#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"
RegsAvailable.set(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;
- CurrDist = 0;
- DistanceMap.clear();
// All registers started out unused.
RegsAvailable.set();
}
MachineInstr *MI = MBBI;
- DistanceMap.insert(std::make_pair(MI, CurrDist++));
if (MI == ScavengeRestore) {
ScavengedReg = 0;
return (Reg == -1) ? 0 : Reg;
}
+/// DistanceMap - Keep track the distance of an MI from the current position.
+typedef DenseMap<MachineInstr*, unsigned> DistanceMap;
+
+/// Build a distance map for instructions from I to E.
+static void buildDistanceMap(DistanceMap &DM,
+ MachineBasicBlock::iterator I,
+ MachineBasicBlock::iterator E) {
+ DM.clear();
+ for (unsigned d = 0; I != E; ++I, ++d)
+ DM.insert(DistanceMap::value_type(I, d));
+}
+
/// findFirstUse - Calculate the distance to the first use of the
-/// specified register.
-MachineInstr*
-RegScavenger::findFirstUse(MachineBasicBlock *MBB,
- MachineBasicBlock::iterator I, unsigned Reg,
- unsigned &Dist) {
+/// specified register in the range covered by DM.
+static MachineInstr *findFirstUse(const MachineBasicBlock *MBB,
+ const DistanceMap &DM,
+ unsigned Reg,
+ unsigned &Dist) {
+ const MachineRegisterInfo *MRI = &MBB->getParent()->getRegInfo();
MachineInstr *UseMI = 0;
Dist = ~0U;
for (MachineRegisterInfo::reg_iterator RI = MRI->reg_begin(Reg),
MachineInstr *UDMI = &*RI;
if (UDMI->getParent() != MBB)
continue;
- DenseMap<MachineInstr*, unsigned>::iterator DI = DistanceMap.find(UDMI);
- if (DI == DistanceMap.end()) {
- // If it's not in map, it's below current MI, let's initialize the
- // map.
- I = next(I);
- unsigned Dist = CurrDist + 1;
- while (I != MBB->end()) {
- DistanceMap.insert(std::make_pair(I, Dist++));
- I = next(I);
- }
- }
- DI = DistanceMap.find(UDMI);
- if (DI->second > CurrDist && DI->second < Dist) {
+ DistanceMap::const_iterator DI = DM.find(UDMI);
+ if (DI == DM.end())
+ continue;
+ if (DI->second < Dist) {
Dist = DI->second;
UseMI = UDMI;
}
Candidates.reset(MO.getReg());
}
+ // Prepare to call findFirstUse() a number of times.
+ DistanceMap DM;
+ buildDistanceMap(DM, I, MBB->end());
+
// Find the register whose use is furthest away.
unsigned SReg = 0;
unsigned MaxDist = 0;
int Reg = Candidates.find_first();
while (Reg != -1) {
unsigned Dist;
- MachineInstr *UseMI = findFirstUse(MBB, I, Reg, Dist);
+ MachineInstr *UseMI = findFirstUse(MBB, DM, Reg, Dist);
for (const unsigned *AS = TRI->getAliasSet(Reg); *AS; ++AS) {
unsigned AsDist;
- MachineInstr *AsUseMI = findFirstUse(MBB, I, *AS, AsDist);
+ MachineInstr *AsUseMI = findFirstUse(MBB, DM, *AS, AsDist);
if (AsDist < Dist) {
Dist = AsDist;
UseMI = AsUseMI;
}
}
+
+ // If we found an unused register that is defined by a later instruction,
+ // 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(Reg) && UseMI != NULL)
+ return Reg;
+
if (Dist >= MaxDist) {
MaxDist = Dist;
MaxUseMI = UseMI;