bool AllUsesDominatedByBlock(unsigned Reg, MachineBasicBlock *MBB,
MachineBasicBlock *DefMBB,
bool &BreakPHIEdge, bool &LocalUse) const;
+ MachineBasicBlock *FindSuccToSinkTo(MachineInstr *MI, bool &BreakPHIEdge);
+
bool PerformTrivialForwardCoalescing(MachineInstr *MI,
MachineBasicBlock *MBB);
};
assert(TargetRegisterInfo::isVirtualRegister(Reg) &&
"Only makes sense for vregs");
+ // Ignore debug uses because debug info doesn't affect the code.
if (MRI->use_nodbg_empty(Reg))
return true;
- // Ignoring debug uses is necessary so debug info doesn't affect the code.
- // This may leave a referencing dbg_value in the original block, before
- // the definition of the vreg. Dwarf generator handles this although the
- // user might not get the right info at runtime.
-
// BreakPHIEdge is true if all the uses are in the successor MBB being sunken
// into and they are all PHI nodes. In this case, machine-sink must break
// the critical edge first. e.g.
if (!CEBCandidates.insert(std::make_pair(From, To)))
return true;
- if (!MI->isCopy() && !MI->getDesc().isAsCheapAsAMove())
+ if (!MI->isCopy() && !MI->isAsCheapAsAMove())
return true;
// MI is cheap, we probably don't want to break the critical edge for it.
return MI->isInsertSubreg() || MI->isSubregToReg() || MI->isRegSequence();
}
-/// SinkInstruction - Determine whether it is safe to sink the specified machine
-/// instruction out of its current block into a successor.
-bool MachineSinking::SinkInstruction(MachineInstr *MI, bool &SawStore) {
- // Don't sink insert_subreg, subreg_to_reg, reg_sequence. These are meant to
- // be close to the source to make it easier to coalesce.
- if (AvoidsSinking(MI, MRI))
- return false;
-
- // Check if it's safe to move the instruction.
- if (!MI->isSafeToMove(TII, AA, SawStore))
- return false;
+/// collectDebgValues - Scan instructions following MI and collect any
+/// matching DBG_VALUEs.
+static void collectDebugValues(MachineInstr *MI,
+ SmallVector<MachineInstr *, 2> & DbgValues) {
+ DbgValues.clear();
+ if (!MI->getOperand(0).isReg())
+ return;
+
+ MachineBasicBlock::iterator DI = MI; ++DI;
+ for (MachineBasicBlock::iterator DE = MI->getParent()->end();
+ DI != DE; ++DI) {
+ if (!DI->isDebugValue())
+ return;
+ if (DI->getOperand(0).isReg() &&
+ DI->getOperand(0).getReg() == MI->getOperand(0).getReg())
+ DbgValues.push_back(DI);
+ }
+}
- // FIXME: This should include support for sinking instructions within the
- // block they are currently in to shorten the live ranges. We often get
- // instructions sunk into the top of a large block, but it would be better to
- // also sink them down before their first use in the block. This xform has to
- // be careful not to *increase* register pressure though, e.g. sinking
- // "x = y + z" down if it kills y and z would increase the live ranges of y
- // and z and only shrink the live range of x.
+/// FindSuccToSinkTo - Find a successor to sink this instruction to.
+MachineBasicBlock *MachineSinking::FindSuccToSinkTo(MachineInstr *MI,
+ bool &BreakPHIEdge) {
// Loop over all the operands of the specified instruction. If there is
// anything we can't handle, bail out.
// decide.
MachineBasicBlock *SuccToSinkTo = 0;
- bool BreakPHIEdge = false;
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
const MachineOperand &MO = MI->getOperand(i);
if (!MO.isReg()) continue; // Ignore non-register operands.
// and we can freely move its uses. Alternatively, if it's allocatable,
// it could get allocated to something with a def during allocation.
if (!MRI->def_empty(Reg))
- return false;
+ return NULL;
if (AllocatableSet.test(Reg))
- return false;
+ return NULL;
// Check for a def among the register's aliases too.
for (const unsigned *Alias = TRI->getAliasSet(Reg); *Alias; ++Alias) {
unsigned AliasReg = *Alias;
if (!MRI->def_empty(AliasReg))
- return false;
+ return NULL;
if (AllocatableSet.test(AliasReg))
- return false;
+ return NULL;
}
} else if (!MO.isDead()) {
// A def that isn't dead. We can't move it.
- return false;
+ return NULL;
}
} else {
// Virtual register uses are always safe to sink.
