[Serialization] Add support for (de)serializing #pragma pack

Serialization of tokens is required when PCH is used with late parsed
templates, including annotation tokens used for pragmas.

This patch implements the serialization for annot_pragma_pack.

Fixes https://github.com/llvm/llvm-project/issues/60543

Differential Revision: https://reviews.llvm.org/D143410

clang/include/clang/Sema/Sema.h

@@ -483,6 +483,12 @@ public:
     PSK_Pop_Set   = PSK_Pop | PSK_Set,  // #pragma (pop[, id], value)
   };
 
+  struct PragmaPackInfo {
+    PragmaMsStackAction Action;
+    StringRef SlotLabel;
+    Token Alignment;
+  };
+
   // #pragma pack and align.
   class AlignPackInfo {
   public:

clang/include/clang/Serialization/ASTReader.h

@@ -2236,7 +2236,7 @@ public:
                               unsigned &Idx, LocSeq *Seq = nullptr);
 
   // Read a string
-  static std::string ReadString(const RecordData &Record, unsigned &Idx);
+  static std::string ReadString(const RecordDataImpl &Record, unsigned &Idx);
 
   // Skip a string
   static void SkipString(const RecordData &Record, unsigned &Idx) {

clang/lib/Parse/ParsePragma.cpp

@@ -665,18 +665,10 @@ void Parser::HandlePragmaVisibility() {
   Actions.ActOnPragmaVisibility(VisType, VisLoc);
 }
 
-namespace {
-struct PragmaPackInfo {
-  Sema::PragmaMsStackAction Action;
-  StringRef SlotLabel;
-  Token Alignment;
-};
-} // end anonymous namespace
-
 void Parser::HandlePragmaPack() {
   assert(Tok.is(tok::annot_pragma_pack));
-  PragmaPackInfo *Info =
-    static_cast<PragmaPackInfo *>(Tok.getAnnotationValue());
+  Sema::PragmaPackInfo *Info =
+      static_cast<Sema::PragmaPackInfo *>(Tok.getAnnotationValue());
   SourceLocation PragmaLoc = Tok.getLocation();
   ExprResult Alignment;
   if (Info->Alignment.is(tok::numeric_constant)) {
@@ -2110,8 +2102,8 @@ void PragmaPackHandler::HandlePragma(Preprocessor &PP,
     return;
   }
 
-  PragmaPackInfo *Info =
-      PP.getPreprocessorAllocator().Allocate<PragmaPackInfo>(1);
+  Sema::PragmaPackInfo *Info =
+      PP.getPreprocessorAllocator().Allocate<Sema::PragmaPackInfo>(1);
   Info->Action = Action;
   Info->SlotLabel = SlotLabel;
   Info->Alignment = Alignment;

clang/lib/Serialization/ASTReader.cpp

@@ -1687,6 +1687,16 @@ Token ASTReader::ReadToken(ModuleFile &F, const RecordDataImpl &Record,
       Tok.setAnnotationValue(static_cast<void *>(Info));
       break;
     }
+    case tok::annot_pragma_pack: {
+      auto *Info = new (PP.getPreprocessorAllocator()) Sema::PragmaPackInfo;
+      Info->Action = static_cast<Sema::PragmaMsStackAction>(Record[Idx++]);
+      auto SlotLabel = ReadString(Record, Idx);
+      Info->SlotLabel =
+          llvm::StringRef(SlotLabel).copy(PP.getPreprocessorAllocator());
+      Info->Alignment = ReadToken(F, Record, Idx);
+      Tok.setAnnotationValue(static_cast<void *>(Info));
+      break;
+    }
     // Some annotation tokens do not use the PtrData field.
     case tok::annot_pragma_openmp:
     case tok::annot_pragma_openmp_end:
@@ -9084,7 +9094,7 @@ llvm::APFloat ASTRecordReader::readAPFloat(const llvm::fltSemantics &Sem) {
 }
 
