[llvm] [AMDGPU] Enable amdgpu-sw-lower-lds pass to lower LDS accesses to use device global memory (PR #87265)

Matt Arsenault via llvm-commits llvm-commits at lists.llvm.org
Tue Apr 2 08:04:06 PDT 2024


================
@@ -0,0 +1,865 @@
+//===-- AMDGPUSwLowerLDS.cpp -----------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass lowers the local data store, LDS, uses in kernel and non-kernel
+// functions in module with dynamically allocated device global memory.
+//
+// Replacement of Kernel LDS accesses:
+//    For a kernel, LDS access can be static or dynamic which are direct
+//    (accessed within kernel) and indirect (accessed through non-kernels).
+//    A device global memory equal to size of all these LDS globals will be
+//    allocated. At the prologue of the kernel, a single work-item from the
+//    work-group, does a "malloc" and stores the pointer of the allocation in
+//    new LDS global that will be created for the kernel. This will be called
+//    "malloc LDS global" in this pass.
+//    Each LDS access corresponds to an offset in the allocated memory.
+//    All static LDS accesses will be allocated first and then dynamic LDS
+//    will occupy the device global memoery.
+//    To store the offsets corresponding to all LDS accesses, another global
+//    variable is created which will be called "metadata global" in this pass.
+//    - Malloc LDS Global:
+//        It is LDS global of ptr type with name
+//        "llvm.amdgcn.sw.lds.<kernel-name>".
+//    - Metadata Global:
+//        It is of struct type, with n members. n equals the number of LDS
+//        globals accessed by the kernel(direct and indirect). Each member of
+//        struct is another struct of type {i32, i32}. First member corresponds
+//        to offset, second member corresponds to size of LDS global being
+//        replaced. It will have name "llvm.amdgcn.sw.lds.<kernel-name>.md".
+//        This global will have an intializer with static LDS related offsets
+//        and sizes initialized. But for dynamic LDS related entries, offsets
+//        will be intialized to previous static LDS allocation end offset. Sizes
+//        for them will be zero initially. These dynamic LDS offset and size
+//        values will be updated with in the kernel, since kernel can read the
+//        dynamic LDS size allocation done at runtime with query to
+//        "hidden_dynamic_lds_size" hidden kernel argument.
+//
+//    LDS accesses within the kernel will be replaced by "gep" ptr to
+//    corresponding offset into allocated device global memory for the kernel.
+//    At the epilogue of kernel, allocated memory would be made free by the same
+//    single work-item.
+//
+// Replacement of non-kernel LDS accesses:
+//    Multiple kernels can access the same non-kernel function.
+//    All the kernels accessing LDS through non-kernels are sorted and
+//    assigned a kernel-id. All the LDS globals accessed by non-kernels
+//    are sorted. This information is used to build two tables:
+//    - Base table:
+//        Base table will have single row, with elements of the row
+//        placed as per kernel ID. Each element in the row corresponds
+//        to addresss of "malloc LDS global" variable created for
+//        that kernel.
+//    - Offset table:
+//        Offset table will have multiple rows and columns.
+//        Rows are assumed to be from 0 to (n-1). n is total number
+//        of kernels accessing the LDS through non-kernels.
+//        Each row will have m elements. m is the total number of
+//        unique LDS globals accessed by all non-kernels.
+//        Each element in the row correspond to the address of
+//        the replacement of LDS global done by that particular kernel.
+//    A LDS variable in non-kernel will be replaced based on the information
+//    from base and offset tables. Based on kernel-id query, address of "malloc
+//    LDS global" for that corresponding kernel is obtained from base table.
+//    The Offset into the base "malloc LDS global" is obtained from
+//    corresponding element in offset table. With this information, replacement
