This change tightens and documents the use of libc_internal, then
strengthens the VxWorks crtstuff objects for the support of shared
libraries. In particular:
- Define __dso_handle, which libstdc++.so requires,
- Provide _init and _fini functions to run through the init/fini arrays
for shared libs in configurations which HAVE_INITFINI_ARRAY_SUPPORT.
The init/fini functions are provided by libc_internal.a for static links
but with slightly different names and we don't want to risk dragging other
libc_internal contents in the closure accidentally so make sure we don't
link with it.
As for the !vxworks crtstuff, the new shared libs specific bits are
conditioned by a CRTSTUFFS_O macro, for which we provide new Makefile
fragment.
The bits to actually use the fragment and the shared objects will
be added by a forthcoming change, as part of a more general configury
update for shared libs.
The change also adds guards the eh table registration code
in vxcrtstuff so the objects can be used for either init/fini
or eh tables independently.
2021-12-07 Fred Konrad <konrad@adacore.com>
Olivier Hainque <hainque@adacore.com>
gcc/
* config/vxworks.h (VXWORKS_BASE_LIBS_RTP): Guard -lc_internal
on !shared+!non-static and document.
(VXWORKS_LIB_SPEC): Remove the bits intended to drag the
init/fini functions from libc_internal in the shared lib case.
(VX_CRTBEGIN_SPEC/VX_CRTEND_SPEC): Use vxcrtstuff objects also in
configurations with shared lib and INITFINI_ARRAY support.
libgcc/
* config/t-vxcrtstuffS: New Makefile fragment.
* config/vxcrtstuff.c: Provide __dso_handle. Provide _init/_fini
functions for INITFINI_ARRAY support in shared libs and guard
the definition of eh table registration functions on conditions
indicating they are needed.
The unconditional assignment performed in t-vxworks to handle
include flags currently overrides what specific cpu ports had
for the regular (!vxworks) crtstuff objects.
This was not done on purpose and the proposed change adjusts the
configuration bits to apply the vxworks specific flags on top of
the cpu ones instead.
2021-12-07 Olivier Hainque <hainque@adacore.com>
* config.host (powerpc*-wrs-vxworks7*): Place t-crtstuff
ahead of the other files in tmake_files.
* config/t-vxworks: Add to CRTSTUFF_T_CFLAGS instead of
overriding it.
The build of a VxWorks toolchain relies a lot on system headers
and VxWorks has a few very specific features that require special
processing. For example, different sets of headers for the kernel
vs the rtp modes, which the compiler knows about by way of -mrtp
on the command line.
If we manage to avoid the need for fixincludes on recent versions
of VxWorks (>= 7), we still need to handle at least VxWorks 6.9 at
this stage.
We sort of get away with locating the correct headers at
run-time thanks to environment variables and various tests for
-mrtp in cpp specs, but getting fixincludes to work for old
configurations has always been tricky and getting a toolchain
to build with c++/libstdc++ support gets trickier with every
move to a more recent release.
sysroot_headers_suffix_spec is a pretty powerful device to help
address such issues, and this patch introduces changes that let
us get advantage of it.
The general idea is to leverage the assumption that compilations
occur with --sysroot=$VSB_DIR on vx7 or --sysroot=$WIND_BASE/target
prior to that.
For the toolchains we build, this is achieved with a few
configure options like:
--with-sysroot
--with-build-sysroot=${WIND_BASE}/target
--with-specs=%{!sysroot=*:--sysroot=%:getenv(WIND_BASE /target)}
This also allows simplifying the libgcc compilation flags control
and we take the opportunity to merge t-vxworks7 into t-vxworks as
the two files were differing only on the libgcc2 flags part.
2021-12-09 Olivier Hainque <hainque@adacore.com>
gcc/
* config/t-vxworks: Clear NATIVE_SYSTEM_HEADER_DIR.
* config/vxworks.h (SYSROOT_HEADERS_SUFFIX_SPEC): Define, for
VxWorks 7 and earlier.
(VXWORKS_ADDITIONAL_CPP_SPEC): Simplify accordingly.
