We can help optimizations by making sure we use the team state whenever
it is clear there is no thread state. To this end we introduce a new
state flag (`state::HasThreadState`) and explicit control for the
`state::ValueRAII` helpers, including a dedicated "assert equal".
Differential Revision: https://reviews.llvm.org/D130113
Our conditional writes in the runtime look like this:
```
if (active)
*ptr = value;
```
In the RAII we need to assign `ptr` which comes from a lookup call.
If a thread that is not the main thread calls lookup with the intention
to write the pointer, we'll create a new thread state. As such, we need
to avoid calling lookup for inactive threads. We used to use `nullptr`
as their `ptr` value but that can cause pessimistic reasoning. We now
use `undef` instead.
Differential Revision: https://reviews.llvm.org/D130114
We used to inline the `lookup` calls such that the runtime had "known"
access offsets when it was shipped. With the new static library build it
doesn't as the lookup is an indirection we cannot look through. This
should help us optimize the code better until we can do LTO for the
runtime again.
Differential Revision: https://reviews.llvm.org/D130111
Currently the OpenMP offloading device runtime is only expected to be
compiled for the specific architecture it's targeting. This is
problematic if we want to make compiling the device runtime more general
via the standar `clang` driver rather than invoking the clang front-end
directly. This patch addresses this by primarily changing the declare
type to `nohost` so the host will not contain any of this code.
Additionally we forward declare the functions that are defined via
variants, otherwise these would cause problems on the host.
Reviewed By: jdoerfert, tianshilei1992
Differential Revision: https://reviews.llvm.org/D125260
This patch replaces the ValueRAII pointer with a default 'nullptr'
value. Previously this was initialized as a reference to an existing
variable. The use of this variable caused overhead as the compiler could
not look through the uses and determine that it was unused if 'Active'
was not set. Because of this accesses to the variable would be left in
the runtime once compiled.
Fixes#53641
Reviewed By: jdoerfert
Differential Revision: https://reviews.llvm.org/D119187
IdentTy objects are useful for debugging and profiling so we want to
keep them around in more places, especially those that have a large
impact on performance, e.g., everything related to state.
Reviewed By: tianshilei1992
Differential Revision: https://reviews.llvm.org/D112494
This patch adds support for using dynamic shared memory in the new
device runtime. The new function `__kmpc_get_dynamic_shared` will return a
pointer to the buffer of dynamic shared memory. Currently the amount of memory
allocated is set by an environment variable.
In the future this amount will be added to the amount used for the smart stack
which will be configured in a similar way.
Reviewed By: tianshilei1992
Differential Revision: https://reviews.llvm.org/D110006
The "old" OpenMP GPU device runtime (D14254) has served us well for many
years but modernizing it has caused some pain recently. This patch
introduces an alternative which is mostly written from scratch embracing
OpenMP 5.X, C++, LLVM coding style (where applicable), and conceptual
interfaces. This new runtime is opt-in through a clang flag (D106793).
The new runtime is currently only build for nvptx and has "-new" in its
name.
The design is tailored towards middle-end optimizations rather than
front-end code generation choices, a trend we already started in the old
runtime a while back. In contrast to the old one, state is organized in
a simple manner rather than a "smart" one. While this can induce costs
it helps optimizations. Our expectation is that the majority of codes
can be optimized and a "simple" design is therefore preferable. The new
runtime does also avoid users to pay for things they do not use,
especially wrt. memory. The unlikely case of nested parallelism is
supported but costly to make the more likely case use less resources.
The worksharing and reduction implementation have been taken from the
old runtime and will be rewritten in the future if necessary.
Documentation and debug features are still mostly missing and will be
added over time.
All external symbols start with `__kmpc` for legacy reasons but should
be renamed once we switch over to a single runtime. All internal symbols
are placed in appropriate namespaces (anonymous or `_OMP`) to avoid name
clashes with user symbols.
Differential Revision: https://reviews.llvm.org/D106803
Johannes Doerfert