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+//===-- RegisterScavenging.cpp - Machine register scavenging --------------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the machine register scavenger. It can provide
+// information, such as unused registers, at any point in a machine basic block.
+// It also provides a mechanism to make registers available by evicting them to
+// spill slots.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "reg-scavenging"
+#include "llvm/CodeGen/RegisterScavenging.h"
+#include "llvm/CodeGen/MachineFrameInfo.h"
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/CodeGen/MachineBasicBlock.h"
+#include "llvm/CodeGen/MachineInstr.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Target/TargetRegisterInfo.h"
+#include "llvm/Target/TargetInstrInfo.h"
+#include "llvm/Target/TargetMachine.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/STLExtras.h"
+using namespace llvm;
+
+/// setUsed - Set the register and its sub-registers as being used.
+void RegScavenger::setUsed(unsigned Reg) {
+ RegsAvailable.reset(Reg);
+
+ for (const unsigned *SubRegs = TRI->getSubRegisters(Reg);
+ unsigned SubReg = *SubRegs; ++SubRegs)
+ RegsAvailable.reset(SubReg);
+}
+
+bool RegScavenger::isAliasUsed(unsigned Reg) const {
+ if (isUsed(Reg))
+ return true;
+ for (const unsigned *R = TRI->getAliasSet(Reg); *R; ++R)
+ if (isUsed(*R))
+ return true;
+ return false;
+}
+
+void RegScavenger::initRegState() {
+ ScavengedReg = 0;
+ ScavengedRC = NULL;
+ ScavengeRestore = NULL;
+
+ // All registers started out unused.
+ RegsAvailable.set();
+
+ // Reserved registers are always used.
+ RegsAvailable ^= ReservedRegs;
+
+ if (!MBB)
+ return;
+
+ // Live-in registers are in use.
+ for (MachineBasicBlock::livein_iterator I = MBB->livein_begin(),
+ E = MBB->livein_end(); I != E; ++I)
+ setUsed(*I);
+
+ // Pristine CSRs are also unavailable.
+ BitVector PR = MBB->getParent()->getFrameInfo()->getPristineRegs(MBB);
+ for (int I = PR.find_first(); I>0; I = PR.find_next(I))
+ setUsed(I);
+}
+
+void RegScavenger::enterBasicBlock(MachineBasicBlock *mbb) {
+ MachineFunction &MF = *mbb->getParent();
+ const TargetMachine &TM = MF.getTarget();
+ TII = TM.getInstrInfo();
+ TRI = TM.getRegisterInfo();
+ MRI = &MF.getRegInfo();
+
+ assert((NumPhysRegs == 0 || NumPhysRegs == TRI->getNumRegs()) &&
+ "Target changed?");
+
+ // Self-initialize.
+ if (!MBB) {
+ NumPhysRegs = TRI->getNumRegs();
+ RegsAvailable.resize(NumPhysRegs);
+
+ // Create reserved registers bitvector.
+ ReservedRegs = TRI->getReservedRegs(MF);
+
+ // Create callee-saved registers bitvector.
+ CalleeSavedRegs.resize(NumPhysRegs);
+ const unsigned *CSRegs = TRI->getCalleeSavedRegs();
+ if (CSRegs != NULL)
+ for (unsigned i = 0; CSRegs[i]; ++i)
+ CalleeSavedRegs.set(CSRegs[i]);
+ }
+
+ MBB = mbb;
+ initRegState();
+
+ Tracking = false;
+}
+
+void RegScavenger::addRegWithSubRegs(BitVector &BV, unsigned Reg) {
+ BV.set(Reg);
+ for (const unsigned *R = TRI->getSubRegisters(Reg); *R; R++)
+ BV.set(*R);
+}
+
+void RegScavenger::addRegWithAliases(BitVector &BV, unsigned Reg) {
+ BV.set(Reg);
+ for (const unsigned *R = TRI->getAliasSet(Reg); *R; R++)
+ BV.set(*R);
+}
+
+void RegScavenger::forward() {
+ // Move ptr forward.
+ if (!Tracking) {
+ MBBI = MBB->begin();
+ Tracking = true;
+ } else {
+ assert(MBBI != MBB->end() && "Already at the end of the basic block!");
+ MBBI = llvm::next(MBBI);
+ }
+
+ MachineInstr *MI = MBBI;
+
+ if (MI == ScavengeRestore) {
+ ScavengedReg = 0;
+ ScavengedRC = NULL;
+ ScavengeRestore = NULL;
+ }
+
+ if (MI->isDebugValue())
+ return;
+
+ // Find out which registers are early clobbered, killed, defined, and marked
+ // def-dead in this instruction.
