[SYCL][CUDA] DPC++ build warning and error related to unrolling, optimization for CUDA plugin

[abagusetty]

While building for the CUDA backend, I was seeing some strange warning and errors as shown below but however leading to a cleaner installation.

warning: <unknown>:0:0: loop not unrolled: the optimizer was unable to perform the requested transformation; the transformation might be disabled or specified as part of an unsupported transformation ordering
error: unknown argument: '-fno-lifetime-dse'

Using CUDA-11.4.4/11.8.0, gcc-11.2.0, OS SLSE 15.3,

Towards the very end when generating the bc files for spirv

For instance

warning: <unknown>:0:0: loop not unrolled: the optimizer was unable to perform the requested transformation; the transformation might be disabled or specified as part of an unsupported transformation ordering
warning: <unknown>:0:0: loop not unrolled: the optimizer was unable to perform the requested transformation; the transformation might be disabled or specified as part of an unsupported transformation ordering
warning: <unknown>:0:0: loop not unrolled: the optimizer was unable to perform the requested transformation; the transformation might be disabled or specified as part of an unsupported transformation ordering
[ 97%] Built target opt.libspirv-nvptx64--nvidiacl.bc
[ 97%] Generating ../../lib/clc/libspirv-nvptx64--nvidiacl.bc
[ 97%] Built target prepare-libspirv-nvptx64--nvidiacl.bc
[ 97%] Generating ../../lib/clc/libclc_dummy_in.cc
[ 97%] Generating ../../lib/clc/libclc_dummy_in.cc
[ 97%] Generating ../../lib/clc/libclc_dummy_in.cc
[ 97%] Generating ../../lib/clc/libclc_dummy_in.cc
[ 97%] Generating ../../lib/clc/remangled-l64-unsigned_char.libspirv-nvptx64-nvidia-cuda.bc
[ 97%] Generating ../../lib/clc/remangled-l32-unsigned_char.libspirv-nvptx64-nvidia-cuda.bc
[ 97%] Generating ../../lib/clc/remangled-l32-signed_char.libspirv-nvptx64-nvidia-cuda.bc
[ 97%] Generating ../../lib/clc/remangled-l64-signed_char.libspirv-nvptx64-nvidia-cuda.bc
error: unknown argument: '-fno-lifetime-dse'
error: unknown argument: '-fno-lifetime-dse'
error: unknown argument: '-fno-lifetime-dse'
error: unknown argument: '-fno-lifetime-dse'

Upon compiling a test with the above built compilers leads to following errors:

.../bin/llvm-link: /soft/compilers/oneapi/llvm/build/lib/clang/17/../../clc/remangled-l64-signed_char.libspirv-nvptx64-nvidia-cuda.bc: error: Opaque pointers are only supported in -opaque-pointers mode (Producer: 'LLVM17.0.0git' Reader: 'LLVM 17.0.0git')
/soft/compilers/oneapi/llvm/build/bin/llvm-link: error: loading file '/soft/compilers/oneapi/llvm/build/lib/clang/17/../../clc/remangled-l64-signed_char.libspirv-nvptx64-nvidia-cuda.bc'
clang++: error: sycl-link command failed with exit code 1 (use -v to see invocation)

[jinz2014]

Again, error: Opaque pointers are only supported in -opaque-pointers mode

[abagusetty]

The above error related to optimization flags error: unknown argument: '-fno-lifetime-dse' build issue seems to be unrelated to -opaque-pointers. By default, the DPCPP is built with the support for opaque pointers.

Reverting this commit fixed the dse optimizations errors: 94f7c96

[npmiller]

@jchlanda could you have a quick look at this error message: error: unknown argument: '-fno-lifetime-dse', I confirmed that it comes from the libclc-remangler invocations, so it's most likely coming from the frontend invocation we use in there for the remangling.

[jchlanda]

@jchlanda could you have a quick look at this error message: error: unknown argument: '-fno-lifetime-dse', I confirmed that it comes from the libclc-remangler invocations, so it's most likely coming from the frontend invocation we use in there for the remangling.

Yeap, spotted it on Friday and added to my TODO, will report back.

[AlexeySachkov]

FYI: the error showed up once in our CI: https://github.com/intel/llvm/actions/runs/5278855878/jobs/9548777110

[jchlanda]

#9974 should address the error: unknown argument: '-fno-lifetime-dse'. WRT the loop warning it seems to be a genuine one coming from WarnMissedTransforms Pass that is part of our opt run. Unlikely to do with the remangler itself, maybe an incorrect use of unroll pragma in the libclc?

[jchlanda]

llvm is not able to satisfy user forced unroll, coming from: https://github.com/jchlanda/llvm/blob/jakub/libclc_DSE_fix/libclc/ptx-nvidiacl/libspirv/group/collectives.cl#L456 will investigate a bit more.