@rsmith wrote:
> This seems very weird to me. Can you explain a bit about the background for
this?
Certainly.
> Is this to support writing variadic __attribute__((ms_abi)) functions when
not targeting Win64?
Yes. Some software in the wild (Wine, for instance) has variadic `ms_abi`
functions. (I wouldn't be surprised, frankly, if this were originally
implemented in GCC at the behest of Wine. I know that the `ms_hook_prologue`
attribute was.)
> How is this is supposed to work when we *are* targeting Win64 directly?
Exactly the same as a normal `va_list`. I even added a test for this.
> (Do we get a corresponding __builtin_sysv_va_list to go in the opposite
direction, for instance? Are the two types the same in that case?)
We don't. Obviously, this is something GCC overlooked--probably because it
was implemented specifically so Wine could use it (see above). (To be honest, I
contemplated this myself before submitting. I wanted to add an orthogonal
extension for `va_list`s in a `sysv_abi` function. But I decided that was
better suited for another patch--this one's big enough as it is.)
================
Comment at: include/clang/Serialization/ASTBitCodes.h:1343
@@ -1340,1 +1342,3 @@
+ EXPR_LAMBDA, // LambdaExpr
+ EXPR_MS_VA_ARG // VAArgExpr (with isMicrosoftABI() true).
};
----------------
Richard Smith wrote:
> Why are you using a separate StmtCode here, rather than just serializing the
> flag normally?
I think it was because I didn't want to break backwards compatibility with the
existing encoding of `clang::VAArgExpr` in a PCH/module. (That's going to
become important later when modules are ready for primetime.) But, if you want
me to serialize the bit normally, I can go do that.
http://llvm-reviews.chandlerc.com/D1623
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