Index: lib/CodeGen/MachineCopyPropagation.cpp
===================================================================
--- lib/CodeGen/MachineCopyPropagation.cpp
+++ lib/CodeGen/MachineCopyPropagation.cpp
@@ -399,7 +399,9 @@
     MachineInstr *MI = &*I;
     ++I;
 
-    if (MI->isCopy()) {
+    // Analyze copies (which don't overlap themselves).
+    if (MI->isCopy() && !TRI->regsOverlap(MI->getOperand(0).getReg(),
+                                          MI->getOperand(1).getReg())) {
       unsigned Def = MI->getOperand(0).getReg();
       unsigned Src = MI->getOperand(1).getReg();
 
Index: test/CodeGen/AArch64/machine-dead-copy.mir
===================================================================
--- test/CodeGen/AArch64/machine-dead-copy.mir
+++ test/CodeGen/AArch64/machine-dead-copy.mir
@@ -6,6 +6,8 @@
   define i32 @copyprop2(i32 %a, i32 %b) { ret i32 %a }
   define i32 @copyprop3(i32 %a, i32 %b) { ret i32 %a }
   define i32 @copyprop4(i32 %a, i32 %b) { ret i32 %a }
+  define i32 @copyprop5(i32 %a, i32 %b) { ret i32 %a }
+  define i32 @copyprop6(i32 %a, i32 %b) { ret i32 %a }
   declare i32 @foo(i32)
 ...
 ---
@@ -65,3 +67,33 @@
     RET_ReallyLR implicit $w0
 ...
 
+# Don't try to erase any COPY which overlaps itself.
+# CHECK-LABEL: name: copyprop5
+# CHECK: bb.0:
+# CHECK: COPY killed $q26_q27_q28_q29
+# CHECK: COPY killed $q28_q29_q30_q31
+name: copyprop5
+body: |
+  bb.0:
+    liveins: $q26_q27_q28_q29
+    $q28_q29_q30_q31 = COPY killed $q26_q27_q28_q29
+    $q26_q27_q28_q29 = COPY killed $q28_q29_q30_q31
+    BL @foo, csr_aarch64_aapcs, implicit killed $q26_q27_q28_q29
+    RET_ReallyLR
+...
+
+# Don't try to analyze any COPY which overlaps itself.
+# CHECK-LABEL: name: copyprop6
+# CHECK: bb.0:
+# CHECK: COPY killed $q26_q27_q28_q29
+# CHECK: $q30 = COPY $q28
+name: copyprop6
+body: |
+  bb.0:
+    liveins: $q26_q27_q28_q29
+    $q28_q29_q30_q31 = COPY killed $q26_q27_q28_q29
+    $q30 = COPY $q28
+    BL @foo, csr_aarch64_aapcs, implicit killed $q28_q29_q30_q31
+    RET_ReallyLR
+...
+