[PATCH] Teach Clang how to use response files when calling other tools

[Sean Silva]

Lots of naked const char * type stuff here (that includes unique_ptr<char[]>). Better to use StringRef, SmallVectorImpl<char>&, and raw_ostream& where possible, maybe with judicious use of BumpPtrAllocator, memcpy, and strcpy.

There are a lot of places where you have to separate loops: one for computing a buffer size, and another for actually doing work. This is a maintenance problem (will the length computation stay in sync with the code?) and also causes two traversals over the memory. By directly doing push_back's onto a vector or writing into a raw_ostream, you avoid doing two traversals.

================
Comment at: lib/Driver/Job.cpp:122
@@ +121,3 @@
+/// will escape the regular backslashes (used in Windows paths) and quotes.
+static std::unique_ptr<char[]> FlattenArgs(const char **args) {
+  // First, determine the length of the command line.
----------------
This would be a lot nicer with ArrayRef<const char *>; that way, you won't lose the length.

================
Comment at: lib/Driver/Job.cpp:169
@@ +168,3 @@
+  llvm::SmallVector<const char *, 128> NewArgv;
+  unsigned len = 0;
+  for (auto Input : Inputs) {
----------------
Check your naming here and in other places.

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Comment at: lib/Driver/Tools.h:546-550
@@ +545,7 @@
+    llvm::sys::EncodingMethod getResponseFileEncoding() const override {
+#if defined(LLVM_ON_WIN32)
+      return llvm::sys::EM_CurrentCodePage;
+#else
+      return llvm::sys::EM_UTF8;
+#endif
+    }
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Ew... let's not have a bunch of random #ifdef's all over the code outside libSupport.

http://reviews.llvm.org/D4897