LLVM  14.0.0git
Public Member Functions | Public Attributes | List of all members
llvm::LiveVariables::VarInfo Struct Reference

VarInfo - This represents the regions where a virtual register is live in the program. More...

#include "llvm/CodeGen/LiveVariables.h"

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Public Member Functions

bool removeKill (MachineInstr &MI)
 removeKill - Delete a kill corresponding to the specified machine instruction. More...
 
MachineInstrfindKill (const MachineBasicBlock *MBB) const
 findKill - Find a kill instruction in MBB. Return NULL if none is found. More...
 
bool isLiveIn (const MachineBasicBlock &MBB, Register Reg, MachineRegisterInfo &MRI)
 isLiveIn - Is Reg live in to MBB? This means that Reg is live through MBB, or it is killed in MBB. More...
 
void dump () const
 

Public Attributes

SparseBitVector AliveBlocks
 AliveBlocks - Set of blocks in which this value is alive completely through. More...
 
std::vector< MachineInstr * > Kills
 Kills - List of MachineInstruction's which are the last use of this virtual register (kill it) in their basic block. More...
 

Detailed Description

VarInfo - This represents the regions where a virtual register is live in the program.

We represent this with three different pieces of information: the set of blocks in which the instruction is live throughout, the set of blocks in which the instruction is actually used, and the set of non-phi instructions that are the last users of the value.

In the common case where a value is defined and killed in the same block, There is one killing instruction, and AliveBlocks is empty.

Otherwise, the value is live out of the block. If the value is live throughout any blocks, these blocks are listed in AliveBlocks. Blocks where the liveness range ends are not included in AliveBlocks, instead being captured by the Kills set. In these blocks, the value is live into the block (unless the value is defined and killed in the same block) and lives until the specified instruction. Note that there cannot ever be a value whose Kills set contains two instructions from the same basic block.

PHI nodes complicate things a bit. If a PHI node is the last user of a value in one of its predecessor blocks, it is not listed in the kills set, but does include the predecessor block in the AliveBlocks set (unless that block also defines the value). This leads to the (perfectly sensical) situation where a value is defined in a block, and the last use is a phi node in the successor. In this case, AliveBlocks is empty (the value is not live across any blocks) and Kills is empty (phi nodes are not included). This is sensical because the value must be live to the end of the block, but is not live in any successor blocks.

Definition at line 79 of file LiveVariables.h.

Member Function Documentation

◆ dump()

LLVM_DUMP_METHOD void LiveVariables::VarInfo::dump ( ) const

Definition at line 68 of file LiveVariables.cpp.

References llvm::dbgs(), llvm::numbers::e, and i.

◆ findKill()

MachineInstr * LiveVariables::VarInfo::findKill ( const MachineBasicBlock MBB) const

findKill - Find a kill instruction in MBB. Return NULL if none is found.

Definition at line 60 of file LiveVariables.cpp.

References llvm::numbers::e, getParent(), i, Kills, and MBB.

◆ isLiveIn()

bool LiveVariables::VarInfo::isLiveIn ( const MachineBasicBlock MBB,
Register  Reg,
MachineRegisterInfo MRI 
)

isLiveIn - Is Reg live in to MBB? This means that Reg is live through MBB, or it is killed in MBB.

If Reg is only used by PHI instructions in MBB, it is not considered live in.

Definition at line 713 of file LiveVariables.cpp.

References llvm::tgtok::Def, llvm::MachineBasicBlock::getNumber(), llvm::MachineRegisterInfo::getVRegDef(), MBB, MRI, and Reg.

Referenced by llvm::LiveVariables::isLiveIn().

◆ removeKill()

bool llvm::LiveVariables::VarInfo::removeKill ( MachineInstr MI)
inline

removeKill - Delete a kill corresponding to the specified machine instruction.

Returns true if there was a kill corresponding to this instruction, false otherwise.

Definition at line 94 of file LiveVariables.h.

References llvm::find(), I, Kills, and MI.

Referenced by llvm::LiveVariables::removeVirtualRegistersKilled(), and llvm::MachineBasicBlock::SplitCriticalEdge().

Member Data Documentation

◆ AliveBlocks

SparseBitVector llvm::LiveVariables::VarInfo::AliveBlocks

AliveBlocks - Set of blocks in which this value is alive completely through.

This is a bit set which uses the basic block number as an index.

Definition at line 84 of file LiveVariables.h.

Referenced by llvm::LiveVariables::addNewBlock(), llvm::LiveVariables::HandleVirtRegDef(), llvm::LiveVariables::HandleVirtRegUse(), and llvm::LiveVariables::MarkVirtRegAliveInBlock().

◆ Kills

std::vector<MachineInstr*> llvm::LiveVariables::VarInfo::Kills

The documentation for this struct was generated from the following files: