No description
Find a file
H.J. Lu 49652cd8ec x86: Disable XCHG to MOV optimization
The -O option was added to x86 assembler by

commit b6f8c7c452
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Tue Feb 27 07:36:33 2018 -0800

    x86: Add -O[2|s] assembler command-line options

On x86, some instructions have alternate shorter encodings:

1. When the upper 32 bits of destination registers of

andq $imm31, %r64
testq $imm31, %r64
xorq %r64, %r64
subq %r64, %r64

known to be zero, we can encode them without the REX_W bit:

andl $imm31, %r32
testl $imm31, %r32
xorl %r32, %r32
subl %r32, %r32

This optimization is enabled with -O, -O2 and -Os.
2. Since 0xb0 mov with 32-bit destination registers zero-extends 32-bit
immediate to 64-bit destination register, we can use it to encode 64-bit
mov with 32-bit immediates.  This optimization is enabled with -O, -O2
and -Os.
3. Since the upper bits of destination registers of VEX128 and EVEX128
instructions are extended to zero, if all bits of destination registers
of AVX256 or AVX512 instructions are zero, we can use VEX128 or EVEX128
encoding to encode AVX256 or AVX512 instructions.  When 2 source
registers are identical, AVX256 and AVX512 andn and xor instructions:

VOP %reg, %reg, %dest_reg

can be encoded with

VOP128 %reg, %reg, %dest_reg

This optimization is enabled with -O2 and -Os.
4. 16-bit, 32-bit and 64-bit register tests with immediate may be
encoded as 8-bit register test with immediate.  This optimization is
enabled with -Os.

These optimizations were intended for compiler generated assembly codes.
The optimization changes may take a long time to be put into GCC.  The
similar SSE move encoding optimization for GCC was first proposed in
Feb, 2019:

https://gcc.gnu.org/pipermail/gcc-patches/2019-February/516941.html

It finally went in Mar, 2020:

commit 5358e8f5800daa0012fc9d06705d64bbb21fa07b
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Thu Mar 5 16:45:05 2020 -0800

    i386: Properly encode vector registers in vector move

Such optimizations are useful for compiler generated codes since they
work with released versions of GCC which don't have such optimized
encoding.  We assume that it is safe to use on compiler generated codes.
When we are informed that an assembler optimization introduces a
significant drawback, we will investigate its drawbacks and benefits.
If its drawbacks outweigh its benefits, such optimization should be
removed.

commit 1c3c3e4b3c
Author: Jan Beulich <jbeulich@suse.com>
Date:   Fri Jun 19 09:47:21 2026 +0200

    x86: optimize XCHG to MOV for same-register forms

breaks valgrind:

https://bugs.kde.org/show_bug.cgi?id=522533

"xchgl %ecx,%ecx" in VALGRIND_GET_NR_CONTEXT, which is defined in
/usr/include/valgrind/valgrind.h:

 #define VALGRIND_GET_NR_CONTEXT(_zzq_rlval)                       \
  { volatile OrigFn* _zzq_orig = &(_zzq_rlval);                   \
    volatile unsigned int __addr;                                 \
    __asm__ volatile(__SPECIAL_INSTRUCTION_PREAMBLE               \
                     /* %EAX = guest_NRADDR */                    \
                     "xchgl %%ecx,%%ecx"                          \
                     : "=a" (__addr)                              \
                     :                                            \
                     : "cc", "memory"                             \
                    );                                            \
    _zzq_orig->nraddr = __addr;                                   \
  }

has special meanings and shouldn't be changed by assembler even when
assembler optimization is enabled.  Since there are no any evidences
to show its benefits, we can't say that it is useful at all.  This
patch disables this optimization, which may be enabled with a different
option.

