[PATCH] D42326: [COFF] don't replace import library if contents are unchanged

[Bob Haarman via Phabricator via llvm-commits]

inglorion updated this revision to Diff 130741.
inglorion marked 5 inline comments as done.
inglorion added a comment.

simplifications suggested by @ruiu


https://reviews.llvm.org/D42326

Files:
  lld/COFF/Driver.cpp
  lld/test/COFF/unchanged-importlib.test


Index: lld/test/COFF/unchanged-importlib.test
===================================================================
--- /dev/null
+++ lld/test/COFF/unchanged-importlib.test
@@ -0,0 +1,7 @@
+# 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=CHECK %s
+
+# CHECK: Feb 1 1980
Index: lld/COFF/Driver.cpp
===================================================================
--- lld/COFF/Driver.cpp
+++ lld/COFF/Driver.cpp
@@ -533,10 +533,38 @@
     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 the import library already exists, replace it only if the contents
+  // have changed.
+  ErrorOr<std::unique_ptr<MemoryBuffer>> OldBuf = MemoryBuffer::getFile(Path);
+  if (!OldBuf) {
+    HandleError(
+        writeImportLibrary(LibName, Path, Exports, Config->Machine, false));
+    return;
+  }
+
+  SmallString<128> TmpName;
+  if (auto EC = sys::fs::createUniqueFile(Path + ".tmp-%%%%%%%%.lib", TmpName))
+    fatal("cannot create temporary file for import library " + Path + ": " +
+          EC.message());
+
+  if (Error E = writeImportLibrary(LibName, TmpName, Exports, Config->Machine,
+                                   false)) {
+    HandleError(std::move(E));
+    return;
+  }
+
+  auto NewBuf = check(MemoryBuffer::getFile(TmpName));
+  if ((*OldBuf)->getBuffer() != NewBuf->getBuffer()) {
+    OldBuf->reset();
+    HandleError(errorCodeToError(sys::fs::rename(TmpName, Path)));
+  }
 }
 
 static void parseModuleDefs(StringRef Path) {


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