Fix a nasty problem on two-address machines in the following situation:
store EAX -> [ss#0] [ss#0] += 1 ... use(EAX) In this case, it is not valid to rewrite this as: store EAX -> [ss#0] EAX += 1 store EAX -> [ss#0] ;;; this would also delete the store above ... use(EAX) ... because EAX is not a dead at that point. Keep track of which registers we are allowed to clobber, and which ones we aren't, and don't clobber the ones we're not supposed to. :) This should resolve the issues on X86 last night. llvm-svn: 25948
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@ -233,6 +233,14 @@ namespace {
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/// AvailableSpills - As the local spiller is scanning and rewriting an MBB from
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/// top down, keep track of which spills slots are available in each register.
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///
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/// Note that not all physregs are created equal here. In particular, some
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/// physregs are reloads that we are allowed to clobber or ignore at any time.
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/// Other physregs are values that the register allocated program is using that
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/// we cannot CHANGE, but we can read if we like. We keep track of this on a
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/// per-stack-slot basis as the low bit in the value of the SpillSlotsAvailable
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/// entries. The predicate 'canClobberPhysReg()' checks this bit and
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/// addAvailable sets it if.
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class AvailableSpills {
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const MRegisterInfo *MRI;
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const TargetInstrInfo *TII;
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@ -258,20 +266,28 @@ public:
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unsigned getSpillSlotPhysReg(int Slot) const {
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std::map<int, unsigned>::const_iterator I = SpillSlotsAvailable.find(Slot);
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if (I != SpillSlotsAvailable.end())
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return I->second;
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return I->second >> 1; // Remove the CanClobber bit.
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return 0;
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}
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/// addAvailable - Mark that the specified stack slot is available in the
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/// specified physreg.
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void addAvailable(int Slot, unsigned Reg) {
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/// specified physreg. If CanClobber is true, the physreg can be modified at
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/// any time without changing the semantics of the program.
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void addAvailable(int Slot, unsigned Reg, bool CanClobber = true) {
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PhysRegsAvailable.insert(std::make_pair(Reg, Slot));
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SpillSlotsAvailable[Slot] = Reg;
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SpillSlotsAvailable[Slot] = (Reg << 1) | CanClobber;
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DEBUG(std::cerr << "Remembering SS#" << Slot << " in physreg "
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<< MRI->getName(Reg) << "\n");
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}
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/// canClobberPhysReg - Return true if the spiller is allowed to change the
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/// value of the specified stackslot register if it desires. The specified
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/// stack slot must be available in a physreg for this query to make sense.
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bool canClobberPhysReg(int Slot) const {
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assert(SpillSlotsAvailable.count(Slot) && "Slot not available!");
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return SpillSlotsAvailable.find(Slot)->second & 1;
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}
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/// ClobberPhysReg - This is called when the specified physreg changes
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/// value. We use this to invalidate any info about stuff we thing lives in
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@ -292,7 +308,7 @@ void AvailableSpills::ClobberPhysRegOnly(unsigned PhysReg) {
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while (I != PhysRegsAvailable.end() && I->first == PhysReg) {
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int Slot = I->second;
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PhysRegsAvailable.erase(I++);
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assert(SpillSlotsAvailable[Slot] == PhysReg &&
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assert((SpillSlotsAvailable[Slot] >> 1) == PhysReg &&
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"Bidirectional map mismatch!");
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SpillSlotsAvailable.erase(Slot);
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DEBUG(std::cerr << "PhysReg " << MRI->getName(PhysReg)
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@ -315,7 +331,7 @@ void AvailableSpills::ClobberPhysReg(unsigned PhysReg) {
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void AvailableSpills::ModifyStackSlot(int Slot) {
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std::map<int, unsigned>::iterator It = SpillSlotsAvailable.find(Slot);
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if (It == SpillSlotsAvailable.end()) return;
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unsigned Reg = It->second;
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unsigned Reg = It->second >> 1;
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SpillSlotsAvailable.erase(It);
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// This register may hold the value of multiple stack slots, only remove this
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@ -435,7 +451,10 @@ void LocalSpiller::RewriteMBB(MachineBasicBlock &MBB, const VirtRegMap &VRM) {
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unsigned PhysReg;
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// Check to see if this stack slot is available.
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if ((PhysReg = Spills.getSpillSlotPhysReg(StackSlot))) {
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if ((PhysReg = Spills.getSpillSlotPhysReg(StackSlot)) &&
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// Don't reuse it for a def&use operand if we aren't allowed to change
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// the physreg!
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(!MO.isDef() || Spills.canClobberPhysReg(StackSlot))) {
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// If this stack slot value is already available, reuse it!
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DEBUG(std::cerr << "Reusing SS#" << StackSlot << " from physreg "
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<< MRI->getName(PhysReg) << " for vreg"
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@ -613,7 +632,7 @@ void LocalSpiller::RewriteMBB(MachineBasicBlock &MBB, const VirtRegMap &VRM) {
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// If the stack slot value was previously available in some other
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// register, change it now. Otherwise, make the register available,
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// in PhysReg.
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Spills.addAvailable(StackSlot, SrcReg);
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Spills.addAvailable(StackSlot, SrcReg, false /*don't clobber*/);
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}
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}
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}
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@ -698,7 +717,6 @@ void LocalSpiller::RewriteMBB(MachineBasicBlock &MBB, const VirtRegMap &VRM) {
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// in PhysReg.
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Spills.ModifyStackSlot(StackSlot);
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Spills.ClobberPhysReg(PhysReg);
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Spills.addAvailable(StackSlot, PhysReg);
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++NumStores;
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}
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