Index: lib/CodeGen/MachineCopyPropagation.cpp
===================================================================
--- lib/CodeGen/MachineCopyPropagation.cpp
+++ lib/CodeGen/MachineCopyPropagation.cpp
@@ -75,10 +75,9 @@
            I != E; ++I) {
         unsigned MappedDef = *I;
         // Source of copy is no longer available for propagation.
-        if (AvailCopyMap.erase(MappedDef)) {
-          for (MCSubRegIterator SR(MappedDef, TRI); SR.isValid(); ++SR)
-            AvailCopyMap.erase(*SR);
-        }
+        AvailCopyMap.erase(MappedDef);
+        for (MCSubRegIterator SR(MappedDef, TRI); SR.isValid(); ++SR)
+          AvailCopyMap.erase(*SR);
       }
     }
   }
Index: test/CodeGen/AArch64/machine-copy-prop.ll
===================================================================
--- /dev/null
+++ test/CodeGen/AArch64/machine-copy-prop.ll
@@ -0,0 +1,101 @@
+; RUN: llc -mtriple=aarch64-linux-gnu -mcpu=cortex-a57 -verify-machineinstrs < %s | FileCheck %s
+
+; This file check a bug in MachineCopyPropagation pass. The last COPY will be
+; incorrectly removed if the machine instructions are as follows:
+;   %Q5_Q6<def> = COPY %Q2_Q3
+;   %D5<def> =
+;   %D3<def> =
+;   %D3<def> = COPY %D6
+; This is caused by a bug in function SourceNoLongerAvailable(), which fails to
+; remove the relationship of D6 and "%Q5_Q6<def> = COPY %Q2_Q3".
+
+@failed = internal unnamed_addr global i1 false
+
+; CHECK-LABEL: foo:
+; CHECK: ld2
+; CHECK-NOT: // kill: D{{[0-9]+}}<def> D{{[0-9]+}}<kill>
+define void @foo(<2 x i32> %shuffle251, <8 x i8> %vtbl1.i, i8* %t2, <2 x i32> %vrsubhn_v2.i1364) {
+entry:
+  %val0 = alloca [2 x i64], align 8
+  %val1 = alloca <2 x i64>, align 16
+  %vmull = tail call <2 x i64> @llvm.aarch64.neon.umull.v2i64(<2 x i32> <i32 -1, i32 -1>, <2 x i32> %shuffle251)
+  %vgetq_lane = extractelement <2 x i64> %vmull, i32 0
+  %cmp = icmp eq i64 %vgetq_lane, 1
+  br i1 %cmp, label %if.end, label %if.then
+
+if.then:                                          ; preds = %entry
+  store i1 true, i1* @failed, align 1
+  br label %if.end
+
+if.end:                                           ; preds = %if.then, %entry
+  tail call void @f2()
+  %sqdmull = tail call <4 x i32> @llvm.aarch64.neon.sqdmull.v4i32(<4 x i16> <i16 1, i16 0, i16 0, i16 0>, <4 x i16> <i16 2, i16 0, i16 0, i16 0>)
+  %sqadd = tail call <4 x i32> @llvm.aarch64.neon.sqadd.v4i32(<4 x i32> zeroinitializer, <4 x i32> %sqdmull)
+  %shuffle = shufflevector <4 x i32> %sqadd, <4 x i32> undef, <2 x i32> zeroinitializer
+  %0 = mul <2 x i32> %shuffle, <i32 -1, i32 0>
+  %sub = add <2 x i32> %0, <i32 1, i32 0>
+  %sext = sext <2 x i32> %sub to <2 x i64>
+  %vset_lane603 = shufflevector <2 x i64> %sext, <2 x i64> undef, <1 x i32> zeroinitializer
+  %t1 = bitcast [2 x i64]* %val0 to i8*
+  call void @llvm.aarch64.neon.st2lane.v2i64.p0i8(<2 x i64> zeroinitializer, <2 x i64> zeroinitializer, i64 1, i8* %t1)
+  call void @llvm.aarch64.neon.st2lane.v1i64.p0i8(<1 x i64> <i64 4096>, <1 x i64> <i64 -1>, i64 0, i8* %t2)
+  %vld2_lane = call { <1 x i64>, <1 x i64> } @llvm.aarch64.neon.ld2lane.v1i64.p0i8(<1 x i64> <i64 11>, <1 x i64> <i64 11>, i64 0, i8* %t2)
