[PATCH] Implement no_sanitize attribute.

[Peter Collingbourne]

On Thu, May 14, 2015 at 10:42:50AM -0400, Aaron Ballman wrote:
> On Wed, May 13, 2015 at 6:40 PM, Peter Collingbourne <peter at pcc.me.uk> wrote:
> > These constructs were added to clang in r237055 and r237056.
> 
> Thank you; I was just slightly too out of date to have them. Having
> fetched, I'm back on the same page.
> 
> I don't think a variadic enumeration argument will be worth the effort
> given the structure of Sanitizers.def. However, the current approach
> is still incorrect. For instance, the attribute will not round-trip a
> pretty printing, and it fails to diagnose illogical values that wind
> up being ignored.

FWIW, this is deliberate. We shouldn't diagnose unknown sanitizers because
there ought to be a way to supply a no_sanitize attribute for any particular
sanitizer in a way that is backwards compatible with older versions of Clang
that do not support the sanitizer.

> The semantic attribute needs to carry around the
> valid original information the user provided, but I can see why you'd
> also want it to carry it around in mask format.

It seems that the mask will require custom serialization/deserialization
support if we don't want it treated as a syntactic attribute, and there
doesn't seem to be infrastructure for doing this right now. Instead I just
added a method that calculates the mask on demand.

> I think the correct approach for this is:
> 
> 1) Make a VariadicStringArgument tablegen type (model it after
> VariadicExprArgument, roughly). (Attr.td, ClangAttrEmitter.cpp)
> 2) Implement no_sanitize in terms of a VariadicStringArgument (Attr.td)
> 3) Add an additional public member to hold the SanitizerMask value (Attr.td)
> 4) Issue diagnostics for invalid members when creating the sanitizer
> mask value (SemaDeclAttr.cpp)
> 5) Create the attribute, then attach the flattened SanitizerMask
> value, then attach it to the declaration (SemaDeclAttr.cpp)

Mostly followed this design, modulo the mask thing.

Thanks,
-- 
Peter