From 8c5f0c3115d3066bf35b5e0c2456356d8dbb6c07 Mon Sep 17 00:00:00 2001
From: Jakob Stoklund Olesen <stoklund@2pi.dk>
Date: Wed, 8 Dec 2010 23:51:35 +0000
Subject: [PATCH] Properly deal with empty intervals when checking for
 interference.

llvm-svn: 121319
---
 llvm/lib/CodeGen/LiveIntervalUnion.cpp | 3 ++-
 llvm/lib/CodeGen/RegAllocGreedy.cpp    | 1 +
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/llvm/lib/CodeGen/LiveIntervalUnion.cpp b/llvm/lib/CodeGen/LiveIntervalUnion.cpp
index bedf22b5bad8..4b9a2d302c09 100644
--- a/llvm/lib/CodeGen/LiveIntervalUnion.cpp
+++ b/llvm/lib/CodeGen/LiveIntervalUnion.cpp
@@ -111,9 +111,10 @@ void LiveIntervalUnion::verify(LiveVirtRegBitSet& VisitedVRegs) {
 // Assumes that segments are sorted by start position in both
 // LiveInterval and LiveSegments.
 void LiveIntervalUnion::Query::findIntersection(InterferenceResult &IR) const {
-
   // Search until reaching the end of the LiveUnion segments.
   LiveInterval::iterator VirtRegEnd = VirtReg->end();
+  if (IR.VirtRegI == VirtRegEnd)
+    return;
   while (IR.LiveUnionI.valid()) {
     // Slowly advance the live virtual reg iterator until we surpass the next
     // segment in LiveUnion.
diff --git a/llvm/lib/CodeGen/RegAllocGreedy.cpp b/llvm/lib/CodeGen/RegAllocGreedy.cpp
index c88d474315e7..f69979bf2aaa 100644
--- a/llvm/lib/CodeGen/RegAllocGreedy.cpp
+++ b/llvm/lib/CodeGen/RegAllocGreedy.cpp
@@ -173,6 +173,7 @@ unsigned RAGreedy::selectOrSplit(LiveInterval &VirtReg,
       // Found an available register.
       return PhysReg;
     }
+    assert(!VirtReg.empty() && "Empty VirtReg has interference");
     LiveInterval *interferingVirtReg =
       Queries[interfReg].firstInterference().liveUnionPos().value();