(STARTFILE_PREFIX_SPEC): Adjust accordingly.
* config/rs6000/vxworks.h (STARTFILE_PREFIX_SPEC): Adjust.
libgcc/
* config/t-vxworks (LIBGCC2_INCLUDES): Simplify and handle
both VxWorks7 and earlier.
* config/t-vxworks7: Remove.
* config.host: Remove special case for vxworks7.
When the translation unit itself creates pointers to the ctors/dtors
in a specific section handled by the linker (whether .init_array or
.ctors.*), there's no reason for the functions to have external
linkage. That ends up polluting the symbol table in the running
kernel.
This makes vxcrtstuff.c on par with the generic crtstuff.c which also
defines e.g. frame_dummy and __do_global_dtors_aux static.
libgcc/
* config/vxcrtstuff.c: Make constructor and destructor
functions static when possible.
These declarations prevent the priority given in the
constructor/destructor attributes from taking effect, thus emitting
the function pointers in the ordinary (lowest-priority)
.init_array/.fini_array sections.
libgcc/
* config/vxcrtstuff.c: Remove constructor/destructor
declarations.
We include libgcc_tm.h to provide a prototype for this shim
so add that to the make dependencies.
Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
libgcc/ChangeLog:
* config/t-darwin: Add libgcc_tm.h to the dependencies
for darwin10-unwind-find-enc-func.
This removes ibm-ldouble.c and a few eabi crt files from the build
closure, which were producing objects we don't use anyway.
2021-12-07 Rasmus Villemoes <rv@rasmusvillemoes.dk>
libgcc/
* config/rs6000/t-vxworks: New file.
* config.host (powerpc*-*-vxworks*): Use it instead of
t-ppccomm.
This change arranges to provide the vxworks alternate stdint.h
at build time instead of at install time, so it is used instead
of the system one while building the libraries.
This is a lot more consistent and helps the build on configurations
where the system does not come with stdint.h at all.
The change uses a similar mechanism as the one previsouly introduced
for glimits.h and takes the opportunity to simplify the glimits.h
command to use an automatic variable.
This introduces an indirect dependency on the VxWorks version.h
for vxcrtstuff objects, for which we then need to apply the same
tricks as for libgcc2 regarding include paths (to select the system
header instead of the gcc one).
2021-02-12 Olivier Hainque <hainque@adacore.com>
Rasmus Villemoes <rv@rasmusvillemoes.dk>
gcc/
* Makefile.in (T_STDINT_GCC_H): New variable, path to
stdint-gcc.h that a target configuration may override when
use_gcc_stdint is "provide".
(stmp-int-hdrs): Depend on it and copy that for
USE_GCC_INT=provide.
* config.gcc (vxworks): Revert to use_gcc_stdint=provide.
* config/t-vxworks (T_STDINT_GCC_H): Define, as vxw-stdint-gcc.h.
(vxw-stdint-gcc.h): New target, produced from the original
stdint-gcc.h.
(vxw-glimits.h): Use an automatic variable to designate the
first and only prerequisite.
* config/vxworks/stdint.h: Remove.
libgcc/
* config/t-vxworks: Set CRTSTUFF_T_CFLAGS to
$(LIBGCC2_INCLUDES).
* config/t-vxworks7: Likewise.
In order to reslve a long-standing issue with inter-operation
with libSystem, we have bumped the SO name for libgcc_s.
Distributions might wish to install this new version into a
structure where exisiting code is already linked with the
compiler-local libgcc_s.1 (providing symbols exported by the
now-retired libgcc_ext.10.x shims).
The replacement libgcc_s.1 forwards the symbols from the new SO.
In order to support DYLD_LIBRARY_PATH on systems (where it works)
we forward the libSystem unwinder symbols from 10.7+ and a
compiler-local version of the libgcc unwinder on earlier.
For macOS 10.4 to 10.6 this is 'bug-compatible' with existing uses.
For 10.7+ the behaviour will now actually be correct.
This should be squashed with the initial libgcc changes for PR80556
in any backport (r12-5418-gd4943ce939d)
libgcc/ChangeLog:
* config.host (*-*-darwin*): Add logic to build a shared
unwinder library for Darwin8-10.
