1 //===-- AMDGPULowerKernelArguments.cpp ------------------------------------------===// 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 /// \file This pass replaces accesses to kernel arguments with loads from 10 /// offsets from the kernarg base pointer. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #include "AMDGPU.h" 15 #include "GCNSubtarget.h" 16 #include "llvm/CodeGen/TargetPassConfig.h" 17 #include "llvm/IR/IntrinsicsAMDGPU.h" 18 #include "llvm/IR/IRBuilder.h" 19 #include "llvm/IR/MDBuilder.h" 20 #include "llvm/Target/TargetMachine.h" 21 #define DEBUG_TYPE "amdgpu-lower-kernel-arguments" 22 23 using namespace llvm; 24 25 namespace { 26 27 class AMDGPULowerKernelArguments : public FunctionPass{ 28 public: 29 static char ID; 30 31 AMDGPULowerKernelArguments() : FunctionPass(ID) {} 32 33 bool runOnFunction(Function &F) override; 34 35 void getAnalysisUsage(AnalysisUsage &AU) const override { 36 AU.addRequired<TargetPassConfig>(); 37 AU.setPreservesAll(); 38 } 39 }; 40 41 } // end anonymous namespace 42 43 // skip allocas 44 static BasicBlock::iterator getInsertPt(BasicBlock &BB) { 45 BasicBlock::iterator InsPt = BB.getFirstInsertionPt(); 46 for (BasicBlock::iterator E = BB.end(); InsPt != E; ++InsPt) { 47 AllocaInst *AI = dyn_cast<AllocaInst>(&*InsPt); 48 49 // If this is a dynamic alloca, the value may depend on the loaded kernargs, 50 // so loads will need to be inserted before it. 51 if (!AI || !AI->isStaticAlloca()) 52 break; 53 } 54 55 return InsPt; 56 } 57 58 bool AMDGPULowerKernelArguments::runOnFunction(Function &F) { 59 CallingConv::ID CC = F.getCallingConv(); 60 if (CC != CallingConv::AMDGPU_KERNEL || F.arg_empty()) 61 return false; 62 63 auto &TPC = getAnalysis<TargetPassConfig>(); 64 65 const TargetMachine &TM = TPC.getTM<TargetMachine>(); 66 const GCNSubtarget &ST = TM.getSubtarget<GCNSubtarget>(F); 67 LLVMContext &Ctx = F.getParent()->getContext(); 68 const DataLayout &DL = F.getParent()->getDataLayout(); 69 BasicBlock &EntryBlock = *F.begin(); 70 IRBuilder<> Builder(&*getInsertPt(EntryBlock)); 71 72 const Align KernArgBaseAlign(16); // FIXME: Increase if necessary 73 const uint64_t BaseOffset = ST.getExplicitKernelArgOffset(); 74 75 Align MaxAlign; 76 // FIXME: Alignment is broken with explicit arg offset.; 77 const uint64_t TotalKernArgSize = ST.getKernArgSegmentSize(F, MaxAlign); 78 if (TotalKernArgSize == 0) 79 return false; 80 81 CallInst *KernArgSegment = 82 Builder.CreateIntrinsic(Intrinsic::amdgcn_kernarg_segment_ptr, {}, {}, 83 nullptr, F.getName() + ".kernarg.segment"); 84 85 KernArgSegment->addRetAttr(Attribute::NonNull); 86 KernArgSegment->addRetAttr( 87 Attribute::getWithDereferenceableBytes(Ctx, TotalKernArgSize)); 88 89 uint64_t ExplicitArgOffset = 0; 90 91 for (Argument &Arg : F.args()) { 92 const bool IsByRef = Arg.hasByRefAttr(); 93 Type *ArgTy = IsByRef ? Arg.getParamByRefType() : Arg.getType(); 94 MaybeAlign ParamAlign = IsByRef ? Arg.getParamAlign() : std::nullopt; 95 Align ABITypeAlign = DL.getValueOrABITypeAlignment(ParamAlign, ArgTy); 96 97 uint64_t Size = DL.getTypeSizeInBits(ArgTy); 98 uint64_t AllocSize = DL.getTypeAllocSize(ArgTy); 99 100 uint64_t EltOffset = alignTo(ExplicitArgOffset, ABITypeAlign) + BaseOffset; 101 ExplicitArgOffset = alignTo(ExplicitArgOffset, ABITypeAlign) + AllocSize; 102 103 if (Arg.use_empty()) 104 continue; 105 106 // If this is byval, the loads are already explicit in the function. We just 107 // need to rewrite the pointer values. 108 if (IsByRef) { 109 Value *ArgOffsetPtr = Builder.CreateConstInBoundsGEP1_64( 110 Builder.getInt8Ty(), KernArgSegment, EltOffset, 111 Arg.getName() + ".byval.kernarg.offset"); 112 113 Value *CastOffsetPtr = 114 Builder.CreateAddrSpaceCast(ArgOffsetPtr, Arg.getType()); 115 Arg.replaceAllUsesWith(CastOffsetPtr); 116 continue; 117 } 118 119 if (PointerType *PT = dyn_cast<PointerType>(ArgTy)) { 120 // FIXME: Hack. We rely on AssertZext to be able to fold DS addressing 121 // modes on SI to know the high bits are 0 so pointer adds don't wrap. We 122 // can't represent this with range metadata because it's only allowed for 123 // integer types. 