Avoid dereferencing end() in collectInterferingVRegs() when there is no

interference.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122108 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/LiveInterval.h

@@ -250,6 +250,7 @@ namespace llvm {
     /// position is in a hole, this method returns an iterator pointing to the
     /// LiveRange immediately after the hole.
     iterator advanceTo(iterator I, SlotIndex Pos) {
+      assert(I != end());
       if (Pos >= endIndex())
         return end();
       while (I->end <= Pos) ++I;

lib/CodeGen/LiveIntervalUnion.cpp

@@ -238,7 +238,7 @@ collectInterferingVRegs(unsigned MaxInterferingRegs) {
   InterferenceResult IR = firstInterference();
   LiveInterval::iterator VirtRegEnd = VirtReg->end();
   LiveInterval *RecentInterferingVReg = NULL;
-  while (IR.LiveUnionI.valid()) {
+  if (IR.VirtRegI != VirtRegEnd) while (IR.LiveUnionI.valid()) {
     // Advance the union's iterator to reach an unseen interfering vreg.
     do {
       if (IR.LiveUnionI.value() == RecentInterferingVReg)