Recommit r308327 2nd time: Add a warning for missing

'#pragma pack (pop)' and suspicious uses of '#pragma pack' in included files

The first recommit (r308441) caused a "non-default #pragma pack value might
change the alignment of struct or union members in the included file" warning
in LLVM itself. This recommit tweaks the added warning to avoid warnings for
#includes that don't have any records that are affected by the non-default
alignment. This tweak avoids the previously emitted warning in LLVM.

Original message:

This commit adds a new -Wpragma-pack warning. It warns in the following cases:

- When a translation unit is missing terminating #pragma pack (pop) directives.
- When entering an included file if the current alignment value as determined
  by '#pragma pack' directives is different from the default alignment value.
- When leaving an included file that changed the state of the current alignment
  value.

rdar://10184173

Differential Revision: https://reviews.llvm.org/D35484

llvm-svn: 309106

1 files changed, 54 insertions, 0 deletions

diff --git a/clang/lib/Sema/Sema.cpp b/clang/lib/Sema/Sema.cpp
index 6f0db6ce1c6..40ffa09de1a 100644
--- a/clang/lib/Sema/Sema.cpp
+++ b/clang/lib/Sema/Sema.cpp
@@ -70,6 +70,49 @@ void Sema::ActOnTranslationUnitScope(Scope *S) {
   PushDeclContext(S, Context.getTranslationUnitDecl());
 }
 
+namespace clang {
+namespace sema {
+
+class SemaPPCallbacks : public PPCallbacks {
+  Sema *S = nullptr;
+  llvm::SmallVector<SourceLocation, 8> IncludeStack;
+
+public:
+  void set(Sema &S) { this->S = &S; }
+
+  void reset() { S = nullptr; }
+
+  virtual void FileChanged(SourceLocation Loc, FileChangeReason Reason,
+                           SrcMgr::CharacteristicKind FileType,
+                           FileID PrevFID) override {
+    if (!S)
+      return;
+    switch (Reason) {
+    case EnterFile: {
+      SourceManager &SM = S->getSourceManager();
+      SourceLocation IncludeLoc = SM.getIncludeLoc(SM.getFileID(Loc));
+      if (IncludeLoc.isValid()) {
+        IncludeStack.push_back(IncludeLoc);
+        S->DiagnoseNonDefaultPragmaPack(
+            Sema::PragmaPackDiagnoseKind::NonDefaultStateAtInclude, IncludeLoc);
+      }
+      break;
+    }
+    case ExitFile:
+      if (!IncludeStack.empty())
+        S->DiagnoseNonDefaultPragmaPack(
+            Sema::PragmaPackDiagnoseKind::ChangedStateAtExit,
+            IncludeStack.pop_back_val());
+      break;
+    default:
+      break;
+    }
+  }
+};
+
+} // end namespace sema
+} // end namespace clang
+
 Sema::Sema(Preprocessor &pp, ASTContext &ctxt, ASTConsumer &consumer,
            TranslationUnitKind TUKind, CodeCompleteConsumer *CodeCompleter)
     : ExternalSource(nullptr), isMultiplexExternalSource(false),
@@ -122,6 +165,12 @@ Sema::Sema(Preprocessor &pp, ASTContext &ctxt, ASTConsumer &consumer,
 
   // Initilization of data sharing attributes stack for OpenMP
   InitDataSharingAttributesStack();
+
+  std::unique_ptr<sema::SemaPPCallbacks> Callbacks =
+      llvm::make_unique<sema::SemaPPCallbacks>();
+  SemaPPCallbackHandler = Callbacks.get();
+  PP.addPPCallbacks(std::move(Callbacks));
+  SemaPPCallbackHandler->set(*this);
 }
 
 void Sema::addImplicitTypedef(StringRef Name, QualType T) {
@@ -306,6 +355,10 @@ Sema::~Sema() {
   // Destroys data sharing attributes stack for OpenMP
   DestroyDataSharingAttributesStack();
 
+  // Detach from the PP callback handler which outlives Sema since it's owned
+  // by the preprocessor.
+  SemaPPCallbackHandler->reset();
+
   assert(DelayedTypos.empty() && "Uncorrected typos!");
 }
 
@@ -766,6 +819,7 @@ void Sema::ActOnEndOfTranslationUnit() {
     CheckDelayedMemberExceptionSpecs();
   }
 
+  DiagnoseUnterminatedPragmaPack();
   DiagnoseUnterminatedPragmaAttribute();
 
   // All delayed member exception specs should be checked or we end up accepting