Summary:
These were originally intended to represent the functions that are
present on the GPU as to be provided by the LLVM libc implementation.
The original plan was that LLVM libc would report which functions were
supported and then the offload interface would mark those as supported.
The problem is that these wrapper headers are very difficult to make
work given the various libc extensions everyone does so they were
extremely fragile.
OpenMP already declares all functions used inside of a target region as
implicitly host / device, while these headers weren't even used for CUDA
/ HIP yet anyway. The only things we need to define right now are the
stdio FILE types. If we want to make this work for CUDA we'd need to
define these manually, but we're a ways off and that's way easier
because they do proper overloading.
Move the hdrgen code under a subdirectory to treat it as a Python
module.
This mimics the structure used by llvm/utils/lit and
llvm/utils/mlgo-utils and simplifies integration of hdrgen to the build
system which rely on Python modules. In addition to that, it clarifies
which imports are coming from the hdrgen-specific helpers (e.g. "from
type import ..." becomes "from hdrgen.type import ...".
Leave the entrypoints (top-level main.py and yaml_to_classes.py) as-is:
they can keep being referred by the CMake build system w/o any changes.
The .yaml files should live next to the corresponding .h.def
files in libc/include/, rather than next to the implementation of
the tool in libc/utils/hdrgen/. As with the .h.def files, there
is no need for a yaml/ subdirectory under include/. This simpler
layout is more natural for maintenance and also simplifies build
integration outside the LLVM CMake build.
Thanks to the effort of @RoseZhang03 and @aaryanshukla under the
guidance of
@michaelrj-google and @amykhuang, we now have newhdrgen and no longer
have a
dependency on TableGen and thus LLVM in order to start bootstrapping a
full
build.
This PR removes:
- LIBC_HDRGEN_EXE; the in tree newhdrgen is the only hdrgen that can be
used.
- LIBC_USE_NEW_HEADER_GEN; newhdrgen is the default and only option.
- LIBC_HDRGEN_ONLY; there is no need to have a distinct build step for
old
hdrgen.
- libc-api-test and libc-api-test-tidy build targets.
- Deletes all .td files.
It does not rename newhdrgen to just hdrgen. Will follow up with a
distinct PR
for that.
Link: #117209
Link: #117254Fixes: #117208
Since new headergen is now the default for building LLVM-libc, the docs
need to be updated to reflect that. While I was editing those docs, I
took a quick pass at updating other out-of-date pages.
Some of the files in the docs/ directory are from 2019 and haven't been
updated since. This patch updates implementation_standard.rst,
source_tree_layout.rst, and has some minor fixes for strings.rst. It
also marks the most severely out of date files with a warning. These
files will be updated in a later patch.
