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| 1 | +//==- RISCVPromoteConstant.cpp - Promote constant fp to global for RISC-V --==// |
| 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 | +#include "RISCV.h" |
| 10 | +#include "RISCVSubtarget.h" |
| 11 | +#include "llvm/ADT/DenseMap.h" |
| 12 | +#include "llvm/ADT/SmallVector.h" |
| 13 | +#include "llvm/ADT/Statistic.h" |
| 14 | +#include "llvm/CodeGen/TargetLowering.h" |
| 15 | +#include "llvm/CodeGen/TargetPassConfig.h" |
| 16 | +#include "llvm/IR/BasicBlock.h" |
| 17 | +#include "llvm/IR/Constant.h" |
| 18 | +#include "llvm/IR/Constants.h" |
| 19 | +#include "llvm/IR/Function.h" |
| 20 | +#include "llvm/IR/GlobalValue.h" |
| 21 | +#include "llvm/IR/GlobalVariable.h" |
| 22 | +#include "llvm/IR/IRBuilder.h" |
| 23 | +#include "llvm/IR/InstIterator.h" |
| 24 | +#include "llvm/IR/Instruction.h" |
| 25 | +#include "llvm/IR/Instructions.h" |
| 26 | +#include "llvm/IR/IntrinsicInst.h" |
| 27 | +#include "llvm/IR/Module.h" |
| 28 | +#include "llvm/IR/Type.h" |
| 29 | +#include "llvm/InitializePasses.h" |
| 30 | +#include "llvm/Pass.h" |
| 31 | +#include "llvm/Support/Casting.h" |
| 32 | +#include "llvm/Support/Debug.h" |
| 33 | + |
| 34 | +using namespace llvm; |
| 35 | + |
| 36 | +#define DEBUG_TYPE "riscv-promote-const" |
| 37 | +#define RISCV_PROMOTE_CONSTANT_NAME "RISC-V Promote Constants" |
| 38 | + |
| 39 | +STATISTIC(NumPromoted, "Number of constant literals promoted to globals"); |
| 40 | +STATISTIC(NumPromotedUses, "Number of uses of promoted literal constants"); |
| 41 | + |
| 42 | +namespace { |
| 43 | + |
| 44 | +class RISCVPromoteConstant : public ModulePass { |
| 45 | +public: |
| 46 | + static char ID; |
| 47 | + RISCVPromoteConstant() : ModulePass(ID) {} |
| 48 | + |
| 49 | + StringRef getPassName() const override { return RISCV_PROMOTE_CONSTANT_NAME; } |
| 50 | + |
| 51 | + void getAnalysisUsage(AnalysisUsage &AU) const override { |
| 52 | + AU.addRequired<TargetPassConfig>(); |
| 53 | + AU.setPreservesCFG(); |
| 54 | + } |
| 55 | + |
| 56 | + /// Iterate over the functions and promote the double fp constants that |
| 57 | + /// would otherwise go into the constant pool to a constant array. |
| 58 | + bool runOnModule(Module &M) override { |
| 59 | + if (skipModule(M)) |
| 60 | + return false; |
| 61 | + // TargetMachine and Subtarget are needed to query isFPImmlegal. |
| 62 | + const TargetPassConfig &TPC = getAnalysis<TargetPassConfig>(); |
| 63 | + const TargetMachine &TM = TPC.getTM<TargetMachine>(); |
| 64 | + bool Changed = false; |
| 65 | + for (Function &F : M) { |
| 66 | + const RISCVSubtarget &ST = TM.getSubtarget<RISCVSubtarget>(F); |
| 67 | + const RISCVTargetLowering *TLI = ST.getTargetLowering(); |
| 68 | + Changed |= runOnFunction(F, TLI); |
| 69 | + } |
| 70 | + return Changed; |
| 71 | + } |
| 72 | + |
| 73 | +private: |
| 74 | + bool runOnFunction(Function &F, const RISCVTargetLowering *TLI); |
| 75 | +}; |
| 76 | +} // end anonymous namespace |
| 77 | + |
| 78 | +char RISCVPromoteConstant::ID = 0; |
