mirror of
git://gcc.gnu.org/git/gcc.git
synced 2025-02-05 14:59:45 +08:00
680e4202f2
The x86 backend doesn't have EQ or NE floating point comparisons,
so splits x != y into x unord y || x <> y. The problem with that is
that unord comparison doesn't trap on qNaN operands but LTGT does.
The end effect is that it doesn't trap on qNaN operands, because x unord y
will be true for those and so LTGT will not be performed, but as the backend
is currently unable to merge signalling and non-signalling comparisons (and
after all, with this exact exception it shouldn't unless the first one is
signalling and the second one is non-signalling) it means we end up with:
ucomiss %xmm1, %xmm0
jp .L4
comiss %xmm1, %xmm0
jne .L4
ret
.p2align 4,,10
.p2align 3
.L4:
xorl %eax, %eax
jmp foo
where the comiss is the signalling comparison, but we already know that
the right flags bits are already computed by the ucomiss insn.
The following patch, if target supports UNEQ comparisons, splits NE
as x unord y || !(x uneq y) instead, which in the end means we end up with
just:
ucomiss %xmm1, %xmm0
jp .L4
jne .L4
ret
.p2align 4,,10
.p2align 3
.L4:
jmp foo
because UNEQ is like UNORDERED non-signalling.
2020-12-10 Jakub Jelinek <jakub@redhat.com>
PR rtl-optimization/98212
* dojump.c (do_compare_rtx_and_jump): When splitting NE and backend
can do UNEQ, prefer splitting x != y into x unord y || !(x uneq y)
instead of into x unord y || x ltgt y.
* gcc.target/i386/pr98212.c: New test.
|
||
|---|---|---|
| config | ||
| contrib | ||
| fixincludes | ||
| gcc | ||
| gnattools | ||
| gotools | ||
| include | ||
| INSTALL | ||
| intl | ||
| libada | ||
| libatomic | ||
| libbacktrace | ||
| libcc1 | ||
| libcpp | ||
| libdecnumber | ||
| libffi | ||
| libgcc | ||
| libgfortran | ||
| libgo | ||
| libgomp | ||
| libhsail-rt | ||
| 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.