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335 lines
13 KiB
C++
335 lines
13 KiB
C++
//===-- LiveVariables.cpp - Live Variable Analysis for Machine Code -------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file was developed by the LLVM research group and is distributed under
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// the University of Illinois Open Source License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements the LiveVariable analysis pass. For each machine
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// instruction in the function, this pass calculates the set of registers that
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// are immediately dead after the instruction (i.e., the instruction calculates
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// the value, but it is never used) and the set of registers that are used by
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// the instruction, but are never used after the instruction (i.e., they are
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// killed).
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//
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// This class computes live variables using are sparse implementation based on
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// the machine code SSA form. This class computes live variable information for
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// each virtual and _register allocatable_ physical register in a function. It
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// uses the dominance properties of SSA form to efficiently compute live
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// variables for virtual registers, and assumes that physical registers are only
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// live within a single basic block (allowing it to do a single local analysis
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// to resolve physical register lifetimes in each basic block). If a physical
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// register is not register allocatable, it is not tracked. This is useful for
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// things like the stack pointer and condition codes.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/CodeGen/LiveVariables.h"
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#include "llvm/CodeGen/MachineInstr.h"
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#include "llvm/Target/MRegisterInfo.h"
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#include "llvm/Target/TargetInstrInfo.h"
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#include "llvm/Target/TargetMachine.h"
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#include "llvm/ADT/DepthFirstIterator.h"
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#include "llvm/ADT/STLExtras.h"
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#include "llvm/Config/alloca.h"
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using namespace llvm;
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static RegisterAnalysis<LiveVariables> X("livevars", "Live Variable Analysis");
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LiveVariables::VarInfo &LiveVariables::getVarInfo(unsigned RegIdx) {
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assert(MRegisterInfo::isVirtualRegister(RegIdx) &&
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"getVarInfo: not a virtual register!");
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RegIdx -= MRegisterInfo::FirstVirtualRegister;
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if (RegIdx >= VirtRegInfo.size()) {
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if (RegIdx >= 2*VirtRegInfo.size())
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VirtRegInfo.resize(RegIdx*2);
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else
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VirtRegInfo.resize(2*VirtRegInfo.size());
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}
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return VirtRegInfo[RegIdx];
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}
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void LiveVariables::MarkVirtRegAliveInBlock(VarInfo &VRInfo,
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MachineBasicBlock *MBB) {
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unsigned BBNum = MBB->getNumber();
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// Check to see if this basic block is one of the killing blocks. If so,
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// remove it...
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for (unsigned i = 0, e = VRInfo.Kills.size(); i != e; ++i)
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if (VRInfo.Kills[i]->getParent() == MBB) {
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VRInfo.Kills.erase(VRInfo.Kills.begin()+i); // Erase entry
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break;
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}
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if (MBB == VRInfo.DefInst->getParent()) return; // Terminate recursion
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if (VRInfo.AliveBlocks.size() <= BBNum)
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VRInfo.AliveBlocks.resize(BBNum+1); // Make space...
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if (VRInfo.AliveBlocks[BBNum])
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return; // We already know the block is live
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// Mark the variable known alive in this bb
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VRInfo.AliveBlocks[BBNum] = true;
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for (MachineBasicBlock::const_pred_iterator PI = MBB->pred_begin(),
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E = MBB->pred_end(); PI != E; ++PI)
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MarkVirtRegAliveInBlock(VRInfo, *PI);
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}
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void LiveVariables::HandleVirtRegUse(VarInfo &VRInfo, MachineBasicBlock *MBB,
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MachineInstr *MI) {
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assert(VRInfo.DefInst && "Register use before def!");
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// Check to see if this basic block is already a kill block...
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if (!VRInfo.Kills.empty() && VRInfo.Kills.back()->getParent() == MBB) {
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// Yes, this register is killed in this basic block already. Increase the
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// live range by updating the kill instruction.
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VRInfo.Kills.back() = MI;
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return;
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}
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#ifndef NDEBUG
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for (unsigned i = 0, e = VRInfo.Kills.size(); i != e; ++i)
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assert(VRInfo.Kills[i]->getParent() != MBB && "entry should be at end!");
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#endif
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assert(MBB != VRInfo.DefInst->getParent() &&
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"Should have kill for defblock!");
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// Add a new kill entry for this basic block.
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VRInfo.Kills.push_back(MI);
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// Update all dominating blocks to mark them known live.
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for (MachineBasicBlock::const_pred_iterator PI = MBB->pred_begin(),
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E = MBB->pred_end(); PI != E; ++PI)
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MarkVirtRegAliveInBlock(VRInfo, *PI);
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}
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void LiveVariables::HandlePhysRegUse(unsigned Reg, MachineInstr *MI) {
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PhysRegInfo[Reg] = MI;
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PhysRegUsed[Reg] = true;
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for (const unsigned *AliasSet = RegInfo->getAliasSet(Reg);
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unsigned Alias = *AliasSet; ++AliasSet) {
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PhysRegInfo[Alias] = MI;
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PhysRegUsed[Alias] = true;
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}
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}
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void LiveVariables::HandlePhysRegDef(unsigned Reg, MachineInstr *MI) {
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// Does this kill a previous version of this register?
