Implementation of #pragma (data|code|const|bss)_seg

[whunt]

Summary

This patch implements the microsoft segment pragmas. As posted it works up to testing but it needs a little polish and some lit tests. Particularly I'm pretty sure that the way I assign the code_seg attribute in CheckFunctionDeclaration is wrong. Another thing to note about this patch is that it introduces a unified pragma lexer for microsoft pragmas. This lexer basically just snarfs up some tokens, adds a marker token and passes them all onto the parser, which actually parses the tokens. The idea is that all past and future ms pragmas would migrate to this pattern.

[whunt]

Also, to note, we can't actually emit appropriate section properties. See http://lists.cs.uiuc.edu/pipermail/llvmdev/2014-March/071058.html . Either way, I still need to add diagnostics for when the section type requested is not fulfillable.

[whunt]

Ping.

Also, I looked at all of the Microsoft pragams and 6 of them use a labeled stack data_seg, bss_seg, const_seg, code_seg, pack and conform. If we choose to template MSSegmentStack, we can reasonably pull in pack (a value of 0 isn't a ligitimate argument and can be used, like nullptr, to indicate that we're pushing or poping w/o changing the setting). Putting in conform is much trickier because conform takes multiple extra arguments. There is significantly more error checking code in the pragma pack handler than in the ms one (for example #pragma_bss(pop) with no stack or after a reset is a no-op not an error). Fusing the logic for stack with the others would either involve a bunch of special-casing or we'd end up having much stricter rules about how some of these pragmas work than msvc does.

Pragmas float_control, managed, unmanaged, strict_gs_check, warning and vtordisp use an unlabeled stack. the first 4 push booleans, as does vtordisp, although in a slightly different way. warning pushes a small integer.

[rsmith]

include/clang/Sema/Sema.h

307–308

I can't guess what these three fields are. Maybe this should be a struct?

313–316

We should serialize/deserialize these if they occur in a PCH (but we shouldn't do so if they're in a module). I don't think anyone is particularly likely to care about this, but please at least add a FIXME.

lib/Parse/ParseDeclCXX.cpp

2618–2621

Do you really need to check for this in so many places? (Do none of them call the other ones?) ;(

lib/Parse/ParsePragma.cpp

1313–1323

Dropping the eod delimiter from the stream here looks questionable. You have no way to distinguish between

#pragma code_seg(blah)

and

#pragma code_seg
(blah)

Error recovery might also do strange things if the tokens from the pragma are in the normal token stream, since the rest of the parser isn't aware that annot_pragma_ms_pragma opens some kind of token scope. Maybe you could set the list of tokens as the annotation value on the annot_pragma_ms_pragma token instead?

lib/Sema/SemaDecl.cpp

7498

Commented-out code?

[whunt]

include/clang/Sema/Sema.h

307–308

Done.

313–316

FIXME added.

lib/Parse/ParseDeclCXX.cpp

2618–2621

Other patches that add pragmas touch each of these places.

lib/Parse/ParsePragma.cpp

1313–1323

Fixed.

lib/Sema/SemaDecl.cpp

7498

Moved to ActOnFunctionDeclarator to get the definitionness.

[whunt]

This update constitutes a significant re-write of the previous version of the patch.
The unified MS-pragma handler has been updated to consume the token stream for the pragma up to eod and attach it to the annotation token, capped with an eof. The parser inserts the tokens back into the stream and parses them.
PragmaStack has been templated for future unification with the stack used by pragma pack.

[rnk]

include/clang/Sema/Sema.h

7066–7089

IMO we should only have one action here, and make the attribute kind a parameter. We'll need to add one more for init_seg anyway.

lib/Parse/ParsePragma.cpp

441

Rather than making a new enum, how about using MSSegmentAttr::CodeSeg, etc? We should be able to include clang/AST/Attr.h from here.

449

gotos aren't common in LLVM, and there aren't any ALL_CAPS names, even for macros or enums.

