Make the peephole optimizer clear kill flags on a vreg if it's about to add new

uses of the vreg, since the old kills may no longer be valid.  This was causing
-verify-machineinstrs to complain about uses after kills, and could potentially
have been causing subtle register allocation issues, but I haven't come across a
test case yet.

llvm-svn: 151425

llvm/lib/CodeGen/PeepholeOptimizer.cpp

@@ -237,6 +237,10 @@ OptimizeExtInstr(MachineInstr *MI, MachineBasicBlock *MBB,
       if (PHIBBs.count(UseMBB))
         continue;
 
+      // About to add uses of DstReg, clear DstReg's kill flags.
+      if (!Changed)
+        MRI->clearKillFlags(DstReg);
+
       unsigned NewVR = MRI->createVirtualRegister(RC);
       BuildMI(*UseMBB, UseMI, UseMI->getDebugLoc(),
               TII->get(TargetOpcode::COPY), NewVR)