* config/i386/t-darwin: Build legacy libgcc_s.1.
* config/rs6000/t-darwin: Likewise.
* config/t-darwin: Reorganise the EH fragments to place
them for inclusion in a shared EH lib.
* config/t-slibgcc-darwin: Build a legacy libgcc_s.1 and
the supporting pieces (all FAT libs).
* config/t-darwin-noeh: Removed.
* config/darwin-unwind.ver: New file.
* config/rs6000/t-darwin-ehs: New file.
* config/t-darwin-ehs: New file.
This is the original binutils bugzilla report,
https://sourceware.org/bugzilla/show_bug.cgi?id=28509
And this is the first version of the proposed binutils patch,
https://sourceware.org/pipermail/binutils/2021-November/118398.html
After applying the binutils patch, I get the the unexpected error when
building libgcc,
/scratch/nelsonc/riscv-gnu-toolchain/riscv-gcc/libgcc/config/riscv/div.S:42:
/scratch/nelsonc/build-upstream/rv64gc-linux/build-install/riscv64-unknown-linux-gnu/bin/ld: relocation R_RISCV_JAL against `__udivdi3' which may bind externally can not be used when making a shared object; recompile with -fPIC
Therefore, this patch add an extra hidden alias symbol for __udivdi3, and
then use HIDDEN_JUMPTARGET to target a non-preemptible symbol instead.
The solution is similar to glibc as follows,
https://sourceware.org/git/?p=glibc.git;a=commit;h=68389203832ab39dd0dbaabbc4059e7fff51c29b
libgcc/ChangeLog:
* config/riscv/div.S: Add the hidden alias symbol for __udivdi3, and
then use HIDDEN_JUMPTARGET to target it since it is non-preemptible.
* config/riscv/riscv-asm.h: Added new macros HIDDEN_JUMPTARGET and
HIDDEN_DEF.
When vxcrtstuff.c was created, the set of #includes was copied from
crtstuff.c. But crtstuff.c also has a bunch of #undefs after the first
#include, because, as the comment says, including auto-host.h when
building objects that are meant for target is technically not
correct.
This manifests when I try do do a canadian cross, with build=linux,
host=windows and target=vxworks, in that we pick up a
#define caddr_t char *
from auto-host.h, which then of course creates a problem when we later
include a target header that has
typedef char * caddr_t;
I assume that the #undefs in crtstuff.c have been added for similar
reasons.
These potentially problematic #defines all seem to be guarded by
#ifndef USED_FOR_TARGET, which tconfig.h defines before including
auto-host.h. So at first, it seems that one could avoid the problem
by simply removing the initial include of auto-host.h. Unfortunately,
we do need some of the things defined in auto-host.h within such an
ifndef USED_FOR_TARGET, namely the define of
HAVE_INITFINI_ARRAY_SUPPORT, which is what later causes
initfini-array.h to define USE_INITFINI_ARRAY. So as the next best
fix, just copy the #undefs from crtstuff.c.
libgcc/
* config/vxcrtstuff.c: Undefine caddr_t, pid_t, rlim_t,
ssize_t and vfork after including auto-host.h.
This addresses a long-standing problem where a work-around for an unwinder
issue (also a regression) regresses other functionality. The patch replaces
several work-arounds with a fix for PR80556 and a work-around for PR88590.
* The fix for PR80556 requires a bump to the SO name for libgcc_s, since we
need to remove the unwinder symbols from it. This would trigger PR88590
hence the work-around for that.
* We weaken the symbols for emulated TLS support so that it is possible
for a DSO linked with static-libgcc to interoperate with a DSO linked with
libgcc_s. Likewise main exes.
* We remove all the gcc-4.2.1 era stubs machinery and workarounds.
* libgcc is always now linked ahead of libc, which avoids fails where the
libc (libSystem) builtins implementations are not up to date.
* The unwinder now always comes from the system
- for Darwin9 from /usr/lib/libgcc_s.1.dylib
- for Darwin10 from /usr/lib/libSystem.dylib
- for Darwin11+ from /usr/lib/system/libunwind.dylib.