I'd rather have a static helper like eatPastEOFToken() and do 'return eatPastEOFToken(PP)' for all of these gotos. Nevermind that we're returning void. :)

502–509

Once we use MSSegmentAttr::Kind, we collapse these Sema actions down to ActOnPragmaMSSegment() and make the kind a parameter.

[rsmith]

lib/Parse/ParsePragma.cpp

438

It's strange to use PP.Lex here -- in the parser you should generally be using ConsumeToken instead. If you're trying to avoid updating PrevTokLocation (which seems like a good idea, since pragma tokens aren't tokens in the usual sense), you're not doing enough, because BalancedDelimiterTracker and ParseStringLiteralExpression will update it. Maybe save and restore it on entry to/exit from this function, and use ConsumeToken here?

485

Don't call this unless isTokenStringLiteral(), or it'll assert.

487

In this case, a diagnostic will already have been produced. (Generally speaking, when a function returns you an invalid *Result or a function returning bool on error returns true, that indicates that it has already produced a diagnostic.)

490–493

This would fit better in the ActOn... functions. Generally, we try to avoid the parser inspecting AST nodes.

[whunt]

A major overhaul. The patch now considers attribute((section())), declspec(allocate()) and #pragma section. I've also added gcc style diagnostics for section conflicts (a behavior clang lacked for attribute__((section()))). I've added test cases for both Sema and CodeGen. The CodeGen test case reuses an old file-name and moves its contents to a more appropriately named test.

Note: There is one known outstanding issue with the patch: In C mode, due to tentative declarations, we don't actually process uninitialized variables until the end of the TU, which means they get stuck in whatever section the last #pragma bss_seg() dictates, rather than the one that was active when they were defined.

[whunt]

Addresses Aaron's comments. Also rebased and incorporates init_seg using the unified MS pragma handling machinery.
Specific comments:

• added documentation for the __declspec(allocate) attribute
• warnings were added and expanded upon, but could not be fused
• XXXXSeg renamed to Segment
• Fixed style issues around &and *
• SectionInfo will be read during codegen (we can make it private and add an interface if we really need to, noone's going to access it for anything they don't need...)
• Added a significant number of parser tests, found a bug and fixed that
• Added a custom diagnostic for shared, nopage, nocache, discard and remove
• Fixed things that would break MSVC2012
• Other random small fixes requested.

Specific Replies:

• We're using eof instead of eod for our pragmas due to the way that certain parser helpers work. Things like parsestringliteral can walk through an eod but not an eof. Richard Smith suggested this.
• After talking to a couple people here about [&] for the lambdas (I'm new to lambdas and am looking for guidance) there was some consensus that these lambdas are both so short and used so locally that being more explicit about what exactly they capture is not particularly more clear and adds code.
• The Add followed by Remove process (rather than making the add conditional based on it not being immediately removed) significantly simplified the implantation logic by allowing Unify to always look at the attribute. Given that this particular piece of code is colder than cold (someone is mis-using an extremely rare and specific pragma) I opted for code size/simplicity over performance.

[rnk]

Looks good, feel free to commit with some tweaks.

include/clang/Basic/DiagnosticParseKinds.td

775

I think you omitted "in" before '#pragma'

include/clang/Sema/Sema.h

277

Looks like these are used as flags. Can you give the enumerators explicit hex values to make that clear? I thought "Val & PSK_Push" was a bug.

7092

I'm not sure what the S in PSK stands for. Maybe PMK for PragmaMsKind?

7111

This can be SectionInfo() = default so the default ctor is still trivial.

lib/Parse/ParsePragma.cpp

563

indentation

lib/Sema/SemaAttr.cpp

328–342

This function looks like it has bugs, but it's dead and should be deleted.

lib/Sema/SemaDecl.cpp

7070

indentation

8972

indentation

[Eugene.Zelenko]

Committed in rL205810.

