commit 10bcc4d1db5c4b506aff7fa9f5e9e0d8226c84c6
author Peter Collingbourne <pcc@chromium.org> Fri Jun 15 00:52:04 2018
committer Commit Bot <commit-bot@chromium.org> Fri Jun 15 00:52:04 2018
tree 83e8744ddbd610a4f4d73cb050389c35a115b56b
parent 68bd2e31608bc0fdb34a0f6f9c59e681e1c6c320

Reland "build: Pass -fcomplete-member-pointers when building with clang."

This is a reland of 4a2a5c4aa89b2718f60d775896784a96068fcacf
with an additional check for use_xcode_clang.

Original change's description:
> build: Pass -fcomplete-member-pointers when building with clang.
>
> This prevents member pointers of incomplete base type from being used in
> cases where they might cause problems under the Microsoft ABI.
>
> Specifically, the Microsoft ABI has different kinds of member pointers with
> different sizes, and the choice of member pointer representation depends on
> the inheritance hierarchy of the member pointer's base type. C++ allows a
> member pointer's base type to be incomplete, so if it is incomplete at the
> point where a variable of that member pointer type is declared, that forces
> the compiler to pick the most general (i.e. largest) one. That can lead to
> ODR violations since the most general representation wouldn't necessarily
> be the one that would be chosen if the base type happened to be complete at
> the point where the variable was declared. It can also be less size efficient
> because the compiler will generally be able to choose a smaller representation
> than the most general one if it were complete at the point where it is needed.
>
> This flag also enables additional semantic analysis that we'll need in order
> to correctly implement -fsanitize=cfi for member function pointer calls. This
> is because the inheritance hierarchy of the base type must be available in
> order to make the CFI checks as precise as possible.
>
> Note that the flag is a -f flag rather than a -W flag. This is because
> requiring member pointer base types to be complete is technically a
> non-conforming language extension, as it may, for example, cause templates
> to be instantiated which would otherwise not be, which may be observable
> after code generation in conforming programs that were crafted to observe
> it. However, the effects of this language extension should not be observable
> in most ordinary programs.
>
> Bug: 847724
> Change-Id: I8d823fd4a6f21dfcadba55eefc0a69ef2e0c3479
> Reviewed-on: https://chromium-review.googlesource.com/1098217
> Commit-Queue: Peter Collingbourne <pcc@chromium.org>
> Reviewed-by: Nico Weber <thakis@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#567086}

Bug: 847724
Change-Id: I1b97980691914492945d170931d33438c68e8d0b
Reviewed-on: https://chromium-review.googlesource.com/1101477
Reviewed-by: Nico Weber <thakis@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Peter Collingbourne <pcc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#567505}