| 79 | + |
| 80 | +INITIALIZE_PASS(RISCVPromoteConstant, DEBUG_TYPE, RISCV_PROMOTE_CONSTANT_NAME, |
| 81 | + false, false) |
| 82 | + |
| 83 | +ModulePass *llvm::createRISCVPromoteConstantPass() { |
| 84 | + return new RISCVPromoteConstant(); |
| 85 | +} |
| 86 | + |
| 87 | +bool RISCVPromoteConstant::runOnFunction(Function &F, |
| 88 | + const RISCVTargetLowering *TLI) { |
| 89 | + if (F.hasOptNone() || F.hasOptSize()) |
| 90 | + return false; |
| 91 | + |
| 92 | + // Bail out and make no transformation if the target doesn't support |
| 93 | + // doubles, or if we're not targeting RV64 as we currently see some |
| 94 | + // regressions for those targets. |
| 95 | + if (!TLI->isTypeLegal(MVT::f64) || !TLI->isTypeLegal(MVT::i64)) |
| 96 | + return false; |
| 97 | + |
| 98 | + // Collect all unique double constants and their uses in the function. Use |
| 99 | + // MapVector to preserve insertion order. |
| 100 | + MapVector<ConstantFP *, SmallVector<Use *, 8>> ConstUsesMap; |
| 101 | + |
| 102 | + for (Instruction &I : instructions(F)) { |
| 103 | + for (Use &U : I.operands()) { |
| 104 | + auto *C = dyn_cast<ConstantFP>(U.get()); |
| 105 | + if (!C || !C->getType()->isDoubleTy()) |
| 106 | + continue; |
| 107 | + // Do not promote if it wouldn't be loaded from the constant pool. |
| 108 | + if (TLI->isFPImmLegal(C->getValueAPF(), MVT::f64, |
| 109 | + /*ForCodeSize=*/false)) |
| 110 | + continue; |
| 111 | + // Do not promote a constant if it is used as an immediate argument |
| 112 | + // for an intrinsic. |
| 113 | + if (auto *II = dyn_cast<IntrinsicInst>(U.getUser())) { |
| 114 | + Function *IntrinsicFunc = II->getFunction(); |
| 115 | + unsigned OperandIdx = U.getOperandNo(); |
| 116 | + if (IntrinsicFunc && IntrinsicFunc->getAttributes().hasParamAttr( |
| 117 | + OperandIdx, Attribute::ImmArg)) { |
| 118 | + LLVM_DEBUG(dbgs() << "Skipping promotion of constant in: " << *II |
| 119 | + << " because operand " << OperandIdx |
| 120 | + << " must be an immediate.\n"); |
| 121 | + continue; |
| 122 | + } |
| 123 | + } |
| 124 | + // Note: FP args to inline asm would be problematic if we had a |
| 125 | + // constraint that required an immediate floating point operand. At the |
| 126 | + // time of writing LLVM doesn't recognise such a constraint. |
| 127 | + ConstUsesMap[C].push_back(&U); |
| 128 | + } |
| 129 | + } |
| 130 | + |
| 131 | + int PromotableConstants = ConstUsesMap.size(); |
| 132 | + LLVM_DEBUG(dbgs() << "Found " << PromotableConstants |
| 133 | + << " promotable constants in " << F.getName() << "\n"); |
| 134 | + // Bail out if no promotable constants found, or if only one is found. |
| 135 | + if (PromotableConstants < 2) { |
| 136 | + LLVM_DEBUG(dbgs() << "Performing no promotions as insufficient promotable " |
| 137 | + "constants found\n"); |
| 138 | + return false; |
| 139 | + } |
| 140 | + |
| 141 | + NumPromoted += PromotableConstants; |
| 142 | + |
| 143 | + // Create a global array containing the promoted constants. |
| 144 | + Module *M = F.getParent(); |
