Changes in directory llvm/lib/CodeGen:
VirtRegMap.cpp updated: 1.52 -> 1.53
---
Log message:
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.
---
Diffs of the changes: (+27 -9)
VirtRegMap.cpp | 36 +++++++++++++++++++++++++++---------
1 files changed, 27 insertions(+), 9 deletions(-)
Index: llvm/lib/CodeGen/VirtRegMap.cpp
diff -u llvm/lib/CodeGen/VirtRegMap.cpp:1.52
llvm/lib/CodeGen/VirtRegMap.cpp:1.53
--- llvm/lib/CodeGen/VirtRegMap.cpp:1.52 Fri Feb 3 17:13:58 2006
+++ llvm/lib/CodeGen/VirtRegMap.cpp Fri Feb 3 17:28:46 2006
@@ -233,6 +233,14 @@
/// 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 @@
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 @@
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::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 @@
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 @@
// 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 @@
// in PhysReg.
Spills.ModifyStackSlot(StackSlot);
Spills.ClobberPhysReg(PhysReg);
-
Spills.addAvailable(StackSlot, PhysReg);
++NumStores;
}
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