diff --git a/llvm/lib/CodeGen/MachineBasicBlock.cpp b/llvm/lib/CodeGen/MachineBasicBlock.cpp
--- a/llvm/lib/CodeGen/MachineBasicBlock.cpp
+++ b/llvm/lib/CodeGen/MachineBasicBlock.cpp
@@ -1406,6 +1406,10 @@
       return LQR_Dead;
   }
 
+  // Skip over debug instructions.
+  if (I != end() && I->isDebugInstr())
+    ++I;
+
   // If we reached the end, it is safe to clobber Reg at the end of a block of
   // no successor has it live in.
   if (I == end()) {
@@ -1462,6 +1466,11 @@
     } while (I != begin() && N > 0);
   }
 
+  // If all the instructions before this in the block are debug instructions,
+  // skip over them.
+  while (I != begin() && std::prev(I)->isDebugInstr())
+    --I;
+
   // Did we get to the start of the block?
   if (I == begin()) {
     // If so, the register's state is definitely defined by the live-in state.
diff --git a/llvm/test/CodeGen/X86/leaFixup64.mir b/llvm/test/CodeGen/X86/leaFixup64.mir
--- a/llvm/test/CodeGen/X86/leaFixup64.mir
+++ b/llvm/test/CodeGen/X86/leaFixup64.mir
@@ -148,6 +148,10 @@
     ret i32 0
   }
 
+  define i32 @pr43758() {
+    ret i32 0
+  }
+
 
 ...
 ---
@@ -1129,6 +1133,62 @@
     RETQ $ebp
 
 ...
+---
+name:            pr43758
+alignment:       16
+exposesReturnsTwice: false
+legalized:       false
+regBankSelected: false
+selected:        false
+tracksRegLiveness: true
+liveins:
+  - { reg: '$rax' }
+  - { reg: '$rbp' }
+frameInfo:
+  isFrameAddressTaken: false
+  isReturnAddressTaken: false
+  hasStackMap:     false
+  hasPatchPoint:   false
+  stackSize:       0
+  offsetAdjustment: 0
+  maxAlignment:    0
+  adjustsStack:    false
+  hasCalls:        false
+  maxCallFrameSize: 0
+  hasOpaqueSPAdjustment: false
+  hasVAStart:      false
+  hasMustTailInVarArgFunc: false
+body:             |
+  bb.0 (%ir-block.0):
+    liveins: $rax, $rbp
+
+    ; CHECK-LABEL: name: pr43758
+    ; CHECK: liveins: $rax, $rbp
+    ; CHECK: DBG_VALUE 0, $noreg
+    ; CHECK: NOOP
+    ; CHECK: NOOP
+    ; CHECK: NOOP
+    ; CHECK: NOOP
+    ; CHECK: $ebp = ADD32rr $ebp, $eax, implicit-def $eflags, implicit $rbp, implicit $rax
+    ; CHECK: NOOP
+    ; CHECK: NOOP
+    ; CHECK: NOOP
+    ; CHECK: NOOP
+    ; CHECK: RETQ $ebp
+    DBG_VALUE 0, $noreg
+    NOOP
+    NOOP
+    NOOP
+    NOOP
+    $ebp = LEA64_32r killed $rbp, 1, killed $rax, 0, $noreg
+    NOOP
+    NOOP
+    NOOP
+    NOOP
+    RETQ $ebp
+
+...
+...