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LLVM 24.0.0git
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MIR-level target-independent rematerializer. More...
#include "llvm/CodeGen/Rematerializer.h"
Classes | |
| struct | DependencyReuseInfo |
| When rematerializating a register (called the "root" register in this context) to a given position, we must decide what to do with all its rematerializable dependencies (for unrematerializable dependencies, we have no choice but to re-use the same register). More... | |
| class | Listener |
| Rematerializer listener. More... | |
| struct | Reg |
| A rematerializable register defined by a single machine instruction. More... | |
Public Types | |
| using | RegisterIdx = unsigned |
| Index type for rematerializable registers. | |
| using | RegionBoundaries |
| A region's boundaries i.e. | |
| using | RematsOf = SmallDenseSet<RegisterIdx, 4> |
Public Member Functions | |
| LLVM_ABI | Rematerializer (MachineFunction &MF, SmallVectorImpl< RegionBoundaries > &Regions, LiveIntervals &LIS) |
| Simply initializes some internal state, does not identify rematerialization candidates. | |
| LLVM_ABI bool | analyze () |
| Goes through the whole MF and identifies all rematerializable registers. | |
| void | addListener (Listener *Listen) |
| Adds a new listener to the rematerializer. | |
| void | removeListener (Listener *Listen) |
| Removes a listener from the rematerializer. | |
| void | clearListeners () |
| Removes all listeners from the rematerializer. | |
| const Reg & | getReg (RegisterIdx RegIdx) const |
| ArrayRef< Reg > | getRegs () const |
| unsigned | getNumRegs () const |
| bool | isPermanentlyDead (RegisterIdx RegIdx) const |
Determines whether register RegIdx fully disappeared from the MIR. | |
| const RegionBoundaries & | getRegion (RegisterIdx RegionIdx) const |
| unsigned | getNumRegions () const |
| bool | isOriginalRegister (RegisterIdx RegIdx) const |
Whether register RegIdx is an original register. | |
| bool | isRematerializedRegister (RegisterIdx RegIdx) const |
Whether register RegIdx is a rematerialization of some original register. | |
| RegisterIdx | getOriginOf (RegisterIdx RematRegIdx) const |
Returns the origin index of rematerializable register RegIdx. | |
| RegisterIdx | getOriginOrSelf (RegisterIdx RegIdx) const |
If RegIdx is a rematerialization, returns its origin's index. | |
| ArrayRef< std::pair< Register, LaneBitmask > > | getUnrematableDeps (RegisterIdx RegIdx) const |
Returns unreamaterializable read lanes of register operands for register RegIdx. | |
| LLVM_ABI RegisterIdx | getDefRegIdx (const MachineInstr &MI) const |
If MI's first operand defines a register and that register is a rematerializable register tracked by the rematerializer, returns its index in the Regs vector. | |
| LLVM_ABI RegisterIdx | rematerializeToRegion (RegisterIdx RootIdx, unsigned UseRegion, DependencyReuseInfo &DRI) |
Rematerializes register RootIdx just before its first user inside region UseRegion (or at the end of the region if it has no user), transfers all its users in the region to the new register, and returns the latter's index. | |
| LLVM_ABI RegisterIdx | rematerializeToPos (RegisterIdx RootIdx, unsigned UseRegion, MachineBasicBlock::iterator InsertPos, DependencyReuseInfo &DRI) |
Rematerializes register RootIdx before position InsertPos in UseRegion and returns the new register's index. | |
| LLVM_ABI RegisterIdx | rematerializeReg (RegisterIdx RegIdx, unsigned UseRegion, MachineBasicBlock::iterator InsertPos, SmallVectorImpl< RegisterIdx > &&Dependencies) |
Rematerializes register RegIdx before InsertPos in UseRegion, adding the new rematerializable register to the backing vector Regs and returning its index inside the vector. | |
| LLVM_ABI void | recreateReg (RegisterIdx RegIdx, MachineBasicBlock::iterator InsertPos, Register DefReg) |
Re-creates a previously deleted register RegIdx before InsertPos, which must be in the register's original defining region. | |
