e2a58ed6dc
This patch implements worker-partitioning support in the middle end,
by rewriting gimple. The OpenACC execution model requires that code
can run in either "worker single" mode where only a single worker per
gang is active, or "worker partitioned" mode, where multiple workers
per gang are active. This means we need to do something equivalent
to spawning additional workers when transitioning from worker-single
to worker-partitioned mode. However, GPUs typically fix the number of
threads of invoked kernels at launch time, so we need to do something
with the "extra" threads when they are not wanted.
The scheme used is to conditionalise each basic block that executes
in "worker single" mode for worker 0 only. Conditional branches
are handled specially so "idle" (non-0) workers follow along with
worker 0. On transitioning to "worker partitioned" mode, any variables
modified by worker 0 are propagated to the other workers via GPU shared
memory. Special care is taken for routine calls, writes through pointers,
and so forth, as follows:
- There are two types of function calls to consider in worker-single
mode: "normal" calls to maths library routines, etc. are called from
worker 0 only. OpenACC routines may contain worker-partitioned loops
themselves, so are called from all workers, including "idle" ones.
- SSA names set in worker-single mode, but used in worker-partitioned
mode, are copied to shared memory in worker 0. Other workers retrieve
the value from the appropriate shared-memory location after a barrier,
and new phi nodes are introduced at the convergence point to resolve
the worker 0/other worker copies of the value.
- Local scalar variables (on the stack) also need special handling. We
broadcast any variables that are written in the current worker-single
block, and that are read in any worker-partitioned block. (This is
believed to be safe, and is flow-insensitive to ease analysis.)
- Local aggregates (arrays and composites) on the stack are *not*
broadcast. Instead we force gimple stmts modifying elements/fields of
local aggregates into fully-partitioned mode. The RHS of the
assignment is a scalar, and is thus subject to broadcasting as above.
- Writes through pointers may affect any local variable that has
its address taken. We use points-to analysis to determine the set
of potentially-affected variables for a given pointer indirection.
We broadcast any such variable which is used in worker-partitioned
mode, on a per-block basis for any block containing a write through
a pointer.
Some slides about the implementation (from 2018) are available at:
https://jtb20.github.io/gcnworkers.pdf
gcc/
* Makefile.in (OBJS): Add omp-oacc-neuter-broadcast.o.
* doc/tm.texi.in (TARGET_GOACC_CREATE_WORKER_BROADCAST_RECORD):
Add documentation hook.
* doc/tm.texi: Regenerate.
* omp-oacc-neuter-broadcast.cc: New file.
* omp-builtins.def (BUILT_IN_GOACC_BARRIER)
(BUILT_IN_GOACC_SINGLE_START, BUILT_IN_GOACC_SINGLE_COPY_START)
(BUILT_IN_GOACC_SINGLE_COPY_END): New builtins.
* passes.def (pass_omp_oacc_neuter_broadcast): Add pass.
* target.def (goacc.create_worker_broadcast_record): Add target
hook.
* tree-pass.h (make_pass_omp_oacc_neuter_broadcast): Add
prototype.
* config/gcn/gcn-protos.h (gcn_goacc_adjust_propagation_record):
Rename prototype to...
(gcn_goacc_create_worker_broadcast_record): ... this.
* config/gcn/gcn-tree.c (gcn_goacc_adjust_propagation_record): Rename
function to...
(gcn_goacc_create_worker_broadcast_record): ... this.
* config/gcn/gcn.c (TARGET_GOACC_ADJUST_PROPAGATION_RECORD):
Rename to...
(TARGET_GOACC_CREATE_WORKER_BROADCAST_RECORD): ... this.
Co-Authored-By: Nathan Sidwell <nathan@codesourcery.com> (via 'gcc/config/nvptx/nvptx.c' master)
Co-Authored-By: Kwok Cheung Yeung <kcy@codesourcery.com>
Co-Authored-By: Thomas Schwinge <thomas@codesourcery.com>
|
||
|---|---|---|
| INSTALL | ||
| c++tools | ||
| config | ||
| contrib | ||
| fixincludes | ||
| gcc | ||
| gnattools | ||
| gotools | ||
| include | ||
| intl | ||
| libada | ||
| libatomic | ||
| libbacktrace | ||
| libcc1 | ||
| libcody | ||
| libcpp | ||
| libdecnumber | ||
| libffi | ||
| libgcc | ||
| libgfortran | ||
| libgo | ||
| libgomp | ||
| libiberty | ||
| libitm | ||
| libobjc | ||
| liboffloadmic | ||
| libphobos | ||
| libquadmath | ||
| libsanitizer | ||
| libssp | ||
| libstdc++-v3 | ||
| libvtv | ||
| lto-plugin | ||
| maintainer-scripts | ||
| zlib | ||
| .dir-locals.el | ||
| .gitattributes | ||
| .gitignore | ||
| ABOUT-NLS | ||
| COPYING | ||
| COPYING.LIB | ||
| COPYING.RUNTIME | ||
| COPYING3 | ||
| COPYING3.LIB | ||
| ChangeLog | ||
| ChangeLog.jit | ||
| ChangeLog.tree-ssa | ||
| MAINTAINERS | ||
| Makefile.def | ||
| Makefile.in | ||
| Makefile.tpl | ||
| README | ||
| ar-lib | ||
| compile | ||
| config-ml.in | ||
| config.guess | ||
| config.rpath | ||
| config.sub | ||
| configure | ||
| configure.ac | ||
| depcomp | ||
| install-sh | ||
| libtool-ldflags | ||
| libtool.m4 | ||
| ltgcc.m4 | ||
| ltmain.sh | ||
| ltoptions.m4 | ||
| ltsugar.m4 | ||
| ltversion.m4 | ||
| lt~obsolete.m4 | ||
| missing | ||
| mkdep | ||
| mkinstalldirs | ||
| move-if-change | ||
| multilib.am | ||
| symlink-tree | ||
| test-driver | ||
| ylwrap | ||
README
This directory contains the GNU Compiler Collection (GCC). The GNU Compiler Collection is free software. See the files whose names start with COPYING for copying permission. The manuals, and some of the runtime libraries, are under different terms; see the individual source files for details. The directory INSTALL contains copies of the installation information as HTML and plain text. The source of this information is gcc/doc/install.texi. The installation information includes details of what is included in the GCC sources and what files GCC installs. See the file gcc/doc/gcc.texi (together with other files that it includes) for usage and porting information. An online readable version of the manual is in the files gcc/doc/gcc.info*. See http://gcc.gnu.org/bugs/ for how to report bugs usefully. Copyright years on GCC source files may be listed using range notation, e.g., 1987-2012, indicating that every year in the range, inclusive, is a copyrightable year that could otherwise be listed individually.