[LLVMdev] RFP: Metadata is being used poorly to paper over missing IR constructs

[Chris Lattner]

On Jan 8, 2015, at 2:06 PM, Chandler Carruth <chandlerc at gmail.com> wrote:
> #1
> We need the ability to put semantic information in the IR that can be used by targets without extending the IR itself. In some cases we can do this with target-specific intrinsics, but those don't always fit the problem and have their own set of challenges.

+1, depending on the details :-)

> #2
> We need to make module flags a first class entity of the module, just like datalayout:
> 
>   &flag = ....
> 
> (syntax shamelessly stolen from Duncan's suggestion in IRC)

I disagree.  The concerns about “stability” of metadata don’t apply to module-level metadata that doesn’t refer to the other IR in the module.  A nice thing about module-level metadata is that it eliminates the “need" to encode features like command line flags directly in the IR in a custom tailored way.  There should be no need to design bitcode and .ll syntax for new things like command line flags.  If we had module-level metadata back in day 1, targetdata would be using it...

-Chris