| LLVM_ABI void | transferRegionUsers (RegisterIdx FromRegIdx, RegisterIdx ToRegIdx, unsigned UseRegion) |
Transfers all users of register FromRegIdx in region UseRegion to ToRegIdx, the latter of which must be a rematerialization of the former or have the same origin register. | |
| LLVM_ABI void | transferUser (RegisterIdx FromRegIdx, RegisterIdx ToRegIdx, unsigned UserRegion, MachineInstr &UserMI) |
Transfers user UserMI in region UserRegion from register FromRegIdx to ToRegIdx, the latter of which must be a rematerialization of the former or have the same origin register. | |
| LLVM_ABI void | transferAllUsers (RegisterIdx FromRegIdx, RegisterIdx ToRegIdx) |
Transfers all users of register FromRegIdx to register ToRegIdx, the latter of which must be a rematerialization of the former or have the same origin register. | |
| LLVM_ABI bool | isMOIdenticalAtUses (MachineOperand &MO, ArrayRef< SlotIndex > Uses) const |
Determines whether (sub-)register operand MO has the same value at all Uses as at MO. | |
| LLVM_ABI bool | isRegIdenticalAtUses (Register Reg, LaneBitmask Mask, SlotIndex RefSlot, ArrayRef< SlotIndex > Uses) const |
Determines whether lanes Mask of register Reg habe the same value at all Uses as at RefSlot. | |
| LLVM_ABI RegisterIdx | findRematInRegion (RegisterIdx RegIdx, unsigned Region, SlotIndex Before) const |
Finds the closest rematerialization of register RegIdx in region Region that exists before slot Before. | |
| LLVM_ABI Printable | printDependencyDAG (RegisterIdx RootIdx) const |
| LLVM_ABI Printable | printID (RegisterIdx RegIdx) const |
| LLVM_ABI Printable | printRematReg (RegisterIdx RegIdx, bool SkipRegions=false) const |
| LLVM_ABI Printable | printRegUsers (RegisterIdx RegIdx) const |
| LLVM_ABI Printable | printUser (const MachineInstr *MI, std::optional< unsigned > UseRegion=std::nullopt) const |
Static Public Attributes | |
| static constexpr unsigned | NoReg = ~0 |
| Error value for register indices. | |
MIR-level target-independent rematerializer.
Provides an API to identify and rematerialize registers within a machine function.
At the moment this supports rematerializing registers that meet all of the following constraints.
Rematerializable registers (represented by Rematerializer::Reg) form a DAG of their own, with every register having incoming edges from all rematerializable registers which are read by the instruction defining it. It is possible to rematerialize registers with unrematerializable dependencies; however the latter are not considered part of this DAG since their position/identity never change and therefore do not require the same level of tracking.
Each register has a "dependency DAG" which is defined as the subset of nodes in the overall DAG that have at least one path to the register, which is called the "root" register in this context. Semantically, these nodes are the registers which are involved into the computation of the root register i.e., all of its transitive dependencies. We use the term "root" because all paths within the dependency DAG of a register terminate at it; however, there may be multiple paths between a non-root node and the root node, so a dependency DAG is not always a tree.
The API uses dense unsigned integers starting at 0 to reference rematerializable registers. These indices are immutable i.e., even when registers are deleted their respective integer handle remain valid. Method which perform actual rematerializations should however be assumed to invalidate addresses to Rematerializer::Reg objects.
The rematerializer tracks def/use points of registers based on regions. These are alike the regions the machine scheduler works on. A region is simply a pair on MBB iterators encoding a range of machine instructions. The first iterator (beginning of the region) is inclusive whereas the second iterator (end of the region) is exclusive and can either point to a MBB's end sentinel or an actual MI (not necessarily a terminator). Regions must be non-empty, cannot overlap, and cannot contain terminators. However, they do not have to cover the whole function.
