PR40642: Fix determination of whether the final statement of a statement

expression is a discarded-value expression.

Summary:
We used to get this wrong in three ways:

1) During parsing, an expression-statement followed by the }) ending a
   statement expression was always treated as producing the value of the
   statement expression. That's wrong for ({ if (1) expr; })
2) During template instantiation, various kinds of statement (most
   statements not appearing directly in a compound-statement) were not
   treated as discarded-value expressions, resulting in missing volatile
   loads (etc).
3) In all contexts, an expression-statement with attributes was not
   treated as producing the value of the statement expression, eg
   ({ [[attr]] expr; }).

Also fix incorrect enforcement of OpenMP rule that directives can "only
be placed in the program at a position where ignoring or deleting the
directive would result in a program with correct syntax". In particular,
a label (be it goto, case, or default) should not affect whether
directives are permitted.

Reviewers: aaron.ballman, rjmccall

Subscribers: cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D57984

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@354090 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 78 insertions, 54 deletions

diff --git a/lib/Parse/ParseObjc.cpp b/lib/Parse/ParseObjc.cpp
index 0a1dbf7bff..5ac01f6f0a 100644
--- a/lib/Parse/ParseObjc.cpp
+++ b/lib/Parse/ParseObjc.cpp
@@ -2703,7 +2703,8 @@ Decl *Parser::ParseObjCMethodDefinition() {
   return MDecl;
 }
 
-StmtResult Parser::ParseObjCAtStatement(SourceLocation AtLoc) {
+StmtResult Parser::ParseObjCAtStatement(SourceLocation AtLoc,
+                                        ParsedStmtContext StmtCtx) {
   if (Tok.is(tok::code_completion)) {
     Actions.CodeCompleteObjCAtStatement(getCurScope());
     cutOffParsing();
@@ -2740,7 +2741,7 @@ StmtResult Parser::ParseObjCAtStatement(SourceLocation AtLoc) {
 
   // Otherwise, eat the semicolon.
   ExpectAndConsumeSemi(diag::err_expected_semi_after_expr);
-  return Actions.ActOnExprStmt(Res, isExprValueDiscarded());
+  return handleExprStmt(Res, StmtCtx);
 }
 
 ExprResult Parser::ParseObjCAtExpression(SourceLocation AtLoc) {
diff --git a/lib/Parse/ParseOpenMP.cpp b/lib/Parse/ParseOpenMP.cpp
index 5b8670e928..d0463416f5 100644
--- a/lib/Parse/ParseOpenMP.cpp
+++ b/lib/Parse/ParseOpenMP.cpp
@@ -1132,8 +1132,8 @@ Parser::DeclGroupPtrTy Parser::ParseOpenMPDeclarativeDirectiveWithExtDecl(
 ///         'target teams distribute simd' {clause}
 ///         annot_pragma_openmp_end
 ///
-StmtResult Parser::ParseOpenMPDeclarativeOrExecutableDirective(
-    AllowedConstructsKind Allowed) {
+StmtResult
+Parser::ParseOpenMPDeclarativeOrExecutableDirective(ParsedStmtContext StmtCtx) {
   assert(Tok.is(tok::annot_pragma_openmp) && "Not an OpenMP directive!");
   ParenBraceBracketBalancer BalancerRAIIObj(*this);
   SmallVector<OMPClause *, 5> Clauses;
@@ -1152,7 +1152,9 @@ StmtResult Parser::ParseOpenMPDeclarativeOrExecutableDirective(
 
