Index: lib/CodeGen/MachineCopyPropagation.cpp
===================================================================
--- lib/CodeGen/MachineCopyPropagation.cpp
+++ lib/CodeGen/MachineCopyPropagation.cpp
@@ -85,16 +85,29 @@
 }
 
 static bool NoInterveningSideEffect(const MachineInstr *CopyMI,
-                                    const MachineInstr *MI) {
+                                    const MachineInstr *MI, unsigned Reg) {
   const MachineBasicBlock *MBB = CopyMI->getParent();
   if (MI->getParent() != MBB)
     return false;
 
   for (MachineBasicBlock::const_iterator I = std::next(CopyMI->getIterator()),
        E = MBB->end(), E2 = MI->getIterator(); I != E && I != E2; ++I) {
-    if (I->hasUnmodeledSideEffects() || I->isCall() ||
-        I->isTerminator())
+    if (I->isTerminator())
       return false;
+    if (I->hasUnmodeledSideEffects() || I->isCall()) {
+      // Continue if the instruction explicitely preserves the register
+      // (calls often do)
+      bool RegIsPreserved = false;
+      for (const MachineOperand &MO : MI->operands()) {
+        if (MO.isRegMask() &&
+            !MachineOperand::clobbersPhysReg(MO.getRegMask(), Reg)) {
+          RegIsPreserved = true;
+          break;
+        }
+      }
+      if (!RegIsPreserved)
+        return false;
+    }
   }
   return true;
 }
@@ -142,9 +155,9 @@
       DenseMap<unsigned, MachineInstr*>::iterator CI = AvailCopyMap.find(Src);
       if (CI != AvailCopyMap.end()) {
         MachineInstr *CopyMI = CI->second;
-        if (!MRI->isReserved(Def) &&
-            (!MRI->isReserved(Src) || NoInterveningSideEffect(CopyMI, MI)) &&
-            isNopCopy(CopyMI, Def, Src, TRI)) {
+        if (!MRI->isReserved(Def) && isNopCopy(CopyMI, Def, Src, TRI) &&
+            (!MRI->isReserved(Src) ||
+             NoInterveningSideEffect(CopyMI, MI, Src))) {
           // The two copies cancel out and the source of the first copy
           // hasn't been overridden, eliminate the second one. e.g.
           //  %ECX<def> = COPY %EAX<kill>
@@ -276,13 +289,35 @@
         Changed = true;
         ++NumDeletes;
       }
-
-      // Clear all data structures as if we were beginning a new basic block.
       MaybeDeadCopies.clear();
-      AvailCopyMap.clear();
-      CopyMap.clear();
-      SrcMap.clear();
-      continue;
+
+      for (Reg2MIMap::iterator I = AvailCopyMap.begin(), E = AvailCopyMap.end(),
+           Next; I != E; I = Next) {
+        Next = std::next(I);
+        unsigned Reg = I->first;
+        if (RegMask->clobbersPhysReg(Reg))
+          AvailCopyMap.erase(I);
+      }
+      for (Reg2MIMap::iterator I = CopyMap.begin(), E = CopyMap.end(), Next;
+           I != E; I = Next) {
+        Next = std::next(I);
+        unsigned Reg = I->first;
+        if (RegMask->clobbersPhysReg(Reg))
+          CopyMap.erase(I);
+      }
+      for (SourceMap::iterator I = SrcMap.begin(), E = SrcMap.end(), Next;
+           I != E; I = Next) {
+        Next = std::next(I);
+        unsigned Reg = I->first;
+        if (RegMask->clobbersPhysReg(Reg)) {
+          const DestList &Defs = I->second;
+          for (unsigned MappedDef : Defs) {
+            // Source of copy is no longer available for propagation.
+            for (MCSubRegIterator SR(MappedDef, TRI, true); SR.isValid(); ++SR)
+              AvailCopyMap.erase(*SR);
+          }
+        }
+      }
     }
 
     for (unsigned Reg : Defs) {
Index: test/CodeGen/X86/machine-copy-prop.mir
===================================================================
--- /dev/null
+++ test/CodeGen/X86/machine-copy-prop.mir
@@ -0,0 +1,21 @@
+# RUN: llc -march=x86 -run-pass machine-cp -o /dev/null %s 2>&1 | FileCheck %s
+
+--- |
+  declare preserve_mostcc void @foo()
+  define void @copyprop1() { ret void }
+...
+---
+# CHECK-LABEL: name: copyprop1
+# CHECK: bb.0:
+# CHECK-NEXT: %rax = COPY %rdi
+# CHECK-NEXT: CALL64pcrel32 @foo, csr_64_rt_mostregs, implicit %rsp, implicit-def %rsp
+# CHECK-NOT: %rdi = COPY %rax
+# CHECK-NEXT: NOOP implicit %rax, implicit %rdi
+name: copyprop1
+body: |
+  bb.0:
+    %rax = COPY %rdi
+    CALL64pcrel32 @foo, csr_64_rt_mostregs, implicit %rsp, implicit-def %rsp
+    %rdi = COPY %rax
+    NOOP implicit %rax, implicit %rdi
+...