1 files changed, 86 insertions, 0 deletions
diff --git a/utils/FileUpdate/FileUpdate.cpp b/utils/FileUpdate/FileUpdate.cpp
new file mode 100644
index 0000000..26fd75e
--- /dev/null
+++ b/utils/FileUpdate/FileUpdate.cpp
@@ -0,0 +1,86 @@
+//===- FileUpdate.cpp - Conditionally update a file -----------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// FileUpdate is a utility for conditionally updating a file from its input
+// based on whether the input differs from the output. It is used to avoid
+// unnecessary modifications in a build system.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/MemoryBuffer.h"
+#include "llvm/Support/PrettyStackTrace.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/System/Signals.h"
+using namespace llvm;
+
+static cl::opt<bool>
+Quiet("quiet", cl::desc("Don't print unnecessary status information"),
+      cl::init(false));
+
+static cl::opt<std::string>
+InputFilename("input-file", cl::desc("Input file (defaults to stdin)"),
+              cl::init("-"), cl::value_desc("filename"));
+
+static cl::opt<std::string>
+OutputFilename(cl::Positional, cl::desc("<output-file>"), cl::Required);
+
+int main(int argc, char **argv) {
+  sys::PrintStackTraceOnErrorSignal();
+  PrettyStackTraceProgram X(argc, argv);
+  cl::ParseCommandLineOptions(argc, argv);
+
+  // Get the input data.
+  std::string ErrorStr;
+  MemoryBuffer *In =
+    MemoryBuffer::getFileOrSTDIN(InputFilename.c_str(), &ErrorStr);
+  if (In == 0) {
+    errs() << argv[0] << ": error: Unable to get input '"
+           << InputFilename << "': " << ErrorStr << '\n';
+    return 1;
+  }
+
+  // Get the output data.
+  MemoryBuffer *Out = MemoryBuffer::getFile(OutputFilename.c_str(), &ErrorStr);
+
+  // If the output exists and the contents match, we are done.
+  if (Out && In->getBufferSize() == Out->getBufferSize() &&
+      memcmp(In->getBufferStart(), Out->getBufferStart(),
+             Out->getBufferSize()) == 0) {
+    if (!Quiet)
+      outs() << argv[0] << ": Not updating '" << OutputFilename
+             << "', contents match input.\n";
+    return 0;
+  }
+
+  delete Out;
+
+  // Otherwise, overwrite the output.
+  if (!Quiet)
+    outs() << argv[0] << ": Updating '" << OutputFilename
+           << "', contents changed.\n";
+  raw_fd_ostream OutStream(OutputFilename.c_str(), ErrorStr,
+                           raw_fd_ostream::F_Binary);
+  if (!ErrorStr.empty()) {
+    errs() << argv[0] << ": Unable to write output '"
+           << OutputFilename << "': " << ErrorStr << '\n';
+    return 1;
+  }
+
+  OutStream.write(In->getBufferStart(), In->getBufferSize());
+  OutStream.close();
+
+  if (OutStream.has_error()) {
+    errs() << argv[0] << ": Could not open output file '"
+           << OutputFilename << "': " << ErrorStr << '\n';
+    return 1;
+  }
+
+  return 0;
+}