We still insert a shim on Darwin10 to fix an omitted unwind function, but
the underlying unwinder remains the system one.
* The work-around for PR88590 has two parts (1) we always link libgcc from
its convenience lib on affected system versions (avoiding the need to find
the DSO path); (2) we add and export the emutls functions from DSOs - this
makes a relatively small (20k) addition to a DSO. These can be backed out
when a proper fix for PR88590 is committed.
For distributions that wish to install a libgcc_s.1.dylib to satisfy linkage
from exes that linked against the stubs can use a reexported libgcc_s.1.1
(since that contains all the symbols that were previously exported via the
stubs).
Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
gcc/ChangeLog:
PR target/80556
* config/darwin-driver.c (darwin_driver_init): Handle exported
symbols and symbol lists (suppress automatic export of the TLS
symbols).
* config/darwin.c (darwin_rename_builtins): Remove workaround.
* config/darwin.h (LINK_GCC_C_SEQUENCE_SPEC): Likewise.
(REAL_LIBGCC_SPEC): Handle revised library uses.
* config/darwin.opt (nodefaultexport): New.
* config/i386/darwin.h (PR80556_WORKAROUND): Remove.
* config/i386/darwin32-biarch.h (PR80556_WORKAROUND): Likewise.
* config/i386/darwin64-biarch.h (PR80556_WORKAROUND): Likewise.
libgcc/ChangeLog:
* config.host: Add weak emutls crt to the extra_parts.
* config/i386/darwin-lib.h (DECLARE_LIBRARY_RENAMES): Remove
workaround.
* config/libgcc-libsystem.ver: Add exclude list for the system-
provided unwinder.
* config/t-slibgcc-darwin: Bump SO version, remove stubs code.
* config/i386/libgcc-darwin.10.4.ver: Removed.
* config/i386/libgcc-darwin.10.5.ver: Removed.
* config/rs6000/libgcc-darwin.10.4.ver: Removed.
* config/rs6000/libgcc-darwin.10.5.ver: Removed.
* config/t-darwin-noeh: New file.
gcc/testsuite/ChangeLog:
* gcc.dg/torture/fp-int-convert-timode-3.c: Remove XFAIL.
* gcc.dg/torture/fp-int-convert-timode-4.c: Likewise.
In order to better support use of the emulated TLS between objects with
DSO dependencies and static-linked libgcc, allow a target to make weak
definitions.
Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
libgcc/ChangeLog:
* config/t-darwin: Build weak-defined emutls objects.
* emutls.c (__emutls_get_address): Add optional attributes.
(__emutls_register_common): Likewise.
(EMUTLS_ATTR): New.
At the end of the backtrace stream _Unwind_Find_FDE() may not be able
to find the frame unwind info and will later call the backtrace fallback
instead of finishing. This occurs when using an old libc on ppc64 due to
dl_iterate_phdr() not being able to set the fde in the last trace.
When this occurs the cfa of the trace will be behind of context's cfa.
Also, libgo’s probestackmaps() calls the backtrace with a null pointer
and can get to the backchain fallback with the same problem, in this case
we are only interested in find a stack map, we don't need nor can do a
backchain.
_Unwind_ForcedUnwind_Phase2() can hit the same issue as it uses
uw_frame_state_for(), so we need to treat _URC_NORMAL_STOP.
libgcc/ChangeLog:
PR libgcc/103044
* config/rs6000/linux-unwind.h (ppc_backchain_fallback): Check if it's
called with a null argument or at the end of the backtrace and return.
* unwind.inc (_Unwind_ForcedUnwind_Phase2): Treat _URC_NORMAL_STOP.
Jonathan reported and I've verified a
In file included from ../../../libgcc/unwind-dw2.c:412:
./md-unwind-support.h:398:6: warning: no previous prototype for ‘ppc_backchain_fallback’ [-Wmissing-prototypes]
398 | void ppc_backchain_fallback (struct _Unwind_Context *context, void *a)
| ^~~~~~~~~~~~~~~~~~~~~~
warning on powerpc*-linux* libgcc build.
