[SystemZ] Call erase() on the right MBB in SystemZTargetLowering::emitSelect()

Since MBB was split *before* MI, the MI(s) will reside in JoinMBB (MBB) at
the point of erasing them, so calling StartMBB->erase() is actually wrong,
although it is "working" by all appearances.

Review: Ulrich Weigand
llvm-svn: 371995

llvm/lib/Target/SystemZ/SystemZISelLowering.cpp

@@ -6678,7 +6678,7 @@ SystemZTargetLowering::emitSelect(MachineInstr &MI,
       std::next(MachineBasicBlock::iterator(LastMI)), MBB->end());
   createPHIsForSelects(MIItBegin, MIItEnd, StartMBB, FalseMBB, MBB);
 
-  StartMBB->erase(MIItBegin, MIItEnd);
+  MBB->erase(MIItBegin, MIItEnd);
   return JoinMBB;
 }