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[RAGreedy] Empty live-ranges always succeed in last chance recoloring. 

Relax the constraint for empty live-ranges while doing last chance
recoloring. Indeed, those live-ranges do not need an actual color to be
fond for the recoloring to work.
Empty live-range may happen as a result of splitting/spilling.

Unfortunately no test case for in-tree targets.

llvm-svn: 284152
This commit is contained in:
Quentin Colombet 2016-10-13 19:27:48 +00:00
parent 4b36957243
commit 52ffa6711b
1 changed files with 12 additions and 1 deletions
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13
llvm/lib/CodeGen/RegAllocGreedy.cpp
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@ -2223,10 +2223,21 @@ bool RAGreedy::tryRecoloringCandidates(PQueue &RecoloringQueue,
DEBUG(dbgs() << "Try to recolor: " << *LI << '\n');
unsigned PhysReg;
PhysReg = selectOrSplitImpl(*LI, NewVRegs, FixedRegisters, Depth + 1);
if (PhysReg == ~0u || !PhysReg)
// When splitting happens, the live-range may actually be empty.
// In that case, this is okay to continue the recoloring even
// if we did not find an alternative color for it. Indeed,
// there will not be anything to color for LI in the end.
if (PhysReg == ~0u || (!PhysReg && !LI->empty()))
return false;
if (!PhysReg) {
assert(LI->empty() && "Only empty live-range do not require a register");
DEBUG(dbgs() << "Recoloring of " << *LI << " succeeded. Empty LI.\n");
continue;
}
DEBUG(dbgs() << "Recoloring of " << *LI
<< " succeeded with: " << PrintReg(PhysReg, TRI) << '\n');
Matrix->assign(*LI, PhysReg);
FixedRegisters.insert(LI->reg);
}