[PATCH] D143587: [Docs] Multilib design

[Michael Platings via Phabricator via cfe-commits]

michaelplatings added a comment.

> Could be worth adding a design principles section at the end

That was a very helpful suggestion, thank you. Writing them out helped me examine the compatibility story more carefully. Consequently I added a requirement for a "minimumClangVersion" property, although I haven't implemented that in the other patches yet.

> May be worth a quick description of how we might model some awkward cases

Not done yet. This certainly can be modelled but I agree an example would be helpful to provide.



================
Comment at: clang/docs/Multilib.rst:105
+
+This decision is hard-coded per ToolChain subclass.
+
----------------
peter.smith wrote:
> Considering the BareMetal ToolChain is used by RISC-V, Arm and AArch64 is there scope for a different choice per toolchain. I guess that we could put a predicate function for the ToolChain that could change due to architecture.
For the BareMetal ToolChain the only one RISC-V multilibs can ever match a given set of command line options so this isn't a problem in practice.


================
Comment at: clang/docs/Multilib.rst:122
+``-fno-exceptions`` multilib variant need only contain C++ libraries.
+
+Stability
----------------
peter.smith wrote:
> Although it can be worked out by looking at the example, which I think is your intention from the comment. It may be worth a section on Syntax that extracts some of these.
> ```
> Syntax of multilib.yaml
> ===============
> ```
> Some suggestions/questions:
> * Does the file have to contain both variants: and flagmap: are either of them optional?
> * Do variants have to come before flagmap, or is order not important.
> * Will be worth highlighting that the order of the variants may be significant depending on the toolchain.
> * Each variant is made up of dir: (path added to sysroot?), flags: [comma separated list of flags] and printArgs: [comma separated list of command line options for -print-multi-lib and -print-multi-directory, but not important for multilib selection]
> * Each flagmap is made up of a POSIX extended syntax regex: that matches a flag, and (one of?) matchFlags/noMatchFlags which either adds or removes respecively a [comma separated list of flags] 
I opted to keep the spec, such as it is, in the example, but I've expanded it to answer your questions, unless it's implicit in it being YAML (e.g. lists //can// be comma separated but there are other ways to express them in YAML).


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