   switch (DKind) {
   case OMPD_threadprivate: {
-    if (Allowed != ACK_Any) {
+    // FIXME: Should this be permitted in C++?
+    if ((StmtCtx & ParsedStmtContext::AllowDeclarationsInC) ==
+        ParsedStmtContext()) {
       Diag(Tok, diag::err_omp_immediate_directive)
           << getOpenMPDirectiveName(DKind) << 0;
     }
@@ -1219,7 +1221,8 @@ StmtResult Parser::ParseOpenMPDeclarativeOrExecutableDirective(
   case OMPD_target_enter_data:
   case OMPD_target_exit_data:
   case OMPD_target_update:
-    if (Allowed == ACK_StatementsOpenMPNonStandalone) {
+    if ((StmtCtx & ParsedStmtContext::AllowStandaloneOpenMPDirectives) ==
+        ParsedStmtContext()) {
       Diag(Tok, diag::err_omp_immediate_directive)
           << getOpenMPDirectiveName(DKind) << 0;
     }
@@ -1322,7 +1325,8 @@ StmtResult Parser::ParseOpenMPDeclarativeOrExecutableDirective(
     // If the depend clause is specified, the ordered construct is a stand-alone
     // directive.
     if (DKind == OMPD_ordered && FirstClauses[OMPC_depend].getInt()) {
-      if (Allowed == ACK_StatementsOpenMPNonStandalone) {
+      if ((StmtCtx & ParsedStmtContext::AllowStandaloneOpenMPDirectives) ==
+          ParsedStmtContext()) {
         Diag(Loc, diag::err_omp_immediate_directive)
             << getOpenMPDirectiveName(DKind) << 1
             << getOpenMPClauseName(OMPC_depend);
diff --git a/lib/Parse/ParseStmt.cpp b/lib/Parse/ParseStmt.cpp
index 3fc29253f0..267003b518 100644
--- a/lib/Parse/ParseStmt.cpp
+++ b/lib/Parse/ParseStmt.cpp
@@ -29,17 +29,14 @@ using namespace clang;
 /// Parse a standalone statement (for instance, as the body of an 'if',
 /// 'while', or 'for').
 StmtResult Parser::ParseStatement(SourceLocation *TrailingElseLoc,
-                                  bool AllowOpenMPStandalone) {
+                                  ParsedStmtContext StmtCtx) {
   StmtResult Res;
 
   // We may get back a null statement if we found a #pragma. Keep going until
   // we get an actual statement.
   do {
     StmtVector Stmts;
-    Res = ParseStatementOrDeclaration(
-        Stmts, AllowOpenMPStandalone ? ACK_StatementsOpenMPAnyExecutable
-                                     : ACK_StatementsOpenMPNonStandalone,
-        TrailingElseLoc);
+    Res = ParseStatementOrDeclaration(Stmts, StmtCtx, TrailingElseLoc);
   } while (!Res.isInvalid() && !Res.get());
 
   return Res;
@@ -96,7 +93,7 @@ StmtResult Parser::ParseStatement(SourceLocation *TrailingElseLoc,
 ///
 StmtResult
 Parser::ParseStatementOrDeclaration(StmtVector &Stmts,
-                                    AllowedConstructsKind Allowed,
+                                    ParsedStmtContext StmtCtx,
                                     SourceLocation *TrailingElseLoc) {
 
   ParenBraceBracketBalancer BalancerRAIIObj(*this);
@@ -107,7 +104,7 @@ Parser::ParseStatementOrDeclaration(StmtVector &Stmts,
     return StmtError();
 
   StmtResult Res = ParseStatementOrDeclarationAfterAttributes(
-      Stmts, Allowed, TrailingElseLoc, Attrs);
+      Stmts, StmtCtx, TrailingElseLoc, Attrs);
 
   assert((Attrs.empty() || Res.isInvalid() || Res.isUsable()) &&
          "attributes on empty statement");
@@ -147,10 +144,9 @@ private:
 };
 }
 
-StmtResult
-Parser::ParseStatementOrDeclarationAfterAttributes(StmtVector &Stmts,
-          AllowedConstructsKind Allowed, SourceLocation *TrailingElseLoc,
-          ParsedAttributesWithRange &Attrs) {
+StmtResult Parser::ParseStatementOrDeclarationAfterAttributes(
+    StmtVector &Stmts, ParsedStmtContext StmtCtx,
+    SourceLocation *TrailingElseLoc, ParsedAttributesWithRange &Attrs) {
   const char *SemiError = nullptr;
   StmtResult Res;
 
@@ -165,7 +161,7 @@ Retry:
     {
       ProhibitAttributes(Attrs); // TODO: is it correct?
       AtLoc = ConsumeToken();  // consume @
-      return ParseObjCAtStatement(AtLoc);
+      return ParseObjCAtStatement(AtLoc, StmtCtx);
     }
 
   case tok::code_completion:
@@ -177,7 +173,7 @@ Retry:
     Token Next = NextToken();
     if (Next.is(tok::colon)) { // C99 6.8.1: labeled-statement
       // identifier ':' statement
-      return ParseLabeledStatement(Attrs);
+      return ParseLabeledStatement(Attrs, StmtCtx);
     }
 
     // Look up the identifier, and typo-correct it to a keyword if it's not
@@ -207,7 +203,8 @@ Retry:
 
   default: {
     if ((getLangOpts().CPlusPlus || getLangOpts().MicrosoftExt ||
-         Allowed == ACK_Any) &&
+         (StmtCtx & ParsedStmtContext::AllowDeclarationsInC) !=
+             ParsedStmtContext()) &&
         isDeclarationStatement()) {
       SourceLocation DeclStart = Tok.getLocation(), DeclEnd;
       DeclGroupPtrTy Decl = ParseDeclaration(DeclaratorContext::BlockContext,
@@ -220,13 +217,13 @@ Retry:
       return StmtError();
     }
 
