[cfe-commits] [patch] Add codegen for the __noop intrinsic

[Nico Weber]

On Wed, Sep 26, 2012 at 2:49 PM, Eli Friedman <eli.friedman at gmail.com> wrote:
> On Tue, Sep 25, 2012 at 10:05 PM, Nico Weber <thakis at chromium.org> wrote:
>> Hi,
>>
>> similar to the __debugbreak patch, this adds codegen support for __noop.
>
> You don't actually have to call llvm.donothing... like the name says,
> it doesn't do anything. :)  "return RValue::get(0);" should be
> sufficient.

My patch has nicer -S -emit-llvm output :-) But sure, I'll change it.

>
> Do we actually perform semantic analysis correctly for __noop?

Not completely.

> In MSVC, are the arguments unevaluated in the semantic analysis sense?

cl seems to do sema for __noop, __noop(3 + someclassinstanc) results
in a syntax error. So does wrapping a statement in __noop.

> Do we do the right thing for expressions with non-POD type?
> Expressions with cleanups?

It looks like cl runs cleanups, __noop(MyClass()) runs destructors
with cl (but not with clang). Do you want me to fix this before
landing this patch?

>
> -Eli