables: TableLookupVariablesOrdered, kernels: OrderedKernels, KernelToReplacement);
1011 replaceUsesInInstructionsWithTableLookup(M, ModuleScopeVariables: TableLookupVariablesOrdered,
1012 LookupTable);
1013
1014 // Strip amdgpu-no-lds-kernel-id from all functions reachable from the
1015 // kernel. We may have inferred this wasn't used prior to the pass.
1016 //
1017 // TODO: We could filter out subgraphs that do not access LDS globals.
1018 for (Function *F : KernelsThatAllocateTableLDS)
1019 removeFnAttrFromReachable(CG, KernelRoot: F, FnAttrs: {"amdgpu-no-lds-kernel-id"});
1020 }
1021
1022 DenseMap<Function *, GlobalVariable *> KernelToCreatedDynamicLDS =
1023 lowerDynamicLDSVariables(M, LDSUsesInfo,
1024 KernelsThatIndirectlyAllocateDynamicLDS,
1025 DynamicVariables, OrderedKernels);
1026
1027 // All kernel frames have been allocated. Calculate and record the
1028 // addresses.
1029 {
1030 const DataLayout &DL = M.getDataLayout();
1031
1032 for (Function &Func : M.functions()) {
1033 if (Func.isDeclaration() || !isKernelLDS(F: &Func))
1034 continue;
1035
1036 // All three of these are optional. The first variable is allocated at
1037 // zero. They are allocated by AMDGPUMachineFunction as one block.
1038 // Layout:
1039 //{
1040 // module.lds
1041 // alignment padding
1042 // kernel instance
1043 // alignment padding
1044 // dynamic lds variables
1045 //}
1046
1047 const bool AllocateModuleScopeStruct =
1048 MaybeModuleScopeStruct &&
1049 KernelsThatAllocateModuleLDS.contains(V: &Func);
1050
1051 auto Replacement = KernelToReplacement.find(Val: &Func);
1052 const bool AllocateKernelScopeStruct =
1053 Replacement != KernelToReplacement.end();
1054
1055 const bool AllocateDynamicVariable =
1056 KernelToCreatedDynamicLDS.contains(Val: &Func);
1057
1058 uint32_t Offset = 0;
1059
1060 if (AllocateModuleScopeStruct) {
1061 // Allocated at zero, recorded once on construction, not once per
1062 // kernel
1063 Offset += DL.getTypeAllocSize(Ty: MaybeModuleScopeStruct->getValueType());
1064 }
1065
1066 if (AllocateKernelScopeStruct) {
1067 GlobalVariable *KernelStruct = Replacement->second.SGV;
1068 Offset = alignTo(Size: Offset, A: AMDGPU::getAlign(DL, GV: KernelStruct));
1069 recordLDSAbsoluteAddress(M: &M, GV: KernelStruct, Address: Offset);
1070 Offset += DL.getTypeAllocSize(Ty: KernelStruct->getValueType());
1071 }
1072
1073 // If there is dynamic allocation, the alignment needed is included in
1074 // the static frame size. There may be no reference to the dynamic
1075 // variable in the kernel itself, so without including it here, that
1076 // alignment padding could be missed.
1077 if (AllocateDynamicVariable) {
1078 GlobalVariable *DynamicVariable = KernelToCreatedDynamicLDS[&Func];
1079 Offset = alignTo(Size: Offset, A: AMDGPU::getAlign(DL, GV: DynamicVariable));
1080 recordLDSAbsoluteAddress(M: &M, GV: DynamicVariable, Address: Offset);
1081 }
1082
1083 if (Offset != 0) {
1084 (void)TM; // TODO: Account for target maximum LDS
1085 std::string Buffer;
1086 raw_string_ostream SS{Buffer};
1087 SS << format(Fmt: "%u", Vals: Offset);
1088
1089 // Instead of explicitly marking kernels that access dynamic variables
1090 // using special case metadata, annotate with min-lds == max-lds, i.e.
1091 // that there is no more space available for allocating more static
1092 // LDS variables. That is the right condition to prevent allocating
1093 // more variables which would collide with the addresses assigned to
1094 // dynamic variables.
