[PATCH] D43110: [Sema] Don't mark plain MS enums as fixed

[Reid Kleckner via Phabricator via cfe-commits]

rnk created this revision.
rnk added a reviewer: rsmith.

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.


https://reviews.llvm.org/D43110

Files:
  clang/include/clang/AST/Decl.h
  clang/include/clang/Sema/Sema.h
  clang/lib/AST/Type.cpp
  clang/lib/Sema/SemaDecl.cpp
  clang/lib/Sema/SemaTemplateInstantiateDecl.cpp

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