62acc72a95
unroll and jam can decide to unroll the outer loop of a nest like:
for (int j = 0; j < n; ++j)
for (int i = 0; i < n; ++i)
x[i] += __builtin_expf (y[j][i]);
It then uses a tail loop to handle any left-over iterations.
However, the code is structured so that this tail loop is always used.
If n is a multiple of the unroll factor UF, the final UF iterations will
use the tail loop rather than the unrolled loop.
“Fixing” that for variable loop counts would mean introducing another
runtime test: a branch around the tail loop if there are no more
iterations. There's at least an argument that the overhead of doing
that test might not pay for itself.
But we use this structure even if the iteration count is provably
a multiple of UF at compile time. E.g. with s/n/100/ and an
unroll factor of 2, the first 98 iterations use the unrolled loop
and the final 2 iterations use the original loop.
This patch makes the unroller avoid a tail loop in that case.
The end result seemed easier to follow if variables were declared
at the point of initialisation, so that it's more obvious which
ones are meaningful even when there's no tail loop.
gcc/
* tree-ssa-loop-manip.c (determine_exit_conditions): Return a null
exit condition if no tail loop is needed, and if the original exit
condition should therefore be kept as-is.
(tree_transform_and_unroll_loop): Handle that case here too.
gcc/testsuite/
* gcc.dg/unroll-9.c: New test/
|
||
|---|---|---|
| c++tools | ||
| config | ||
| contrib | ||
| fixincludes | ||
| gcc | ||
| gnattools | ||
| gotools | ||
| include | ||
| INSTALL | ||
| 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 | ||
| ar-lib | ||
| ChangeLog | ||
| ChangeLog.jit | ||
| ChangeLog.tree-ssa | ||
| compile | ||
| config-ml.in | ||
| config.guess | ||
| config.rpath | ||
| config.sub | ||
| configure | ||
| configure.ac | ||
| COPYING | ||
| COPYING3 | ||
| COPYING3.LIB | ||
| COPYING.LIB | ||
| COPYING.RUNTIME | ||
| depcomp | ||
| install-sh | ||
| libtool-ldflags | ||
| libtool.m4 | ||
| lt~obsolete.m4 | ||
| ltgcc.m4 | ||
| ltmain.sh | ||
| ltoptions.m4 | ||
| ltsugar.m4 | ||
| ltversion.m4 | ||
| MAINTAINERS | ||
| Makefile.def | ||
| Makefile.in | ||
| Makefile.tpl | ||
| missing | ||
| mkdep | ||
| mkinstalldirs | ||
| move-if-change | ||
| multilib.am | ||
| README | ||
| symlink-tree | ||
| test-driver | ||
| ylwrap | ||
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.