The API uses dense unsigned integers starting at 0 to reference regions. These map directly to the indices of the corresponding regions in the region vector passed during construction.
The rematerializer supports rematerializing arbitrary complex DAGs of registers to regions where these registers are used, with the option of re-using non-root registers or their previous rematerializations instead of rematerializing them again.
Throughout its lifetime, the rematerializer tracks new registers it creates (which are rematerializable by construction) and their relations to other registers. It performs DAG and live interval updates immediately on rematerialization and/or user transfer. Importantly, missing dead flags on partial definitions of unrematerializable registers can yield dead definitions when rematerializing their users. They are deleted to preserve live interval validity. These deletions can cascade to other (un)rematerializable registers that also become dead as a result.
In its nomenclature, the rematerializer differentiates between "original registers" (registers that were present when it analyzed the function) and rematerializations of these original registers. Rematerializations have an "origin" which is the index of the original regiser they were rematerialized from (transitivity applies; a rematerialization and all of its own rematerializations have the same origin). Semantically, only original registers have rematerializations.
Definition at line 96 of file Rematerializer.h.
A region's boundaries i.e.
a pair of instruction bundle iterators. The lower boundary is inclusive, the upper boundary is exclusive.
Definition at line 199 of file Rematerializer.h.
Index type for rematerializable registers.
Definition at line 99 of file Rematerializer.h.
| using llvm::Rematerializer::RematsOf = SmallDenseSet<RegisterIdx, 4> |
Definition at line 202 of file Rematerializer.h.
| Rematerializer::Rematerializer | ( | MachineFunction & | MF, |
| SmallVectorImpl< RegionBoundaries > & | Regions, | ||
| LiveIntervals & | LIS ) |
Simply initializes some internal state, does not identify rematerialization candidates.
Definition at line 397 of file Rematerializer.cpp.
References assert(), llvm::detail::DenseSetImpl< ValueT, MapTy >::insert(), and MI.
Referenced by llvm::Rematerializer::Listener::rematerializerNoteMIWillBeDeleted(), llvm::Rematerializer::Listener::rematerializerNoteRegCreated(), and llvm::Rematerializer::Listener::rematerializerNoteRegWillBeDeleted().
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Adds a new listener to the rematerializer.
Definition at line 215 of file Rematerializer.h.
References assert(), and llvm_unreachable.
| bool Rematerializer::analyze | ( | ) |
Goes through the whole MF and identifies all rematerializable registers.
Returns whether there is any rematerializable register in regions.
Maps all MIs to their parent region. Region terminators are considered part of the region they terminate.
Definition at line 420 of file Rematerializer.cpp.
References assert(), llvm::DenseMapBase< DerivedT, KeyT, ValueT, KeyInfoT, BucketT >::contains(), llvm::dbgs(), getNumRegs(), llvm::RegionBase< Tr >::getParent(), I, llvm::DenseMapBase< DerivedT, KeyT, ValueT, KeyInfoT, BucketT >::insert(), LLVM_DEBUG, MBB, MI, and printDependencyDAG().
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Removes all listeners from the rematerializer.
Definition at line 228 of file Rematerializer.h.
| RegisterIdx Rematerializer::findRematInRegion | ( | RegisterIdx | RegIdx, |
| unsigned | Region, | ||
| SlotIndex | Before ) const |
Finds the closest rematerialization of register RegIdx in region Region that exists before slot Before.
If no such rematerialization exists, returns Rematerializer::NoReg.
Definition at line 222 of file Rematerializer.cpp.
References llvm::Rematerializer::Reg::DefMI, llvm::Rematerializer::Reg::DefRegion, getOriginOrSelf(), getReg(), llvm::SlotIndex::getRegSlot(), NoReg, and llvm::Rematerializer::Reg::Uses.
| RegisterIdx Rematerializer::getDefRegIdx | ( | const MachineInstr & | MI | ) | const |
If MI's first operand defines a register and that register is a rematerializable register tracked by the rematerializer, returns its index in the Regs vector.
