3 files changed, 66 insertions, 0 deletions

diff --git a/clang/lib/Sema/SemaAttr.cpp b/clang/lib/Sema/SemaAttr.cpp
index 34744cbdd99..3ffaab23a18 100644
--- a/clang/lib/Sema/SemaAttr.cpp
+++ b/clang/lib/Sema/SemaAttr.cpp
@@ -215,6 +215,7 @@ void Sema::PragmaStack<ValueType>::Act(SourceLocation PragmaLocation,
                                        ValueType Value) {
   if (Action == PSK_Reset) {
     CurrentValue = DefaultValue;
+    CurrentPragmaLocation = PragmaLocation;
     return;
   }
   if (Action & PSK_Push)
diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index 20a27607aca..9ef1378972e 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -3298,6 +3298,28 @@ ASTReader::ReadASTBlock(ModuleFile &F, unsigned ClientLoadCapabilities) {
       }
       ForceCUDAHostDeviceDepth = Record[0];
       break;
+
+    case PACK_PRAGMA_OPTIONS: {
+      if (Record.size() < 3) {
+        Error("invalid pragma pack record");
+        return Failure;
+      }
+      PragmaPackCurrentValue = Record[0];
+      PragmaPackCurrentLocation = ReadSourceLocation(F, Record[1]);
+      unsigned NumStackEntries = Record[2];
+      unsigned Idx = 3;
+      // Reset the stack when importing a new module.
+      PragmaPackStack.clear();
+      for (unsigned I = 0; I < NumStackEntries; ++I) {
+        PragmaPackStackEntry Entry;
+        Entry.Value = Record[Idx++];
+        Entry.Location = ReadSourceLocation(F, Record[Idx++]);
+        PragmaPackStrings.push_back(ReadString(Record, Idx));
+        Entry.SlotLabel = PragmaPackStrings.back();
+        PragmaPackStack.push_back(Entry);
+      }
+      break;
+    }
     }
   }
 }
@@ -7419,6 +7441,34 @@ void ASTReader::UpdateSema() {
         PointersToMembersPragmaLocation);
   }
   SemaObj->ForceCUDAHostDeviceDepth = ForceCUDAHostDeviceDepth;
+
+  if (PragmaPackCurrentValue) {
+    // The bottom of the stack might have a default value. It must be adjusted
+    // to the current value to ensure that the packing state is preserved after
+    // popping entries that were included/imported from a PCH/module.
+    bool DropFirst = false;
+    if (!PragmaPackStack.empty() &&
+        PragmaPackStack.front().Location.isInvalid()) {
+      assert(PragmaPackStack.front().Value == SemaObj->PackStack.DefaultValue &&
+             "Expected a default alignment value");
+      SemaObj->PackStack.Stack.emplace_back(
+          PragmaPackStack.front().SlotLabel, SemaObj->PackStack.CurrentValue,
+          SemaObj->PackStack.CurrentPragmaLocation);
+      DropFirst = true;
+    }
+    for (const auto &Entry :
+         llvm::makeArrayRef(PragmaPackStack).drop_front(DropFirst ? 1 : 0))
+      SemaObj->PackStack.Stack.emplace_back(Entry.SlotLabel, Entry.Value,
+                                            Entry.Location);
+    if (PragmaPackCurrentLocation.isInvalid()) {
+      assert(*PragmaPackCurrentValue == SemaObj->PackStack.DefaultValue &&
+             "Expected a default alignment value");
+      // Keep the current values.
+    } else {
+      SemaObj->PackStack.CurrentValue = *PragmaPackCurrentValue;
+      SemaObj->PackStack.CurrentPragmaLocation = PragmaPackCurrentLocation;
+    }
+  }
 }
 
 IdentifierInfo *ASTReader::get(StringRef Name) {
diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
index d2907bebbaa..9b479c24e20 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -4170,6 +4170,20 @@ void ASTWriter::WriteMSPointersToMembersPragmaOptions(Sema &SemaRef) {
   Stream.EmitRecord(POINTERS_TO_MEMBERS_PRAGMA_OPTIONS, Record);
 }
 
+/// \brief Write the state of 'pragma pack' at the end of the module.
+void ASTWriter::WritePackPragmaOptions(Sema &SemaRef) {
+  RecordData Record;
+  Record.push_back(SemaRef.PackStack.CurrentValue);
+  AddSourceLocation(SemaRef.PackStack.CurrentPragmaLocation, Record);
+  Record.push_back(SemaRef.PackStack.Stack.size());
+  for (const auto &StackEntry : SemaRef.PackStack.Stack) {
+    Record.push_back(StackEntry.Value);
+    AddSourceLocation(StackEntry.PragmaLocation, Record);
+    AddString(StackEntry.StackSlotLabel, Record);
+  }
+  Stream.EmitRecord(PACK_PRAGMA_OPTIONS, Record);
+}
+
 void ASTWriter::WriteModuleFileExtension(Sema &SemaRef,
                                          ModuleFileExtensionWriter &Writer) {
   // Enter the extension block.
@@ -4860,6 +4874,7 @@ ASTFileSignature ASTWriter::WriteASTCore(Sema &SemaRef, StringRef isysroot,
     WriteMSStructPragmaOptions(SemaRef);
     WriteMSPointersToMembersPragmaOptions(SemaRef);
   }
+  WritePackPragmaOptions(SemaRef);
 
   // Some simple statistics
   RecordData::value_type Record[] = {