-    return ParseExprStatement();
+    return ParseExprStatement(StmtCtx);
   }
 
   case tok::kw_case:                // C99 6.8.1: labeled-statement
-    return ParseCaseStatement();
+    return ParseCaseStatement(StmtCtx);
   case tok::kw_default:             // C99 6.8.1: labeled-statement
-    return ParseDefaultStatement();
+    return ParseDefaultStatement(StmtCtx);
 
   case tok::l_brace:                // C99 6.8.2: compound-statement
     return ParseCompoundStatement();
@@ -363,7 +360,7 @@ Retry:
 
   case tok::annot_pragma_openmp:
     ProhibitAttributes(Attrs);
-    return ParseOpenMPDeclarativeOrExecutableDirective(Allowed);
+    return ParseOpenMPDeclarativeOrExecutableDirective(StmtCtx);
 
   case tok::annot_pragma_ms_pointers_to_members:
     ProhibitAttributes(Attrs);
@@ -382,7 +379,7 @@ Retry:
 
   case tok::annot_pragma_loop_hint:
     ProhibitAttributes(Attrs);
-    return ParsePragmaLoopHint(Stmts, Allowed, TrailingElseLoc, Attrs);
+    return ParsePragmaLoopHint(Stmts, StmtCtx, TrailingElseLoc, Attrs);
 
   case tok::annot_pragma_dump:
     HandlePragmaDump();
@@ -407,7 +404,7 @@ Retry:
 }
 
 /// Parse an expression statement.
-StmtResult Parser::ParseExprStatement() {
+StmtResult Parser::ParseExprStatement(ParsedStmtContext StmtCtx) {
   // If a case keyword is missing, this is where it should be inserted.
   Token OldToken = Tok;
 
@@ -433,12 +430,12 @@ StmtResult Parser::ParseExprStatement() {
       << FixItHint::CreateInsertion(OldToken.getLocation(), "case ");
 
     // Recover parsing as a case statement.
-    return ParseCaseStatement(/*MissingCase=*/true, Expr);
+    return ParseCaseStatement(StmtCtx, /*MissingCase=*/true, Expr);
   }
 
   // Otherwise, eat the semicolon.
   ExpectAndConsumeSemi(diag::err_expected_semi_after_expr);
-  return Actions.ActOnExprStmt(Expr, isExprValueDiscarded());
+  return handleExprStmt(Expr, StmtCtx);
 }
 
 /// ParseSEHTryBlockCommon
@@ -577,10 +574,15 @@ StmtResult Parser::ParseSEHLeaveStatement() {
 ///         identifier ':' statement
 /// [GNU]   identifier ':' attributes[opt] statement
 ///
-StmtResult Parser::ParseLabeledStatement(ParsedAttributesWithRange &attrs) {
+StmtResult Parser::ParseLabeledStatement(ParsedAttributesWithRange &attrs,
+                                         ParsedStmtContext StmtCtx) {
   assert(Tok.is(tok::identifier) && Tok.getIdentifierInfo() &&
          "Not an identifier!");
 
+  // The substatement is always a 'statement', not a 'declaration', but is
+  // otherwise in the same context as the labeled-statement.
+  StmtCtx &= ~ParsedStmtContext::AllowDeclarationsInC;
+
   Token IdentTok = Tok;  // Save the whole token.
   ConsumeToken();  // eat the identifier.
 
@@ -610,9 +612,8 @@ StmtResult Parser::ParseLabeledStatement(ParsedAttributesWithRange &attrs) {
       // statement, but that doesn't work correctly (because ProhibitAttributes
       // can't handle GNU attributes), so only call it in the one case where
       // GNU attributes are allowed.
-      SubStmt = ParseStatementOrDeclarationAfterAttributes(
-          Stmts, /*Allowed=*/ACK_StatementsOpenMPNonStandalone, nullptr,
-          TempAttrs);
+      SubStmt = ParseStatementOrDeclarationAfterAttributes(Stmts, StmtCtx,
+                                                           nullptr, TempAttrs);
       if (!TempAttrs.empty() && !SubStmt.isInvalid())
         SubStmt = Actions.ProcessStmtAttributes(SubStmt.get(), TempAttrs,
                                                 TempAttrs.Range);
@@ -623,7 +624,7 @@ StmtResult Parser::ParseLabeledStatement(ParsedAttributesWithRange &attrs) {
 
