Re: [RFC][V2] RISC-V: Support -mcmodel=large.

[Jeff Law <jeffreyalaw@gmail.com>]

On 12/20/23 11:21, Palmer Dabbelt wrote:

>> Yea, the implementation relies largely on just pushing stuff into the
>> constant pool, so we're largely independent ABI stuff with the likely
>> exception being relocations.
> 
> Ya, but I think we'd only need the relocations if we were going to try 
> relaxing stuff.  We'd kicked around some ideas there: we could 
> de-duplicate constant pools or inline smaller constants.  That's all way 
> to complex to try and get into this upcoming binutils release, though 
> (doubly so with this LEB128 ABI break we're still trying to deal with).
Agreed.  And note that de-duplication is mostly implemented without need 
for the target to do anything.  I was kindof amazed to see some of the 
places it kicked in on other ports I've worked with.


>> In theory (and I did not test this), it should be possible to use large
>> code model codegen in a smaller mode and it should interoperate.  I
>> seriously pondered doing that as an additional test, then figured I had
>> other higher priority items on my list.
> 
> IMO we should test that.  At least the common case of a medlow libc 
> linked into medany programs should be easy.
> 
> +Patrick: let's add some configs to the CI for this?
I was pondering a one-off by turning on the large code model by default, 
then doing a bootstrap & regression test in QEMU.  But integrated into 
CI is even better.

Jeff