Skip DBG instr in OptimizePHIs when looking for dead PHI cycles

Summary:
Changed use_instructions() to use_nodbg_instructions() when
building an instruction set.

We don't want the presence of debug info to affect the code
we generate.

Reviewers: dblaikie, Eugene.Zelenko, chandlerc, aprantl

Reviewed By: aprantl

Subscribers: aprantl, llvm-commits

Differential Revision: https://reviews.llvm.org/D40882

llvm-svn: 320010
diff --git a/llvm/lib/CodeGen/OptimizePHIs.cpp b/llvm/lib/CodeGen/OptimizePHIs.cpp
index 82ec1cb..5421b44 100644
--- a/llvm/lib/CodeGen/OptimizePHIs.cpp
+++ b/llvm/lib/CodeGen/OptimizePHIs.cpp
@@ -154,7 +154,7 @@
   if (PHIsInCycle.size() == 16)
     return false;
 
-  for (MachineInstr &UseMI : MRI->use_instructions(DstReg)) {
+  for (MachineInstr &UseMI : MRI->use_nodbg_instructions(DstReg)) {
     if (!UseMI.isPHI() || !IsDeadPHICycle(&UseMI, PHIsInCycle))
       return false;
   }