gas/

	PR gas/34343
	* config/tc-i386.c (optimize_for_disabled_optimizations): New.
	(optimize_encoding): Optimize "xchg %rN, %rN" to "mov %rN, %rN"
	only if optimize_for_disabled_optimizations isn't 0.
	* testsuite/gas/i386/optimize-2b.d: Updated.
	* testsuite/gas/i386/x86-64-optimize-3b.d: Likewise.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
2026-07-14 04:53:04 +08:00
archive [gdb] Move ChangeLog files to archive dir 2026-07-13 13:33:42 +02:00
bfd Automatic date update in version.in 2026-07-13 00:00:07 +00:00
binutils Change version number to 2.47.50 and regenerate files 2026-07-12 10:50:36 +01:00
config Support MinGW & 64-bit libraries/paths in Tcl autoconf scripts 2026-04-02 17:00:30 +02:00
contrib contrib: Make dg-extract-results.py tolerant of unparseable files 2026-05-29 17:28:56 -07:00
cpu Re: bfd/ELF: fold BFD_RELOC_<arch>_GOTOFF* 2026-07-12 21:43:19 +09:30
elfcpp gas, bfd, gold: Rename Arm v8/v9 architecture tags 2026-05-28 11:33:39 +00:00
etc Update year range in copyright notice of binutils files 2026-01-01 23:22:14 +10:30
gas x86: Disable XCHG to MOV optimization 2026-07-14 04:53:04 +08:00
gdb [gdb/exp] Fix ns var lookup when stopped at inlined fn call 2026-07-13 19:09:35 +02:00
gdbserver [gdb] More codespell fixes 2026-07-13 15:23:12 +02:00
gdbsupport [gdb] Convert anonymous struct typedefs 2026-07-13 15:06:35 +02:00
gnulib gnulib: re-generate Makefile.in 2026-01-06 15:14:50 -05:00
gold Change version number to 2.47.50 and regenerate files 2026-07-12 10:50:36 +01:00
gprof Change version number to 2.47.50 and regenerate files 2026-07-12 10:50:36 +01:00
gprofng Change version number to 2.47.50 and regenerate files 2026-07-12 10:50:36 +01:00
include aarch64: Add support for FEAT_SME_FA64 2026-07-10 16:09:06 +01:00
ld Change version number to 2.47.50 and regenerate files 2026-07-12 10:50:36 +01:00
libbacktrace tidy m4 plugin config support 2025-11-03 10:59:50 +10:30
libctf PR 34275 double free in ctf_link_deduplicating_per_cu 2026-07-04 09:23:00 +09:30
libdecnumber regen config 2023-08-12 10:27:57 +09:30
libiberty libiberty d_compact_number signed integer overflow 2026-07-01 10:57:51 +09:30
libsframe libsframe testsuite format mismatches on 32-bit host 2026-04-06 10:46:06 +09:30
opcodes Change version number to 2.47.50 and regenerate files 2026-07-12 10:50:36 +01:00
readline readline/tcap.h: Update definitions for C23 2025-05-02 12:00:05 -06:00
sim Fix typo in sim/ppc/std-config.h 2026-04-21 08:47:46 -06:00
texinfo
zlib tidy m4 plugin config support 2025-11-03 10:59:50 +10:30
.clang-format Remove ARI 2026-06-26 09:17:29 -06:00
.cvsignore
.editorconfig toplevel: unify the GCC and GDB/binutils .editorconfig files 2025-10-01 16:20:29 +01:00
.gitattributes binutils-gdb/git: Handle *.ac and *.m4 files in .gitattributes 2025-12-18 10:00:54 +01:00
.gitignore Add .clang-format 2026-02-11 07:53:01 -07:00
.pre-commit-config.yaml [pre-commit] Remove duplication in config file 2026-07-13 13:11:06 +02:00
ar-lib
ChangeLog Import the following commits from the master config sources: a2287c3041a3f2a204eb942e09c015eab00dc7dd 973e3e6af23b73a4f1b8d95680454cae22593bf8 3a71dc102953608d4592ec401b519837c28a672a f91a544533876c70f43b9fd51064b2bcf3fa7382 484648c73f3843b256dd011bd415e81594300a0a 7f4149527babe92cb5da1032734f5cb90cefdac5 9f6e0fe8ce04628bbd4a455118ff3f8309a1aef9 2026-01-08 11:20:38 +00:00
compile
config-ml.in MSP430: Add -fno-exceptions multilib 2023-08-12 10:24:26 +09:30
config.guess Import the following commits from the master config sources: a2287c3041a3f2a204eb942e09c015eab00dc7dd 973e3e6af23b73a4f1b8d95680454cae22593bf8 3a71dc102953608d4592ec401b519837c28a672a f91a544533876c70f43b9fd51064b2bcf3fa7382 484648c73f3843b256dd011bd415e81594300a0a 7f4149527babe92cb5da1032734f5cb90cefdac5 9f6e0fe8ce04628bbd4a455118ff3f8309a1aef9 2026-01-08 11:20:38 +00:00
config.rpath
config.sub Import the following commits from the master config sources: a2287c3041a3f2a204eb942e09c015eab00dc7dd 973e3e6af23b73a4f1b8d95680454cae22593bf8 3a71dc102953608d4592ec401b519837c28a672a f91a544533876c70f43b9fd51064b2bcf3fa7382 484648c73f3843b256dd011bd415e81594300a0a 7f4149527babe92cb5da1032734f5cb90cefdac5 9f6e0fe8ce04628bbd4a455118ff3f8309a1aef9 2026-01-08 11:20:38 +00:00
configure AMDGCN: Disable subdirectory configuration for unsupported GAS and LD 2026-02-18 17:32:32 +00:00
configure.ac AMDGCN: Disable subdirectory configuration for unsupported GAS and LD 2026-02-18 17:32:32 +00:00
COPYING
COPYING.LIB
COPYING.LIBGLOSS
COPYING.NEWLIB
COPYING3
COPYING3.LIB
depcomp
djunpack.bat
install-sh
libtool.m4 Binutils/GCC: Add clang LTO support to AR, NM and RANLIB 2025-09-25 12:30:13 +08:00
ltgcc.m4
ltmain.sh ltmain.sh: allow more flags at link-time 2024-09-25 19:06:10 +01:00
ltoptions.m4
ltsugar.m4
ltversion.m4
lt~obsolete.m4
MAINTAINERS Fix compiling bfd/vms-lib.c for a 32-bit host. 2024-03-18 10:26:16 +00:00
Makefile.def Sync top-level with GCC 2025-11-03 09:53:04 +00:00
Makefile.in Sync toplevel files from gcc 2025-10-02 07:42:18 +08:00
Makefile.tpl Sync toplevel files from gcc 2025-10-02 07:42:18 +08:00
makefile.vms
missing
mkdep
mkinstalldirs
move-if-change
multilib.am
README README: don't talk about libg++ 2025-09-07 04:06:01 +01:00
README-maintainer-mode
SECURITY.txt Add a SECURITY.txt file describing the GNU Binutils' project's stance on security related bugs. 2023-04-20 16:52:11 +01:00
setup.com
src-release.sh Rename 'binutils' to 'binutils_with_gold'. Rename 'bin_no_gold' to 'binutils'. Add 'gold' 2025-02-04 11:50:02 +00:00
symlink-tree
test-driver
ylwrap

