Index: llvm/trunk/include/llvm/LTO/legacy/ThinLTOCodeGenerator.h
===================================================================
--- llvm/trunk/include/llvm/LTO/legacy/ThinLTOCodeGenerator.h
+++ llvm/trunk/include/llvm/LTO/legacy/ThinLTOCodeGenerator.h
@@ -151,8 +151,12 @@
   /// Cache policy: interval (seconds) between two prune of the cache. Set to a
   /// negative value (default) to disable pruning. A value of 0 will be ignored.
   void setCachePruningInterval(int Interval) {
+    static_assert(std::is_same<decltype(CacheOptions.Policy.Interval),
+                               std::chrono::seconds>::value,
+                  "ensure same types to avoid risk of overflow");
     if (Interval)
-      CacheOptions.Policy.Interval = std::chrono::seconds(Interval);
+      CacheOptions.Policy.Interval = Interval > 0 ? std::chrono::seconds(Interval)
+                                                  : std::chrono::seconds::max();
   }
 
   /// Cache policy: expiration (in seconds) for an entry.
Index: llvm/trunk/lib/Support/CachePruning.cpp
===================================================================
--- llvm/trunk/lib/Support/CachePruning.cpp
+++ llvm/trunk/lib/Support/CachePruning.cpp
@@ -155,7 +155,8 @@
   SmallString<128> TimestampFile(Path);
   sys::path::append(TimestampFile, "llvmcache.timestamp");
   sys::fs::file_status FileStatus;
-  const auto CurrentTime = system_clock::now();
+  const auto CurrentTime =
+      time_point_cast<decltype(Policy.Interval)>(system_clock::now());
   if (auto EC = sys::fs::status(TimestampFile, FileStatus)) {
     if (EC == errc::no_such_file_or_directory) {
       // If the timestamp file wasn't there, create one now.
@@ -168,7 +169,8 @@
     if (Policy.Interval != seconds(0)) {
       // Check whether the time stamp is older than our pruning interval.
       // If not, do nothing.
-      const auto TimeStampModTime = FileStatus.getLastModificationTime();
+      const auto TimeStampModTime = time_point_cast<decltype(Policy.Interval)>(
+          FileStatus.getLastModificationTime());
       auto TimeStampAge = CurrentTime - TimeStampModTime;
       if (TimeStampAge <= Policy.Interval) {
         DEBUG(dbgs() << "Timestamp file too recent ("
Index: llvm/trunk/test/ThinLTO/X86/cache.ll
===================================================================
--- llvm/trunk/test/ThinLTO/X86/cache.ll
+++ llvm/trunk/test/ThinLTO/X86/cache.ll
@@ -5,7 +5,7 @@
 
 ; Verify that enabling caching is ignoring module without hash
 ; RUN: rm -Rf %t.cache && mkdir %t.cache
-; RUN: llvm-lto -thinlto-action=run -exported-symbol=globalfunc %t2.bc  %t.bc -thinlto-cache-dir %t.cache
+; RUN: llvm-lto -thinlto-action=run -exported-symbol=globalfunc %t2.bc %t.bc -thinlto-cache-dir %t.cache
 ; RUN: ls %t.cache/llvmcache.timestamp
 ; RUN: ls %t.cache | count 1
 
@@ -27,7 +27,7 @@
 ; files matching the pattern "llvmcache-*".
 ; RUN: rm -Rf %t.cache && mkdir %t.cache
 ; RUN: touch -t 197001011200 %t.cache/llvmcache-foo %t.cache/foo
-; RUN: llvm-lto -thinlto-action=run -exported-symbol=globalfunc %t2.bc  %t.bc -thinlto-cache-dir %t.cache
+; RUN: llvm-lto -thinlto-action=run -exported-symbol=globalfunc %t2.bc %t.bc -thinlto-cache-dir %t.cache
 ; RUN: ls %t.cache | count 4
 ; RUN: ls %t.cache/llvmcache.timestamp
 ; RUN: ls %t.cache/foo
@@ -36,13 +36,29 @@
 
 ; Verify that enabling caching is working with llvm-lto2
 ; RUN: rm -Rf %t.cache
-; RUN: llvm-lto2 run -o %t.o %t2.bc  %t.bc -cache-dir %t.cache \
+; RUN: llvm-lto2 run -o %t.o %t2.bc %t.bc -cache-dir %t.cache \
 ; RUN:  -r=%t2.bc,_main,plx \
 ; RUN:  -r=%t2.bc,_globalfunc,lx \
 ; RUN:  -r=%t.bc,_globalfunc,plx
 ; RUN: ls %t.cache | count 2
 ; RUN: ls %t.cache/llvmcache-* | count 2
 
+; Verify that caches with a timestamp older than the pruning interval
+; will be pruned
+; RUN: rm -Rf %t.cache && mkdir %t.cache
+; RUN: touch -t 197001011200 %t.cache/llvmcache-foo
+; RUN: touch -t 197001011200 %t.cache/llvmcache.timestamp
+; RUN: llvm-lto -thinlto-action=run -exported-symbol=globalfunc %t2.bc %t.bc -thinlto-cache-dir %t.cache
+; RUN: not ls %t.cache/llvmcache-foo
+
+; Verify that specifying a negative number for the pruning interval
+; effectively disables the pruning
+; RUN: rm -Rf %t.cache && mkdir %t.cache
+; RUN: touch -t 197001011200 %t.cache/llvmcache-foo
+; RUN: touch -t 197001011200 %t.cache/llvmcache.timestamp
+; RUN: llvm-lto -thinlto-action=run -exported-symbol=globalfunc %t2.bc %t.bc -thinlto-cache-dir %t.cache --thinlto-cache-pruning-interval -1
+; RUN: ls %t.cache/llvmcache-foo
+
 target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-apple-macosx10.11.0"
 
Index: llvm/trunk/tools/llvm-lto/llvm-lto.cpp
===================================================================
--- llvm/trunk/tools/llvm-lto/llvm-lto.cpp
+++ llvm/trunk/tools/llvm-lto/llvm-lto.cpp
@@ -156,6 +156,9 @@
 static cl::opt<std::string>
     ThinLTOCacheDir("thinlto-cache-dir", cl::desc("Enable ThinLTO caching."));
 
+static cl::opt<int>
+    ThinLTOCachePruningInterval("thinlto-cache-pruning-interval", cl::desc("Set ThinLTO cache pruning interval."));
+
 static cl::opt<std::string> ThinLTOSaveTempsPrefix(
     "thinlto-save-temps",
     cl::desc("Save ThinLTO temp files using filenames created by adding "
@@ -470,6 +473,7 @@
     ThinGenerator.setCodePICModel(getRelocModel());
     ThinGenerator.setTargetOptions(Options);
     ThinGenerator.setCacheDir(ThinLTOCacheDir);
+    ThinGenerator.setCachePruningInterval(ThinLTOCachePruningInterval);
     ThinGenerator.setFreestanding(EnableFreestanding);
 
     // Add all the exported symbols to the table of symbols to preserve.