124 if ((PT->getAddressSpace() == AMDGPUAS::LOCAL_ADDRESS || 125 PT->getAddressSpace() == AMDGPUAS::REGION_ADDRESS) && 126 !ST.hasUsableDSOffset()) 127 continue; 128 129 // FIXME: We can replace this with equivalent alias.scope/noalias 130 // metadata, but this appears to be a lot of work. 131 if (Arg.hasNoAliasAttr()) 132 continue; 133 } 134 135 auto *VT = dyn_cast<FixedVectorType>(ArgTy); 136 bool IsV3 = VT && VT->getNumElements() == 3; 137 bool DoShiftOpt = Size < 32 && !ArgTy->isAggregateType(); 138 139 VectorType *V4Ty = nullptr; 140 141 int64_t AlignDownOffset = alignDown(EltOffset, 4); 142 int64_t OffsetDiff = EltOffset - AlignDownOffset; 143 Align AdjustedAlign = commonAlignment( 144 KernArgBaseAlign, DoShiftOpt ? AlignDownOffset : EltOffset); 145 146 Value *ArgPtr; 147 Type *AdjustedArgTy; 148 if (DoShiftOpt) { // FIXME: Handle aggregate types 149 // Since we don't have sub-dword scalar loads, avoid doing an extload by 150 // loading earlier than the argument address, and extracting the relevant 151 // bits. 152 // 153 // Additionally widen any sub-dword load to i32 even if suitably aligned, 154 // so that CSE between different argument loads works easily. 155 ArgPtr = Builder.CreateConstInBoundsGEP1_64( 156 Builder.getInt8Ty(), KernArgSegment, AlignDownOffset, 157 Arg.getName() + ".kernarg.offset.align.down"); 158 AdjustedArgTy = Builder.getInt32Ty(); 159 } else { 160 ArgPtr = Builder.CreateConstInBoundsGEP1_64( 161 Builder.getInt8Ty(), KernArgSegment, EltOffset, 162 Arg.getName() + ".kernarg.offset"); 163 AdjustedArgTy = ArgTy; 164 } 165 166 if (IsV3 && Size >= 32) { 167 V4Ty = FixedVectorType::get(VT->getElementType(), 4); 168 // Use the hack that clang uses to avoid SelectionDAG ruining v3 loads 169 AdjustedArgTy = V4Ty; 170 } 171 172 LoadInst *Load = 173 Builder.CreateAlignedLoad(AdjustedArgTy, ArgPtr, AdjustedAlign); 174 Load->setMetadata(LLVMContext::MD_invariant_load, MDNode::get(Ctx, {})); 175 176 MDBuilder MDB(Ctx); 177 178 if (isa<PointerType>(ArgTy)) { 179 if (Arg.hasNonNullAttr()) 180 Load->setMetadata(LLVMContext::MD_nonnull, MDNode::get(Ctx, {})); 181 182 uint64_t DerefBytes = Arg.getDereferenceableBytes(); 183 if (DerefBytes != 0) { 184 Load->setMetadata( 185 LLVMContext::MD_dereferenceable, 186 MDNode::get(Ctx, 187 MDB.createConstant( 188 ConstantInt::get(Builder.getInt64Ty(), DerefBytes)))); 189 } 190 191 uint64_t DerefOrNullBytes = Arg.getDereferenceableOrNullBytes(); 192 if (DerefOrNullBytes != 0) { 193 Load->setMetadata( 194 LLVMContext::MD_dereferenceable_or_null, 195 MDNode::get(Ctx, 196 MDB.createConstant(ConstantInt::get(Builder.getInt64Ty(), 197 DerefOrNullBytes)))); 198 } 199 200 if (MaybeAlign ParamAlign = Arg.getParamAlign()) { 201 Load->setMetadata( 202 LLVMContext::MD_align, 203 MDNode::get(Ctx, MDB.createConstant(ConstantInt::get( 204 Builder.getInt64Ty(), ParamAlign->value())))); 205 } 206 } 207 208 // TODO: Convert noalias arg to !noalias 209 210 if (DoShiftOpt) { 211 Value *ExtractBits = OffsetDiff == 0 ? 212 Load : Builder.CreateLShr(Load, OffsetDiff * 8); 213 214 IntegerType *ArgIntTy = Builder.getIntNTy(Size); 215 Value *Trunc = Builder.CreateTrunc(ExtractBits, ArgIntTy); 216 Value *NewVal = Builder.CreateBitCast(Trunc, ArgTy, 217 Arg.getName() + ".load"); 218 Arg.replaceAllUsesWith(NewVal); 219 } else if (IsV3) { 220 Value *Shuf = Builder.CreateShuffleVector(Load, ArrayRef<int>{0, 1, 2}, 221 Arg.getName() + ".load"); 222 Arg.replaceAllUsesWith(Shuf); 223 } else { 224 Load->setName(Arg.getName() + ".load"); 225 Arg.replaceAllUsesWith(Load); 226 } 227 } 228 229 KernArgSegment->addRetAttr( 230 Attribute::getWithAlignment(Ctx, std::max(KernArgBaseAlign, MaxAlign))); 231 232 return true; 233 } 234 235 INITIALIZE_PASS_BEGIN(AMDGPULowerKernelArguments, DEBUG_TYPE, 236 "AMDGPU Lower Kernel Arguments", false, false) 237 INITIALIZE_PASS_END(AMDGPULowerKernelArguments, DEBUG_TYPE, "AMDGPU Lower Kernel Arguments", 238 false, false) 239 240 char AMDGPULowerKernelArguments::ID = 0; 241 242 FunctionPass *llvm::createAMDGPULowerKernelArgumentsPass() { 243 return new AMDGPULowerKernelArguments(); 244 } 245