LTO: Try to open cache files before renaming them.

It appears that a potential race between the cache client and the cache
pruner that I thought was unlikely actually happened in practice [1].
Try to avoid the race condition by opening the temporary file before
renaming it. Do this only on non-Windows platforms because we cannot
rename open files on Windows using the sys::fs::rename function.

[1] https://luci-logdog.appspot.com/v/?s=chromium%2Fbb%2Fchromium.memory%2FLinux_CFI%2F1610%2F%2B%2Frecipes%2Fsteps%2Fcompile%2F0%2Fstdout

Differential Revision: https://reviews.llvm.org/D37410

llvm-svn: 312567

1 files changed, 2 insertions, 1 deletions

diff --git a/llvm/tools/llvm-lto2/llvm-lto2.cpp b/llvm/tools/llvm-lto2/llvm-lto2.cpp
index 1c7038e6a2e..bc22b509b65 100644
--- a/llvm/tools/llvm-lto2/llvm-lto2.cpp
+++ b/llvm/tools/llvm-lto2/llvm-lto2.cpp
@@ -296,7 +296,8 @@ static int run(int argc, char **argv) {
     return llvm::make_unique<lto::NativeObjectStream>(std::move(S));
   };
 
-  auto AddBuffer = [&](size_t Task, std::unique_ptr<MemoryBuffer> MB) {
+  auto AddBuffer = [&](size_t Task, std::unique_ptr<MemoryBuffer> MB,
+                       StringRef Path) {
     *AddStream(Task)->OS << MB->getBuffer();
   };