MachineVerifier: Don't crash in LiveIntervals checks on generic vregs

[arsenm]

Summary

If llvm-reduce is going to unconditionally verify functions with
LiveIntervals, it needs to be tolerant of generic vregs.

[arsenm]

a68d72a9950f01b7ed7e8be98eabab5f69d254be

llvm/include/llvm/CodeGen/MachineRegisterInfo.h

public:
 
   /// Returns true if liveness for register class @p RC should be tracked at
   /// the subregister level.
   bool shouldTrackSubRegLiveness(const TargetRegisterClass &RC) const {
     return subRegLivenessEnabled() && RC.HasDisjunctSubRegs;
   }
   bool shouldTrackSubRegLiveness(Register VReg) const {
     assert(VReg.isVirtual() && "Must pass a VReg");
-    return shouldTrackSubRegLiveness(*getRegClass(VReg));
+    const TargetRegisterClass *RC = getRegClassOrNull(VReg);
+    return LLVM_LIKELY(RC) ? shouldTrackSubRegLiveness(*RC) : false;
   }
   bool subRegLivenessEnabled() const {
     return TracksSubRegLiveness;
   }
 
   //===--------------------------------------------------------------------===//
   // Register Info
   //===--------------------------------------------------------------------===//

llvm/lib/CodeGen/MachineVerifier.cpp

for (LiveRange::const_iterator I = LR.begin(), E = LR.end(); I != E; ++I)
     verifyLiveRangeSegment(LR, I, Reg, LaneMask);
 }
 
 void MachineVerifier::verifyLiveInterval(const LiveInterval &LI) {
   Register Reg = LI.reg();
   assert(Register::isVirtualRegister(Reg));
   verifyLiveRange(LI, Reg);
 
+  if (LI.hasSubRanges()) {
     LaneBitmask Mask;
     LaneBitmask MaxMask = MRI->getMaxLaneMaskForVReg(Reg);
     for (const LiveInterval::SubRange &SR : LI.subranges()) {
       if ((Mask & SR.LaneMask).any()) {
         report("Lane masks of sub ranges overlap in live interval", MF);
         report_context(LI);
       }
       if ((SR.LaneMask & ~MaxMask).any()) {
         report("Subrange lanemask is invalid", MF);
         report_context(LI);
       }
       if (SR.empty()) {
         report("Subrange must not be empty", MF);
         report_context(SR, LI.reg(), SR.LaneMask);
       }
       Mask |= SR.LaneMask;
       verifyLiveRange(SR, LI.reg(), SR.LaneMask);
       if (!LI.covers(SR)) {
         report("A Subrange is not covered by the main range", MF);
         report_context(LI);
       }
     }
+  }
 
   // Check the LI only has one connected component.
   ConnectedVNInfoEqClasses ConEQ(*LiveInts);
   unsigned NumComp = ConEQ.Classify(LI);
   if (NumComp > 1) {
     report("Multiple connected components in live interval", MF);
     report_context(LI);
     for (unsigned comp = 0; comp != NumComp; ++comp) {