llvm/lib/CodeGen/LiveVariables.cpp
Alkis Evlogimenos c55640f019 Remove unneeded check (with the recent change in live variables a use
of a physical register is always dominated by a def).


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@10821 91177308-0d34-0410-b5e6-96231b3b80d8
2004-01-13 21:16:25 +00:00

305 lines
12 KiB
C++

//===-- LiveVariables.cpp - Live Variable Analysis for Machine Code -------===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the LiveVariable analysis pass. For each machine
// instruction in the function, this pass calculates the set of registers that
// are immediately dead after the instruction (i.e., the instruction calculates
// the value, but it is never used) and the set of registers that are used by
// the instruction, but are never used after the instruction (i.e., they are
// killed).
//
// This class computes live variables using are sparse implementation based on
// the machine code SSA form. This class computes live variable information for
// each virtual and _register allocatable_ physical register in a function. It
// uses the dominance properties of SSA form to efficiently compute live
// variables for virtual registers, and assumes that physical registers are only
// live within a single basic block (allowing it to do a single local analysis
// to resolve physical register lifetimes in each basic block). If a physical
// register is not register allocatable, it is not tracked. This is useful for
// things like the stack pointer and condition codes.
//
//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/LiveVariables.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Support/CFG.h"
#include "Support/DepthFirstIterator.h"
namespace llvm {
static RegisterAnalysis<LiveVariables> X("livevars", "Live Variable Analysis");
const std::pair<MachineBasicBlock*, unsigned> &
LiveVariables::getMachineBasicBlockInfo(MachineBasicBlock *MBB) const{
return BBMap.find(MBB->getBasicBlock())->second;
}
LiveVariables::VarInfo &LiveVariables::getVarInfo(unsigned RegIdx) {
assert(RegIdx >= MRegisterInfo::FirstVirtualRegister &&
"getVarInfo: not a virtual register!");
RegIdx -= MRegisterInfo::FirstVirtualRegister;
if (RegIdx >= VirtRegInfo.size()) {
if (RegIdx >= 2*VirtRegInfo.size())
VirtRegInfo.resize(RegIdx*2);
else
VirtRegInfo.resize(2*VirtRegInfo.size());
}
return VirtRegInfo[RegIdx];
}
void LiveVariables::MarkVirtRegAliveInBlock(VarInfo &VRInfo,
const BasicBlock *BB) {
const std::pair<MachineBasicBlock*,unsigned> &Info = BBMap.find(BB)->second;
MachineBasicBlock *MBB = Info.first;
unsigned BBNum = Info.second;
// Check to see if this basic block is one of the killing blocks. If so,
// remove it...
for (unsigned i = 0, e = VRInfo.Kills.size(); i != e; ++i)
if (VRInfo.Kills[i].first == MBB) {
VRInfo.Kills.erase(VRInfo.Kills.begin()+i); // Erase entry
break;
}
if (MBB == VRInfo.DefBlock) return; // Terminate recursion
if (VRInfo.AliveBlocks.size() <= BBNum)
VRInfo.AliveBlocks.resize(BBNum+1); // Make space...
if (VRInfo.AliveBlocks[BBNum])
return; // We already know the block is live
// Mark the variable known alive in this bb
VRInfo.AliveBlocks[BBNum] = true;
for (pred_const_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
MarkVirtRegAliveInBlock(VRInfo, *PI);
}
void LiveVariables::HandleVirtRegUse(VarInfo &VRInfo, MachineBasicBlock *MBB,
MachineInstr *MI) {
// Check to see if this basic block is already a kill block...
if (!VRInfo.Kills.empty() && VRInfo.Kills.back().first == MBB) {
// Yes, this register is killed in this basic block already. Increase the
// live range by updating the kill instruction.
VRInfo.Kills.back().second = MI;
return;
}
#ifndef NDEBUG
for (unsigned i = 0, e = VRInfo.Kills.size(); i != e; ++i)
assert(VRInfo.Kills[i].first != MBB && "entry should be at end!");
#endif
assert(MBB != VRInfo.DefBlock && "Should have kill for defblock!");
// Add a new kill entry for this basic block.
