Add a bit IsUndef to MachineOperand. This indicates the def / use register operand is defined by an implicit_def. That means it can def / use any register and passes (e.g. register scavenger) can feel free to ignore them.
The register allocator, when it allocates a register to a virtual register defined by an implicit_def, can allocate any physical register without worrying about overlapping live ranges. It should mark all of operands of the said virtual register so later passes will do the right thing.
This is not the best solution. But it should be a lot less fragile to having the scavenger try to track what is defined by implicit_def.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@74518 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/VirtRegRewriter.cpp b/lib/CodeGen/VirtRegRewriter.cpp
index bd6584a..bbf1e24 100644
--- a/lib/CodeGen/VirtRegRewriter.cpp
+++ b/lib/CodeGen/VirtRegRewriter.cpp
@@ -356,7 +356,7 @@
SmallVector<unsigned, 2> *KillRegs = NULL) {
for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI.getOperand(i);
- if (!MO.isReg() || !MO.isUse() || !MO.isKill())
+ if (!MO.isReg() || !MO.isUse() || !MO.isKill() || MO.isUndef())
continue;
unsigned Reg = MO.getReg();
if (TargetRegisterInfo::isVirtualRegister(Reg))
@@ -390,12 +390,12 @@
MachineOperand *DefOp = NULL;
for (unsigned i = 0, e = DefMI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = DefMI->getOperand(i);
- if (MO.isReg() && MO.isDef()) {
- if (MO.getReg() == Reg)
- DefOp = &MO;
- else if (!MO.isDead())
- HasLiveDef = true;
- }
+ if (!MO.isReg() || !MO.isUse() || !MO.isKill() || MO.isUndef())
+ continue;
+ if (MO.getReg() == Reg)
+ DefOp = &MO;
+ else if (!MO.isDead())
+ HasLiveDef = true;
}
if (!DefOp)
return false;
@@ -430,7 +430,7 @@
std::vector<MachineOperand*> &KillOps) {
for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI.getOperand(i);
- if (!MO.isReg() || !MO.isUse())
+ if (!MO.isReg() || !MO.isUse() || MO.isUndef())
continue;
unsigned Reg = MO.getReg();
if (Reg == 0)
@@ -1289,8 +1289,7 @@
if (InvalidateRegDef(PrevMII, *MII, KillRegs[j], HasOtherDef)) {
MachineInstr *DeadDef = PrevMII;
if (ReMatDefs.count(DeadDef) && !HasOtherDef) {
- // FIXME: This assumes a remat def does not have side
- // effects.
+ // FIXME: This assumes a remat def does not have side effects.
VRM.RemoveMachineInstrFromMaps(DeadDef);
MBB.erase(DeadDef);
++NumDRM;
@@ -1569,6 +1568,8 @@
if (MO.isImplicit())
// If the virtual register is implicitly defined, emit a implicit_def
// before so scavenger knows it's "defined".
+ // FIXME: This is a horrible hack done the by register allocator to
+ // remat a definition with virtual register operand.
VirtUseOps.insert(VirtUseOps.begin(), i);
else
VirtUseOps.push_back(i);
@@ -1595,6 +1596,7 @@
MI.getOperand(i).setReg(RReg);
MI.getOperand(i).setSubReg(0);
if (VRM.isImplicitlyDefined(VirtReg))
+ // FIXME: Is this needed?
BuildMI(MBB, &MI, MI.getDebugLoc(),
TII->get(TargetInstrInfo::IMPLICIT_DEF), RReg);
continue;
@@ -1604,22 +1606,16 @@
if (!MO.isUse())
continue; // Handle defs in the loop below (handle use&def here though)
- bool AvoidReload = false;
- if (LIs->hasInterval(VirtReg)) {
- LiveInterval &LI = LIs->getInterval(VirtReg);
- if (!LI.liveAt(LIs->getUseIndex(LI.beginNumber())))
- // Must be defined by an implicit def. It should not be spilled. Note,
- // this is for correctness reason. e.g.
- // 8 %reg1024<def> = IMPLICIT_DEF
- // 12 %reg1024<def> = INSERT_SUBREG %reg1024<kill>, %reg1025, 2
- // The live range [12, 14) are not part of the r1024 live interval since
- // it's defined by an implicit def. It will not conflicts with live
- // interval of r1025. Now suppose both registers are spilled, you can
- // easily see a situation where both registers are reloaded before
- // the INSERT_SUBREG and both target registers that would overlap.
- AvoidReload = true;
- }
-
+ bool AvoidReload = MO.isUndef();
+ // Check if it is defined by an implicit def. It should not be spilled.
+ // Note, this is for correctness reason. e.g.
+ // 8 %reg1024<def> = IMPLICIT_DEF
+ // 12 %reg1024<def> = INSERT_SUBREG %reg1024<kill>, %reg1025, 2
+ // The live range [12, 14) are not part of the r1024 live interval since
+ // it's defined by an implicit def. It will not conflicts with live
+ // interval of r1025. Now suppose both registers are spilled, you can
+ // easily see a situation where both registers are reloaded before
+ // the INSERT_SUBREG and both target registers that would overlap.
bool DoReMat = VRM.isReMaterialized(VirtReg);
int SSorRMId = DoReMat
? VRM.getReMatId(VirtReg) : VRM.getStackSlot(VirtReg);