+ BitVector EarlyClobberRegs(NumPhysRegs);
+ BitVector KillRegs(NumPhysRegs);
+ BitVector DefRegs(NumPhysRegs);
+ BitVector DeadRegs(NumPhysRegs);
+ for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
+ const MachineOperand &MO = MI->getOperand(i);
+ if (!MO.isReg() || MO.isUndef())
+ continue;
+ unsigned Reg = MO.getReg();
+ if (!Reg || isReserved(Reg))
+ continue;
+
+ if (MO.isUse()) {
+ // Two-address operands implicitly kill.
+ if (MO.isKill() || MI->isRegTiedToDefOperand(i))
+ addRegWithSubRegs(KillRegs, Reg);
+ } else {
+ assert(MO.isDef());
+ if (MO.isDead())
+ addRegWithSubRegs(DeadRegs, Reg);
+ else
+ addRegWithSubRegs(DefRegs, Reg);
+ if (MO.isEarlyClobber())
+ addRegWithAliases(EarlyClobberRegs, Reg);
+ }
+ }
+
+ // Verify uses and defs.
+ for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
+ const MachineOperand &MO = MI->getOperand(i);
+ if (!MO.isReg() || MO.isUndef())
+ continue;
+ unsigned Reg = MO.getReg();
+ if (!Reg || isReserved(Reg))
+ continue;
+ if (MO.isUse()) {
+ if (!isUsed(Reg)) {
+ // Check if it's partial live: e.g.
+ // D0 = insert_subreg D0<undef>, S0
+ // ... D0
+ // The problem is the insert_subreg could be eliminated. The use of
+ // D0 is using a partially undef value. This is not *incorrect* since
+ // S1 is can be freely clobbered.
+ // Ideally we would like a way to model this, but leaving the
+ // insert_subreg around causes both correctness and performance issues.
+ bool SubUsed = false;
+ for (const unsigned *SubRegs = TRI->getSubRegisters(Reg);
+ unsigned SubReg = *SubRegs; ++SubRegs)
+ if (isUsed(SubReg)) {
+ SubUsed = true;
+ break;
+ }
+ assert(SubUsed && "Using an undefined register!");
+ }
+ assert((!EarlyClobberRegs.test(Reg) || MI->isRegTiedToDefOperand(i)) &&
+ "Using an early clobbered register!");
+ } else {
+ assert(MO.isDef());
+#if 0
+ // FIXME: Enable this once we've figured out how to correctly transfer
+ // implicit kills during codegen passes like the coalescer.
+ assert((KillRegs.test(Reg) || isUnused(Reg) ||
+ isLiveInButUnusedBefore(Reg, MI, MBB, TRI, MRI)) &&
+ "Re-defining a live register!");
+#endif
+ }
+ }
+
+ // Commit the changes.
+ setUnused(KillRegs);
+ setUnused(DeadRegs);
+ setUsed(DefRegs);
+}
+
+void RegScavenger::getRegsUsed(BitVector &used, bool includeReserved) {
+ if (includeReserved)
+ used = ~RegsAvailable;
+ else
+ used = ~RegsAvailable & ~ReservedRegs;
+}
+
+/// CreateRegClassMask - Set the bits that represent the registers in the
+/// TargetRegisterClass.
+static void CreateRegClassMask(const TargetRegisterClass *RC, BitVector &Mask) {
+ for (TargetRegisterClass::iterator I = RC->begin(), E = RC->end(); I != E;
+ ++I)
+ Mask.set(*I);
+}
+
+unsigned RegScavenger::FindUnusedReg(const TargetRegisterClass *RC) const {
+ for (TargetRegisterClass::iterator I = RC->begin(), E = RC->end();
+ I != E; ++I)
+ if (!isAliasUsed(*I))
+ return *I;
+ return 0;
+}
+
+/// findSurvivorReg - Return the candidate register that is unused for the
+/// longest after MBBI. UseMI is set to the instruction where the search
+/// stopped.
+///
+/// No more than InstrLimit instructions are inspected.