VRInfo.Kills.push_back(std::make_pair(MBB, MI));
// Update all dominating blocks to mark them known live.
const BasicBlock *BB = MBB->getBasicBlock();
for (pred_const_iterator PI = pred_begin(BB), E = pred_end(BB);
PI != E; ++PI)
MarkVirtRegAliveInBlock(VRInfo, *PI);
}
void LiveVariables::HandlePhysRegUse(unsigned Reg, MachineInstr *MI) {
PhysRegInfo[Reg] = MI;
PhysRegUsed[Reg] = true;
}
void LiveVariables::HandlePhysRegDef(unsigned Reg, MachineInstr *MI) {
// Does this kill a previous version of this register?
if (MachineInstr *LastUse = PhysRegInfo[Reg]) {
if (PhysRegUsed[Reg])
RegistersKilled.insert(std::make_pair(LastUse, Reg));
else
RegistersDead.insert(std::make_pair(LastUse, Reg));
}
PhysRegInfo[Reg] = MI;
PhysRegUsed[Reg] = false;
for (const unsigned *AliasSet = RegInfo->getAliasSet(Reg);
*AliasSet; ++AliasSet) {
if (MachineInstr *LastUse = PhysRegInfo[*AliasSet]) {
if (PhysRegUsed[*AliasSet])
RegistersKilled.insert(std::make_pair(LastUse, *AliasSet));
else
RegistersDead.insert(std::make_pair(LastUse, *AliasSet));
}
PhysRegInfo[*AliasSet] = MI;
PhysRegUsed[*AliasSet] = false;
}
}
bool LiveVariables::runOnMachineFunction(MachineFunction &MF) {
// First time though, initialize AllocatablePhysicalRegisters for the target
if (AllocatablePhysicalRegisters.empty()) {
const MRegisterInfo &MRI = *MF.getTarget().getRegisterInfo();
assert(&MRI && "Target doesn't have register information?");
// Make space, initializing to false...
AllocatablePhysicalRegisters.resize(MRegisterInfo::FirstVirtualRegister);
// Loop over all of the register classes...
for (MRegisterInfo::regclass_iterator RCI = MRI.regclass_begin(),
E = MRI.regclass_end(); RCI != E; ++RCI)
// Loop over all of the allocatable registers in the function...
for (TargetRegisterClass::iterator I = (*RCI)->allocation_order_begin(MF),
E = (*RCI)->allocation_order_end(MF); I != E; ++I)
AllocatablePhysicalRegisters[*I] = true; // The reg is allocatable!
}
// Build BBMap...
unsigned BBNum = 0;
for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
BBMap[I->getBasicBlock()] = std::make_pair(I, BBNum++);
// PhysRegInfo - Keep track of which instruction was the last use of a
// physical register. This is a purely local property, because all physical
// register references as presumed dead across basic blocks.
//
MachineInstr *PhysRegInfoA[MRegisterInfo::FirstVirtualRegister];
bool PhysRegUsedA[MRegisterInfo::FirstVirtualRegister];
std::fill(PhysRegInfoA, PhysRegInfoA+MRegisterInfo::FirstVirtualRegister,
(MachineInstr*)0);
PhysRegInfo = PhysRegInfoA;
PhysRegUsed = PhysRegUsedA;
const TargetInstrInfo &TII = MF.getTarget().getInstrInfo();
RegInfo = MF.getTarget().getRegisterInfo();
/// Get some space for a respectable number of registers...
VirtRegInfo.resize(64);
// Calculate live variable information in depth first order on the CFG of the
// function. This guarantees that we will see the definition of a virtual
// register before its uses due to dominance properties of SSA (except for PHI
// nodes, which are treated as a special case).