include/clang/Basic/Attr.td

   let Documentation = [MSInheritanceDocs];
 }
 
+def MSSegment : Attr {
+  // This attribute has no spellings as it is only ever created implicitly.
+  let Spellings = [];
+  let Args = [StringArgument<"SegName">, UnsignedArgument<"kind">];
+
+  let AdditionalMembers = [{
+  enum Kind {
+    DataSeg,
+    BSSSeg,
+    ConstSeg,
+    CodeSeg
+  };
+
+  Kind getSegKind() const { return Kind(kind); }
+  }];
+  let Documentation = [Undocumented];
+}
+
 def MSVtorDisp : InheritableAttr {
   // This attribute has no spellings as it is only ever created implicitly.
   let Spellings = [];

include/clang/Basic/DiagnosticParseKinds.td

   "missing ')' after '#pragma %0' - ignoring">, InGroup<IgnoredPragmas>;
 def warn_pragma_expected_identifier : Warning<
   "expected identifier in '#pragma %0' - ignored">, InGroup<IgnoredPragmas>;
+def warn_pragma_expected_string : Warning<
+  "expected string literal in '#pragma %0' - ignored">, InGroup<IgnoredPragmas>;
 def warn_pragma_expected_integer : Warning<
   "expected integer between %0 and %1 inclusive in '#pragma %2' - ignored">,
   InGroup<IgnoredPragmas>;

include/clang/Basic/TokenKinds.def

 // handles them.
 ANNOTATION(pragma_ms_vtordisp)
 
+// Annotation for all microsoft #pragmas...
+// The lexer produces these so that they only take effect when the parser
+// handles them.
+ANNOTATION(pragma_ms_pragma)
+
 // Annotation for #pragma OPENCL EXTENSION...
 // The lexer produces these so that they only take effect when the parser
 // handles them.

include/clang/Parse/Parser.h

   std::unique_ptr<PragmaHandler> MSDetectMismatchHandler;
   std::unique_ptr<PragmaHandler> MSPointersToMembers;
   std::unique_ptr<PragmaHandler> MSVtorDisp;
+  std::unique_ptr<PragmaHandler> MSDataSeg;
+  std::unique_ptr<PragmaHandler> MSBSSSeg;
+  std::unique_ptr<PragmaHandler> MSConstSeg;
+  std::unique_ptr<PragmaHandler> MSCodeSeg;
 
   std::unique_ptr<CommentHandler> CommentSemaHandler;
 

 
   void HandlePragmaMSVtorDisp();
 
+  void HandlePragmaMSPragma();
+
   /// \brief Handle the annotation token produced for
   /// #pragma align...
   void HandlePragmaAlign();

include/clang/Sema/Sema.h

     PVDK_Reset          ///< #pragma vtordisp()
   };
 
+  enum PragmaMsStackAction {
+    PSK_Reset,    // #pragma ()
+    PSK_Set,      // #pragma ("name")
+    PSK_Push,     // #pragma (push[, id])
+    PSK_Push_Set, // #pragma (push[, id], "name")
+    PSK_Pop,      // #pragma (pop[, id])
+    PSK_Pop_Set,  // #pragma (pop[, id], "name")
+  };
+
   /// \brief Whether to insert vtordisps prior to virtual bases in the Microsoft
   /// C++ ABI.  Possible values are 0, 1, and 2, which mean:
   ///

   /// \brief Source location for newly created implicit MSInheritanceAttrs
   SourceLocation ImplicitMSInheritanceAttrLoc;
 
+  template<typename ValueType>
+  struct PragmaStack {
+    struct Slot {
+      llvm::StringRef StackSlotLabel;
+      ValueType Value;
+      SourceLocation PragmaLocation;
+    };
+    void Act(SourceLocation PragmaLocation,
+             PragmaMsStackAction Action,
+             llvm::StringRef StackSlotLabel,
+             ValueType Value);
+    explicit PragmaStack(const ValueType& Value)
+      : CurrentValue(Value) {}
+    SmallVector<Slot, 2> Stack;
+    ValueType CurrentValue;
+    SourceLocation CurrentPragmaLocation;
+  };
+  // FIXME: We should serialize / deserialize these if they occur in a PCH (but
+  // we shouldn't do so if they're in a module).
+  PragmaStack<StringLiteral *> DataSegStack;
+  PragmaStack<StringLiteral *> BSSSegStack;
+  PragmaStack<StringLiteral *> ConstSegStack;
+  PragmaStack<StringLiteral *> CodeSegStack;
+
   /// VisContext - Manages the stack for \#pragma GCC visibility.
   void *VisContext; // Really a "PragmaVisStack*"
 

   void ActOnPragmaMSVtorDisp(PragmaVtorDispKind Kind, SourceLocation PragmaLoc,
                              MSVtorDispAttr::Mode Value);
 