+///
+unsigned RegScavenger::findSurvivorReg(MachineBasicBlock::iterator StartMI,
+ BitVector &Candidates,
+ unsigned InstrLimit,
+ MachineBasicBlock::iterator &UseMI) {
+ int Survivor = Candidates.find_first();
+ assert(Survivor > 0 && "No candidates for scavenging");
+
+ MachineBasicBlock::iterator ME = MBB->getFirstTerminator();
+ assert(StartMI != ME && "MI already at terminator");
+ MachineBasicBlock::iterator RestorePointMI = StartMI;
+ MachineBasicBlock::iterator MI = StartMI;
+
+ bool inVirtLiveRange = false;
+ for (++MI; InstrLimit > 0 && MI != ME; ++MI, --InstrLimit) {
+ bool isVirtKillInsn = false;
+ bool isVirtDefInsn = false;
+ // Remove any candidates touched by instruction.
+ for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
+ const MachineOperand &MO = MI->getOperand(i);
+ if (!MO.isReg() || MO.isUndef() || !MO.getReg())
+ continue;
+ if (TargetRegisterInfo::isVirtualRegister(MO.getReg())) {
+ if (MO.isDef())
+ isVirtDefInsn = true;
+ else if (MO.isKill())
+ isVirtKillInsn = true;
+ continue;
+ }
+ Candidates.reset(MO.getReg());
+ for (const unsigned *R = TRI->getAliasSet(MO.getReg()); *R; R++)
+ Candidates.reset(*R);
+ }
+ // If we're not in a virtual reg's live range, this is a valid
+ // restore point.
+ if (!inVirtLiveRange) RestorePointMI = MI;
+
+ // Update whether we're in the live range of a virtual register
+ if (isVirtKillInsn) inVirtLiveRange = false;
+ if (isVirtDefInsn) inVirtLiveRange = true;
+
+ // Was our survivor untouched by this instruction?
+ if (Candidates.test(Survivor))
+ continue;
+
+ // All candidates gone?
+ if (Candidates.none())
+ break;
+
+ Survivor = Candidates.find_first();
+ }
+ // If we ran off the end, that's where we want to restore.
+ if (MI == ME) RestorePointMI = ME;
+ assert (RestorePointMI != StartMI &&
+ "No available scavenger restore location!");
+
+ // We ran out of candidates, so stop the search.
+ UseMI = RestorePointMI;
+ return Survivor;
+}
+
+unsigned RegScavenger::scavengeRegister(const TargetRegisterClass *RC,
+ MachineBasicBlock::iterator I,
+ int SPAdj) {
+ // Mask off the registers which are not in the TargetRegisterClass.
+ BitVector Candidates(NumPhysRegs, false);
+ CreateRegClassMask(RC, Candidates);
+ // Do not include reserved registers.
+ Candidates ^= ReservedRegs & Candidates;
+
+ // Exclude all the registers being used by the instruction.
+ for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
+ MachineOperand &MO = I->getOperand(i);
+ if (MO.isReg() && MO.getReg() != 0 &&
+ !TargetRegisterInfo::isVirtualRegister(MO.getReg()))
+ Candidates.reset(MO.getReg());
+ }
+
+ // Find the register whose use is furthest away.
+ MachineBasicBlock::iterator UseMI;
+ unsigned SReg = findSurvivorReg(I, Candidates, 25, UseMI);
+
+ // If we found an unused register there is no reason to spill it. We have
+ // probably found a callee-saved register that has been saved in the
+ // prologue, but happens to be unused at this point.
+ if (!isAliasUsed(SReg))
+ return SReg;
+
+ assert(ScavengedReg == 0 &&
+ "Scavenger slot is live, unable to scavenge another register!");
+
+ // Avoid infinite regress
+ ScavengedReg = SReg;
+
+ // If the target knows how to save/restore the register, let it do so;
+ // otherwise, use the emergency stack spill slot.
+ if (!TRI->saveScavengerRegister(*MBB, I, UseMI, RC, SReg)) {
+ // Spill the scavenged register before I.
+ assert(ScavengingFrameIndex >= 0 &&
+ "Cannot scavenge register without an emergency spill slot!");
+ TII->storeRegToStackSlot(*MBB, I, SReg, true, ScavengingFrameIndex, RC,TRI);
+ MachineBasicBlock::iterator II = prior(I);
+ TRI->eliminateFrameIndex(II, SPAdj, NULL, this);
+
+ // Restore the scavenged register before its use (or first terminator).
+ TII->loadRegFromStackSlot(*MBB, UseMI, SReg, ScavengingFrameIndex, RC, TRI);
+ II = prior(UseMI);
+ TRI->eliminateFrameIndex(II, SPAdj, NULL, this);
+ }
+
+ ScavengeRestore = prior(UseMI);
+
+ // Doing this here leads to infinite regress.
+ // ScavengedReg = SReg;
+ ScavengedRC = RC;
+
+ return SReg;
+}
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