Otherwise returns Rematerializer::NoReg.
Definition at line 556 of file Rematerializer.cpp.
Referenced by printUser().
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Definition at line 249 of file Rematerializer.h.
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Definition at line 235 of file Rematerializer.h.
Referenced by analyze().
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Returns the origin index of rematerializable register RegIdx.
Definition at line 262 of file Rematerializer.h.
References assert(), and isRematerializedRegister().
Referenced by getOriginOrSelf(), recreateReg(), and llvm::Rollbacker::rematerializerNoteRegCreated().
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If RegIdx is a rematerialization, returns its origin's index.
If it is an original register's index, returns the same index.
Definition at line 268 of file Rematerializer.h.
References getOriginOf(), and isRematerializedRegister().
Referenced by findRematInRegion(), getUnrematableDeps(), isPermanentlyDead(), and rematerializeReg().
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Definition at line 230 of file Rematerializer.h.
References assert().
Referenced by findRematInRegion(), isPermanentlyDead(), printDependencyDAG(), printID(), printRegUsers(), printRematReg(), recreateReg(), llvm::Rollbacker::rematerializerNoteRegWillBeDeleted(), rematerializeToPos(), rematerializeToRegion(), and llvm::Rollbacker::rollback().
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Definition at line 245 of file Rematerializer.h.
References assert().
Definition at line 234 of file Rematerializer.h.
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Returns unreamaterializable read lanes of register operands for register RegIdx.
Definition at line 276 of file Rematerializer.h.
References getOriginOrSelf().
| bool Rematerializer::isMOIdenticalAtUses | ( | MachineOperand & | MO, |
| ArrayRef< SlotIndex > | Uses ) const |
Determines whether (sub-)register operand MO has the same value at all Uses as at MO.
This implies that it is also available at all Uses according to its current live interval.
Definition at line 198 of file Rematerializer.cpp.
References llvm::MachineOperand::getParent(), llvm::MachineOperand::getReg(), llvm::MachineOperand::getSubReg(), isRegIdenticalAtUses(), and Uses.
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Whether register RegIdx is an original register.
Definition at line 252 of file Rematerializer.h.
References isRematerializedRegister().
Referenced by recreateReg().
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Determines whether register RegIdx fully disappeared from the MIR.
This may happen when it was only used by instructions which became dead during the rematerializer's lifetime.
Definition at line 240 of file Rematerializer.h.
References getOriginOrSelf(), getReg(), and llvm::Rematerializer::Reg::isAlive().
Referenced by llvm::Rollbacker::rollback().
| bool Rematerializer::isRegIdenticalAtUses | ( | Register | Reg, |
| LaneBitmask | Mask, | ||
| SlotIndex | RefSlot, | ||
| ArrayRef< SlotIndex > | Uses ) const |
Determines whether lanes Mask of register Reg habe the same value at all Uses as at RefSlot.
This implies that it is also available at all Uses according to its current live interval.
Definition at line 208 of file Rematerializer.cpp.
References llvm::LiveRange::getVNInfoAt(), isIdenticalAtUse(), and Uses.
Referenced by isMOIdenticalAtUses().
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Whether register RegIdx is a rematerialization of some original register.
Definition at line 257 of file Rematerializer.h.
References assert().
Referenced by getOriginOf(), getOriginOrSelf(), isOriginalRegister(), llvm::Rollbacker::rematerializerNoteRegCreated(), and llvm::Rollbacker::rematerializerNoteRegWillBeDeleted().
| Printable Rematerializer::printDependencyDAG | ( | RegisterIdx | RootIdx | ) | const |
Definition at line 846 of file Rematerializer.cpp.
References llvm::DenseMapBase< DerivedT, KeyT, ValueT, KeyInfoT, BucketT >::begin(), llvm::Depth, llvm::DenseMapBase< DerivedT, KeyT, ValueT, KeyInfoT, BucketT >::emplace_or_assign(), llvm::DenseMapBase< DerivedT, KeyT, ValueT, KeyInfoT, BucketT >::end(), getReg(), llvm::DenseMapBase< DerivedT, KeyT, ValueT, KeyInfoT, BucketT >::lookup_or(), printID(), printRegUsers(), printRematReg(), and llvm::sort().