 // Read a string
-std::string ASTReader::ReadString(const RecordData &Record, unsigned &Idx) {
+std::string ASTReader::ReadString(const RecordDataImpl &Record, unsigned &Idx) {
   unsigned Len = Record[Idx++];
   std::string Result(Record.data() + Idx, Record.data() + Idx + Len);
   Idx += Len;

clang/lib/Serialization/ASTWriter.cpp

@@ -4412,6 +4412,14 @@ void ASTWriter::AddToken(const Token &Tok, RecordDataImpl &Record) {
         AddToken(T, Record);
       break;
     }
+    case tok::annot_pragma_pack: {
+      auto *Info =
+          static_cast<Sema::PragmaPackInfo *>(Tok.getAnnotationValue());
+      Record.push_back(static_cast<unsigned>(Info->Action));
+      AddString(Info->SlotLabel, Record);
+      AddToken(Info->Alignment, Record);
+      break;
+    }
     // Some annotation tokens do not use the PtrData field.
     case tok::annot_pragma_openmp:
     case tok::annot_pragma_openmp_end:

clang/test/PCH/delayed-template-with-pragma-pack.cpp

@@ -0,0 +1,78 @@
+// RUN: %clang_cc1 -triple x86_64-pc-windows-msvc -emit-pch -o %t.pch %s
+// RUN: %clang_cc1 -triple x86_64-pc-windows-msvc -fdelayed-template-parsing -emit-pch -o %t.delayed.pch %s
+// RUN: %clang_cc1 -triple x86_64-pc-windows-msvc -DMAIN_FILE \
+// RUN:   -include-pch %t.pch \
+// RUN:   -emit-llvm -verify -o - %s | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-pc-windows-msvc -DMAIN_FILE -fdelayed-template-parsing \
+// RUN:   -include-pch %t.delayed.pch \
+// RUN:   -emit-llvm -verify -o - %s | FileCheck %s
+
+#ifndef MAIN_FILE
+
+extern "C" void consume(int b);
+
+template <int I>
+void function() {
+#pragma pack(push, 1)
+  struct packedAt1 {
+    char a;
+    unsigned long long b;
+    char c;
+    unsigned long long d;
+    // 18 bytes total
+  };
+#pragma pack(push, slot1, 2)
+  struct packedAt2 {
+    char a; // +1 byte of padding
+    unsigned long long b;
+    char c; // +1 byte of padding
+    unsigned long long d;
+    // 20 bytes total
+  };
+#pragma pack(push, 4)
+  struct packedAt4 {
+    char a; // +3 bytes of padding
+    unsigned long long b;
+    char c; // +3 bytes of padding
+    unsigned long long d;
+    // 24 bytes total
+  };
+#pragma pack(push, 16)
+  struct packedAt16 {
+    char a; // +7 bytes of padding
+    unsigned long long b;
+    char c; // +7 bytes of padding
+    unsigned long long d;
+    // 32 bytes total
+  };
+#pragma pack(pop, slot1) // This should return packing to 1 (established before push(slot1))
+  struct packedAfterPopBackTo1 {
+    char a;
+    unsigned long long b;
+    char c;
+    unsigned long long d;
+  };
+#pragma pack(pop)
+
+  consume(sizeof(packedAt1)); // 18
+  consume(sizeof(packedAt2)); // 20
+  consume(sizeof(packedAt4)); // 24
+  consume(sizeof(packedAt16)); // 32
+  consume(sizeof(packedAfterPopBackTo1)); // 18 again
+}
+
+#else
+
+// CHECK-LABEL: define linkonce_odr dso_local void @"??$function@$0A@@@YAXXZ"(
+// CHECK: call void @consume(i32 noundef 18)
+// CHECK-NEXT: call void @consume(i32 noundef 20)
+// CHECK-NEXT: call void @consume(i32 noundef 24)
+// CHECK-NEXT: call void @consume(i32 noundef 32)
+// CHECK-NEXT: call void @consume(i32 noundef 18)
+void foo() {
+  function<0>();
+}
+
+// expected-no-diagnostics
+
+#endif