[clang][modules] HeaderSearch::MarkFileModuleHeader creates extra HeaderFileInfo, breaks PCM reuse

HeaderSearch::MarkFileModuleHeader is no longer properly checking for no-changes, and so creates a new HeaderFileInfo for every `textual header`, causes PCM use to go ballistic.

Author: ian-twilightcoder

clang/include/clang/Lex/HeaderSearch.h

@@ -84,7 +84,9 @@ struct HeaderFileInfo {
   LLVM_PREFERRED_TYPE(bool)
   unsigned isModuleHeader : 1;
 
-  /// Whether this header is a `textual header` in a module.
+  /// Whether this header is a `textual header` in a module. If a header is
+  /// textual in one module and normal in another module, this bit will not be
+  /// set, only `isModuleHeader`.
   LLVM_PREFERRED_TYPE(bool)
   unsigned isTextualModuleHeader : 1;
 

clang/lib/Lex/HeaderSearch.cpp

@@ -1313,11 +1313,19 @@ OptionalFileEntryRef HeaderSearch::LookupSubframeworkHeader(
 // File Info Management.
 //===----------------------------------------------------------------------===//
 
+static bool moduleMembershipNeedsMerge(const HeaderFileInfo *HFI,
+                                       ModuleMap::ModuleHeaderRole Role) {
+  if (ModuleMap::isModular(Role))
+    return !HFI->isModuleHeader || HFI->isTextualModuleHeader;
+  else if (!HFI->isModuleHeader && (Role & ModuleMap::TextualHeader))
+    return !HFI->isTextualModuleHeader;
+  else
+    return false;
+}
+
 static void mergeHeaderFileInfoModuleBits(HeaderFileInfo &HFI,
                                           bool isModuleHeader,
                                           bool isTextualModuleHeader) {
-  assert((!isModuleHeader || !isTextualModuleHeader) &&
-         "A header can't build with a module and be textual at the same time");
   HFI.isModuleHeader |= isModuleHeader;
   if (HFI.isModuleHeader)
     HFI.isTextualModuleHeader = false;
@@ -1432,7 +1440,7 @@ void HeaderSearch::MarkFileModuleHeader(FileEntryRef FE,
     if ((Role & ModuleMap::ExcludedHeader))
       return;
     auto *HFI = getExistingFileInfo(FE);
-    if (HFI && HFI->isModuleHeader)
+    if (HFI && !moduleMembershipNeedsMerge(HFI, Role))
       return;
   }