Build core with nvptx target

[termoshtt]

Experiment to use nvptx-enabled rustc at https://github.com/rust-accel/rust

Features

• Use libstd (based on wasm implementations)
• Linking LLVM bitcodes by llvm-link in rustc
• Compile into a linked LLVM bitcode

Links

• Enable nvptx target Enable nvptx64-nvidia-cuda target rust-accel/rust#1
• llvm-link in rustc Add llvm-link flavor rust-accel/rust#3

See also #31

[termoshtt]

There is no [lib] section in Cargo.toml, i.e. this crate is compiled as rlib:

# rust-accel/rust:llvm-link has been compiled as +nvptx target
$ cargo +nvptx build -vv
   Compiling accel-core v0.2.0-alpha (file:///accel/accel-core)
     Running `rustc --crate-name accel_core src/lib.rs
 --crate-type lib --emit=dep-info,link -C debuginfo=2
 -C metadata=89823dc66a8c0ad6
 -C extra-filename=-89823dc66a8c0ad6
 --out-dir /accel/accel-core/target/nvptx64-nvidia-cuda/debug/deps
 --target nvptx64-nvidia-cuda
 -C incremental=/accel/accel-core/target/nvptx64-nvidia-cuda/debug/incremental
 -L dependency=/accel/accel-core/target/nvptx64-nvidia-cuda/debug/deps
 -L dependency=/accel/accel-core/target/debug/deps`

This creates target/nvptx64-nvidia-cuda/debug/libaccel_core.rlib, which is an ar archive:

$ ar t libaccel_core.rlib
accel_core-89823dc66a8c0ad6.524p119z00bm6tv7.rcgu.o       # LLVM bitcode
rust.metadata.bin
accel_core-89823dc66a8c0ad6.524p119z00bm6tv7.rcgu.bc.z   # Rust Object

$ xxd accel_core-89823dc66a8c0ad6.524p119z00bm6tv7.rcgu.o | head -1
00000000: 4243 c0de 3514 0000 0500 0000 620c 3024  BC..5.......b.0$

$ xxd accel_core-89823dc66a8c0ad6.524p119z00bm6tv7.rcgu.bc.z | head -n1
00000000: 5255 5354 5f4f 424a 4543 5402 0000 0034  RUST_OBJECT....4

[termoshtt]

What we need is the LLVM bitcode (*.o files), but it is composed in ar archive. The ar archive is a simple archive format like zip, and it can compose any files. However, it is not natural to compose bitcodes as an ar archive, it should be linked by llvm-link

[termoshtt]

Furthermore, there only one bitcode file. It may be due to the intriniscs.rs module contains intrinsics only. We need another code :<

[termoshtt]

$ ar t libaccel_core.rlib
accel_core-89823dc66a8c0ad6.2wq0crelc49frk0q.rcgu.o
accel_core-89823dc66a8c0ad6.524p119z00bm6tv7.rcgu.o
rust.metadata.bin
accel_core-89823dc66a8c0ad6.2wq0crelc49frk0q.rcgu.bc.z
accel_core-89823dc66a8c0ad6.524p119z00bm6tv7.rcgu.bc.z

Two bitcodes corresponding to lib.rs and indexing.rs

[termoshtt]

$ cargo +nvptx build -vv
   Compiling accel-core v0.2.0-alpha (file://accel/accel-core)
     Running `rustc --crate-name accel_core src/lib.rs --crate-type cdylib --emit=dep-info,link
 -C debuginfo=2
 -C metadata=085c35af2a1f581a
 --out-dir /accel/accel-core/target/nvptx64-nvidia-cuda/debug/deps
 --target nvptx64-nvidia-cuda
 -C incremental=/accel/accel-core/target/nvptx64-nvidia-cuda/debug/incremental
 -L dependency=/accel/accel-core/target/nvptx64-nvidia-cuda/debug/deps
 -L dependency=/accel/accel-core/target/debug/deps`

error: linking with `llvm-link` failed: exit code: 1
  = note: "llvm-link" "/accel/accel-core/target/nvptx64-nvidia-cuda/debug/deps/accel_core.1y16o1qfye96o7m0.rcgu.o"
 "-o" "/accel/accel-core/target/nvptx64-nvidia-cuda/debug/deps/libaccel_core.bc"
 "/accel/accel-core/target/nvptx64-nvidia-cuda/debug/deps/accel_core.crate.allocator.rcgu.o"
 "/stage1/lib/rustlib/nvptx64-nvidia-cuda/lib/libstd-73892a84db388a4b.rlib"
 "/stage1/lib/rustlib/nvptx64-nvidia-cuda/lib/libpanic_abort-dbdbba248951650b.rlib"
 "/stage1/lib/rustlib/nvptx64-nvidia-cuda/lib/libunwind-e8ee297dbe25844d.rlib"
 "/stage1/lib/rustlib/nvptx64-nvidia-cuda/lib/liballoc_system-5e948e8e93b206b3.rlib"
 "/stage1/lib/rustlib/nvptx64-nvidia-cuda/lib/liblibc-8a689bacec06a191.rlib"
 "/stage1/lib/rustlib/nvptx64-nvidia-cuda/lib/liballoc-057d09441be39ab5.rlib"
 "/stage1/lib/rustlib/nvptx64-nvidia-cuda/lib/libcore-b8b7fb254e56b0ab.rlib"
 "/stage1/lib/rustlib/nvptx64-nvidia-cuda/lib/libcompiler_builtins-371c588c1a3805de.rlib"

  = note: llvm-link: /stage1/lib/rustlib/nvptx64-nvidia-cuda/lib/libstd-73892a84db388a4b.rlib:1:2: error: expected integer
          !<arch>
           ^
          llvm-link: error:  loading file '/stage1/lib/rustlib/nvptx64-nvidia-cuda/lib/libstd-73892a84db388a4b.rlib'

This means that the compiler-runtime (+nvptx = /stage1 on my machine) are compiled into rlib, and llvm-link cannot be linked them. These rlibs are generated while x.py to build rustc. We need to fix it...

[termoshtt]

Give up to link by llvm-link (´・ω・｀)