[SYCL] Don't emit exception handling code for device

[ilyastepykin]

In order to support exception handling, the compiler
generates additional code inside functions to perform
cleanup, catch unexpected exceptions. This is done
by calling a function that may throw using "invoke"
LLVM instruction with additional landing pad code
instead of simple "call".
Previously, when such code is generated, llvm-spirv
would fail to translate it as it doesn't know how to
handle "invoke" instruction.

There is no support for exceptions on device side,
so generation of such exception handling code
(including "invoke" instruction) can be simply disabled.

Signed-off-by: Ilya Stepykin ilya.stepykin@intel.com

[erichkeane]

Otherwise acceptable to me.

[mibintc]

We have code in SemaSYCL which creates a diagnostic on exception code when seen in sycl device right? like try, throw, etc?

[premanandrao]

LGTM

[agozillon]

We have code in SemaSYCL which creates a diagnostic on exception code when seen in sycl device right? like try, throw, etc?

Yes, but I believe it's still possible to inject exception related code in certain cases through things like this I think: #77 I've not tested this in a while though, so perhaps it's fixed.

[asavonic]

Can we just pass -fno-exceptions flag from the driver instead of making changes in Clang CodeGen?

[agozillon]

Can we just pass -fno-exceptions flag from the driver instead of making changes in Clang CodeGen?

I tried something similar in the issue I referenced I think, but I didn't dig too deep and perhaps I misdiagnosed the problem. As I recall it breaks on try catches in host code as even if the device isn't using them, the device compiler still needs to compile it as it compiles both the host and device source. At least at the time anyway. I mention it briefly at the bottom of the issue as that was my original hopeful solution to the problem. As OpenCL does what you mention I believe but it only compiles the device code, so doesn't have the same problem.

[ilyastepykin]

Can we just pass -fno-exceptions flag from the driver instead of making changes in Clang CodeGen?

If we pass -fno-exceptions the exception check is applied for both host and device code. So in this case we won't be able to compile code whose host part uses exceptions, but its device part doesn't use them.

We have code in SemaSYCL which creates a diagnostic on exception code when seen in sycl device right? like try, throw, etc?

Yes, but in this case we have implicitly generate code and we should not produce a diagnostic for it. Instead we simply ignore it like it's done when -fno-exception is used.