[AMDGPU] Add EXPENSIVE_CHECK into GCNRPTracker::reset

[vpykhtin]

Summary

This would check if passed in live-ins registers match those calculated using LIS.

This check currently breaks 420 lit tests when enabled.

[arsenm]

llvm/lib/Target/AMDGPU/GCNRegPressure.cpp

274

llvm_unreachable

[vpykhtin]

replaced assert with llvm_unreachable

llvm/lib/Target/AMDGPU/GCNRegPressure.cpp

if (LiveRegsCopy) {
     if (&LiveRegs != LiveRegsCopy)
       LiveRegs = *LiveRegsCopy;
   } else {
     LiveRegs = After ? getLiveRegsAfter(MI, LIS)
                      : getLiveRegsBefore(MI, LIS);
   }
 
   MaxPressure = CurPressure = getRegPressure(*MRI, LiveRegs);
+
+  LLVM_DEBUG(dbgs() << "\nReset " << (After ? "after" : "before") << ": " << MI
+                    << print(LiveRegs, *MRI));
+#if defined(EXPENSIVE_CHECKS) && !defined(NDEBUG)
+  if (LiveRegsCopy) {
+    auto LISLRS =
+        After ? getLiveRegsAfter(MI, LIS) : getLiveRegsBefore(MI, LIS);
+    if (!isEqual(LISLRS, *LiveRegsCopy)) {
+      dbgs() << "RP mismatch: "
+             << reportMismatch(LISLRS, *LiveRegsCopy,
+                               MRI->getTargetRegisterInfo());
+      llvm_unreachable("GCNRPTracker::reset LiveRegsCopy doens't match those "
+                       "calculated by LIS");
+    }
+  }
+#endif
 }
 
 void GCNUpwardRPTracker::reset(const MachineInstr &MI,
                                const LiveRegSet *LiveRegsCopy) {
   GCNRPTracker::reset(MI, LiveRegsCopy, true);
 }
 
 void GCNUpwardRPTracker::recede(const MachineInstr &MI) {