Index: lib/CodeGen/MachineInstr.cpp
===================================================================
--- lib/CodeGen/MachineInstr.cpp
+++ lib/CodeGen/MachineInstr.cpp
@@ -2080,14 +2080,28 @@
   if (!MI.getOperand(0).isReg())
     return;
 
-  MachineBasicBlock::iterator DI = MI; ++DI;
-  for (MachineBasicBlock::iterator DE = MI.getParent()->end();
-       DI != DE; ++DI) {
+  auto *MRI = getRegInfo();
+#ifndef NDEBUG
+  // There are no guarantees on DBG_VALUE availability and ordering after
+  // regalloc, they must be sought manually.
+  auto *TRI = MRI->getTargetRegisterInfo();
+  assert(!TRI->isPhysicalRegister(MI.getOperand(0).getReg()));
+#endif
+
+  for (auto &MO : MRI->use_operands(MI.getOperand(0).getReg())) {
+    auto *DI = MO.getParent();
     if (!DI->isDebugValue())
-      return;
+      continue;
+    // XXX XXX XXX numerous things explode if we "update" or move DBG_VALUEs
+    // from outside the current BB. These were previously ignored anyway by
+    // the prior implementation of collectDebugValues, so technically this
+    // isn't a regression...
+    if (DI->getParent() != getParent())
+      continue;
     if (DI->getOperand(0).isReg() &&
-        DI->getOperand(0).getReg() == MI.getOperand(0).getReg())
-      DbgValues.push_back(&*DI);
+        DI->getOperand(0).getReg() == MI.getOperand(0).getReg()) {
+      DbgValues.push_back(DI);
+    }
   }
 }
 
Index: lib/CodeGen/MachineSink.cpp
===================================================================
--- lib/CodeGen/MachineSink.cpp
+++ lib/CodeGen/MachineSink.cpp
@@ -367,10 +367,13 @@
     MachineInstr &MI = *I;  // The instruction to sink.
 
     // Predecrement I (if it's not begin) so that it isn't invalidated by
-    // sinking.
-    ProcessedBegin = I == MBB.begin();
-    if (!ProcessedBegin)
-      --I;
+    // sinking. Continue to decrement it past any debug insns, which might
+    // be sunk out of this BB.
+    do {
+      ProcessedBegin = I == MBB.begin();
+      if (!ProcessedBegin)
+        --I;
+    } while (!ProcessedBegin && I->isDebugInstr());
 
     if (MI.isDebugInstr())
       continue;