   // If we've not parsed a statement yet, parse one now.
   if (!SubStmt.isInvalid() && !SubStmt.isUsable())
-    SubStmt = ParseStatement();
+    SubStmt = ParseStatement(nullptr, StmtCtx);
 
   // Broken substmt shouldn't prevent the label from being added to the AST.
   if (SubStmt.isInvalid())
@@ -643,9 +644,14 @@ StmtResult Parser::ParseLabeledStatement(ParsedAttributesWithRange &attrs) {
 ///         'case' constant-expression ':' statement
 /// [GNU]   'case' constant-expression '...' constant-expression ':' statement
 ///
-StmtResult Parser::ParseCaseStatement(bool MissingCase, ExprResult Expr) {
+StmtResult Parser::ParseCaseStatement(ParsedStmtContext StmtCtx,
+                                      bool MissingCase, ExprResult Expr) {
   assert((MissingCase || Tok.is(tok::kw_case)) && "Not a case stmt!");
 
+  // The substatement is always a 'statement', not a 'declaration', but is
+  // otherwise in the same context as the labeled-statement.
+  StmtCtx &= ~ParsedStmtContext::AllowDeclarationsInC;
+
   // It is very very common for code to contain many case statements recursively
   // nested, as in (but usually without indentation):
   //  case 1:
@@ -737,8 +743,7 @@ StmtResult Parser::ParseCaseStatement(bool MissingCase, ExprResult Expr) {
     // continue parsing the sub-stmt.
     if (Case.isInvalid()) {
       if (TopLevelCase.isInvalid())  // No parsed case stmts.
-        return ParseStatement(/*TrailingElseLoc=*/nullptr,
-                              /*AllowOpenMPStandalone=*/true);
+        return ParseStatement(/*TrailingElseLoc=*/nullptr, StmtCtx);
       // Otherwise, just don't add it as a nested case.
     } else {
       // If this is the first case statement we parsed, it becomes TopLevelCase.
@@ -758,8 +763,7 @@ StmtResult Parser::ParseCaseStatement(bool MissingCase, ExprResult Expr) {
   StmtResult SubStmt;
 
   if (Tok.isNot(tok::r_brace)) {
-    SubStmt = ParseStatement(/*TrailingElseLoc=*/nullptr,
-                             /*AllowOpenMPStandalone=*/true);
+    SubStmt = ParseStatement(/*TrailingElseLoc=*/nullptr, StmtCtx);
   } else {
     // Nicely diagnose the common error "switch (X) { case 4: }", which is
     // not valid.  If ColonLoc doesn't point to a valid text location, there was
@@ -789,8 +793,13 @@ StmtResult Parser::ParseCaseStatement(bool MissingCase, ExprResult Expr) {
 ///         'default' ':' statement
 /// Note that this does not parse the 'statement' at the end.
 ///
-StmtResult Parser::ParseDefaultStatement() {
+StmtResult Parser::ParseDefaultStatement(ParsedStmtContext StmtCtx) {
   assert(Tok.is(tok::kw_default) && "Not a default stmt!");
+
+  // The substatement is always a 'statement', not a 'declaration', but is
+  // otherwise in the same context as the labeled-statement.
+  StmtCtx &= ~ParsedStmtContext::AllowDeclarationsInC;
+
   SourceLocation DefaultLoc = ConsumeToken();  // eat the 'default'.
 
   SourceLocation ColonLoc;
@@ -811,8 +820,7 @@ StmtResult Parser::ParseDefaultStatement() {
   StmtResult SubStmt;
 
   if (Tok.isNot(tok::r_brace)) {
-    SubStmt = ParseStatement(/*TrailingElseLoc=*/nullptr,
-                             /*AllowOpenMPStandalone=*/true);
+    SubStmt = ParseStatement(/*TrailingElseLoc=*/nullptr, StmtCtx);
   } else {
     // Diagnose the common error "switch (X) {... default: }", which is
     // not valid.
@@ -943,7 +951,8 @@ bool Parser::ConsumeNullStmt(StmtVector &Stmts) {
     EndLoc = Tok.getLocation();
 
     // Don't just ConsumeToken() this tok::semi, do store it in AST.
-    StmtResult R = ParseStatementOrDeclaration(Stmts, ACK_Any);
+    StmtResult R =
+        ParseStatementOrDeclaration(Stmts, ParsedStmtContext::SubStmt);
     if (R.isUsable())
       Stmts.push_back(R.get());
   }
@@ -957,14 +966,18 @@ bool Parser::ConsumeNullStmt(StmtVector &Stmts) {
   return true;
 }
 
