Store (priority,regnum) pairs in the priority queue instead of providing an

abstract priority queue interface in subclasses that want to override the
priority calculations.

Subclasses must provide a getPriority() implementation instead.

This approach requires less code as long as priorities are expressable as simple
floats, and it avoids the dangers of defining potentially expensive priority
comparison functions.

It also should speed up priority_queue operations since they no longer have to
chase pointers when comparing registers. This is not measurable, though.

Preferably, we shouldn't use floats to guide code generation. The use of floats
here is derived from the use of floats for spill weights. Spill weights have a
dynamic range that doesn't lend itself easily to a fixpoint implementation.

When someone invents a stable spill weight representation, it can be reused for
allocation priorities.

llvm-svn: 121294

1 files changed, 2 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/RegAllocGreedy.cpp b/llvm/lib/CodeGen/RegAllocGreedy.cpp
index 96e5531840b..5f2be811aa6 100644
--- a/llvm/lib/CodeGen/RegAllocGreedy.cpp
+++ b/llvm/lib/CodeGen/RegAllocGreedy.cpp
@@ -70,6 +70,8 @@ public:
 
   virtual Spiller &spiller() { return *SpillerInstance; }
 
+  virtual float getPriority(LiveInterval *LI) { return LI->weight; }
+
   virtual unsigned selectOrSplit(LiveInterval &VirtReg,
                                  SmallVectorImpl<LiveInterval*> &SplitVRegs);