1095 if (AllocateDynamicVariable)
1096 SS << format(Fmt: ",%u", Vals: Offset);
1097
1098 Func.addFnAttr(Kind: "amdgpu-lds-size", Val: Buffer);
1099 }
1100 }
1101 }
1102
1103 for (auto &GV : make_early_inc_range(Range: M.globals()))
1104 if (AMDGPU::isLDSVariableToLower(GV)) {
1105 // probably want to remove from used lists
1106 GV.removeDeadConstantUsers();
1107 if (GV.use_empty())
1108 GV.eraseFromParent();
1109 }
1110
1111 return Changed;
1112 }
1113
1114private:
1115 // Increase the alignment of LDS globals if necessary to maximise the chance
1116 // that we can use aligned LDS instructions to access them.
1117 static bool superAlignLDSGlobals(Module &M) {
1118 const DataLayout &DL = M.getDataLayout();
1119 bool Changed = false;
1120 if (!SuperAlignLDSGlobals) {
1121 return Changed;
1122 }
1123
1124 for (auto &GV : M.globals()) {
1125 if (GV.getType()->getPointerAddressSpace() != AMDGPUAS::LOCAL_ADDRESS) {
1126 // Only changing alignment of LDS variables
1127 continue;
1128 }
1129 if (!GV.hasInitializer()) {
1130 // cuda/hip extern __shared__ variable, leave alignment alone
1131 continue;
1132 }
1133
1134 Align Alignment = AMDGPU::getAlign(DL, GV: &GV);
1135 TypeSize GVSize = DL.getTypeAllocSize(Ty: GV.getValueType());
1136
1137 if (GVSize > 8) {
1138 // We might want to use a b96 or b128 load/store
1139 Alignment = std::max(a: Alignment, b: Align(16));
1140 } else if (GVSize > 4) {
1141 // We might want to use a b64 load/store
1142 Alignment = std::max(a: Alignment, b: Align(8));
1143 } else if (GVSize > 2) {
1144 // We might want to use a b32 load/store
1145 Alignment = std::max(a: Alignment, b: Align(4));
1146 } else if (GVSize > 1) {
1147 // We might want to use a b16 load/store
1148 Alignment = std::max(a: Alignment, b: Align(2));
1149 }
1150
1151 if (Alignment != AMDGPU::getAlign(DL, GV: &GV)) {
1152 Changed = true;
1153 GV.setAlignment(Alignment);
1154 }
1155 }
1156 return Changed;
1157 }
1158
1159 static LDSVariableReplacement createLDSVariableReplacement(
1160 Module &M, std::string VarName,
1161 DenseSet<GlobalVariable *> const &LDSVarsToTransform) {
1162 // Create a struct instance containing LDSVarsToTransform and map from those
1163 // variables to ConstantExprGEP
1164 // Variables may be introduced to meet alignment requirements. No aliasing
1165 // metadata is useful for these as they have no uses. Erased before return.
1166
1167 LLVMContext &Ctx = M.getContext();
1168 const DataLayout &DL = M.getDataLayout();
1169 assert(!LDSVarsToTransform.empty());
1170
1171 SmallVector<OptimizedStructLayoutField, 8> LayoutFields;
1172 LayoutFields.reserve(N: LDSVarsToTransform.size());
1173 {
1174 // The order of fields in this struct depends on the order of
1175 // variables in the argument which varies when changing how they
1176 // are identified, leading to spurious test breakage.
