[Attr] Support _attribute__ ((fallthrough))

Summary: Fixed extraneous matches of non-NullStmt

Reviewers: aaron.ballman, rsmith, efriedma, xbolva00

Reviewed By: aaron.ballman, rsmith, xbolva00

Subscribers: riccibruno, arphaman, ziangwan, ojeda, xbolva00, nickdesaulniers, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D64838

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@369414 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/Basic/Attr.td

@@ -1170,7 +1170,7 @@ def ExtVectorType : Attr {
 
 def FallThrough : StmtAttr {
   let Spellings = [CXX11<"", "fallthrough", 201603>, C2x<"", "fallthrough">,
-                   CXX11<"clang", "fallthrough">];
+                   CXX11<"clang", "fallthrough">, GCC<"fallthrough">];
 //  let Subjects = [NullStmt];
   let Documentation = [FallthroughDocs];
 }

include/clang/Parse/Parser.h

@@ -2107,12 +2107,13 @@ private:
 
   DeclGroupPtrTy ParseDeclaration(DeclaratorContext Context,
                                   SourceLocation &DeclEnd,
-                                  ParsedAttributesWithRange &attrs);
-  DeclGroupPtrTy ParseSimpleDeclaration(DeclaratorContext Context,
-                                        SourceLocation &DeclEnd,
-                                        ParsedAttributesWithRange &attrs,
-                                        bool RequireSemi,
-                                        ForRangeInit *FRI = nullptr);
+                                  ParsedAttributesWithRange &attrs,
+                                  SourceLocation *DeclSpecStart = nullptr);
+  DeclGroupPtrTy
+  ParseSimpleDeclaration(DeclaratorContext Context, SourceLocation &DeclEnd,
+                         ParsedAttributesWithRange &attrs, bool RequireSemi,
+                         ForRangeInit *FRI = nullptr,
+                         SourceLocation *DeclSpecStart = nullptr);
   bool MightBeDeclarator(DeclaratorContext Context);
   DeclGroupPtrTy ParseDeclGroup(ParsingDeclSpec &DS, DeclaratorContext Context,
                                 SourceLocation *DeclEnd = nullptr,

lib/Parse/ParseDecl.cpp

@@ -1741,9 +1741,10 @@ void Parser::stripTypeAttributesOffDeclSpec(ParsedAttributesWithRange &Attrs,
 /// [C++11/C11] static_assert-declaration
 ///         others... [FIXME]
 ///
-Parser::DeclGroupPtrTy Parser::ParseDeclaration(DeclaratorContext Context,
-                                                SourceLocation &DeclEnd,
-                                          ParsedAttributesWithRange &attrs) {
+Parser::DeclGroupPtrTy
+Parser::ParseDeclaration(DeclaratorContext Context, SourceLocation &DeclEnd,
+                         ParsedAttributesWithRange &attrs,
+                         SourceLocation *DeclSpecStart) {
   ParenBraceBracketBalancer BalancerRAIIObj(*this);
   // Must temporarily exit the objective-c container scope for
   // parsing c none objective-c decls.
@@ -1763,8 +1764,8 @@ Parser::DeclGroupPtrTy Parser::ParseDeclaration(DeclaratorContext Context,
       SourceLocation InlineLoc = ConsumeToken();
       return ParseNamespace(Context, DeclEnd, InlineLoc);
     }
-    return ParseSimpleDeclaration(Context, DeclEnd, attrs,
-                                  true);
+    return ParseSimpleDeclaration(Context, DeclEnd, attrs, true, nullptr,
+                                  DeclSpecStart);
   case tok::kw_namespace:
     ProhibitAttributes(attrs);
     return ParseNamespace(Context, DeclEnd);
@@ -1777,7 +1778,8 @@ Parser::DeclGroupPtrTy Parser::ParseDeclaration(DeclaratorContext Context,
     SingleDecl = ParseStaticAssertDeclaration(DeclEnd);
     break;
   default:
-    return ParseSimpleDeclaration(Context, DeclEnd, attrs, true);
+    return ParseSimpleDeclaration(Context, DeclEnd, attrs, true, nullptr,
+                                  DeclSpecStart);
   }
 
   // This routine returns a DeclGroup, if the thing we parsed only contains a
@@ -1802,11 +1804,14 @@ Parser::DeclGroupPtrTy Parser::ParseDeclaration(DeclaratorContext Context,
 /// If FRI is non-null, we might be parsing a for-range-declaration instead
 /// of a simple-declaration. If we find that we are, we also parse the
 /// for-range-initializer, and place it here.
-Parser::DeclGroupPtrTy
-Parser::ParseSimpleDeclaration(DeclaratorContext Context,
-                               SourceLocation &DeclEnd,
-                               ParsedAttributesWithRange &Attrs,
-                               bool RequireSemi, ForRangeInit *FRI) {
+///
+/// DeclSpecStart is used when decl-specifiers are parsed before parsing
+/// the Declaration. The SourceLocation for this Decl is set to
+/// DeclSpecStart if DeclSpecStart is non-null.
+Parser::DeclGroupPtrTy Parser::ParseSimpleDeclaration(
+    DeclaratorContext Context, SourceLocation &DeclEnd,
+    ParsedAttributesWithRange &Attrs, bool RequireSemi, ForRangeInit *FRI,
+    SourceLocation *DeclSpecStart) {
   // Parse the common declaration-specifiers piece.
   ParsingDeclSpec DS(*this);
 
