[PATCH] [Parse] Allow 'constexpr' in condition declarations

[Meador Inge]

Hi rsmith,

This patch implements the functionality specified by DR948.
The changes are two fold.  First, the parser was modified
to allow 'constexpr's to appear in condition declarations
(which was a hard error before).  Second, Sema was modified
to cleanup maybe odr-used declarations.  As 'constexpr's
were not allowed in condition declarations before the cleanup
wasn't necessary (such declarations were always odr-used).

This fixes PR22491.

http://reviews.llvm.org/D8978

Files:
  include/clang/Parse/Parser.h
  lib/Parse/ParseDecl.cpp
  lib/Parse/ParseExprCXX.cpp
  lib/Sema/SemaExprCXX.cpp
  test/CXX/stmt.stmt/stmt.select/p6.cpp

Index: include/clang/Parse/Parser.h
===================================================================
--- include/clang/Parse/Parser.h
+++ include/clang/Parse/Parser.h
@@ -1756,7 +1756,8 @@
                                        LateParsedAttrList *LateAttrs = nullptr);
 
   void ParseSpecifierQualifierList(DeclSpec &DS, AccessSpecifier AS = AS_none,
-                                   DeclSpecContext DSC = DSC_normal);
+                                   DeclSpecContext DSC = DSC_normal,
+                                   bool AllowConstexprs = false);
 
   void ParseObjCTypeQualifierList(ObjCDeclSpec &DS,
                                   Declarator::TheContext Context);
Index: lib/Parse/ParseDecl.cpp
===================================================================
--- lib/Parse/ParseDecl.cpp
+++ lib/Parse/ParseDecl.cpp
@@ -2063,7 +2063,8 @@
 /// [GNU]    attributes     specifier-qualifier-list[opt]
 ///
 void Parser::ParseSpecifierQualifierList(DeclSpec &DS, AccessSpecifier AS,
-                                         DeclSpecContext DSC) {
+                                         DeclSpecContext DSC,
+                                         bool AllowConstexprs) {
   /// specifier-qualifier-list is a subset of declaration-specifiers.  Just
   /// parse declaration-specifiers and complain about extra stuff.
   /// TODO: diagnose attribute-specifiers and alignment-specifiers.
@@ -2103,7 +2104,7 @@
   }
 
   // Issue diagnostic and remove constexpr specfier if present.
-  if (DS.isConstexprSpecified()) {
+  if (DS.isConstexprSpecified() && !AllowConstexprs) {
     Diag(DS.getConstexprSpecLoc(), diag::err_typename_invalid_constexpr);
     DS.ClearConstexprSpec();
   }
Index: lib/Parse/ParseExprCXX.cpp
===================================================================
--- lib/Parse/ParseExprCXX.cpp
+++ lib/Parse/ParseExprCXX.cpp
@@ -1688,7 +1688,8 @@
   // type-specifier-seq
   DeclSpec DS(AttrFactory);
   DS.takeAttributesFrom(attrs);
-  ParseSpecifierQualifierList(DS);
+  ParseSpecifierQualifierList(DS, AS_none, DSC_normal,
+                              /*AllowConstexprs=*/true);
 
   // declarator
   Declarator DeclaratorInfo(DS, Declarator::ConditionContext);
Index: lib/Sema/SemaExprCXX.cpp
===================================================================
--- lib/Sema/SemaExprCXX.cpp
+++ lib/Sema/SemaExprCXX.cpp
@@ -2582,6 +2582,8 @@
       return ExprError();
   }
 
+  Condition = MaybeCreateExprWithCleanups(Condition.get());
+
   return Condition;
 }
 
Index: test/CXX/stmt.stmt/stmt.select/p6.cpp
===================================================================
--- /dev/null
+++ test/CXX/stmt.stmt/stmt.select/p6.cpp
@@ -0,0 +1,17 @@
+// RUN: %clang_cc1 -std=c++11 %s -verify
+// expected-no-diagnostics
+
+// This test verifies the functionality specified by DR948:
+// http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#948
+
+constexpr int id(int x)
+{
+  return x;
+}
+
+void f() {
+   if (constexpr int i = id(101)) { }
+   switch (constexpr int i = id(2)) { default: break; case 2: break; }
+   for (; constexpr int i = id(0); ) { }
+   while (constexpr int i = id(0)) { }
+}

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