1177 auto Sorted = sortByName(V: std::vector<GlobalVariable *>(
1178 LDSVarsToTransform.begin(), LDSVarsToTransform.end()));
1179
1180 for (GlobalVariable *GV : Sorted) {
1181 OptimizedStructLayoutField F(GV,
1182 DL.getTypeAllocSize(Ty: GV->getValueType()),
1183 AMDGPU::getAlign(DL, GV));
1184 LayoutFields.emplace_back(Args&: F);
1185 }
1186 }
1187
1188 performOptimizedStructLayout(Fields: LayoutFields);
1189
1190 std::vector<GlobalVariable *> LocalVars;
1191 BitVector IsPaddingField;
1192 LocalVars.reserve(n: LDSVarsToTransform.size()); // will be at least this large
1193 IsPaddingField.reserve(N: LDSVarsToTransform.size());
1194 {
1195 uint64_t CurrentOffset = 0;
1196 for (auto &F : LayoutFields) {
1197 GlobalVariable *FGV =
1198 static_cast<GlobalVariable *>(const_cast<void *>(F.Id));
1199 Align DataAlign = F.Alignment;
1200
1201 uint64_t DataAlignV = DataAlign.value();
1202 if (uint64_t Rem = CurrentOffset % DataAlignV) {
1203 uint64_t Padding = DataAlignV - Rem;
1204
1205 // Append an array of padding bytes to meet alignment requested
1206 // Note (o + (a - (o % a)) ) % a == 0
1207 // (offset + Padding ) % align == 0
1208
1209 Type *ATy = ArrayType::get(ElementType: Type::getInt8Ty(C&: Ctx), NumElements: Padding);
1210 LocalVars.push_back(x: new GlobalVariable(
1211 M, ATy, false, GlobalValue::InternalLinkage,
1212 PoisonValue::get(T: ATy), "", nullptr, GlobalValue::NotThreadLocal,
1213 AMDGPUAS::LOCAL_ADDRESS, false));
1214 IsPaddingField.push_back(Val: true);
1215 CurrentOffset += Padding;
1216 }
1217
1218 LocalVars.push_back(x: FGV);
1219 IsPaddingField.push_back(Val: false);
1220 CurrentOffset += F.Size;
1221 }
1222 }
1223
1224 std::vector<Type *> LocalVarTypes;
1225 LocalVarTypes.reserve(n: LocalVars.size());
1226 std::transform(
1227 first: LocalVars.cbegin(), last: LocalVars.cend(), result: std::back_inserter(x&: LocalVarTypes),
1228 unary_op: [](const GlobalVariable *V) -> Type * { return V->getValueType(); });
1229
1230 StructType *LDSTy = StructType::create(Context&: Ctx, Elements: LocalVarTypes, Name: VarName + ".t");
1231
1232 Align StructAlign = AMDGPU::getAlign(DL, GV: LocalVars[0]);
1233
1234 GlobalVariable *SGV = new GlobalVariable(
1235 M, LDSTy, false, GlobalValue::InternalLinkage, PoisonValue::get(T: LDSTy),
1236 VarName, nullptr, GlobalValue::NotThreadLocal, AMDGPUAS::LOCAL_ADDRESS,
1237 false);
1238 SGV->setAlignment(StructAlign);
1239
1240 DenseMap<GlobalVariable *, Constant *> Map;
1241 Type *I32 = Type::getInt32Ty(C&: Ctx);
1242 for (size_t I = 0; I < LocalVars.size(); I++) {
1243 GlobalVariable *GV = LocalVars[I];
1244 Constant *GEPIdx[] = {ConstantInt::get(Ty: I32, V: 0), ConstantInt::get(Ty: I32, V: I)};
1245 Constant *GEP = ConstantExpr::getGetElementPtr(Ty: LDSTy, C: SGV, IdxList: GEPIdx, NW: true);
1246 if (IsPaddingField[I]) {
1247 assert(GV->use_empty());
1248 GV->eraseFromParent();
1249 } else {
1250 Map[GV] = GEP;
1251 }
1252 }
1253 assert(Map.size() == LDSVarsToTransform.size());
1254 return {.SGV: SGV, .LDSVarsToConstantGEP: std::move(Map)};
1255 }
1256
1257 template <typename PredicateTy>
1258 static void replaceLDSVariablesWithStruct(
1259 Module &M, DenseSet<GlobalVariable *> const &LDSVarsToTransformArg,
1260 const LDSVariableReplacement &Replacement, PredicateTy Predicate) {
1261 LLVMContext &Ctx = M.getContext();
1262 const DataLayout &DL = M.getDataLayout();
1263
1264 // A hack... we need to insert the aliasing info in a predictable order for
1265 // lit tests. Would like to have them in a stable order already, ideally the
1266 // same order they get allocated, which might mean an ordered set container
1267 auto LDSVarsToTransform = sortByName(V: std::vector<GlobalVariable *>(
1268 LDSVarsToTransformArg.begin(), LDSVarsToTransformArg.end()));
1269
1270 // Create alias.scope and their lists. Each field in the new structure
1271 // does not alias with all other fields.