+//    value is obtained.
+//===----------------------------------------------------------------------===//
+
+#include "AMDGPU.h"
+#include "Utils/AMDGPUMemoryUtils.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/DenseSet.h"
+#include "llvm/ADT/SetOperations.h"
+#include "llvm/ADT/SetVector.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Analysis/CallGraph.h"
+#include "llvm/Analysis/DomTreeUpdater.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/IRBuilder.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicsAMDGPU.h"
+#include "llvm/IR/MDBuilder.h"
+#include "llvm/IR/ReplaceConstant.h"
+#include "llvm/InitializePasses.h"
+#include "llvm/Pass.h"
+#include "llvm/Transforms/Utils/ModuleUtils.h"
+
+#include <algorithm>
+
+#define DEBUG_TYPE "amdgpu-sw-lower-lds"
+
+using namespace llvm;
+using namespace AMDGPU;
+
+namespace {
+
+using DomTreeCallback = function_ref<DominatorTree *(Function &F)>;
+
+struct LDSAccessTypeInfo {
+  SetVector<GlobalVariable *> StaticLDSGlobals;
+  SetVector<GlobalVariable *> DynamicLDSGlobals;
+};
+
+// Struct to hold all the Metadata required for a kernel
+// to replace a LDS global uses with corresponding offset
+// in to device global memory.
+struct KernelLDSParameters {
+  GlobalVariable *MallocLDSGlobal{nullptr};
+  GlobalVariable *MallocMetadataGlobal{nullptr};
+  LDSAccessTypeInfo DirectAccess;
+  LDSAccessTypeInfo IndirectAccess;
+  DenseMap<GlobalVariable *, SmallVector<uint32_t, 3>>
+      LDSToReplacementIndicesMap;
+  int32_t KernelId{-1};
+  uint32_t MallocSize{0};
+};
+
+// Struct to store infor for creation of offset table
+// for all the non-kernel LDS accesses.
+struct NonKernelLDSParameters {
+  GlobalVariable *LDSBaseTable{nullptr};
+  GlobalVariable *LDSOffsetTable{nullptr};
+  SetVector<Function *> OrderedKernels;
+  SetVector<GlobalVariable *> OrdereLDSGlobals;
+};
+
+class AMDGPUSwLowerLDS {
+public:
+  AMDGPUSwLowerLDS(Module &mod, DomTreeCallback Callback)
+      : M(mod), IRB(M.getContext()), DTCallback(Callback) {}
+  bool Run();
+  void GetUsesOfLDSByNonKernels(CallGraph const &CG,
+                                FunctionVariableMap &functions);
+  SetVector<Function *>
+  GetOrderedIndirectLDSAccessingKernels(SetVector<Function *> &&Kernels);
+  SetVector<GlobalVariable *>
+  GetOrderedNonKernelAllLDSGlobals(SetVector<GlobalVariable *> &&Variables);
+  void PopulateMallocLDSGlobal(Function *Func);
+  void PopulateMallocMetadataGlobal(Function *Func);
+  void PopulateLDSToReplacementIndicesMap(Function *Func);
+  void ReplaceKernelLDSAccesses(Function *Func);
+  void LowerKernelLDSAccesses(Function *Func, DomTreeUpdater &DTU);
+  void BuildNonKernelLDSOffsetTable(
+      std::shared_ptr<NonKernelLDSParameters> &NKLDSParams);
+  void BuildNonKernelLDSBaseTable(
+      std::shared_ptr<NonKernelLDSParameters> &NKLDSParams);
+  Constant *
+  GetAddressesOfVariablesInKernel(Function *Func,
+                                  SetVector<GlobalVariable *> &Variables);
+  void LowerNonKernelLDSAccesses(
+      Function *Func, SetVector<GlobalVariable *> &LDSGlobals,
+      std::shared_ptr<NonKernelLDSParameters> &NKLDSParams);
+
+private:
+  Module &M;
+  IRBuilder<> IRB;
+  DomTreeCallback DTCallback;
+  DenseMap<Function *, std::shared_ptr<KernelLDSParameters>>
+      KernelToLDSParametersMap;
+};
+
+template <typename T> SetVector<T> SortByName(std::vector<T> &&V) {
+  // Sort the vector of globals or Functions based on their name.
+  // Returns a SetVector of globals/Functions.
+  llvm::sort(V.begin(), V.end(), [](const auto *L, const auto *R) {
+    return L->getName() < R->getName();
+  });
+  return {std::move(SetVector<T>(V.begin(), V.end()))};
+}
+
+SetVector<GlobalVariable *> AMDGPUSwLowerLDS::GetOrderedNonKernelAllLDSGlobals(
+    SetVector<GlobalVariable *> &&Variables) {
+  // Sort all the non-kernel LDS accesses based on theor name.
+  SetVector<GlobalVariable *> Ordered = SortByName(
+      std::vector<GlobalVariable *>(Variables.begin(), Variables.end()));
+  return std::move(Ordered);
+}
+
+SetVector<Function *> AMDGPUSwLowerLDS::GetOrderedIndirectLDSAccessingKernels(