+  /// \brief Called on well formed \#pragma data_seg().
+  void ActOnPragmaMSDataSeg(SourceLocation PragmaLocation,
+                            PragmaMsStackAction Action,
+                            llvm::StringRef StackSlotLabel,
+                            StringLiteral *SegmentName);
+
+  /// \brief Called on well formed \#pragma bss_seg().
+  void ActOnPragmaMSBSSSeg(SourceLocation PragmaLocation,
+                          PragmaMsStackAction Action,
+                          llvm::StringRef StackSlotLabel,
+                          StringLiteral *SegmentName);
+
+  /// \brief Called on well formed \#pragma const_seg().
+  void ActOnPragmaMSConstSeg(SourceLocation PragmaLocation,
+                             PragmaMsStackAction Action,
+                             llvm::StringRef StackSlotLabel,
+                             StringLiteral *SegmentName);
+
+  /// \brief Called on well formed \#pragma code_seg().
+  void ActOnPragmaMSCodeSeg(SourceLocation PragmaLocation,
+                            PragmaMsStackAction Action,
+                            llvm::StringRef StackSlotLabel,
+                            StringLiteral *SegmentName);
+
   /// ActOnPragmaDetectMismatch - Call on well-formed \#pragma detect_mismatch
   void ActOnPragmaDetectMismatch(StringRef Name, StringRef Value);
 

lib/CodeGen/CodeGenModule.cpp

   if (const SectionAttr *SA = D->getAttr<SectionAttr>())
     GV->setSection(SA->getName());
 
+  if (D->hasAttr<MSSegmentAttr>())
+    GV->setSection(D->getAttr<MSSegmentAttr>()->getSegName());
+
   // Alias cannot have attributes. Filter them here.
   if (!isa<llvm::GlobalAlias>(GV))
     getTargetCodeGenInfo().SetTargetAttributes(D, GV, *this);

lib/Parse/ParseDeclCXX.cpp

         continue;
       }
 
+      if (Tok.is(tok::annot_pragma_ms_pragma)) {
+        HandlePragmaMSPragma();
+        continue;
+      }
+
       // If we see a namespace here, a close brace was missing somewhere.
       if (Tok.is(tok::kw_namespace)) {
         DiagnoseUnexpectedNamespace(cast<NamedDecl>(TagDecl));

lib/Parse/ParsePragma.cpp

 //
 //===----------------------------------------------------------------------===//
 
+#include "RAIIObjectsForParser.h"
 #include "clang/Lex/Preprocessor.h"
 #include "clang/Parse/ParseDiagnostic.h"
 #include "clang/Parse/Parser.h"

                     Token &FirstToken) override;
 };
 
+struct PragmaMSPragma : public PragmaHandler {
+  explicit PragmaMSPragma(const char *name) : PragmaHandler(name) {}
+  virtual void HandlePragma(Preprocessor &PP, PragmaIntroducerKind Introducer,
+    Token &FirstToken);
+};
+
 }  // end namespace
 
 void Parser::initializePragmaHandlers() {

     PP.AddPragmaHandler(MSPointersToMembers.get());
     MSVtorDisp.reset(new PragmaMSVtorDisp());
     PP.AddPragmaHandler(MSVtorDisp.get());
+    MSDataSeg.reset(new PragmaMSPragma("data_seg"));
+    PP.AddPragmaHandler(MSDataSeg.get());
+    MSBSSSeg.reset(new PragmaMSPragma("bss_seg"));
+    PP.AddPragmaHandler(MSBSSSeg.get());
+    MSConstSeg.reset(new PragmaMSPragma("const_seg"));
+    PP.AddPragmaHandler(MSConstSeg.get());
+    MSCodeSeg.reset(new PragmaMSPragma("code_seg"));
+    PP.AddPragmaHandler(MSCodeSeg.get());
   }
 }
 

