2 files changed, 12 insertions, 0 deletions
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 19e26c18bfd..42fd2a13313 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -1002,6 +1002,7 @@ static void ParseDependencyOutputArgs(DependencyOutputOptions &Opts,
   Opts.Targets = Args.getAllArgValues(OPT_MT);
   Opts.IncludeSystemHeaders = Args.hasArg(OPT_sys_header_deps);
   Opts.IncludeModuleFiles = Args.hasArg(OPT_module_file_deps);
+  Opts.CanonicalSystemHeaders = !Args.hasArg(OPT_fno_canonical_system_headers);
   Opts.UsePhonyTargets = Args.hasArg(OPT_MP);
   Opts.ShowHeaderIncludes = Args.hasArg(OPT_H);
   Opts.HeaderIncludeOutputFile = Args.getLastArgValue(OPT_header_include_file);
diff --git a/clang/lib/Frontend/DependencyFile.cpp b/clang/lib/Frontend/DependencyFile.cpp
index 561eb9c4a31..b6e4cfa3385 100644
--- a/clang/lib/Frontend/DependencyFile.cpp
+++ b/clang/lib/Frontend/DependencyFile.cpp
@@ -161,6 +161,7 @@ class DFGImpl : public PPCallbacks {
   bool AddMissingHeaderDeps;
   bool SeenMissingHeader;
   bool IncludeModuleFiles;
+  bool CanonicalSystemHeaders;
   DependencyOutputFormat OutputFormat;
 
 private:
@@ -176,6 +177,7 @@ public:
       AddMissingHeaderDeps(Opts.AddMissingHeaderDeps),
       SeenMissingHeader(false),
       IncludeModuleFiles(Opts.IncludeModuleFiles),
+      CanonicalSystemHeaders(Opts.CanonicalSystemHeaders),
       OutputFormat(Opts.OutputFormat) {
     for (const auto &ExtraDep : Opts.ExtraDeps) {
       AddFilename(ExtraDep);
@@ -288,6 +290,15 @@ void DFGImpl::FileChanged(SourceLocation Loc,
   if (!FileMatchesDepCriteria(Filename.data(), FileType))
     return;
 
+  // Try to shorten system header paths like GCC does (unless
+  // -fno-canonical-system-headers is given).
+  if (CanonicalSystemHeaders && isSystem(FileType)) {
+    StringRef RealPath = FE->tryGetRealPathName();
+    if (!RealPath.empty() && RealPath.size() < Filename.size()) {
+      Filename = RealPath;
+    }
+  }
+
   AddFilename(llvm::sys::path::remove_leading_dotslash(Filename));
 }