@@ -1836,6 +1841,9 @@ Parser::ParseSimpleDeclaration(DeclaratorContext Context,
     return Actions.ConvertDeclToDeclGroup(TheDecl);
   }
 
+  if (DeclSpecStart)
+    DS.SetRangeStart(*DeclSpecStart);
+
   DS.takeAttributesFrom(Attrs);
   return ParseDeclGroup(DS, Context, &DeclEnd, FRI);
 }

lib/Parse/ParseStmt.cpp

@@ -153,6 +153,7 @@ StmtResult Parser::ParseStatementOrDeclarationAfterAttributes(
     SourceLocation *TrailingElseLoc, ParsedAttributesWithRange &Attrs) {
   const char *SemiError = nullptr;
   StmtResult Res;
+  SourceLocation GNUAttributeLoc;
 
   // Cases in this switch statement should fall through if the parser expects
   // the token to end in a semicolon (in which case SemiError should be set),
@@ -208,10 +209,17 @@ Retry:
     if ((getLangOpts().CPlusPlus || getLangOpts().MicrosoftExt ||
          (StmtCtx & ParsedStmtContext::AllowDeclarationsInC) !=
              ParsedStmtContext()) &&
-        isDeclarationStatement()) {
+        (GNUAttributeLoc.isValid() || isDeclarationStatement())) {
       SourceLocation DeclStart = Tok.getLocation(), DeclEnd;
-      DeclGroupPtrTy Decl = ParseDeclaration(DeclaratorContext::BlockContext,
-                                             DeclEnd, Attrs);
+      DeclGroupPtrTy Decl;
+      if (GNUAttributeLoc.isValid()) {
+        DeclStart = GNUAttributeLoc;
+        Decl = ParseDeclaration(DeclaratorContext::BlockContext, DeclEnd, Attrs,
+                                &GNUAttributeLoc);
+      } else {
+        Decl =
+            ParseDeclaration(DeclaratorContext::BlockContext, DeclEnd, Attrs);
+      }
       return Actions.ActOnDeclStmt(Decl, DeclStart, DeclEnd);
     }
 
@@ -223,6 +231,12 @@ Retry:
     return ParseExprStatement(StmtCtx);
   }
 
+  case tok::kw___attribute: {
+    GNUAttributeLoc = Tok.getLocation();
+    ParseGNUAttributes(Attrs);
+    goto Retry;
+  }
+
   case tok::kw_case:                // C99 6.8.1: labeled-statement
     return ParseCaseStatement(StmtCtx);
   case tok::kw_default:             // C99 6.8.1: labeled-statement

lib/Sema/AnalysisBasedWarnings.cpp

@@ -1215,7 +1215,7 @@ static StringRef getFallthroughAttrSpelling(Preprocessor &PP,
     tok::r_square, tok::r_square
   };
 
-  bool PreferClangAttr = !PP.getLangOpts().CPlusPlus17;
+  bool PreferClangAttr = !PP.getLangOpts().CPlusPlus17 && !PP.getLangOpts().C2x;
 
   StringRef MacroName;
   if (PreferClangAttr)
@@ -1224,24 +1224,19 @@ static StringRef getFallthroughAttrSpelling(Preprocessor &PP,
     MacroName = PP.getLastMacroWithSpelling(Loc, FallthroughTokens);
   if (MacroName.empty() && !PreferClangAttr)
     MacroName = PP.getLastMacroWithSpelling(Loc, ClangFallthroughTokens);
-  if (MacroName.empty())
-    MacroName = PreferClangAttr ? "[[clang::fallthrough]]" : "[[fallthrough]]";
+  if (MacroName.empty()) {
+    if (!PreferClangAttr)
+      MacroName = "[[fallthrough]]";
+    else if (PP.getLangOpts().CPlusPlus)
+      MacroName = "[[clang::fallthrough]]";
+    else
+      MacroName = "__attribute__((fallthrough))";
+  }
   return MacroName;
 }
 
 static void DiagnoseSwitchLabelsFallthrough(Sema &S, AnalysisDeclContext &AC,
                                             bool PerFunction) {
-  // Only perform this analysis when using [[]] attributes. There is no good
-  // workflow for this warning when not using C++11. There is no good way to
-  // silence the warning (no attribute is available) unless we are using
-  // [[]] attributes. One could use pragmas to silence the warning, but as a
-  // general solution that is gross and not in the spirit of this warning.
-  //
-  // NOTE: This an intermediate solution. There are on-going discussions on
-  // how to properly support this warning outside of C++11 with an annotation.
-  if (!AC.getASTContext().getLangOpts().DoubleSquareBracketAttributes)
-    return;
-
   FallthroughMapper FM(S);
   FM.TraverseStmt(AC.getBody());
 