+  %vld2_lane.0.extract = extractvalue { <1 x i64>, <1 x i64> } %vld2_lane, 0
+  %vld2_lane.1.extract = extractvalue { <1 x i64>, <1 x i64> } %vld2_lane, 1
+  %vld2_lane1 = call { <1 x i64>, <1 x i64> } @llvm.aarch64.neon.ld2lane.v1i64.p0i8(<1 x i64> %vld2_lane.0.extract, <1 x i64> %vld2_lane.1.extract, i64 0, i8* %t1)
+  %vld2_lane1.0.extract = extractvalue { <1 x i64>, <1 x i64> } %vld2_lane1, 0
+  %vld2_lane1.1.extract = extractvalue { <1 x i64>, <1 x i64> } %vld2_lane1, 1
+  %t3 = bitcast <2 x i64>* %val1 to i8*
+  call void @llvm.aarch64.neon.st2.v1i64.p0i8(<1 x i64> %vld2_lane1.0.extract, <1 x i64> %vld2_lane1.1.extract, i8* %t3)
+  %t4 = load <2 x i64>, <2 x i64>* %val1, align 16
+  %vsubhn = sub <2 x i64> <i64 11, i64 0>, %t4
+  %vsubhn1 = lshr <2 x i64> %vsubhn, <i64 32, i64 32>
+  %vsubhn2 = trunc <2 x i64> %vsubhn1 to <2 x i32>
+  %neg = xor <2 x i32> %vsubhn2, <i32 -1, i32 -1>
+  %sqadd1 = call <1 x i64> @llvm.aarch64.neon.usqadd.v1i64(<1 x i64> <i64 -1>, <1 x i64> <i64 1>)
+  %sqadd2 = call <1 x i64> @llvm.aarch64.neon.usqadd.v1i64(<1 x i64> %vset_lane603, <1 x i64> %sqadd1)
+  %sqadd3 = call <1 x i64> @llvm.aarch64.neon.usqadd.v1i64(<1 x i64> <i64 1>, <1 x i64> %sqadd2)
+  %shuffle.i = shufflevector <2 x i32> <i32 undef, i32 0>, <2 x i32> %vrsubhn_v2.i1364, <2 x i32> <i32 1, i32 3>
+  %cmp.i = icmp uge <2 x i32> %shuffle.i, %neg
+  %sext.i = sext <2 x i1> %cmp.i to <2 x i32>
+  %vpadal = call <1 x i64> @llvm.aarch64.neon.uaddlp.v1i64.v2i32(<2 x i32> %sext.i)
+  %t5 = sub <1 x i64> %vpadal, %sqadd3
+  %vget_lane1 = extractelement <1 x i64> %t5, i32 0
+  %cmp2 = icmp eq i64 %vget_lane1, 15
+  br i1 %cmp2, label %if.end2, label %if.then2
+
+if.then2:                                       ; preds = %if.end
+  store i1 true, i1* @failed, align 1
+  br label %if.end2
+
+if.end2:                                        ; preds = %if.then682, %if.end
+  call void @f2()
+  %vext = shufflevector <8 x i8> <i8 undef, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1>, <8 x i8> %vtbl1.i, <8 x i32> <i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 8>
+  %t6 = bitcast <8 x i8> %vext to <2 x i32>
+  call void @f0(<2 x i32> %t6)
+  ret void
+}
+
+declare void @f0(<2 x i32>)
+
+declare <8 x i8> @f1()
+
+declare void @f2()
+
+declare <4 x i32> @llvm.aarch64.neon.sqdmull.v4i32(<4 x i16>, <4 x i16>)
+
+declare void @llvm.aarch64.neon.st2lane.v2i64.p0i8(<2 x i64>, <2 x i64>, i64, i8* nocapture)
+
+declare void @llvm.aarch64.neon.st2lane.v1i64.p0i8(<1 x i64>, <1 x i64>, i64, i8* nocapture)
+
+declare { <1 x i64>, <1 x i64> } @llvm.aarch64.neon.ld2lane.v1i64.p0i8(<1 x i64>, <1 x i64>, i64, i8*)
+
+declare void @llvm.aarch64.neon.st2.v1i64.p0i8(<1 x i64>, <1 x i64>, i8* nocapture)
+
+declare <1 x i64> @llvm.aarch64.neon.usqadd.v1i64(<1 x i64>, <1 x i64>)
+
+declare <1 x i64> @llvm.aarch64.neon.uaddlp.v1i64.v2i32(<2 x i32>)
+
+declare <4 x i32> @llvm.aarch64.neon.sqadd.v4i32(<4 x i32>, <4 x i32>)
+
+declare <2 x i64> @llvm.aarch64.neon.umull.v2i64(<2 x i32>, <2 x i32>)