[clang-cl] Print /showIncludes to stderr, if used in combination with /E, /EP or /P

This replicates 'cl.exe' behavior and allows for both preprocessor output and
dependency information to be extraced with a single compiler invocation.

This is especially useful for compiler caching with tools like Mozilla's sccache.

See: https://github.com/mozilla/sccache/issues/246

Patch By: fxb

Differential Revision: https://reviews.llvm.org/D46394

llvm-svn: 331533

1 files changed, 15 insertions, 1 deletions

diff --git a/clang/lib/Frontend/HeaderIncludeGen.cpp b/clang/lib/Frontend/HeaderIncludeGen.cpp
index 5bff4ec..9dc107c 100644
--- a/clang/lib/Frontend/HeaderIncludeGen.cpp
+++ b/clang/lib/Frontend/HeaderIncludeGen.cpp
@@ -80,9 +80,23 @@ void clang::AttachHeaderIncludeGen(Preprocessor &PP,
                                    const DependencyOutputOptions &DepOpts,
                                    bool ShowAllHeaders, StringRef OutputPath,
                                    bool ShowDepth, bool MSStyle) {
-  raw_ostream *OutputFile = MSStyle ? &llvm::outs() : &llvm::errs();
+  raw_ostream *OutputFile = &llvm::errs();
   bool OwnsOutputFile = false;
 
+  // Choose output stream, when printing in cl.exe /showIncludes style.
+  if (MSStyle) {
+    switch (DepOpts.ShowIncludesDest) {
+    default:
+      llvm_unreachable("Invalid destination for /showIncludes output!");
+    case ShowIncludesDestination::Stderr:
+      OutputFile = &llvm::errs();
+      break;
+    case ShowIncludesDestination::Stdout:
+      OutputFile = &llvm::outs();
+      break;
+    }
+  }
+
   // Open the output file, if used.
   if (!OutputPath.empty()) {
     std::error_code EC;