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Fix a nasty problem on two-address machines in the following situation:

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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.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@25948 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2006-02-03 23:28:46 +00:00
parent 66cf80f226
commit 593c95878b
1 changed files with 27 additions and 9 deletions
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36
lib/CodeGen/VirtRegMap.cpp
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@ -233,6 +233,14 @@ namespace {
/// AvailableSpills - As the local spiller is scanning and rewriting an MBB from
/// top down, keep track of which spills slots are available in each register.
///
/// Note that not all physregs are created equal here. In particular, some
/// physregs are reloads that we are allowed to clobber or ignore at any time.
/// Other physregs are values that the register allocated program is using that
/// we cannot CHANGE, but we can read if we like. We keep track of this on a
/// per-stack-slot basis as the low bit in the value of the SpillSlotsAvailable
/// entries. The predicate 'canClobberPhysReg()' checks this bit and
/// addAvailable sets it if.
class AvailableSpills {
const MRegisterInfo *MRI;
const TargetInstrInfo *TII;
@ -258,20 +266,28 @@ public:
unsigned getSpillSlotPhysReg(int Slot) const {
std::map<int, unsigned>::const_iterator I = SpillSlotsAvailable.find(Slot);
if (I != SpillSlotsAvailable.end())
return I->second;
return I->second >> 1; // Remove the CanClobber bit.
return 0;
}
/// addAvailable - Mark that the specified stack slot is available in the
/// specified physreg.
void addAvailable(int Slot, unsigned Reg) {
/// specified physreg. If CanClobber is true, the physreg can be modified at
/// any time without changing the semantics of the program.
void addAvailable(int Slot, unsigned Reg, bool CanClobber = true) {
PhysRegsAvailable.insert(std::make_pair(Reg, Slot));
SpillSlotsAvailable[Slot] = Reg;
SpillSlotsAvailable[Slot] = (Reg << 1) | CanClobber;
DEBUG(std::cerr << "Remembering SS#" << Slot << " in physreg "
<< MRI->getName(Reg) << "\n");
}
/// canClobberPhysReg - Return true if the spiller is allowed to change the
/// value of the specified stackslot register if it desires. The specified
/// stack slot must be available in a physreg for this query to make sense.
bool canClobberPhysReg(int Slot) const {
assert(SpillSlotsAvailable.count(Slot) && "Slot not available!");
return SpillSlotsAvailable.find(Slot)->second & 1;
}
/// ClobberPhysReg - This is called when the specified physreg changes
/// value. We use this to invalidate any info about stuff we thing lives in
@ -292,7 +308,7 @@ void AvailableSpills::ClobberPhysRegOnly(unsigned PhysReg) {
while (I != PhysRegsAvailable.end() && I->first == PhysReg) {
int Slot = I->second;
PhysRegsAvailable.erase(I++);
assert(SpillSlotsAvailable[Slot] == PhysReg &&
assert((SpillSlotsAvailable[Slot] >> 1) == PhysReg &&
"Bidirectional map mismatch!");
SpillSlotsAvailable.erase(Slot);
DEBUG(std::cerr << "PhysReg " << MRI->getName(PhysReg)
@ -315,7 +331,7 @@ void AvailableSpills::ClobberPhysReg(unsigned PhysReg) {
void AvailableSpills::ModifyStackSlot(int Slot) {
std::map<int, unsigned>::iterator It = SpillSlotsAvailable.find(Slot);
if (It == SpillSlotsAvailable.end()) return;
unsigned Reg = It->second;
unsigned Reg = It->second >> 1;
SpillSlotsAvailable.erase(It);
// This register may hold the value of multiple stack slots, only remove this
@ -435,7 +451,10 @@ void LocalSpiller::RewriteMBB(MachineBasicBlock &MBB, const VirtRegMap &VRM) {
unsigned PhysReg;
// Check to see if this stack slot is available.
if ((PhysReg = Spills.getSpillSlotPhysReg(StackSlot))) {
if ((PhysReg = Spills.getSpillSlotPhysReg(StackSlot)) &&
// Don't reuse it for a def&use operand if we aren't allowed to change
// the physreg!
(!MO.isDef() || Spills.canClobberPhysReg(StackSlot))) {
// If this stack slot value is already available, reuse it!
DEBUG(std::cerr << "Reusing SS#" << StackSlot << " from physreg "
<< MRI->getName(PhysReg) << " for vreg"
@ -613,7 +632,7 @@ void LocalSpiller::RewriteMBB(MachineBasicBlock &MBB, const VirtRegMap &VRM) {
// If the stack slot value was previously available in some other
// register, change it now. Otherwise, make the register available,
// in PhysReg.
Spills.addAvailable(StackSlot, SrcReg);
Spills.addAvailable(StackSlot, SrcReg, false /*don't clobber*/);
}
}
}
@ -698,7 +717,6 @@ void LocalSpiller::RewriteMBB(MachineBasicBlock &MBB, const VirtRegMap &VRM) {
// in PhysReg.
Spills.ModifyStackSlot(StackSlot);
Spills.ClobberPhysReg(PhysReg);
Spills.addAvailable(StackSlot, PhysReg);
++NumStores;
}