+    SetVector<Function *> &&Kernels) {
+  // Sort the non-kernels accessing LDS based on theor name.
+  // Also assign a kernel ID metadata based on the sorted order.
+  LLVMContext &Ctx = M.getContext();
+  if (Kernels.size() > UINT32_MAX) {
+    // 32 bit keeps it in one SGPR. > 2**32 kernels won't fit on the GPU
+    report_fatal_error("Unimplemented SW LDS lowering for > 2**32 kernels");
+  }
+  SetVector<Function *> OrderedKernels =
+      SortByName(std::vector<Function *>(Kernels.begin(), Kernels.end()));
+  for (size_t i = 0; i < Kernels.size(); i++) {
+    Metadata *AttrMDArgs[1] = {
+        ConstantAsMetadata::get(IRB.getInt32(i)),
+    };
+    Function *Func = OrderedKernels[i];
+    Func->setMetadata("llvm.amdgcn.lds.kernel.id",
+                      MDNode::get(Ctx, AttrMDArgs));
+    auto &LDSParams = KernelToLDSParametersMap[Func];
+    assert(LDSParams);
+    LDSParams->KernelId = i;
+  }
+  return std::move(OrderedKernels);
+}
+
+void AMDGPUSwLowerLDS::GetUsesOfLDSByNonKernels(
+    CallGraph const &CG, FunctionVariableMap &functions) {
+  // Get uses from the current function, excluding uses by called functions
+  // Two output variables to avoid walking the globals list twice
+  for (auto &GV : M.globals()) {
+    if (!AMDGPU::isLDSVariableToLower(GV)) {
+      continue;
+    }
+
+    if (GV.isAbsoluteSymbolRef()) {
+      report_fatal_error(
+          "LDS variables with absolute addresses are unimplemented.");
+    }
+
+    for (User *V : GV.users()) {
+      User *FUU = V;
+      bool isCast = isa<BitCastOperator, AddrSpaceCastOperator>(FUU);
+      if (isCast && FUU->hasOneUse() && !FUU->user_begin()->user_empty())
+        FUU = *FUU->user_begin();
+      if (auto *I = dyn_cast<Instruction>(FUU)) {
+        Function *F = I->getFunction();
+        if (!isKernelLDS(F)) {
+          functions[F].insert(&GV);
+        }
+      }
+    }
+  }
+}
+
+void AMDGPUSwLowerLDS::PopulateMallocLDSGlobal(Function *Func) {
+  // Create new LDS global required for each kernel to store
+  // device global memory pointer.
+  auto &LDSParams = KernelToLDSParametersMap[Func];
+  assert(LDSParams);
+  // create new global pointer variable
+  LDSParams->MallocLDSGlobal = new GlobalVariable(
+      M, IRB.getPtrTy(), false, GlobalValue::InternalLinkage,
+      PoisonValue::get(IRB.getPtrTy()),
+      Twine("llvm.amdgcn.sw.lds." + Func->getName()), nullptr,
+      GlobalValue::NotThreadLocal, AMDGPUAS::LOCAL_ADDRESS, false);
+  return;
+}
+
+void AMDGPUSwLowerLDS::PopulateMallocMetadataGlobal(Function *Func) {
+  // Create new metadata global for every kernel and initialize the
+  // start offsets and sizes corresponding to each LDS accesses.
+  auto &LDSParams = KernelToLDSParametersMap[Func];
+  assert(LDSParams);
+  auto &Ctx = M.getContext();
+  auto &DL = M.getDataLayout();
+  std::vector<Type *> Items;
+  Type *Int32Ty = IRB.getInt32Ty();
+  std::vector<Constant *> Initializers;
+  Align MaxAlignment(1);
+  auto UpdateMaxAlignment = [&MaxAlignment, &DL](GlobalVariable *GV) {
+    uint32_t GVAlignValue = GV->getAlignment();
+    Align GVAlign =
+        GVAlignValue ? Align(GVAlignValue) : AMDGPU::getAlign(DL, GV);
+    MaxAlignment = std::max(MaxAlignment, GVAlign);
+  };
+
+  for (GlobalVariable *GV : LDSParams->DirectAccess.StaticLDSGlobals)
+    UpdateMaxAlignment(GV);
+
+  for (GlobalVariable *GV : LDSParams->DirectAccess.DynamicLDSGlobals)
+    UpdateMaxAlignment(GV);
+
+  for (GlobalVariable *GV : LDSParams->IndirectAccess.StaticLDSGlobals)
+    UpdateMaxAlignment(GV);
+
+  for (GlobalVariable *GV : LDSParams->IndirectAccess.DynamicLDSGlobals)
+    UpdateMaxAlignment(GV);
+
+  uint32_t MaxAlignValue = MaxAlignment.value();
+
+  //{StartOffset, SizeInBytes}
+  StructType *LDSItemTy = StructType::create(
+      Ctx, {Int32Ty, Int32Ty},
+      "llvm.amdgcn.sw.lds." + Func->getName().str() + ".md.item");
+
+  auto InitializerLamda = [&](SetVector<GlobalVariable *> &LDSGlobals) {
----------------
arsenm wrote:

Bad name. Can this be a separate helper function? 

https://github.com/llvm/llvm-project/pull/87265


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