     MSPointersToMembers.reset();
     PP.RemovePragmaHandler(MSVtorDisp.get());
     MSVtorDisp.reset();
+    PP.RemovePragmaHandler(MSDataSeg.get());
+    MSDataSeg.reset();
+    PP.RemovePragmaHandler(MSBSSSeg.get());
+    MSBSSSeg.reset();
+    PP.RemovePragmaHandler(MSConstSeg.get());
+    MSConstSeg.reset();
+    PP.RemovePragmaHandler(MSCodeSeg.get());
+    MSCodeSeg.reset();
   }
 
   PP.RemovePragmaHandler("STDC", FPContractHandler.get());

   Actions.ActOnPragmaMSVtorDisp(Kind, PragmaLoc, Mode);
 }
 
+void Parser::HandlePragmaMSPragma() {
+  assert(Tok.is(tok::annot_pragma_ms_pragma));
+  // Grab the tokens out of the annotation and enter them into the stream.
+  auto TheTokens = (std::pair<Token*, size_t> *)Tok.getAnnotationValue();
+  PP.EnterTokenStream(TheTokens->first, TheTokens->second, true, true);
+  SourceLocation PragmaLoc = ConsumeToken(); // The annotation token.
+  assert(Tok.isAnyIdentifier());
+  llvm::StringRef PragmaName = Tok.getIdentifierInfo()->getName();
+  // Note! BalancedDelimiterTracker throws an error if it fails to match
+  // correctly.  This is different than MSVCs behvaior that malformed pragmas
+  // are ignored with a warning.
+  BalancedDelimiterTracker Parens(*this, tok::l_paren, tok::eof);
+  PP.Lex(Tok); // pragma kind
+  // Figure out which #pragma we're dealing with.  The switch has no default
+  // because lex shouldn't emit the annotation token for unrecognized pragmas.
+  enum PragmaMSKind { DataSeg, BSSSeg, ConstSeg, CodeSeg } Kind =
+    llvm::StringSwitch<PragmaMSKind>(PragmaName)
+      .Case("data_seg", DataSeg)
+      .Case("bss_seg", BSSSeg)
+      .Case("const_seg", ConstSeg)
+      .Case("code_seg", CodeSeg);
+  llvm::StringRef SlotLabel;
+  if (Parens.consumeOpen())
+    goto ERROR_RETURN;
+  Sema::PragmaMsStackAction Action = Sema::PSK_Reset;
+  if (Tok.isAnyIdentifier()) {
+    llvm::StringRef PushPop = Tok.getIdentifierInfo()->getName();
+    if (PushPop == "push")
+      Action = Sema::PSK_Push;
+    else if (PushPop == "pop")
+      Action = Sema::PSK_Pop;
+    else {
+      PP.Diag(PragmaLoc, diag::warn_pragma_invalid_action) << PragmaName;
+      goto ERROR_RETURN;
+    }
+    if (Action != Sema::PSK_Reset) {
+      PP.Lex(Tok); // push | pop
+      if (Tok.is(tok::comma)) {
+        PP.Lex(Tok); // ,
+        // If we've got a comma, we either need a 
+        if (Tok.isAnyIdentifier()) {
+          SlotLabel = Tok.getIdentifierInfo()->getName();
+          PP.Lex(Tok); // identifier
+          if (Tok.is(tok::comma))
+            PP.Lex(Tok);
+          else if (Tok.isNot(tok::r_paren)) {
+            PP.Diag(PragmaLoc, diag::warn_pragma_expected_punc) << PragmaName;
+            goto ERROR_RETURN;
+          }
+        }
+      } else if (Tok.isNot(tok::r_paren)) {
+        PP.Diag(PragmaLoc, diag::warn_pragma_expected_punc) << PragmaName;
+        goto ERROR_RETURN;
+      }
+    }
+  }
+  // Grab the string literal for our section name.
+  StringLiteral *SegmentName = nullptr;
+  if (Tok.isNot(tok::r_paren)) {
+    ExprResult SegmentNameExpr = ParseStringLiteralExpression();
+    if (SegmentNameExpr.isInvalid()) {
+      PP.Diag(PragmaLoc, diag::warn_pragma_expected_string) << PragmaName;
+      goto ERROR_RETURN;
+    }
+    SegmentName = cast<StringLiteral>(SegmentNameExpr.get());
+    // Setting section "" has no effect
+    if (SegmentName->getLength())
+      Action = (Sema::PragmaMsStackAction)(Action | Sema::PSK_Set);
+  }
+  if (Parens.consumeClose())
+    goto ERROR_RETURN;
+  if (Tok.isNot(tok::eof)) {
+    PP.Diag(PragmaLoc, diag::warn_pragma_extra_tokens_at_eol) << PragmaName;
+    goto ERROR_RETURN;
+  }
+  PP.Lex(Tok); // eof
+  if (Kind == DataSeg)
+    Actions.ActOnPragmaMSDataSeg(PragmaLoc, Action, SlotLabel, SegmentName);
+  else if (Kind == BSSSeg)
+    Actions.ActOnPragmaMSBSSSeg(PragmaLoc, Action, SlotLabel, SegmentName);
+  else if (Kind == ConstSeg)
+    Actions.ActOnPragmaMSConstSeg(PragmaLoc, Action, SlotLabel, SegmentName);
+  else if (Kind == CodeSeg)
+    Actions.ActOnPragmaMSCodeSeg(PragmaLoc, Action, SlotLabel, SegmentName);
+  return;
+ERROR_RETURN:
+  SkipUntil(tok::eof);
+  PP.Lex(Tok); // tok::eof
+}
+
 // #pragma GCC visibility comes in two variants:
 //   'push' '(' [visibility] ')'
 //   'pop'