Referenced by analyze().
| Printable Rematerializer::printID | ( | RegisterIdx | RegIdx | ) | const |
Definition at line 874 of file Rematerializer.cpp.
References llvm::Rematerializer::Reg::DefMI, llvm::Rematerializer::Reg::DefRegion, llvm::Rematerializer::Reg::getDefReg(), llvm::MachineInstr::getOperand(), getReg(), llvm::MachineOperand::getSubReg(), llvm::Rematerializer::Reg::isAlive(), and llvm::printReg().
Referenced by printDependencyDAG(), printRematReg(), printUser(), recreateReg(), rematerializeReg(), and rematerializeToPos().
| Printable Rematerializer::printRegUsers | ( | RegisterIdx | RegIdx | ) | const |
Definition at line 942 of file Rematerializer.cpp.
References getReg(), MI, printUser(), Users, and Uses.
Referenced by printDependencyDAG().
| Printable Rematerializer::printRematReg | ( | RegisterIdx | RegIdx, |
| bool | SkipRegions = false ) const |
Definition at line 888 of file Rematerializer.cpp.
References assert(), llvm::Rematerializer::Reg::DefMI, llvm::Rematerializer::Reg::DefRegion, llvm::enumerate(), llvm::First, llvm::Rematerializer::Reg::getDefReg(), getReg(), I, llvm::Rematerializer::Reg::isAlive(), llvm::LiveRange::liveAt(), llvm::MachineInstr::print(), printID(), llvm::skipDebugInstructionsBackward(), llvm::skipDebugInstructionsForward(), and llvm::Rematerializer::Reg::Uses.
Referenced by printDependencyDAG(), recreateReg(), and rematerializeReg().
| Printable Rematerializer::printUser | ( | const MachineInstr * | MI, |
| std::optional< unsigned > | UseRegion = std::nullopt ) const |
Definition at line 951 of file Rematerializer.cpp.
References getDefRegIdx(), MI, NoReg, and printID().
Referenced by printRegUsers().
| void Rematerializer::recreateReg | ( | RegisterIdx | RegIdx, |
| MachineBasicBlock::iterator | InsertPos, | ||
| Register | DefReg ) |
Re-creates a previously deleted register RegIdx before InsertPos, which must be in the register's original defining region.
DefReg must be the original virtual register that RegIdx used to define. Dependencies are assumed to already exist in the MIR.
Definition at line 601 of file Rematerializer.cpp.
References assert(), llvm::dbgs(), llvm::Rematerializer::Reg::DefMI, llvm::Rematerializer::Reg::DefRegion, getOriginOf(), getReg(), isOriginalRegister(), LLVM_DEBUG, printID(), and printRematReg().
Referenced by llvm::Rollbacker::rollback().
| RegisterIdx Rematerializer::rematerializeReg | ( | RegisterIdx | RegIdx, |
| unsigned | UseRegion, | ||
| MachineBasicBlock::iterator | InsertPos, | ||
| SmallVectorImpl< RegisterIdx > && | Dependencies ) |
Rematerializes register RegIdx before InsertPos in UseRegion, adding the new rematerializable register to the backing vector Regs and returning its index inside the vector.
Sets the new register's rematerializable dependencies to Dependencies (these are assumed to already exist in the MIR) and its unrematerializable dependencies to the same as RegIdx. The new register initially has no user. Since the method appends to Regs, references to elements within it should be considered invalidated across calls to this method unless the vector can be guaranteed to have enough space for an extra element.
Definition at line 568 of file Rematerializer.cpp.
References llvm::dbgs(), llvm::Rematerializer::Reg::DefMI, llvm::Rematerializer::Reg::DefRegion, llvm::Rematerializer::Reg::Dependencies, llvm::Rematerializer::Reg::getDefReg(), getOriginOrSelf(), LLVM_DEBUG, llvm::Rematerializer::Reg::Mask, printID(), and printRematReg().