| 145 | + Type *DoubleTy = Type::getDoubleTy(M->getContext()); |
| 146 | + |
| 147 | + SmallVector<Constant *, 16> ConstantVector; |
| 148 | + for (auto const &Pair : ConstUsesMap) |
| 149 | + ConstantVector.push_back(Pair.first); |
| 150 | + |
| 151 | + ArrayType *ArrayTy = ArrayType::get(DoubleTy, ConstantVector.size()); |
| 152 | + Constant *GlobalArrayInitializer = |
| 153 | + ConstantArray::get(ArrayTy, ConstantVector); |
| 154 | + |
| 155 | + auto *GlobalArray = new GlobalVariable( |
| 156 | + *M, ArrayTy, |
| 157 | + /*isConstant=*/true, GlobalValue::InternalLinkage, GlobalArrayInitializer, |
| 158 | + ".promoted_doubles." + F.getName()); |
| 159 | + |
| 160 | + // A cache to hold the loaded value for a given constant within a basic block. |
| 161 | + DenseMap<std::pair<ConstantFP *, BasicBlock *>, Value *> LocalLoads; |
| 162 | + |
| 163 | + // Replace all uses with the loaded value. |
| 164 | + unsigned Idx = 0; |
| 165 | + for (auto const &Pair : ConstUsesMap) { |
| 166 | + ConstantFP *Const = Pair.first; |
| 167 | + const SmallVector<Use *, 8> &Uses = Pair.second; |
| 168 | + |
| 169 | + for (Use *U : Uses) { |
| 170 | + Instruction *UserInst = cast<Instruction>(U->getUser()); |
| 171 | + BasicBlock *InsertionBB; |
| 172 | + |
| 173 | + // If the user is a PHI node, we must insert the load in the |
| 174 | + // corresponding predecessor basic block. Otherwise, it's inserted into |
| 175 | + // the same block as the use. |
| 176 | + if ( auto *PN = dyn_cast<PHINode>(UserInst)) |
| 177 | + InsertionBB = PN->getIncomingBlock(*U); |
| 178 | + else |
| 179 | + InsertionBB = UserInst->getParent(); |
| 180 | + |
| 181 | + if (isa<CatchSwitchInst>(InsertionBB->getTerminator())) { |
| 182 | + LLVM_DEBUG(dbgs() << "Bailing out: catchswitch means thre is no valid " |
| 183 | + "insertion point.\n"); |
| 184 | + return false; |
| 185 | + } |
| 186 | + |
| 187 | + auto CacheKey = std::make_pair(Const, InsertionBB); |
| 188 | + Value *LoadedVal = nullptr; |
| 189 | + |
| 190 | + // Re-use a load if it exists in the insertion block. |
| 191 | + if (LocalLoads.count(CacheKey)) { |
| 192 | + LoadedVal = LocalLoads.at(CacheKey); |
| 193 | + } else { |
| 194 | + // Otherwise, create a new GEP and Load at the correct insertion point. |
| 195 | + // It is always safe to insert in the first insertion point in the BB, |
| 196 | + // so do that and let other passes reorder. |
| 197 | + IRBuilder<> Builder(InsertionBB, InsertionBB->getFirstInsertionPt()); |
| 198 | + Value *ElementPtr = Builder.CreateConstInBoundsGEP2_64( |
| 199 | + GlobalArray->getValueType(), GlobalArray, 0, Idx, "double.addr"); |
| 200 | + LoadedVal = Builder.CreateLoad(DoubleTy, ElementPtr, "double.val"); |
| 201 | + |
| 202 | + // Cache the newly created load for this block. |
| 203 | + LocalLoads[CacheKey] = LoadedVal; |
| 204 | + } |
| 205 | + |
| 206 | + U->set(LoadedVal); |
| 207 | + ++NumPromotedUses; |
| 208 | + } |
| 209 | + ++Idx; |
| 210 | + } |
| 211 | + |
| 212 | + return true; |
| 213 | +} |
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