Index: lld/COFF/Config.h
===================================================================
--- lld/COFF/Config.h
+++ lld/COFF/Config.h
@@ -175,6 +175,7 @@
   bool AppContainer = false;
   bool MinGW = false;
   bool WarnLocallyDefinedImported = true;
+  bool KeepUnchangedImplib = false;
 };
 
 extern Configuration *Config;
Index: lld/COFF/Driver.cpp
===================================================================
--- lld/COFF/Driver.cpp
+++ lld/COFF/Driver.cpp
@@ -533,10 +533,42 @@
     Exports.push_back(E2);
   }
 
-  auto E = writeImportLibrary(getImportName(AsLib), getImplibPath(), Exports,
-                              Config->Machine, false);
-  handleAllErrors(std::move(E),
-                  [&](ErrorInfoBase &EIB) { error(EIB.message()); });
+  auto HandleError = [](Error &&E) {
+    handleAllErrors(std::move(E),
+                    [](ErrorInfoBase &EIB) { error(EIB.message()); });
+  };
+  auto LibName = getImportName(AsLib);
+  auto Path = getImplibPath();
+
+  // If Config->KeepUnchangedImplib is true and the import library already
+  // exists, replace it only if the contents have changed.
+  if (Config->KeepUnchangedImplib) {
+    auto OldBuf = MemoryBuffer::getFile(Path);
+    if (OldBuf) {
+      SmallString<128> TmpName;
+      auto EC = sys::fs::createUniqueFile(Path + ".tmp-%%%%%%%%.lib", TmpName);
+      if (EC)
+        fatal("Cannot create temporary file for import library " + Path + ": " +
+              EC.message());
+      Error E =
+          writeImportLibrary(LibName, TmpName, Exports, Config->Machine, false);
+      if (!E) {
+        auto NewBuf = check(MemoryBuffer::getFile(TmpName));
+        if ((*OldBuf)->getBuffer() != NewBuf->getBuffer()) {
+          OldBuf->reset();
+          auto EC = sys::fs::rename(TmpName, Path);
+          if (EC)
+            HandleError(errorCodeToError(EC));
+        }
+      } else {
+        HandleError(std::move(E));
+      }
+      return;
+    }
+  }
+
+  Error E = writeImportLibrary(LibName, Path, Exports, Config->Machine, false);
+  HandleError(std::move(E));
 }
 
 static void parseModuleDefs(StringRef Path) {
@@ -1031,6 +1063,8 @@
   Config->AllowBind = Args.hasFlag(OPT_allowbind, OPT_allowbind_no, true);
   Config->AllowIsolation =
       Args.hasFlag(OPT_allowisolation, OPT_allowisolation_no, true);
+  Config->KeepUnchangedImplib = Args.hasFlag(
+      OPT_keep_unchanged_implib, OPT_keep_unchanged_implib_no, false);
   Config->NxCompat = Args.hasFlag(OPT_nxcompat, OPT_nxcompat_no, true);
   Config->TerminalServerAware = Args.hasFlag(OPT_tsaware, OPT_tsaware_no, true);
   Config->DebugDwarf = Args.hasArg(OPT_debug_dwarf);
Index: lld/COFF/Options.td
===================================================================
--- lld/COFF/Options.td
+++ lld/COFF/Options.td
@@ -121,6 +121,9 @@
 def debug_ghash : F<"debug:ghash">;
 def debug_dwarf : F<"debug:dwarf">;
 def export_all_symbols : F<"export-all-symbols">;
+defm keep_unchanged_implib : B<"keep-unchanged-implib",
+                               "Keep original import library if contents haven't changed",
+                               "Replace import library file even if contents are unchanged (default)">;
 def lldmingw : F<"lldmingw">;
 def msvclto : F<"msvclto">;
 def output_def : Joined<["/", "-"], "output-def:">;
Index: lld/test/COFF/unchanged-importlib.test
===================================================================
--- /dev/null
+++ lld/test/COFF/unchanged-importlib.test
@@ -0,0 +1,14 @@
+# RUN: yaml2obj < %p/Inputs/export.yaml > %t.obj
+# RUN: lld-link -out:%t.dll -dll %t.obj
+# RUN: touch -t 198002011200.00 %t.lib
+# RUN: lld-link -out:%t.dll -dll %t.obj
+# RUN: ls -l %t.lib | FileCheck --check-prefix=NOKEEP %s
+# RUN: touch -t 198002011200.00 %t.lib
+# RUN: lld-link -out:%t.dll -dll -keep-unchanged-implib %t.obj
+# RUN: ls -l %t.lib | FileCheck --check-prefix=KEEP %s
+# RUN: touch -t 198002011200.00 %t.lib
+# RUN: lld-link -out:%t.dll -dll -keep-unchanged-implib:no %t.obj
+# RUN: ls -l %t.lib | FileCheck --check-prefix=NOKEEP %s
+
+# KEEP: Feb 1 1980
+# NOKEEP-NOT: Feb 1 1980