Index: llvm/trunk/lib/CodeGen/MachineCopyPropagation.cpp
===================================================================
--- llvm/trunk/lib/CodeGen/MachineCopyPropagation.cpp
+++ llvm/trunk/lib/CodeGen/MachineCopyPropagation.cpp
@@ -61,6 +61,7 @@
 
   private:
     void ClobberRegister(unsigned Reg);
+    void ReadRegister(unsigned Reg);
     void CopyPropagateBlock(MachineBasicBlock &MBB);
     bool eraseIfRedundant(MachineInstr &Copy, unsigned Src, unsigned Def);
 
@@ -120,6 +121,18 @@
   }
 }
 
+void MachineCopyPropagation::ReadRegister(unsigned Reg) {
+  // If 'Reg' is defined by a copy, the copy is no longer a candidate
+  // for elimination.
+  for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI) {
+    Reg2MIMap::iterator CI = CopyMap.find(*AI);
+    if (CI != CopyMap.end()) {
+      DEBUG(dbgs() << "MCP: Copy is used - not dead: "; CI->second->dump());
+      MaybeDeadCopies.remove(CI->second);
+    }
+  }
+}
+
 /// Return true if \p PreviousCopy did copy register \p Src to register \p Def.
 /// This fact may have been obscured by sub register usage or may not be true at
 /// all even though Src and Def are subregisters of the registers used in
@@ -212,12 +225,14 @@
 
       // If Src is defined by a previous copy, the previous copy cannot be
       // eliminated.
-      for (MCRegAliasIterator AI(Src, TRI, true); AI.isValid(); ++AI) {
-        Reg2MIMap::iterator CI = CopyMap.find(*AI);
-        if (CI != CopyMap.end()) {
-          DEBUG(dbgs() << "MCP: Copy is no longer dead: "; CI->second->dump());
-          MaybeDeadCopies.remove(CI->second);
-        }
+      ReadRegister(Src);
+      for (const MachineOperand &MO : MI->implicit_operands()) {
+        if (!MO.isReg() || !MO.readsReg())
+          continue;
+        unsigned Reg = MO.getReg();
+        if (!Reg)
+          continue;
+        ReadRegister(Reg);
       }
 
       DEBUG(dbgs() << "MCP: Copy is a deletion candidate: "; MI->dump());
@@ -234,6 +249,14 @@
       // ...
       // %xmm2<def> = copy %xmm9
       ClobberRegister(Def);
+      for (const MachineOperand &MO : MI->implicit_operands()) {
+        if (!MO.isReg() || !MO.isDef())
+          continue;
+        unsigned Reg = MO.getReg();
+        if (!Reg)
+          continue;
+        ClobberRegister(Reg);
+      }
 
       // Remember Def is defined by the copy.
       for (MCSubRegIterator SR(Def, TRI, /*IncludeSelf=*/true); SR.isValid();
@@ -269,17 +292,8 @@
       if (MO.isDef()) {
         Defs.push_back(Reg);
         continue;
-      }
-
-      // If 'Reg' is defined by a copy, the copy is no longer a candidate
-      // for elimination.
-      for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI) {
-        Reg2MIMap::iterator CI = CopyMap.find(*AI);
-        if (CI != CopyMap.end()) {
-          DEBUG(dbgs() << "MCP: Copy is used - not dead: "; CI->second->dump());
-          MaybeDeadCopies.remove(CI->second);
-        }
-      }
+      } else if (MO.readsReg())
+        ReadRegister(Reg);
     }
 
     // The instruction has a register mask operand which means that it clobbers
Index: llvm/trunk/test/CodeGen/ARM/machine-copyprop.mir
===================================================================
--- llvm/trunk/test/CodeGen/ARM/machine-copyprop.mir
+++ llvm/trunk/test/CodeGen/ARM/machine-copyprop.mir
@@ -0,0 +1,22 @@
+# RUN: llc -o - %s -mtriple=armv7s-- -run-pass=machine-cp | FileCheck %s
+---
+# Test that machine copy prop recognizes the implicit-def operands on a COPY
+# as clobbering the register.
+# CHECK-LABEL: name: func
+# CHECK: %d2 = VMOVv2i32 2, 14, _
+# CHECK: %s5 = COPY %s0, implicit %q1, implicit-def %q1
+# CHECK: VST1q32 %r0, 0, %q1, 14, _
+# The following two COPYs must not be removed
+# CHECK: %s4 = COPY %s20, implicit-def %q1
+# CHECK: %s5 = COPY %s0, implicit killed %d0, implicit %q1, implicit-def %q1
+# CHECK: VST1q32 %r2, 0, %q1, 14, _
+name: func
+body: |
+  bb.0:
+    %d2 = VMOVv2i32 2, 14, _
+    %s5 = COPY %s0, implicit %q1, implicit-def %q1
+    VST1q32 %r0, 0, %q1, 14, _
+    %s4 = COPY %s20, implicit-def %q1
+    %s5 = COPY %s0, implicit killed %d0, implicit %q1, implicit-def %q1
+    VST1q32 %r2, 0, %q1, 14, _
+...