@@ -1281,25 +1276,24 @@ static void DiagnoseSwitchLabelsFallthrough(Sema &S, AnalysisDeclContext &AC,
       SourceLocation L = Label->getBeginLoc();
       if (L.isMacroID())
         continue;
-      if (S.getLangOpts().CPlusPlus11) {
-        const Stmt *Term = B->getTerminatorStmt();
-        // Skip empty cases.
-        while (B->empty() && !Term && B->succ_size() == 1) {
-          B = *B->succ_begin();
-          Term = B->getTerminatorStmt();
-        }
-        if (!(B->empty() && Term && isa<BreakStmt>(Term))) {
-          Preprocessor &PP = S.getPreprocessor();
-          StringRef AnnotationSpelling = getFallthroughAttrSpelling(PP, L);
-          SmallString<64> TextToInsert(AnnotationSpelling);
-          TextToInsert += "; ";
-          S.Diag(L, diag::note_insert_fallthrough_fixit) <<
-              AnnotationSpelling <<
-              FixItHint::CreateInsertion(L, TextToInsert);
-        }
+
+      const Stmt *Term = B->getTerminatorStmt();
+      // Skip empty cases.
+      while (B->empty() && !Term && B->succ_size() == 1) {
+        B = *B->succ_begin();
+        Term = B->getTerminatorStmt();
+      }
+      if (!(B->empty() && Term && isa<BreakStmt>(Term))) {
+        Preprocessor &PP = S.getPreprocessor();
+        StringRef AnnotationSpelling = getFallthroughAttrSpelling(PP, L);
+        SmallString<64> TextToInsert(AnnotationSpelling);
+        TextToInsert += "; ";
+        S.Diag(L, diag::note_insert_fallthrough_fixit)
+            << AnnotationSpelling
+            << FixItHint::CreateInsertion(L, TextToInsert);
       }
-      S.Diag(L, diag::note_insert_break_fixit) <<
-        FixItHint::CreateInsertion(L, "break; ");
+      S.Diag(L, diag::note_insert_break_fixit)
+          << FixItHint::CreateInsertion(L, "break; ");
     }
   }
 

test/Sema/fallthrough-attr.c

@@ -0,0 +1,24 @@
+// RUN: %clang_cc1 -fsyntax-only -std=gnu89 -verify -Wimplicit-fallthrough %s
+// RUN: %clang_cc1 -fsyntax-only -std=gnu99 -verify -Wimplicit-fallthrough %s
+// RUN: %clang_cc1 -fsyntax-only -std=c99 -verify -Wimplicit-fallthrough %s
+// RUN: %clang_cc1 -fsyntax-only -std=c11 -verify -Wimplicit-fallthrough %s
+// RUN: %clang_cc1 -fsyntax-only -std=c2x -DC2X -verify -Wimplicit-fallthrough %s
+
+int fallthrough_attribute_spelling(int n) {
+  switch (n) {
+  case 0:
+    n++;
+  case 1:
+#if defined(C2X)
+// expected-warning@-2{{unannotated fall-through between switch labels}} expected-note@-2{{insert '[[fallthrough]];' to silence this warning}} expected-note@-2{{insert 'break;' to avoid fall-through}}
+#else
+// expected-warning@-4{{unannotated fall-through between switch labels}} expected-note@-4{{insert '__attribute__((fallthrough));' to silence this warning}} expected-note@-4{{insert 'break;' to avoid fall-through}}
+#endif
+    n++;
+    __attribute__((fallthrough));
+  case 2:
+    n++;
+    break;
+  }
+  return n;
+}

test/SemaCXX/switch-implicit-fallthrough.cpp

@@ -329,3 +329,15 @@ int fallthrough_alt_spelling(int n) {
   }
   return n;
 }
+
+int fallthrough_attribute_spelling(int n) {
+  switch (n) {
+  case 0:
+    n++;
+    __attribute__((fallthrough));
+  case 1:
+    n++;
+    break;
+  }
+  return n;
+}

test/SemaCXX/warn-unused-label-error.cpp

@@ -18,9 +18,9 @@ namespace PR8455 {
   }
 
   void h() {
-    D: // expected-warning {{unused label 'D'}}
-      #pragma weak unused_local_static
-      __attribute__((unused))  // expected-warning {{declaration does not declare anything}}
-      ;
+  D:
+#pragma weak unused_local_static
+    __attribute__((unused)) // expected-error {{'unused' attribute cannot be applied to a statement}}
+    ;
   }
 }