rsmith added a comment.
Everything old is new again. This was discussed when `-fclang-abi-compat` was
introduced; see https://reviews.llvm.org/D36501 for the argument why this patch
is the wrong way of modeling an ABI. Forcing the `ClangABICompat` language
option as a way of "tricking" Clang into producing the PS4 ABI is a hack. The
various ABI changes that `-fclang-abi-compat=` controls are simply part of the
PS4 ABI, and that knowledge should idealistically be carried by the CodeGen
(etc) code that knows about PS4, rather than by imagining that there is some
other PS4 ABI that Clang would produces at version `Latest`, and that we're
asking for a compatibility version of it.
That said, pragmatically speaking, that approach isn't working out well. We
have systematically forgotten to special-case PS4 when adding ABI compatibility
features, so I think I'm convinced that this hack is better than the status
quo. This will go wrong if we ever release (or have ever released) a Clang
version that fails to properly implement the PS4 ABI. In such a case,
`-fclang-abi-compat` should be usable to request that we emulate past ABI bugs,
but would actually have no effect on PS4. I think it's OK to cross that bridge
if/when we come to it.
However, we should not issue a warning for use of the flag. Remember that the
flag means "please be ABI-compatible with Clang version X.Y". Because all
versions of Clang that target PS4 use the same ABI, the flag is a no-op on that
target (at least for now, until we accidentally introduce an ABI break). So we
should not be warning on it, just silently accepting it and doing what it says
-- which for now is nothing.
================
Comment at: lib/Frontend/CompilerInvocation.cpp:2762
+ }
+ Opts.setClangABICompat(LangOptions::ClangABI::Ver6);
+ }
----------------
Is `Ver6` really the right setting? When determining whether to pass objects of
class type indirect, PS4 uses the Clang <= 4 rule, when determining how to pass
a vector of 1 long long, it uses the Clang <= 3.8 rule, and so on. In
SemaDeclCXX.cpp (in `paramCanBeDestoyedInCallee`), I found this comment:
// The PS4 platform ABI follows the behavior of Clang 3.2.
So I *suspect* you should actually be setting this to `Ver3_8` (which is the
oldest version we provide a compatibility flag for).
Repository:
rC Clang
https://reviews.llvm.org/D46767
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