   PP.EnterToken(AnnotTok);
 }
 
+/// \brief Handle all MS pragmas.  Simply forwards the tokens after inserting
+/// an annotation token.
+void PragmaMSPragma::HandlePragma(Preprocessor &PP,
+                                  PragmaIntroducerKind Introducer,
+                                  Token &Tok) {
+  Token EoF, AnnotTok;
+  EoF.startToken();
+  EoF.setKind(tok::eof);
+  AnnotTok.startToken();
+  AnnotTok.setKind(tok::annot_pragma_ms_pragma);
+  AnnotTok.setLocation(Tok.getLocation());
+  SmallVector<Token, 8> TokenVector;
+  // Suck up all of the tokens before the eod.
+  for (; Tok.isNot(tok::eod); PP.Lex(Tok))
+    TokenVector.push_back(Tok);
+  // Add a sentinal EoF token to the end of the list.
+  TokenVector.push_back(EoF);
+  // We must allocate this array with new because EnterTokenStream is going to
+  // delete it later.
+  Token *TokenArray = new Token[TokenVector.size()];
+  memcpy(TokenArray, TokenVector.data(), sizeof(Token) * TokenVector.size());
+  auto Value = new (PP.getPreprocessorAllocator())
+      std::pair<Token*, size_t>(std::make_pair(TokenArray, TokenVector.size()));
+  AnnotTok.setAnnotationValue(Value);
+  PP.EnterToken(AnnotTok);
+}
+
 /// \brief Handle the Microsoft \#pragma detect_mismatch extension.
 ///
 /// The syntax is:

lib/Parse/ParseStmt.cpp

     HandlePragmaMSPointersToMembers();
     return StmtEmpty();
 
+  case tok::annot_pragma_ms_pragma:
+    ProhibitAttributes(Attrs);
+    HandlePragmaMSPragma();
+    return StmtEmpty();
   }
 
   // If we reached this code, the statement must end in a semicolon.