1272 SmallVector<MDNode *> AliasScopes;
1273 SmallVector<Metadata *> NoAliasList;
1274 const size_t NumberVars = LDSVarsToTransform.size();
1275 if (NumberVars > 1) {
1276 MDBuilder MDB(Ctx);
1277 AliasScopes.reserve(N: NumberVars);
1278 MDNode *Domain = MDB.createAnonymousAliasScopeDomain();
1279 for (size_t I = 0; I < NumberVars; I++) {
1280 MDNode *Scope = MDB.createAnonymousAliasScope(Domain);
1281 AliasScopes.push_back(Elt: Scope);
1282 }
1283 NoAliasList.append(in_start: &AliasScopes[1], in_end: AliasScopes.end());
1284 }
1285
1286 // Replace uses of ith variable with a constantexpr to the corresponding
1287 // field of the instance that will be allocated by AMDGPUMachineFunction
1288 for (size_t I = 0; I < NumberVars; I++) {
1289 GlobalVariable *GV = LDSVarsToTransform[I];
1290 Constant *GEP = Replacement.LDSVarsToConstantGEP.at(Val: GV);
1291
1292 GV->replaceUsesWithIf(New: GEP, ShouldReplace: Predicate);
1293
1294 APInt APOff(DL.getIndexTypeSizeInBits(Ty: GEP->getType()), 0);
1295 GEP->stripAndAccumulateInBoundsConstantOffsets(DL, Offset&: APOff);
1296 uint64_t Offset = APOff.getZExtValue();
1297
1298 Align A =
1299 commonAlignment(A: Replacement.SGV->getAlign().valueOrOne(), Offset);
1300
1301 if (I)
1302 NoAliasList[I - 1] = AliasScopes[I - 1];
1303 MDNode *NoAlias =
1304 NoAliasList.empty() ? nullptr : MDNode::get(Context&: Ctx, MDs: NoAliasList);
1305 MDNode *AliasScope =
1306 AliasScopes.empty() ? nullptr : MDNode::get(Context&: Ctx, MDs: {AliasScopes[I]});
1307
1308 refineUsesAlignmentAndAA(Ptr: GEP, A, DL, AliasScope, NoAlias);
1309 }
1310 }
1311
1312 static void refineUsesAlignmentAndAA(Value *Ptr, Align A,
1313 const DataLayout &DL, MDNode *AliasScope,
1314 MDNode *NoAlias, unsigned MaxDepth = 5) {
1315 if (!MaxDepth || (A == 1 && !AliasScope))
1316 return;
1317
1318 for (User *U : Ptr->users()) {
1319 if (auto *I = dyn_cast<Instruction>(Val: U)) {
1320 if (AliasScope && I->mayReadOrWriteMemory()) {
1321 MDNode *AS = I->getMetadata(KindID: LLVMContext::MD_alias_scope);
1322 AS = (AS ? MDNode::getMostGenericAliasScope(A: AS, B: AliasScope)
1323 : AliasScope);
1324 I->setMetadata(KindID: LLVMContext::MD_alias_scope, Node: AS);
1325
1326 MDNode *NA = I->getMetadata(KindID: LLVMContext::MD_noalias);
1327 NA = (NA ? MDNode::intersect(A: NA, B: NoAlias) : NoAlias);
1328 I->setMetadata(KindID: LLVMContext::MD_noalias, Node: NA);
1329 }
1330 }
1331
1332 if (auto *LI = dyn_cast<LoadInst>(Val: U)) {
1333 LI->setAlignment(std::max(a: A, b: LI->getAlign()));
1334 continue;
1335 }
1336 if (auto *SI = dyn_cast<StoreInst>(Val: U)) {
1337 if (SI->getPointerOperand() == Ptr)
1338 SI->setAlignment(std::max(a: A, b: SI->getAlign()));
1339 continue;
1340 }
1341 if (auto *AI = dyn_cast<AtomicRMWInst>(Val: U)) {
1342 // None of atomicrmw operations can work on pointers, but let's
1343 // check it anyway in case it will or we will process ConstantExpr.
