Teach LiveInterval::isZeroLength about null SlotIndexes.

When instructions are deleted, they leave tombstone SlotIndex entries.
The isZeroLength method should ignore these null indexes.

This causes RABasic to sometimes spill a callee-saved register in the
abi-isel.ll test, so don't run that test with -regalloc=basic.  Prioritizing
register allocation according to spill weight can cause more registers to be
used.

llvm-svn: 131436

1 files changed, 3 insertions, 2 deletions

diff --git a/llvm/include/llvm/CodeGen/LiveInterval.h b/llvm/include/llvm/CodeGen/LiveInterval.h
index c5285cec1e2..5fd4d3df266 100644
--- a/llvm/include/llvm/CodeGen/LiveInterval.h
+++ b/llvm/include/llvm/CodeGen/LiveInterval.h
@@ -492,9 +492,10 @@ namespace llvm {
 
     /// Returns true if the live interval is zero length, i.e. no live ranges
     /// span instructions. It doesn't pay to spill such an interval.
-    bool isZeroLength() const {
+    bool isZeroLength(SlotIndexes *Indexes) const {
       for (const_iterator i = begin(), e = end(); i != e; ++i)
-        if (i->end.getPrevIndex() > i->start)
+        if (Indexes->getNextNonNullIndex(i->start).getBaseIndex() <
+            i->end.getBaseIndex())
           return false;
       return true;
     }