//
const BasicBlock *Entry = MF.getFunction()->begin();
for (df_iterator<const BasicBlock*> DFI = df_begin(Entry), E = df_end(Entry);
DFI != E; ++DFI) {
const BasicBlock *BB = *DFI;
std::pair<MachineBasicBlock*, unsigned> &BBRec = BBMap.find(BB)->second;
MachineBasicBlock *MBB = BBRec.first;
unsigned BBNum = BBRec.second;
// Loop over all of the instructions, processing them.
for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
I != E; ++I) {
MachineInstr *MI = *I;
const TargetInstrDescriptor &MID = TII.get(MI->getOpcode());
// Process all of the operands of the instruction...
unsigned NumOperandsToProcess = MI->getNumOperands();
// Unless it is a PHI node. In this case, ONLY process the DEF, not any
// of the uses. They will be handled in other basic blocks.
if (MI->getOpcode() == TargetInstrInfo::PHI)
NumOperandsToProcess = 1;
// Loop over implicit uses, using them.
for (const unsigned *ImplicitUses = MID.ImplicitUses;
*ImplicitUses; ++ImplicitUses)
HandlePhysRegUse(*ImplicitUses, MI);
// Process all explicit uses...
for (unsigned i = 0; i != NumOperandsToProcess; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (MO.isUse()) {
if (MO.isVirtualRegister() && !MO.getVRegValueOrNull()) {
HandleVirtRegUse(getVarInfo(MO.getReg()), MBB, MI);
} else if (MO.isPhysicalRegister() &&
AllocatablePhysicalRegisters[MO.getReg()]) {
HandlePhysRegUse(MO.getReg(), MI);
}
}
}
// Loop over implicit defs, defining them.
for (const unsigned *ImplicitDefs = MID.ImplicitDefs;
*ImplicitDefs; ++ImplicitDefs)
HandlePhysRegDef(*ImplicitDefs, MI);
// Process all explicit defs...
for (unsigned i = 0; i != NumOperandsToProcess; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (MO.isDef()) {
if (MO.isVirtualRegister()) {
VarInfo &VRInfo = getVarInfo(MO.getReg());
assert(VRInfo.DefBlock == 0 && "Variable multiply defined!");
VRInfo.DefBlock = MBB; // Created here...
VRInfo.DefInst = MI;
VRInfo.Kills.push_back(std::make_pair(MBB, MI)); // Defaults to dead
} else if (MO.isPhysicalRegister() &&
AllocatablePhysicalRegisters[MO.getReg()]) {
HandlePhysRegDef(MO.getReg(), MI);
}
}
}
}
// Handle any virtual assignments from PHI nodes which might be at the
// bottom of this basic block. We check all of our successor blocks to see
// if they have PHI nodes, and if so, we simulate an assignment at the end
// of the current block.
for (succ_const_iterator SI = succ_begin(BB), E = succ_end(BB);
SI != E; ++SI) {
MachineBasicBlock *Succ = BBMap.find(*SI)->second.first;
// PHI nodes are guaranteed to be at the top of the block...
for (MachineBasicBlock::iterator I = Succ->begin(), E = Succ->end();
I != E && (*I)->getOpcode() == TargetInstrInfo::PHI; ++I) {
MachineInstr *MI = *I;
for (unsigned i = 1; ; i += 2)
if (MI->getOperand(i+1).getMachineBasicBlock() == MBB) {
MachineOperand &MO = MI->getOperand(i);
if (!MO.getVRegValueOrNull()) {
VarInfo &VRInfo = getVarInfo(MO.getReg());
// Only mark it alive only in the block we are representing...
MarkVirtRegAliveInBlock(VRInfo, BB);
break; // Found the PHI entry for this block...
}
}
}
}
// Loop over PhysRegInfo, killing any registers that are available at the
// end of the basic block. This also resets the PhysRegInfo map.
for (unsigned i = 0, e = MRegisterInfo::FirstVirtualRegister; i != e; ++i)
if (PhysRegInfo[i])
HandlePhysRegDef(i, 0);
}
// Convert the information we have gathered into VirtRegInfo and transform it
// into a form usable by RegistersKilled.
//
for (unsigned i = 0, e = VirtRegInfo.size(); i != e; ++i)
for (unsigned j = 0, e = VirtRegInfo[i].Kills.size(); j != e; ++j) {
if (VirtRegInfo[i].Kills[j].second == VirtRegInfo[i].DefInst)
RegistersDead.insert(std::make_pair(VirtRegInfo[i].Kills[j].second,
i + MRegisterInfo::FirstVirtualRegister));
else
RegistersKilled.insert(std::make_pair(VirtRegInfo[i].Kills[j].second,
i + MRegisterInfo::FirstVirtualRegister));
}
return false;
}
} // End llvm namespace