To find the exiting VN of a LiveInterval from a block, use the previous slot

rather than the previous index. If a block has a single instruction, the
previous index may be in a different basic block.

I have no clue how this used to work on all of test-suite, because now this
failure is seen quite often when trying to compile code with -strong-phi-elim.
This fixes PR10252.

llvm-svn: 141812

1 files changed, 1 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/StrongPHIElimination.cpp b/llvm/lib/CodeGen/StrongPHIElimination.cpp
index 0fabd8e6eef..76e6c9966a7 100644
--- a/llvm/lib/CodeGen/StrongPHIElimination.cpp
+++ b/llvm/lib/CodeGen/StrongPHIElimination.cpp
@@ -674,7 +674,7 @@ void StrongPHIElimination::InsertCopiesForPHI(MachineInstr *PHI,
     if (PHIColor && SrcColor == PHIColor) {
       LiveInterval &SrcInterval = LI->getInterval(SrcReg);
       SlotIndex PredIndex = LI->getMBBEndIdx(PredBB);
-      VNInfo *SrcVNI = SrcInterval.getVNInfoAt(PredIndex.getPrevIndex());
+      VNInfo *SrcVNI = SrcInterval.getVNInfoAt(PredIndex.getPrevSlot());
       assert(SrcVNI);
       SrcVNI->setHasPHIKill(true);
       continue;