Limit the search space in RAGreedy::tryEvict().
When tryEvict() is looking for a cheaper register in the allocation
order, skip the tail of too expensive registers when possible.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@172281 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/RegAllocGreedy.cpp b/lib/CodeGen/RegAllocGreedy.cpp
index 1884452..6344a73 100644
--- a/lib/CodeGen/RegAllocGreedy.cpp
+++ b/lib/CodeGen/RegAllocGreedy.cpp
@@ -632,16 +632,33 @@
// Keep track of the cheapest interference seen so far.
EvictionCost BestCost(~0u);
unsigned BestPhys = 0;
+ unsigned OrderLimit = Order.getOrder().size();
// When we are just looking for a reduced cost per use, don't break any
// hints, and only evict smaller spill weights.
if (CostPerUseLimit < ~0u) {
BestCost.BrokenHints = 0;
BestCost.MaxWeight = VirtReg.weight;
+
+ // Check of any registers in RC are below CostPerUseLimit.
+ const TargetRegisterClass *RC = MRI->getRegClass(VirtReg.reg);
+ unsigned MinCost = RegClassInfo.getMinCost(RC);
+ if (MinCost >= CostPerUseLimit) {
+ DEBUG(dbgs() << RC->getName() << " minimum cost = " << MinCost
+ << ", no cheaper registers to be found.\n");
+ return 0;
+ }
+
+ // It is normal for register classes to have a long tail of registers with
+ // the same cost. We don't need to look at them if they're too expensive.
+ if (TRI->getCostPerUse(Order.getOrder().back()) >= CostPerUseLimit) {
+ OrderLimit = RegClassInfo.getLastCostChange(RC);
+ DEBUG(dbgs() << "Only trying the first " << OrderLimit << " regs.\n");
+ }
}
Order.rewind();
- while (unsigned PhysReg = Order.next()) {
+ while (unsigned PhysReg = Order.nextWithDups(OrderLimit)) {
if (TRI->getCostPerUse(PhysReg) >= CostPerUseLimit)
continue;
// The first use of a callee-saved register in a function has cost 1.