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Summary:
The OpenMP handling using an offload binary should be optional, it's
only used for extra metadata for llvm-objdump. Also the triple was
completely wrong, it didn't let anyone correctly choose between ELF
and COFF handling.
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(#167232)
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This patch adds an Offload Wrapper for the SYCL kind. This is an
essential step for SYCL offloading and the compilation flow. The usage
of offload wrapping is added to the clang-linker-wrapper tool.
Modifications:
Implemented `bundleSYCL()` function to handle SYCL image bundling.
Implemented `wrapSYCLBinaries()` function that is invoked from
clang-linker-wrapper.
SYCL Offload Wrapping uses specific data structures such as
`__sycl.tgt_device_image` and `__sycl.tgt_bin_desc`. Each SYCL image
maintains its own symbol table (unlike shared global tables in other
targets). Therefore, symbols are encoded explicitly during the offload
wrapping. Also, images refer to their own Offloading Entries arrays
unlike other targets.
The proposed `__sycl.tgt_device_image` uses Version 3 to differentiate
from images generated by Intel DPC++. The structure proposed in this
patch doesn't have fields deprecated in DPC++.
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The module currently stores the target triple as a string. This means
that any code that wants to actually use the triple first has to
instantiate a Triple, which is somewhat expensive. The change in #121652
caused a moderate compile-time regression due to this. While it would be
easy enough to work around, I think that architecturally, it makes more
sense to store the parsed Triple in the module, so that it can always be
directly queried.
For this change, I've opted not to add any magic conversions between
std::string and Triple for backwards-compatibilty purses, and instead
write out needed Triple()s or str()s explicitly. This is because I think
a decent number of them should be changed to work on Triple as well, to
avoid unnecessary conversions back and forth.
The only interesting part in this patch is that the default triple is
Triple("") instead of Triple() to preserve existing behavior. The former
defaults to using the ELF object format instead of unknown object
format. We should fix that as well.
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Summary:
The previous offloading entry type did not fit the current use-cases
very well. This widens it and adds a version to prevent further
annoyances. It also includes the kind to better sort who's using it.
The first 64-bytes are reserved as zero so the OpenMP runtime can detect
the old format for binary compatibilitry.
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Follow up to https://github.com/llvm/llvm-project/issues/123569
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Summary:
Previously, managed variables didn't work in rdc mode using the new
driver because we just didn't register them. This was previously ignored
because we didn't have enough space in the current struct format. This
patch amends that by just emitting a struct pair for the two variables
and using the single pointer.
In the future, a more extensible entry format would be nice, but that
can be done later.
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This patch overhauls the `libomptarget` and plugin interface. Currently,
we define a C API and compile each plugin as a separate shared library.
Then, `libomptarget` loads these API functions and forwards its internal
calls to them. This was originally designed to allow multiple
implementations of a library to be live. However, since then no one has
used this functionality and it prevents us from using much nicer
interfaces. If the old behavior is desired it should instead be
implemented as a separate plugin.
This patch replaces the `PluginAdaptorTy` interface with the
`GenericPluginTy` that is used by the plugins. Each plugin exports a
`createPlugin_<name>` function that is used to get the specific
implementation. This code is now shared with `libomptarget`.
There are some notable improvements to this.
1. Massively improved lifetimes of life runtime objects
2. The plugins can use a C++ interface
3. Global state does not need to be duplicated for each plugin +
libomptarget
4. Easier to use and add features and improve error handling
5. Less function call overhead / Improved LTO performance.
Additional changes in this plugin are related to contending with the
fact that state is now shared. Initialization and deinitialization is
now handled correctly and in phase with the underlying runtime, allowing
us to actually know when something is getting deallocated.
Depends on https://github.com/llvm/llvm-project/pull/86971
https://github.com/llvm/llvm-project/pull/86875
https://github.com/llvm/llvm-project/pull/86868
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Caused failures on build-bots, reverting to investigate.
This reverts commit 80f9e814ec896fdc57ee84afad8ac4cb1f8e4627.
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This patch overhauls the `libomptarget` and plugin interface. Currently,
we define a C API and compile each plugin as a separate shared library.
Then, `libomptarget` loads these API functions and forwards its internal
calls to them. This was originally designed to allow multiple
implementations of a library to be live. However, since then no one has
used this functionality and it prevents us from using much nicer
interfaces. If the old behavior is desired it should instead be
implemented as a separate plugin.
This patch replaces the `PluginAdaptorTy` interface with the
`GenericPluginTy` that is used by the plugins. Each plugin exports a
`createPlugin_<name>` function that is used to get the specific
implementation. This code is now shared with `libomptarget`.
