Transpose the calculation of spill weights such that we are calculating one

register at a time. This turns out to be slightly faster than iterating over
instructions, but more importantly, it allows us to compute spill weights for
new registers created after the spill weight pass has run.

Also compute the allocation hint at the same time as the spill weight. This
allows us to use the spill weight as a cost metric for copies, and choose the
most profitable hint if there is more than one possibility.

The new hints provide a very small (< 0.1%) but universal code size improvement.

llvm-svn: 110631

1 files changed, 0 insertions, 12 deletions

diff --git a/llvm/lib/CodeGen/LiveInterval.cpp b/llvm/lib/CodeGen/LiveInterval.cpp
index f4c06b203cb..6820a615e8d 100644
--- a/llvm/lib/CodeGen/LiveInterval.cpp
+++ b/llvm/lib/CodeGen/LiveInterval.cpp
@@ -515,18 +515,6 @@ void LiveInterval::join(LiveInterval &Other,
   }
 
   ComputeJoinedWeight(Other);
-
-  // Update regalloc hint if currently there isn't one.
-  if (TargetRegisterInfo::isVirtualRegister(reg) &&
-      TargetRegisterInfo::isVirtualRegister(Other.reg)) {
-    std::pair<unsigned, unsigned> Hint = MRI->getRegAllocationHint(reg);
-    if (Hint.first == 0 && Hint.second == 0) {
-      std::pair<unsigned, unsigned> OtherHint =
-        MRI->getRegAllocationHint(Other.reg);
-      if (OtherHint.first || OtherHint.second)
-        MRI->setRegAllocationHint(reg, OtherHint.first, OtherHint.second);
-    }
-  }
 }
 
 /// MergeRangesInAsValue - Merge all of the intervals in RHS into this live