1afb81dfaf
This update enhances the implementation of structural hashing for global variables, using their initial contents. Private global variables or constants are often used for metadata, where their names are not unique. This can lead to the creation of different hash results although they could be merged by the linker as they are effectively identical. - Refine the hashing of GlobalVariables for strings or certain Objective-C metadata cases that have section names. This can be further extended to other scenarios. - Expose StructuralHash for GlobalVariable so that this API can be utilized by MachineStableHashing, which is also employed in the global function outliner. This change significantly improves size reduction by an additional 1% on the LLD binary when the global function outliner and merger are enabled together. As discussed in the RFC https://discourse.llvm.org/t/loh-conflicting-with-machineoutliner/83279/8?u=kyulee-com, if we disable or relocate the LOH pass, the size impact could increase to 4%.
242 lines
9.7 KiB
C++
242 lines
9.7 KiB
C++
//===- lib/CodeGen/MachineStableHash.cpp ----------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// Stable hashing for MachineInstr and MachineOperand. Useful or getting a
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// hash across runs, modules, etc.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/CodeGen/MachineStableHash.h"
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#include "llvm/ADT/APFloat.h"
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#include "llvm/ADT/APInt.h"
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#include "llvm/ADT/STLExtras.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/StableHashing.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/CodeGen/MachineBasicBlock.h"
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#include "llvm/CodeGen/MachineFunction.h"
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#include "llvm/CodeGen/MachineInstr.h"
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#include "llvm/CodeGen/MachineMemOperand.h"
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#include "llvm/CodeGen/MachineOperand.h"
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#include "llvm/CodeGen/MachineRegisterInfo.h"
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#include "llvm/CodeGen/Register.h"
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#include "llvm/Config/llvm-config.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/GlobalVariable.h"
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#include "llvm/IR/StructuralHash.h"
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#include "llvm/MC/MCSymbol.h"
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#include "llvm/Support/Alignment.h"
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#include "llvm/Support/ErrorHandling.h"
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#define DEBUG_TYPE "machine-stable-hash"
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using namespace llvm;
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STATISTIC(StableHashBailingMachineBasicBlock,
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"Number of encountered unsupported MachineOperands that were "
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"MachineBasicBlocks while computing stable hashes");
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STATISTIC(StableHashBailingConstantPoolIndex,
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"Number of encountered unsupported MachineOperands that were "
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"ConstantPoolIndex while computing stable hashes");
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STATISTIC(StableHashBailingTargetIndexNoName,
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"Number of encountered unsupported MachineOperands that were "
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"TargetIndex with no name");
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STATISTIC(StableHashBailingGlobalAddress,
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"Number of encountered unsupported MachineOperands that were "
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"GlobalAddress while computing stable hashes");
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STATISTIC(StableHashBailingBlockAddress,
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"Number of encountered unsupported MachineOperands that were "
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"BlockAddress while computing stable hashes");
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STATISTIC(StableHashBailingMetadataUnsupported,
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"Number of encountered unsupported MachineOperands that were "
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"Metadata of an unsupported kind while computing stable hashes");
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stable_hash llvm::stableHashValue(const MachineOperand &MO) {
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switch (MO.getType()) {
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case MachineOperand::MO_Register:
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if (MO.getReg().isVirtual()) {
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const MachineRegisterInfo &MRI = MO.getParent()->getMF()->getRegInfo();
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SmallVector<stable_hash> DefOpcodes;
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for (auto &Def : MRI.def_instructions(MO.getReg()))
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DefOpcodes.push_back(Def.getOpcode());
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return stable_hash_combine(DefOpcodes);
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}
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// Register operands don't have target flags.
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return stable_hash_combine(MO.getType(), MO.getReg(), MO.getSubReg(),
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MO.isDef());
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case MachineOperand::MO_Immediate:
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return stable_hash_combine(MO.getType(), MO.getTargetFlags(), MO.getImm());
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case MachineOperand::MO_CImmediate:
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case MachineOperand::MO_FPImmediate: {
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auto Val = MO.isCImm() ? MO.getCImm()->getValue()
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: MO.getFPImm()->getValueAPF().bitcastToAPInt();
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auto ValHash = stable_hash_combine(
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ArrayRef<stable_hash>(Val.getRawData(), Val.getNumWords()));
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return stable_hash_combine(MO.getType(), MO.getTargetFlags(), ValHash);
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}
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case MachineOperand::MO_MachineBasicBlock:
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++StableHashBailingMachineBasicBlock;
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return 0;
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case MachineOperand::MO_ConstantPoolIndex:
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++StableHashBailingConstantPoolIndex;
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return 0;
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case MachineOperand::MO_BlockAddress:
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++StableHashBailingBlockAddress;
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return 0;
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case MachineOperand::MO_Metadata:
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++StableHashBailingMetadataUnsupported;
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return 0;
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case MachineOperand::MO_GlobalAddress: {
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const GlobalValue *GV = MO.getGlobal();
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stable_hash GVHash = 0;
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if (auto *GVar = dyn_cast<GlobalVariable>(GV))
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GVHash = StructuralHash(*GVar);
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if (!GVHash) {
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if (!GV->hasName()) {
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++StableHashBailingGlobalAddress;
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return 0;
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}
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GVHash = stable_hash_name(GV->getName());
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}
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return stable_hash_combine(MO.getType(), MO.getTargetFlags(), GVHash,
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MO.getOffset());
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}
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case MachineOperand::MO_TargetIndex: {
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if (const char *Name = MO.getTargetIndexName())
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return stable_hash_combine(MO.getType(), MO.getTargetFlags(),
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stable_hash_name(Name), MO.getOffset());
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++StableHashBailingTargetIndexNoName;
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return 0;
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}
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case MachineOperand::MO_FrameIndex:
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case MachineOperand::MO_JumpTableIndex:
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return stable_hash_combine(MO.getType(), MO.getTargetFlags(),
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MO.getIndex());
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case MachineOperand::MO_ExternalSymbol:
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return stable_hash_combine(MO.getType(), MO.getTargetFlags(),
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MO.getOffset(),
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stable_hash_name(MO.getSymbolName()));
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case MachineOperand::MO_RegisterMask:
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case MachineOperand::MO_RegisterLiveOut: {
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if (const MachineInstr *MI = MO.getParent()) {
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if (const MachineBasicBlock *MBB = MI->getParent()) {
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if (const MachineFunction *MF = MBB->getParent()) {
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const TargetRegisterInfo *TRI = MF->getSubtarget().getRegisterInfo();
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unsigned RegMaskSize =
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MachineOperand::getRegMaskSize(TRI->getNumRegs());
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const uint32_t *RegMask = MO.getRegMask();
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std::vector<llvm::stable_hash> RegMaskHashes(RegMask,
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RegMask + RegMaskSize);
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return stable_hash_combine(MO.getType(), MO.getTargetFlags(),
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stable_hash_combine(RegMaskHashes));
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}
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}
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}
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assert(0 && "MachineOperand not associated with any MachineFunction");
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return stable_hash_combine(MO.getType(), MO.getTargetFlags());
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}
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case MachineOperand::MO_ShuffleMask: {
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std::vector<llvm::stable_hash> ShuffleMaskHashes;
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llvm::transform(
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MO.getShuffleMask(), std::back_inserter(ShuffleMaskHashes),
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[](int S) -> llvm::stable_hash { return llvm::stable_hash(S); });
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return stable_hash_combine(MO.getType(), MO.getTargetFlags(),
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stable_hash_combine(ShuffleMaskHashes));
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}
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case MachineOperand::MO_MCSymbol: {
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auto SymbolName = MO.getMCSymbol()->getName();
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return stable_hash_combine(MO.getType(), MO.getTargetFlags(),
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stable_hash_name(SymbolName));
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}
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case MachineOperand::MO_CFIIndex:
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return stable_hash_combine(MO.getType(), MO.getTargetFlags(),
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MO.getCFIIndex());
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case MachineOperand::MO_IntrinsicID:
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return stable_hash_combine(MO.getType(), MO.getTargetFlags(),
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MO.getIntrinsicID());
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case MachineOperand::MO_Predicate:
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return stable_hash_combine(MO.getType(), MO.getTargetFlags(),
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MO.getPredicate());
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case MachineOperand::MO_DbgInstrRef:
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return stable_hash_combine(MO.getType(), MO.getInstrRefInstrIndex(),
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MO.getInstrRefOpIndex());
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}
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llvm_unreachable("Invalid machine operand type");
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}
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/// A stable hash value for machine instructions.
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/// Returns 0 if no stable hash could be computed.
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/// The hashing and equality testing functions ignore definitions so this is
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/// useful for CSE, etc.
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stable_hash llvm::stableHashValue(const MachineInstr &MI, bool HashVRegs,
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bool HashConstantPoolIndices,
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bool HashMemOperands) {
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// Build up a buffer of hash code components.
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SmallVector<stable_hash, 16> HashComponents;
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HashComponents.reserve(MI.getNumOperands() + MI.getNumMemOperands() + 2);
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HashComponents.push_back(MI.getOpcode());
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HashComponents.push_back(MI.getFlags());
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for (const MachineOperand &MO : MI.operands()) {
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if (!HashVRegs && MO.isReg() && MO.isDef() && MO.getReg().isVirtual())
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continue; // Skip virtual register defs.
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if (MO.isCPI()) {
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HashComponents.push_back(stable_hash_combine(
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MO.getType(), MO.getTargetFlags(), MO.getIndex()));
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continue;
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}
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stable_hash StableHash = stableHashValue(MO);
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if (!StableHash)
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return 0;
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HashComponents.push_back(StableHash);
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}
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for (const auto *Op : MI.memoperands()) {
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if (!HashMemOperands)
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break;
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HashComponents.push_back(static_cast<unsigned>(Op->getSize().getValue()));
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HashComponents.push_back(static_cast<unsigned>(Op->getFlags()));
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HashComponents.push_back(static_cast<unsigned>(Op->getOffset()));
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HashComponents.push_back(static_cast<unsigned>(Op->getSuccessOrdering()));
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HashComponents.push_back(static_cast<unsigned>(Op->getAddrSpace()));
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HashComponents.push_back(static_cast<unsigned>(Op->getSyncScopeID()));
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HashComponents.push_back(static_cast<unsigned>(Op->getBaseAlign().value()));
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HashComponents.push_back(static_cast<unsigned>(Op->getFailureOrdering()));
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}
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return stable_hash_combine(HashComponents);
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}
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stable_hash llvm::stableHashValue(const MachineBasicBlock &MBB) {
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SmallVector<stable_hash> HashComponents;
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// TODO: Hash more stuff like block alignment and branch probabilities.
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for (const auto &MI : MBB)
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HashComponents.push_back(stableHashValue(MI));
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return stable_hash_combine(HashComponents);
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}
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stable_hash llvm::stableHashValue(const MachineFunction &MF) {
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SmallVector<stable_hash> HashComponents;
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// TODO: Hash lots more stuff like function alignment and stack objects.
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for (const auto &MBB : MF)
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HashComponents.push_back(stableHashValue(MBB));
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return stable_hash_combine(HashComponents);
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}
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