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if (MachineInstr *LastUse = PhysRegInfo[Reg]) {
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if (PhysRegUsed[Reg])
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RegistersKilled.insert(std::make_pair(LastUse, Reg));
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else
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RegistersDead.insert(std::make_pair(LastUse, Reg));
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}
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PhysRegInfo[Reg] = MI;
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PhysRegUsed[Reg] = false;
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for (const unsigned *AliasSet = RegInfo->getAliasSet(Reg);
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unsigned Alias = *AliasSet; ++AliasSet) {
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if (MachineInstr *LastUse = PhysRegInfo[Alias]) {
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if (PhysRegUsed[Alias])
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RegistersKilled.insert(std::make_pair(LastUse, Alias));
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else
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RegistersDead.insert(std::make_pair(LastUse, Alias));
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}
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PhysRegInfo[Alias] = MI;
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PhysRegUsed[Alias] = false;
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}
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}
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bool LiveVariables::runOnMachineFunction(MachineFunction &MF) {
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const TargetInstrInfo &TII = *MF.getTarget().getInstrInfo();
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RegInfo = MF.getTarget().getRegisterInfo();
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assert(RegInfo && "Target doesn't have register information?");
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AllocatablePhysicalRegisters = RegInfo->getAllocatableSet(MF);
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// PhysRegInfo - Keep track of which instruction was the last use of a
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// physical register. This is a purely local property, because all physical
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// register references as presumed dead across basic blocks.
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//
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PhysRegInfo = (MachineInstr**)alloca(sizeof(MachineInstr*) *
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RegInfo->getNumRegs());
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PhysRegUsed = (bool*)alloca(sizeof(bool)*RegInfo->getNumRegs());
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std::fill(PhysRegInfo, PhysRegInfo+RegInfo->getNumRegs(), (MachineInstr*)0);
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/// Get some space for a respectable number of registers...
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VirtRegInfo.resize(64);
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// Calculate live variable information in depth first order on the CFG of the
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// function. This guarantees that we will see the definition of a virtual
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// register before its uses due to dominance properties of SSA (except for PHI
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// nodes, which are treated as a special case).
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//
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MachineBasicBlock *Entry = MF.begin();
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std::set<MachineBasicBlock*> Visited;
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for (df_ext_iterator<MachineBasicBlock*> DFI = df_ext_begin(Entry, Visited),
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E = df_ext_end(Entry, Visited); DFI != E; ++DFI) {
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MachineBasicBlock *MBB = *DFI;
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unsigned BBNum = MBB->getNumber();
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// Loop over all of the instructions, processing them.
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for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
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I != E; ++I) {
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MachineInstr *MI = I;
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const TargetInstrDescriptor &MID = TII.get(MI->getOpcode());
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// Process all of the operands of the instruction...
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unsigned NumOperandsToProcess = MI->getNumOperands();
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// Unless it is a PHI node. In this case, ONLY process the DEF, not any
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// of the uses. They will be handled in other basic blocks.
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if (MI->getOpcode() == TargetInstrInfo::PHI)
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NumOperandsToProcess = 1;
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// Loop over implicit uses, using them.
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for (const unsigned *ImplicitUses = MID.ImplicitUses;
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*ImplicitUses; ++ImplicitUses)
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HandlePhysRegUse(*ImplicitUses, MI);
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// Process all explicit uses...
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for (unsigned i = 0; i != NumOperandsToProcess; ++i) {
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MachineOperand &MO = MI->getOperand(i);
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if (MO.isUse() && MO.isRegister() && MO.getReg()) {
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if (MRegisterInfo::isVirtualRegister(MO.getReg())){
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HandleVirtRegUse(getVarInfo(MO.getReg()), MBB, MI);
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} else if (MRegisterInfo::isPhysicalRegister(MO.getReg()) &&
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AllocatablePhysicalRegisters[MO.getReg()]) {
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HandlePhysRegUse(MO.getReg(), MI);
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}
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}
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}
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// Loop over implicit defs, defining them.
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for (const unsigned *ImplicitDefs = MID.ImplicitDefs;
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*ImplicitDefs; ++ImplicitDefs)
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HandlePhysRegDef(*ImplicitDefs, MI);
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// Process all explicit defs...