1344 if (AI->getPointerOperand() == Ptr)
1345 AI->setAlignment(std::max(a: A, b: AI->getAlign()));
1346 continue;
1347 }
1348 if (auto *AI = dyn_cast<AtomicCmpXchgInst>(Val: U)) {
1349 if (AI->getPointerOperand() == Ptr)
1350 AI->setAlignment(std::max(a: A, b: AI->getAlign()));
1351 continue;
1352 }
1353 if (auto *GEP = dyn_cast<GetElementPtrInst>(Val: U)) {
1354 unsigned BitWidth = DL.getIndexTypeSizeInBits(Ty: GEP->getType());
1355 APInt Off(BitWidth, 0);
1356 if (GEP->getPointerOperand() == Ptr) {
1357 Align GA;
1358 if (GEP->accumulateConstantOffset(DL, Offset&: Off))
1359 GA = commonAlignment(A, Offset: Off.getLimitedValue());
1360 refineUsesAlignmentAndAA(Ptr: GEP, A: GA, DL, AliasScope, NoAlias,
1361 MaxDepth: MaxDepth - 1);
1362 }
1363 continue;
1364 }
1365 if (auto *I = dyn_cast<Instruction>(Val: U)) {
1366 if (I->getOpcode() == Instruction::BitCast ||
1367 I->getOpcode() == Instruction::AddrSpaceCast)
1368 refineUsesAlignmentAndAA(Ptr: I, A, DL, AliasScope, NoAlias, MaxDepth: MaxDepth - 1);
1369 }
1370 }
1371 }
1372};
1373
1374class AMDGPULowerModuleLDSLegacy : public ModulePass {
1375public:
1376 const AMDGPUTargetMachine *TM;
1377 static char ID;
1378
1379 AMDGPULowerModuleLDSLegacy(const AMDGPUTargetMachine *TM_ = nullptr)
1380 : ModulePass(ID), TM(TM_) {
1381 initializeAMDGPULowerModuleLDSLegacyPass(*PassRegistry::getPassRegistry());
1382 }
1383
1384 void getAnalysisUsage(AnalysisUsage &AU) const override {
1385 if (!TM)
1386 AU.addRequired<TargetPassConfig>();
1387 }
1388
1389 bool runOnModule(Module &M) override {
1390 if (!TM) {
1391 auto &TPC = getAnalysis<TargetPassConfig>();
1392 TM = &TPC.getTM<AMDGPUTargetMachine>();
1393 }
1394
1395 return AMDGPULowerModuleLDS(*TM).runOnModule(M);
1396 }
1397};
1398
1399} // namespace
1400char AMDGPULowerModuleLDSLegacy::ID = 0;
1401
1402char &llvm::AMDGPULowerModuleLDSLegacyPassID = AMDGPULowerModuleLDSLegacy::ID;
1403
1404INITIALIZE_PASS_BEGIN(AMDGPULowerModuleLDSLegacy, DEBUG_TYPE,
1405 "Lower uses of LDS variables from non-kernel functions",
1406 false, false)
1407INITIALIZE_PASS_DEPENDENCY(TargetPassConfig)
1408INITIALIZE_PASS_END(AMDGPULowerModuleLDSLegacy, DEBUG_TYPE,
1409 "Lower uses of LDS variables from non-kernel functions",
1410 false, false)
1411
1412ModulePass *
1413llvm::createAMDGPULowerModuleLDSLegacyPass(const AMDGPUTargetMachine *TM) {
1414 return new AMDGPULowerModuleLDSLegacy(TM);
1415}
1416
1417PreservedAnalyses AMDGPULowerModuleLDSPass::run(Module &M,
1418 ModuleAnalysisManager &) {
1419 return AMDGPULowerModuleLDS(TM).runOnModule(M) ? PreservedAnalyses::none()
1420 : PreservedAnalyses::all();
1421}
1422