     case tok::annot_pragma_ms_pointers_to_members:
       HandlePragmaMSPointersToMembers();
       break;
+    case tok::annot_pragma_ms_pragma:
+      HandlePragmaMSPragma();
+      break;
     default:
       checkForPragmas = false;
       break;

lib/Parse/Parser.cpp

   case tok::annot_pragma_ms_vtordisp:
     HandlePragmaMSVtorDisp();
     return DeclGroupPtrTy();
+  case tok::annot_pragma_ms_pragma:
+    HandlePragmaMSPragma();
+    return DeclGroupPtrTy();
   case tok::semi:
     // Either a C++11 empty-declaration or attribute-declaration.
     SingleDecl = Actions.ActOnEmptyDeclaration(getCurScope(),

lib/Sema/Sema.cpp

     MSPointerToMemberRepresentationMethod(
         LangOpts.getMSPointerToMemberRepresentationMethod()),
     VtorDispModeStack(1, MSVtorDispAttr::Mode(LangOpts.VtorDispMode)),
-    VisContext(0),
+    DataSegStack(nullptr), BSSSegStack(nullptr), ConstSegStack(nullptr),
+    CodeSegStack(nullptr), VisContext(0),
     IsBuildingRecoveryCallExpr(false),
     ExprNeedsCleanups(false), LateTemplateParser(0), OpaqueParser(0),
     IdResolver(pp), StdInitializerList(0), CXXTypeInfoDecl(0), MSVCGuidDecl(0),

lib/Sema/SemaAttr.cpp

   }
 }
 
+template<typename Type> Type
+PopToName(std::vector<llvm::StringRef, Type>& Stack, llvm::StringRef Key) {
+  if (!ActionTarget.empty()) {
+    auto I = std::find_if(DataSegStack.rbegin(), DataSegStack.rend(),
+      [&](const std::pair<llvm::StringRef, StringLiteral *> &x) {
+      return x.first == ActionTarget;
+    });
+    CurrentDataSegment = I->second;
+    if (I != DataSegStack.rend())
+      DataSegStack.erase(std::prev(I.base()), DataSegStack.end());
+  }
+  else if (!DataSegStack.empty()) {
+    CurrentDataSegment = DataSegStack.back().second;
+    DataSegStack.pop_back();
+  }
+}
+
+template<typename ValueType>
+void Sema::PragmaStack<ValueType>::Act(SourceLocation PragmaLocation,
+                                       PragmaMsStackAction Action,
+                                       llvm::StringRef StackSlotLabel,
+                                       ValueType Value) {
+  if (Action == PSK_Reset) {
+    CurrentValue = nullptr;
+    return;
+  }
+  if (Action & PSK_Push)
+    Stack.push_back({StackSlotLabel, CurrentValue, CurrentPragmaLocation});
+  else if (Action & PSK_Pop) {
+    if (!StackSlotLabel.empty()) {
+      // If we've got a label, try to find it and jump there.
+      auto I = std::find_if(Stack.rbegin(), Stack.rend(),
+        [&](const Slot &x) { return x.StackSlotLabel == StackSlotLabel; });
+      // If we found the label so pop from there.
+      if (I != Stack.rend()) {
+        CurrentValue = I->Value;
+        CurrentPragmaLocation = I->PragmaLocation;
+        Stack.erase(std::prev(I.base()), Stack.end());
+      }
+    } else if (!Stack.empty()) {
+      // We don't have a label, just pop the last entry.
+      CurrentValue = Stack.back().Value;
+      CurrentPragmaLocation = Stack.back().PragmaLocation;
+      Stack.pop_back();
+    }
+  }
+  if (Action & PSK_Set) {
+    CurrentValue = Value;
+    CurrentPragmaLocation = PragmaLocation;
+  }
+}
+
+/// \brief Called on well formed \#pragma bss_seg().
+void Sema::ActOnPragmaMSBSSSeg(SourceLocation PragmaLocation,
+                               PragmaMsStackAction Action,
+                               llvm::StringRef StackSlotLabel,
+                               StringLiteral *SegmentName) {
+  if (Action & PSK_Pop && BSSSegStack.Stack.empty())
+    Diag(PragmaLocation, diag::warn_pragma_pop_failed) << "bss_seg"
+    << "stack empty";
+  BSSSegStack.Act(PragmaLocation, Action, StackSlotLabel, SegmentName);
+}
+
+/// \brief Called on well formed \#pragma data_seg().
+void Sema::ActOnPragmaMSDataSeg(SourceLocation PragmaLocation,
+                                PragmaMsStackAction Action,
+                                llvm::StringRef StackSlotLabel,
+                                StringLiteral *SegmentName) {
+  if (Action & PSK_Pop && DataSegStack.Stack.empty())
+    Diag(PragmaLocation, diag::warn_pragma_pop_failed) << "data_seg"
+    << "stack empty";
+  DataSegStack.Act(PragmaLocation, Action, StackSlotLabel, SegmentName);
+}
+
+/// \brief Called on well formed \#pragma bss_seg().
+void Sema::ActOnPragmaMSConstSeg(SourceLocation PragmaLocation,
+                                 PragmaMsStackAction Action,
+                                 llvm::StringRef StackSlotLabel,
+                                 StringLiteral *SegmentName) {
+  if (Action & PSK_Pop && ConstSegStack.Stack.empty())
+    Diag(PragmaLocation, diag::warn_pragma_pop_failed) << "const_seg"
+    << "stack empty";
+  ConstSegStack.Act(PragmaLocation, Action, StackSlotLabel, SegmentName);
+}
+
+/// \brief Called on well formed \#pragma code_seg().
+void Sema::ActOnPragmaMSCodeSeg(SourceLocation PragmaLocation,
+                                PragmaMsStackAction Action,
+                                llvm::StringRef StackSlotLabel,
+                                StringLiteral *SegmentName) {
+  if (Action & PSK_Pop && CodeSegStack.Stack.empty())
+    Diag(PragmaLocation, diag::warn_pragma_pop_failed) << "code_seg"
+    << "stack empty";
+  CodeSegStack.Act(PragmaLocation, Action, StackSlotLabel, SegmentName);
+}
+
 void Sema::ActOnPragmaUnused(const Token &IdTok, Scope *curScope,
                              SourceLocation PragmaLoc) {
 