Referenced by rematerializeToPos().
| RegisterIdx Rematerializer::rematerializeToPos | ( | RegisterIdx | RootIdx, |
| unsigned | UseRegion, | ||
| MachineBasicBlock::iterator | InsertPos, | ||
| DependencyReuseInfo & | DRI ) |
Rematerializes register RootIdx before position InsertPos in UseRegion and returns the new register's index.
The root's dependency DAG is rematerialized or re-used according to DRI.
When the method returns, DRI contains additional entries for non-root registers of the root's dependency DAG that needed to be rematerialized along the root. References to Rematerializer::Reg should be considered invalidated by calls to this method.
Definition at line 93 of file Rematerializer.cpp.
References assert(), llvm::dbgs(), llvm::Rematerializer::DependencyReuseInfo::DependencyMap, getReg(), LLVM_DEBUG, printID(), llvm::SmallVectorTemplateBase< T, bool >::push_back(), rematerializeReg(), and rematerializeToPos().
Referenced by rematerializeToPos(), and rematerializeToRegion().
| RegisterIdx Rematerializer::rematerializeToRegion | ( | RegisterIdx | RootIdx, |
| unsigned | UseRegion, | ||
| DependencyReuseInfo & | DRI ) |
Rematerializes register RootIdx just before its first user inside region UseRegion (or at the end of the region if it has no user), transfers all its users in the region to the new register, and returns the latter's index.
The root's dependency DAG is rematerialized or re-used according to DRI.
When the method returns, DRI contains additional entries for non-root registers of the root's dependency DAG that needed to be rematerialized along the root. References to Rematerializer::Reg should be considered invalidated by calls to this method.
Definition at line 77 of file Rematerializer.cpp.
References getReg(), llvm::Rematerializer::Reg::getRegionUseBounds(), rematerializeToPos(), and transferRegionUsers().
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Removes a listener from the rematerializer.
Definition at line 222 of file Rematerializer.h.
References llvm_unreachable.
| void Rematerializer::transferAllUsers | ( | RegisterIdx | FromRegIdx, |
| RegisterIdx | ToRegIdx ) |
Transfers all users of register FromRegIdx to register ToRegIdx, the latter of which must be a rematerialization of the former or have the same origin register.
Users of FromRegIdx must be reachable from ToRegIdx.
Definition at line 154 of file Rematerializer.cpp.
References llvm::SmallVectorTemplateBase< T, bool >::push_back(), and llvm::Rematerializer::Reg::Uses.
Referenced by llvm::Rollbacker::rollback().
| void Rematerializer::transferRegionUsers | ( | RegisterIdx | FromRegIdx, |
| RegisterIdx | ToRegIdx, | ||
| unsigned | UseRegion ) |
Transfers all users of register FromRegIdx in region UseRegion to ToRegIdx, the latter of which must be a rematerialization of the former or have the same origin register.
Users in UseRegion must be reachable from ToRegIdx.
Definition at line 132 of file Rematerializer.cpp.
References llvm::SmallVectorTemplateBase< T, bool >::push_back(), and llvm::Rematerializer::Reg::Uses.
Referenced by rematerializeToRegion().
| void Rematerializer::transferUser | ( | RegisterIdx | FromRegIdx, |
| RegisterIdx | ToRegIdx, | ||
| unsigned | UserRegion, | ||
| MachineInstr & | UserMI ) |
Transfers user UserMI in region UserRegion from register FromRegIdx to ToRegIdx, the latter of which must be a rematerialization of the former or have the same origin register.
UserMI must be a direct user of FromRegIdx. UserMI must be reachable from ToRegIdx.
Definition at line 121 of file Rematerializer.cpp.
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Error value for register indices.
Definition at line 195 of file Rematerializer.h.
Referenced by findRematInRegion(), getDefRegIdx(), and printUser().