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for (unsigned i = 0; i != NumOperandsToProcess; ++i) {
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MachineOperand &MO = MI->getOperand(i);
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if (MO.isDef() && MO.isRegister() && MO.getReg()) {
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if (MRegisterInfo::isVirtualRegister(MO.getReg())) {
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VarInfo &VRInfo = getVarInfo(MO.getReg());
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assert(VRInfo.DefInst == 0 && "Variable multiply defined!");
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VRInfo.DefInst = MI;
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// Defaults to dead
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VRInfo.Kills.push_back(MI);
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} else if (MRegisterInfo::isPhysicalRegister(MO.getReg()) &&
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AllocatablePhysicalRegisters[MO.getReg()]) {
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HandlePhysRegDef(MO.getReg(), MI);
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}
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}
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}
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}
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// Handle any virtual assignments from PHI nodes which might be at the
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// bottom of this basic block. We check all of our successor blocks to see
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// if they have PHI nodes, and if so, we simulate an assignment at the end
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// of the current block.
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for (MachineBasicBlock::succ_iterator SI = MBB->succ_begin(),
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E = MBB->succ_end(); SI != E; ++SI) {
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MachineBasicBlock *Succ = *SI;
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// PHI nodes are guaranteed to be at the top of the block...
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for (MachineBasicBlock::iterator MI = Succ->begin(), ME = Succ->end();
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MI != ME && MI->getOpcode() == TargetInstrInfo::PHI; ++MI) {
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for (unsigned i = 1; ; i += 2) {
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assert(MI->getNumOperands() > i+1 &&
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"Didn't find an entry for our predecessor??");
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if (MI->getOperand(i+1).getMachineBasicBlock() == MBB) {
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MachineOperand &MO = MI->getOperand(i);
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if (!MO.getVRegValueOrNull()) {
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VarInfo &VRInfo = getVarInfo(MO.getReg());
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// Only mark it alive only in the block we are representing...
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MarkVirtRegAliveInBlock(VRInfo, MBB);
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break; // Found the PHI entry for this block...
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}
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}
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}
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}
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}
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// Loop over PhysRegInfo, killing any registers that are available at the
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// end of the basic block. This also resets the PhysRegInfo map.
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for (unsigned i = 0, e = RegInfo->getNumRegs(); i != e; ++i)
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if (PhysRegInfo[i])
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HandlePhysRegDef(i, 0);
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}
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// Convert the information we have gathered into VirtRegInfo and transform it
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// into a form usable by RegistersKilled.
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//
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for (unsigned i = 0, e = VirtRegInfo.size(); i != e; ++i)
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for (unsigned j = 0, e = VirtRegInfo[i].Kills.size(); j != e; ++j) {
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if (VirtRegInfo[i].Kills[j] == VirtRegInfo[i].DefInst)
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RegistersDead.insert(std::make_pair(VirtRegInfo[i].Kills[j],
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i + MRegisterInfo::FirstVirtualRegister));
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else
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RegistersKilled.insert(std::make_pair(VirtRegInfo[i].Kills[j],
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i + MRegisterInfo::FirstVirtualRegister));
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}
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// Check to make sure there are no unreachable blocks in the MC CFG for the
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// function. If so, it is due to a bug in the instruction selector or some
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// other part of the code generator if this happens.
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#ifndef NDEBUG
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for(MachineFunction::iterator i = MF.begin(), e = MF.end(); i != e; ++i)
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assert(Visited.count(&*i) != 0 && "unreachable basic block found");
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#endif
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return false;
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}
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/// instructionChanged - When the address of an instruction changes, this
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/// method should be called so that live variables can update its internal
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/// data structures. This removes the records for OldMI, transfering them to
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/// the records for NewMI.
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void LiveVariables::instructionChanged(MachineInstr *OldMI,
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MachineInstr *NewMI) {
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// If the instruction defines any virtual registers, update the VarInfo for
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// the instruction.
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for (unsigned i = 0, e = OldMI->getNumOperands(); i != e; ++i) {
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MachineOperand &MO = OldMI->getOperand(i);
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if (MO.isRegister() && MO.isDef() && MO.getReg() &&
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MRegisterInfo::isVirtualRegister(MO.getReg())) {
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unsigned Reg = MO.getReg();
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VarInfo &VI = getVarInfo(Reg);
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if (VI.DefInst == OldMI)
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VI.DefInst = NewMI;
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}
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}
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// Move the killed information over...
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killed_iterator I, E;
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tie(I, E) = killed_range(OldMI);
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std::vector<unsigned> Regs;
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for (killed_iterator A = I; A != E; ++A)
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Regs.push_back(A->second);
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RegistersKilled.erase(I, E);
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for (unsigned i = 0, e = Regs.size(); i != e; ++i)
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RegistersKilled.insert(std::make_pair(NewMI, Regs[i]));
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Regs.clear();
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// Move the dead information over...
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tie(I, E) = dead_range(OldMI);
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for (killed_iterator A = I; A != E; ++A)
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Regs.push_back(A->second);
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RegistersDead.erase(I, E);
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for (unsigned i = 0, e = Regs.size(); i != e; ++i)
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RegistersDead.insert(std::make_pair(NewMI, Regs[i]));
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}
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