lib/Sema/SemaDecl.cpp

     NewFD->setInvalidDecl();
   }
 
+  if (D.isFunctionDefinition() && CodeSegStack.CurrentValue)
+    NewFD->addAttr(MSSegmentAttr::CreateImplicit(
+    Context, CodeSegStack.CurrentValue->getString(),
+    MSSegmentAttr::CodeSeg, CodeSegStack.CurrentPragmaLocation));
+
   // Handle attributes.
   ProcessDeclAttributes(S, NewFD, D);
 

       Diag(var->getLocation(), diag::note_use_thread_local);
   }
 
+  if (var->isThisDeclarationADefinition() &&
+      ActiveTemplateInstantiations.empty()) {
+    if (var->getType().isConstQualified()) {
+      if (ConstSegStack.CurrentValue)
+        var->addAttr(MSSegmentAttr::CreateImplicit(
+        Context, ConstSegStack.CurrentValue->getString(),
+        MSSegmentAttr::ConstSeg, ConstSegStack.CurrentPragmaLocation));
+    }
+    else if (!var->getInit()) {
+      if (BSSSegStack.CurrentValue)
+        var->addAttr(MSSegmentAttr::CreateImplicit(
+        Context, BSSSegStack.CurrentValue->getString(),
+        MSSegmentAttr::BSSSeg, BSSSegStack.CurrentPragmaLocation));
+    }
+    else if (DataSegStack.CurrentValue)
+      var->addAttr(MSSegmentAttr::CreateImplicit(
+      Context, DataSegStack.CurrentValue->getString(),
+      MSSegmentAttr::DataSeg, DataSegStack.CurrentPragmaLocation));
+  }
+
   // All the following checks are C++ only.
   if (!getLangOpts().CPlusPlus) return;