Index: lib/Serialization/ASTWriter.cpp
===================================================================
--- lib/Serialization/ASTWriter.cpp
+++ lib/Serialization/ASTWriter.cpp
@@ -4279,9 +4279,13 @@
     return;
 
   RecordData Record;
+  // Sort to allow reproducible .pch files - https://bugs.debian.org/877359
+  std::map<TypeID, std::set<std::string>> sortedOpenCLTypeExtMap;
   for (const auto &I : SemaRef.OpenCLTypeExtMap) {
-    Record.push_back(
-        static_cast<unsigned>(getTypeID(I.first->getCanonicalTypeInternal())));
+    sortedOpenCLTypeExtMap[getTypeID(I.first->getCanonicalTypeInternal())]=I.second;
+  }
+  for (const auto &I : sortedOpenCLTypeExtMap) {
+    Record.push_back(static_cast<unsigned>(I.first));
     Record.push_back(I.second.size());
     for (auto Ext : I.second)
       AddString(Ext, Record);
@@ -4294,8 +4298,12 @@
     return;
 
   RecordData Record;
+  std::map<DeclID, std::set<std::string>> sortedOpenCLDeclExtMap;
   for (const auto &I : SemaRef.OpenCLDeclExtMap) {
-    Record.push_back(getDeclID(I.first));
+    sortedOpenCLDeclExtMap[getDeclID(I.first)]=I.second;
+  }
+  for (const auto &I : sortedOpenCLDeclExtMap) {
+    Record.push_back(I.first);
     Record.push_back(static_cast<unsigned>(I.second.size()));
     for (auto Ext : I.second)
       AddString(Ext, Record);