// If it's not safe to move defs of the register class, then abort.
if (!TII->isSafeToMoveRegClassDefs(MRI->getRegClass(Reg)))
- return false;
+ return NULL;
// FIXME: This picks a successor to sink into based on having one
// successor that dominates all the uses. However, there are cases where
bool LocalUse = false;
if (!AllUsesDominatedByBlock(Reg, SuccToSinkTo, ParentBlock,
BreakPHIEdge, LocalUse))
- return false;
+ return NULL;
continue;
}
// we should sink to.
for (MachineBasicBlock::succ_iterator SI = ParentBlock->succ_begin(),
E = ParentBlock->succ_end(); SI != E; ++SI) {
+ MachineBasicBlock *SuccBlock = *SI;
bool LocalUse = false;
- if (AllUsesDominatedByBlock(Reg, *SI, ParentBlock,
+ if (AllUsesDominatedByBlock(Reg, SuccBlock, ParentBlock,
BreakPHIEdge, LocalUse)) {
- SuccToSinkTo = *SI;
+ SuccToSinkTo = SuccBlock;
break;
}
if (LocalUse)
// Def is used locally, it's never safe to move this def.
- return false;
+ return NULL;
}
// If we couldn't find a block to sink to, ignore this instruction.
if (SuccToSinkTo == 0)
- return false;
+ return NULL;
}
}
- // If there are no outputs, it must have side-effects.
- if (SuccToSinkTo == 0)
- return false;
+ // It is not possible to sink an instruction into its own block. This can
+ // happen with loops.
+ if (ParentBlock == SuccToSinkTo)
+ return NULL;
// It's not safe to sink instructions to EH landing pad. Control flow into
// landing pad is implicitly defined.
- if (SuccToSinkTo->isLandingPad())
+ if (SuccToSinkTo && SuccToSinkTo->isLandingPad())
+ return NULL;
+
+ return SuccToSinkTo;
+}
+
+/// SinkInstruction - Determine whether it is safe to sink the specified machine
+/// instruction out of its current block into a successor.
+bool MachineSinking::SinkInstruction(MachineInstr *MI, bool &SawStore) {
+ // Don't sink insert_subreg, subreg_to_reg, reg_sequence. These are meant to
+ // be close to the source to make it easier to coalesce.
+ if (AvoidsSinking(MI, MRI))
return false;
- // It is not possible to sink an instruction into its own block. This can
- // happen with loops.
- if (MI->getParent() == SuccToSinkTo)
+ // Check if it's safe to move the instruction.
+ if (!MI->isSafeToMove(TII, AA, SawStore))
+ return false;
+
+ // FIXME: This should include support for sinking instructions within the
+ // block they are currently in to shorten the live ranges. We often get
+ // instructions sunk into the top of a large block, but it would be better to
+ // also sink them down before their first use in the block. This xform has to
+ // be careful not to *increase* register pressure though, e.g. sinking
+ // "x = y + z" down if it kills y and z would increase the live ranges of y
+ // and z and only shrink the live range of x.
+
+ bool BreakPHIEdge = false;
+ MachineBasicBlock *SuccToSinkTo = FindSuccToSinkTo(MI, BreakPHIEdge);
+
+ // If there are no outputs, it must have side-effects.
+ if (SuccToSinkTo == 0)
return false;
+
// If the instruction to move defines a dead physical register which is live
// when leaving the basic block, don't move it because it could turn into a
// "zombie" define of that preg. E.g., EFLAGS. (<rdar://problem/8030636>)
DEBUG(dbgs() << "Sink instr " << *MI << "\tinto block " << *SuccToSinkTo);
+ MachineBasicBlock *ParentBlock = MI->getParent();
+
// If the block has multiple predecessors, this would introduce computation on
// a path that it doesn't already exist. We could split the critical edge,
// but for now we just punt.
while (InsertPos != SuccToSinkTo->end() && InsertPos->isPHI())
++InsertPos;
+ // collect matching debug values.
+ SmallVector<MachineInstr *, 2> DbgValuesToSink;
+ collectDebugValues(MI, DbgValuesToSink);
+
// Move the instruction.
SuccToSinkTo->splice(InsertPos, ParentBlock, MI,
++MachineBasicBlock::iterator(MI));
+ // Move debug values.
+ for (SmallVector<MachineInstr *, 2>::iterator DBI = DbgValuesToSink.begin(),
+ DBE = DbgValuesToSink.end(); DBI != DBE; ++DBI) {
+ MachineInstr *DbgMI = *DBI;
+ SuccToSinkTo->splice(InsertPos, ParentBlock, DbgMI,
+ ++MachineBasicBlock::iterator(DbgMI));
+ }
+
// Conservatively, clear any kill flags, since it's possible that they are no
// longer correct.
MI->clearKillInfo();
projects / oota-llvm.git / blobdiff