Remove command line parameters for platform and device selection

[ellnor01]

Fixes #711

Signed-off-by: Ellen Norris-Thompson ellen.norris-thompson@arm.com

[gwawiork]

Hi.
This change will impact our automated execution. Is there really need to remove this kind of selection without introducing new solution?

[kpet]

There is already another way of selecting devices and platforms using the CL_DEVICE_INDEX, CL_PLATFORM_INDEX and CL_DEVICE_TYPE environment variables. The command-line syntax is quirky and will get in the way of introducing a cleaner command-line parsing logic.

@ellnor01 The help text there would need updating as well.

[kpet]

@gwawiork Any more feedback on this change?

[nikhiljnv]

There is already another way of selecting devices and platforms using the CL_DEVICE_INDEX, CL_PLATFORM_INDEX and CL_DEVICE_TYPE environment variables. The command-line syntax is quirky and will get in the way of introducing a cleaner command-line parsing logic.

@ellnor01 The help text there would need updating as well.

I would prefer command-line arguments over env var as relying on env vars can be fragile (it's easy to miss setting them up etc).
Also, going bit further, just platform_index and device_index doesn't guarantee portability of these indices across different systems due to dependence on enumeration order. We had to add a check for platform name to ensure we indeed run on the intended platform irrespective or enumeration order.

[kpet]

@nikhiljnv Agree that's where we want to end up but currently we have a mix of environment variables and command line parameters for device/platform configuration (with both supported in some cases!) and the command line syntax is non-standard/cryptic/atrocious so we will have to break the existing command line interface. What I'm proposing we do is:

1. Remove the current command line syntax and use environment variables for all things device/platform configuration (already the case for device types). That's this PR. This lowers a bar to re-design command line parsing.
2. Re-introduce a clean command line interface when we get to re-designing command line parsing.
3. Deprecate and remove all the environment variables.

It does mean two breaking changes but we can stage them.

[ahesham-arm]

@kpet Rebased and CI checks are passing.