		   README for GNU development tools

This directory contains various GNU compilers, assemblers, linkers, 
debuggers, etc., plus their support routines, definitions, and documentation.

If you are receiving this as part of a GDB release, see the file gdb/README.
If with a binutils release, see binutils/README, and so on. That'll give you
info about this package -- supported targets, how to use it, how to report
bugs, etc.

It is now possible to automatically configure and build a variety of
tools with one command.  To build all of the tools contained herein,
run the ``configure'' script here, e.g.:

	./configure 
	make

To install them (by default in /usr/local/bin, /usr/local/lib, etc),
then do:
	make install

(If the configure script can't determine your type of computer, give it
the name as an argument, for instance ``./configure sun4''.  You can
use the script ``config.sub'' to test whether a name is recognized; if
it is, config.sub translates it to a triplet specifying CPU, vendor,
and OS.)

If you have more than one compiler on your system, it is often best to
explicitly set CC in the environment before running configure, and to
also set CC when running make.  For example (assuming sh/bash/ksh):

	CC=gcc ./configure
	make

A similar example using csh:

	setenv CC gcc
	./configure
	make

Much of the code and documentation enclosed is copyright by
the Free Software Foundation, Inc.  See the file COPYING or
COPYING.LIB in the various directories, for a description of the
GNU General Public License terms under which you can copy the files.

REPORTING BUGS: Again, see gdb/README, binutils/README, etc., for info
on where and how to report problems.