-bool Parser::isExprValueDiscarded() {
-  if (Actions.isCurCompoundStmtAStmtExpr()) {
-    // Look to see if the next two tokens close the statement expression;
+StmtResult Parser::handleExprStmt(ExprResult E, ParsedStmtContext StmtCtx) {
+  bool IsStmtExprResult = false;
+  if ((StmtCtx & ParsedStmtContext::InStmtExpr) != ParsedStmtContext()) {
+    // Look ahead to see if the next two tokens close the statement expression;
     // if so, this expression statement is the last statement in a
     // statment expression.
-    return Tok.isNot(tok::r_brace) || NextToken().isNot(tok::r_paren);
+    IsStmtExprResult = Tok.is(tok::r_brace) && NextToken().is(tok::r_paren);
   }
-  return true;
+
+  if (IsStmtExprResult)
+    E = Actions.ActOnStmtExprResult(E);
+  return Actions.ActOnExprStmt(E, /*DiscardedValue=*/!IsStmtExprResult);
 }
 
 /// ParseCompoundStatementBody - Parse a sequence of statements and invoke the
@@ -1022,6 +1035,10 @@ StmtResult Parser::ParseCompoundStatementBody(bool isStmtExpr) {
       Stmts.push_back(R.get());
   }
 
+  ParsedStmtContext SubStmtCtx =
+      ParsedStmtContext::Compound |
+      (isStmtExpr ? ParsedStmtContext::InStmtExpr : ParsedStmtContext());
+
   while (!tryParseMisplacedModuleImport() && Tok.isNot(tok::r_brace) &&
          Tok.isNot(tok::eof)) {
     if (Tok.is(tok::annot_pragma_unused)) {
@@ -1034,7 +1051,7 @@ StmtResult Parser::ParseCompoundStatementBody(bool isStmtExpr) {
 
     StmtResult R;
     if (Tok.isNot(tok::kw___extension__)) {
-      R = ParseStatementOrDeclaration(Stmts, ACK_Any);
+      R = ParseStatementOrDeclaration(Stmts, SubStmtCtx);
     } else {
       // __extension__ can start declarations and it can also be a unary
       // operator for expressions.  Consume multiple __extension__ markers here
@@ -1067,11 +1084,12 @@ StmtResult Parser::ParseCompoundStatementBody(bool isStmtExpr) {
           continue;
         }
 
-        // FIXME: Use attributes?
         // Eat the semicolon at the end of stmt and convert the expr into a
         // statement.
         ExpectAndConsumeSemi(diag::err_expected_semi_after_expr);
-        R = Actions.ActOnExprStmt(Res, isExprValueDiscarded());
+        R = handleExprStmt(Res, SubStmtCtx);
+        if (R.isUsable())
+          R = Actions.ProcessStmtAttributes(R.get(), attrs, attrs.Range);
       }
     }
 
@@ -2001,7 +2019,7 @@ StmtResult Parser::ParseReturnStatement() {
 }
 
 StmtResult Parser::ParsePragmaLoopHint(StmtVector &Stmts,
-                                       AllowedConstructsKind Allowed,
+                                       ParsedStmtContext StmtCtx,
                                        SourceLocation *TrailingElseLoc,
                                        ParsedAttributesWithRange &Attrs) {
   // Create temporary attribute list.
@@ -2024,7 +2042,7 @@ StmtResult Parser::ParsePragmaLoopHint(StmtVector &Stmts,
   MaybeParseCXX11Attributes(Attrs);
 
   StmtResult S = ParseStatementOrDeclarationAfterAttributes(
-      Stmts, Allowed, TrailingElseLoc, Attrs);
+      Stmts, StmtCtx, TrailingElseLoc, Attrs);
 
   Attrs.takeAllFrom(TempAttrs);
   return S;
@@ -2329,7 +2347,8 @@ void Parser::ParseMicrosoftIfExistsStatement(StmtVector &Stmts) {
 
   // Condition is true, parse the statements.
   while (Tok.isNot(tok::r_brace)) {
-    StmtResult R = ParseStatementOrDeclaration(Stmts, ACK_Any);
+    StmtResult R =
+        ParseStatementOrDeclaration(Stmts, ParsedStmtContext::Compound);
     if (R.isUsable())
       Stmts.push_back(R.get());
   }