tra added a subscriber: echristo.
tra added a comment.
It looks like you are solving two problems here.
a) you want to create multiple device passes for the same GPU, but with
different options.
b) you may want to pass different compiler options to different device
compilations.
The patch effectively hard-codes {gpu, options} tuple into
--offloading-target-id variant.
Is that correct?
This looks essentially the same as your previous patch D59863
<https://reviews.llvm.org/D59863>.
We have a limited way to deal with (b), but there's currently no way to deal
with (a).
For (a), I think, the real problem is that until now we've assumed that there's
only one device-side compilation per target GPU arch. If we need multiple
device-side compilations, we need a way to name them. Using
`offloading-target-id` as a super-set of `--cuda-gpu-arch` is OK with me.
However, I'm on the fence about the option serving a double-duty of setting
magic compiler flags. On one hand, that's what driver does, so it may be OK. On
the other hand, it's unnecessarily strict. I.e. if we provide ability to create
multiple compilation passes for the same GPU arch, why limit that to only
changing those hard-coded options? A general approach would allow a way to
create more than one device-side compilation and provide arbitrary compiler
options only to *that* compilation. Thiw will also help solving number of
issues we have right now when some host-side compilation options break
device-side compilation and we have to work around that by filtering out some
of them in the driver.
A while back @echristo and I have discussed how it could be handled in a more
generic way.
IIRC we ended up with a strawman proposal that looked roughly like this:
Currently we have rudimentary -Xarch_smXX options implemented for various
toolchains in the driver.
E.g. for HIP:
https://github.com/llvm-mirror/clang/blob/master/lib/Driver/ToolChains/HIP.cpp#L341
We want to generalize it and make it less awkward to use. One way to do it
would be to introduce a `-Xarch TARGET` flag where the option(s) following the
flag would apply only to the compilation for that particular target. `TARGET`
could have special values like `HOST` and `DEVICE` and `ALL` which would widen
the option scope to host/device/all compilation. The `-Xarch` flag could be
either sticky (all following options are affected by it, until the next -Xarch
option) or only affect one option (the way -X options work now). Make option
parser aware of the current compilation target, and it should be fairly
straightforward to control compilation options for particular target.
We could add `--offloading-target-id=X` to create and name a device-side
compilation and then use that name in `-Xarch X` or `-Xtarget X` to pass
appropriate options.
`--cuda-gpu-arch=GPU` would be treated as `--offloading-target-id=GPU -mcpu
GPU`. If we had something like that, then your goal could be achieved with
something like this:
... --offloading-target-id=foo -Xtarget foo -mcpu gfx906 ....
... --offloading-target-id=bar -Xtarget bar -mcpu gfx906 -mxnack -msram-ecc
We could also provide target aliases for the 'standard' offloading targets, so
users do not have to type *all* options specific to the target, but would still
have a way to override them.
This would also give us a flexible way to avoid passing some host-only options
to device-side compilation without having to hard code every special case.
That may be a somewhat larger chunk of work.
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D60620/new/
https://reviews.llvm.org/D60620
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