Be more aggressive about following hints.

RAGreedy::tryAssign will now evict interference from the preferred
register even when another register is free.

To support this, add the EvictionCost struct that counts how many hints
are broken by an eviction. We don't want to break one hint just to
satisfy another.

Rename canEvict to shouldEvict, and add the first bit of eviction policy
that doesn't depend on spill weights: Always make room in the preferred
register as long as the evictees can be split and aren't already
assigned to their preferred register.

Also make the CSR avoidance more accurate. When looking for a cheaper
register it is OK to use a new volatile register. Only CSR aliases that
have never been used before should be avoided.

llvm-svn: 134735

1 files changed, 1 insertions, 5 deletions

diff --git a/llvm/lib/CodeGen/LiveIntervalUnion.cpp b/llvm/lib/CodeGen/LiveIntervalUnion.cpp
index b67f96667bf..70003e7cc86 100644
--- a/llvm/lib/CodeGen/LiveIntervalUnion.cpp
+++ b/llvm/lib/CodeGen/LiveIntervalUnion.cpp
@@ -244,7 +244,7 @@ bool LiveIntervalUnion::Query::isSeenInterference(LiveInterval *VirtReg) const {
 //
 // For comments on how to speed it up, see Query::findIntersection().
 unsigned LiveIntervalUnion::Query::
-collectInterferingVRegs(unsigned MaxInterferingRegs, float MaxWeight) {
+collectInterferingVRegs(unsigned MaxInterferingRegs) {
   InterferenceResult IR = firstInterference();
   LiveInterval::iterator VirtRegEnd = VirtReg->end();
   LiveInterval *RecentInterferingVReg = NULL;
@@ -287,10 +287,6 @@ collectInterferingVRegs(unsigned MaxInterferingRegs, float MaxWeight) {
       RecentInterferingVReg = IR.LiveUnionI.value();
       ++IR.LiveUnionI;
 
-      // Stop collecting when the max weight is exceeded.
-      if (RecentInterferingVReg->weight >= MaxWeight)
-        return InterferingVRegs.size();
-
       continue;
     }
     // VirtRegI may have advanced far beyond LiveUnionI,