There are some notable improvements to this.
1. Massively improved lifetimes of life runtime objects
2. The plugins can use a C++ interface
3. Global state does not need to be duplicated for each plugin +
libomptarget
4. Easier to use and add features and improve error handling
5. Less function call overhead / Improved LTO performance.
Additional changes in this plugin are related to contending with the
fact that state is now shared. Initialization and deinitialization is
now handled correctly and in phase with the underlying runtime, allowing
us to actually know when something is getting deallocated.
Depends on https://github.com/llvm/llvm-project/pull/86971
https://github.com/llvm/llvm-project/pull/86875
https://github.com/llvm/llvm-project/pull/86868
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(#86830)
Summary:
The 'new driver' sets up the lifetime of a registered liftime using
global constructors and destructors. Currently, this is put at priority
1 which isn't strictly conformant as it will conflict with system
utilities. We now use 101 as this is the loweest suggested for
non-system constructors and will still run before user constructors.
Secondly, there were issues with the CUDA runtime when destructed with a
global destructor. Because the global ones are in any order and
potentially run before other things we were hitting an edge case where
the OpenMP runtime was uninitialized *after* `_dl_fini` was called. This
would result in us erroring when we call into a destroyed `libcuda.so`
instance. using `atexit` is what CUDA / HIP use and it prevents this
from happening. Most everything uses `atexit` except system utilities
and because of the constructor priority it will be unregistered *after*
everything else but not after `_fl_fini`.
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Summary:
The standard GPU compilation process embeds each intermediate object
file into the host file at the `.llvm.offloading` section so it can be
linked later. We also use a special section called something like
`omp_offloading_entries` to store all the globals that need to be
registered by the runtime. The linker-wrapper's job is to link the
embedded device code stored at this section and then emit code to
register the linked image and the kernels and globals in the offloading
entry section.
One downside to RDC linking is that it can become quite big for very
large projects that wish to make use of static linking. This patch
changes the support for relocatable linking via `-r` to support a kind
of "partial" RDC compilation for offloading languages.
This primarily requires manually editing the embedded data in the
output object file for the relocatable link. We need to rename the
output section to make it distinct from the input sections that will be
merged. We then delete the old embedded object code so it won't be
linked further. We then need to rename the old offloading section so
that it is private to the module. A runtime solution could also be done
to defer entries that don't belong to the given GPU executable, but this
is easier. Note that this does not work with COFF linking, only the ELF
method for handling offloading entries, that could be made to work
similarly.
Given this support, the following compilation path should produce two
distinct images for OpenMP offloading.
```
$ clang foo.c -fopenmp --offload-arch=native -c
$ clang foo.c -lomptarget.devicertl --offload-link -r -o merged.o
$ clang main.c merged.o -fopenmp --offload-arch=native
$ ./a.out
```
Or similarly for HIP to effectively perform non-RDC mode compilation for
a subset of files.
```
$ clang -x hip foo.c --offload-arch=native --offload-new-driver -fgpu-rdc -c
$ clang -x hip foo.c -lomptarget.devicertl --offload-link -r -o merged.o
$ clang -x hip main.c merged.o --offload-arch=native --offload-new-driver -fgpu-rdc
$ ./a.out
```
One question is whether or not this should be the default behavior of
`-r` when run through the linker-wrapper or a special option. Standard
`-r` behavior is still possible if used without invoking the
linker-wrapper and it guaranteed to be correct.
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llvm/Frontend/Offloading (#78057)
This patch moves `clang/tools/clang-linker-wrapper/OffloadWrapper.*` to
`llvm/Frontend/Offloading` allowing them to be re-utilized by other
projects.
Additionally, it makes minor modifications to the API to make it more
flexible.
Concretely:
- The `wrap*` methods now have additional arguments `EntryArray`,
`Suffix` and `EmitSurfacesAndTextures` to specify some additional options.
- The `EntryArray` is now constructed by the caller. This change is needed to
enable JIT compilation, as ORC doesn't fully support `__start_` and `__stop_`
symbols. Thus, to JIT the code, the `EntryArray` has to be constructed explicitly in the IR.
- The `Suffix` field is used when emitting the descriptor, registration
methods, etc, to make them more readable. It is empty by default.
- The `EmitSurfacesAndTextures` field controls whether to emit surface
and texture registration code, as those functions were removed from `CUDART`
in CUDA 12. It is true by default.
- The function `getOffloadingEntryInitializer` was added to help create
the `EntryArray`, as it returns the constant initializer and not a global
variable.
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