[Sema] Don't mark plain MS enums as fixed

Summary:
This fixes a flaw in our AST: PR27098

MSVC always gives plain enums the underlying type 'int'. Clang does this
as well, but we claim the enum is "fixed", as if the user actually wrote
': int'. It means we end up emitting spurious -Wsign-compare warnings on
code like this:

  enum Vals { E1, E2, E3 };
  bool f(unsigned v1, Vals v2) {
    return v1 == v2;
  }

We think 'v2' can take on negative values because we think 'Vals' is
fixed. This fixes that.

Reviewers: rsmith

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D43110

llvm-svn: 324913

1 files changed, 1 insertions, 6 deletions

diff --git a/clang/lib/AST/Type.cpp b/clang/lib/AST/Type.cpp
index d306f7dd613..2690a3faf72 100644
--- a/clang/lib/AST/Type.cpp
+++ b/clang/lib/AST/Type.cpp
@@ -1997,12 +1997,7 @@ bool Type::isIncompleteType(NamedDecl **Def) const {
     EnumDecl *EnumD = cast<EnumType>(CanonicalType)->getDecl();
     if (Def)
       *Def = EnumD;
-    
-    // An enumeration with fixed underlying type is complete (C++0x 7.2p3).
-    if (EnumD->isFixed())
-      return false;
-    
-    return !EnumD->isCompleteDefinition();
+    return !EnumD->isComplete();
   }
   case Record: {
     // A tagged type (struct/union/enum/class) is incomplete if the decl is a