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Tweak the register allocator priority queue some more. 

New live ranges are assigned in long -> short order, but live ranges that have
been evicted at least once are deferred and assigned in short -> long order.

Also disable splitting and spilling for live ranges seen for the first time.

The intention is to create a realistic interference pattern from the heavy live
ranges before starting splitting and spilling around it.

llvm-svn: 126451
This commit is contained in:
Jakob Stoklund Olesen 2011-02-24 23:21:36 +00:00
parent 1db7b187cb
commit e68a27eecd
1 changed files with 22 additions and 10 deletions
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32
llvm/lib/CodeGen/RegAllocGreedy.cpp
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@ -194,22 +194,26 @@ void RAGreedy::releaseMemory() {
void RAGreedy::enqueue(LiveInterval *LI) {
// Prioritize live ranges by size, assigning larger ranges first.
// The queue holds (size, reg) pairs.
unsigned Size = LI->getSize();
unsigned Reg = LI->reg;
const unsigned Size = LI->getSize();
const unsigned Reg = LI->reg;
assert(TargetRegisterInfo::isVirtualRegister(Reg) &&
"Can only enqueue virtual registers");
const unsigned Hint = VRM->getRegAllocPref(Reg);
unsigned Prio;
// Boost ranges that have a physical register hint.
unsigned Hint = VRM->getRegAllocPref(Reg);
if (TargetRegisterInfo::isPhysicalRegister(Hint))
Size |= (1u << 30);
// Boost ranges that we see for the first time.
Generation.grow(Reg);
if (++Generation[Reg] == 1)
Size |= (1u << 31);
// 1st generation ranges are handled first, long -> short.
Prio = (1u << 31) + Size;
else
// Repeat offenders are handled second, short -> long
Prio = (1u << 30) - Size;
Queue.push(std::make_pair(Size, Reg));
// Boost ranges that have a physical register hint.
if (TargetRegisterInfo::isPhysicalRegister(Hint))
Prio |= (1u << 30);
Queue.push(std::make_pair(Prio, Reg));
}
LiveInterval *RAGreedy::dequeue() {
@ -1311,6 +1315,14 @@ unsigned RAGreedy::selectOrSplit(LiveInterval &VirtReg,
assert(NewVRegs.empty() && "Cannot append to existing NewVRegs");
// The first time we see a live range, don't try to split or spill.
// Wait until the second time, when all smaller ranges have been allocated.
// This gives a better picture of the interference to split around.
if (Generation[VirtReg.reg] == 1) {
NewVRegs.push_back(&VirtReg);
return 0;
}
// Try splitting VirtReg or interferences.
unsigned PhysReg = trySplit(VirtReg, Order, NewVRegs);
if (PhysReg || !NewVRegs.empty())