[ThinLTO] Option to control path of distributed backend files

Summary:
Add support to control where files for a distributed backend (the
individual index files and optional imports files) are created.

This is invoked with a new thinlto-prefix-replace option in the gold
plugin and llvm-lto. If specified, expects a string of the form
"oldprefix:newprefix", and instead of generating these files in the
same directory path as the corresponding bitcode file, will use a path
formed by replacing the bitcode file's path prefix matching oldprefix
with newprefix.

Also add a new replace_path_prefix helper to Path.h in libSupport.

Depends on D19636.

Reviewers: joker.eph

Subscribers: llvm-commits, joker.eph

Differential Revision: http://reviews.llvm.org/D19644

llvm-svn: 269771

1 files changed, 23 insertions, 0 deletions

diff --git a/llvm/lib/Support/Path.cpp b/llvm/lib/Support/Path.cpp
index f9a71b986a8..406a37b2cc0 100644
--- a/llvm/lib/Support/Path.cpp
+++ b/llvm/lib/Support/Path.cpp
@@ -522,6 +522,29 @@ void replace_extension(SmallVectorImpl<char> &path, const Twine &extension) {
   path.append(ext.begin(), ext.end());
 }
 
+void replace_path_prefix(SmallVectorImpl<char> &Path,
+                         const StringRef &OldPrefix,
+                         const StringRef &NewPrefix) {
+  if (OldPrefix.empty() && NewPrefix.empty())
+    return;
+
+  StringRef OrigPath(Path.begin(), Path.size());
+  if (!OrigPath.startswith(OldPrefix))
+    return;
+
+  // If prefixes have the same size we can simply copy the new one over.
+  if (OldPrefix.size() == NewPrefix.size()) {
+    std::copy(NewPrefix.begin(), NewPrefix.end(), Path.begin());
+    return;
+  }
+
+  StringRef RelPath = OrigPath.substr(OldPrefix.size());
+  SmallString<256> NewPath;
+  path::append(NewPath, NewPrefix);
+  path::append(NewPath, RelPath);
+  Path.swap(NewPath);
+}
+
 void native(const Twine &path, SmallVectorImpl<char> &result) {
   assert((!path.isSingleStringRef() ||
           path.getSingleStringRef().data() != result.data()) &&