All the other MD_* macro functions are static, so I think the following
is the right thing rather than adding a previous prototype for
ppc_backchain_fallback.
2021-11-10 Jakub Jelinek <jakub@redhat.com>
* config/rs6000/linux-unwind.h (ppc_back_fallback): Make it static,
formatting fix.
We have a shim crt for Darwin10 that implements functionality
missing in libSystem. Provide this with a prototype to silence the
warning about this.
libgcc/ChangeLog:
* config/darwin10-unwind-find-enc-func.c: Include libgcc_tm.h.
* config/i386/darwin-lib.h: Declare Darwin10 crt function.
Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
This change implements TI mode on PA64. Various new patterns are
added to pa.md. The libgcc build needed modification to build both
DI and TI routines. We also need various softfp routines to
convert to and from TImode.
I added full softfp for the -msoft-float option. At the moment,
this doesn't completely eliminate all use of the floating-point
co-processor. For this, libgcc needs to be built with -msoft-mult.
The floating-point exception support also needs a soft option.
2021-11-05 John David Anglin <danglin@gcc.gnu.org>
PR libgomp/96661
gcc/ChangeLog:
* config/pa/pa-modes.def: Add OImode integer type.
* config/pa/pa.c (pa_scalar_mode_supported_p): Allow TImode
for TARGET_64BIT.
* config/pa/pa.h (MIN_UNITS_PER_WORD) Define to MIN_UNITS_PER_WORD
to UNITS_PER_WORD if IN_LIBGCC2.
* config/pa/pa.md (addti3, addvti3, subti3, subvti3, negti2,
negvti2, ashlti3, shrpd_internal): New patterns.
Change some multi instruction types to multi.
libgcc/ChangeLog:
* config.host (hppa*64*-*-linux*): Revise tmake_file.
(hppa*64*-*-hpux11*): Likewise.
* config/pa/sfp-exceptions.c: New.
* config/pa/sfp-machine.h: New.
* config/pa/t-dimode: New.
* config/pa/t-softfp-sfdftf: New.
The file fptr.c is specific to 32-bit hppa-linux and should not be
included in LIB2ADD on hppa64-linux.
There is a builtin type mismatch in linux-atomic.c using the type
long long unsigned int for 64-bit atomic operations on hppa64-linux.
2021-10-27 John David Anglin <danglin@gcc.gnu.org>
libgcc/ChangeLog:
* config.host (hppa*64*-*-linux*): Don't add pa/t-linux to
tmake_file.
* config/pa/linux-atomic.c: Define u8, u16 and u64 types.
Use them in FETCH_AND_OP_2, OP_AND_FETCH_2, COMPARE_AND_SWAP_2,
SYNC_LOCK_TEST_AND_SET_2 and SYNC_LOCK_RELEASE_1 macros.
* config/pa/t-linux64 (LIB1ASMSRC): New define.
(LIB1ASMFUNCS): Revise.
(HOST_LIBGCC2_CFLAGS): Add "-DLINUX=1".
This was not defined in the spec and not consistent in the
implementation causing incosistent behavior. After review we have
updated the CPU implementations and proposed the spec be updated to
specific that FPU tininess checks check for tininess before roudning.
Architecture change draft:
https://openrisc.io/proposals/p18-fpu-tininess
libgcc/ChangeLog:
* config/or1k/sfp-machine.h (_FP_TININESS_AFTER_ROUNDING):
Change to 0.
Without dwarf2 unwind tables available _Unwind_Backtrace() is not
able to return the full backtrace.
This patch adds a fallback function on powerpc to get the backtrace
by doing a backchain, this code was originally at glibc.
libgcc/ChangeLog:
* config/rs6000/linux-unwind.h (struct rt_sigframe): Move it to
outside of get_regs() in order to use it in another function, this
is done twice: for __powerpc64__ and for !__powerpc64__.
(struct trace_arg): New struct.
(struct layout): New struct.
(ppc_backchain_fallback): New function.
* unwind.inc (_Unwind_Backtrace): Look for _URC_NORMAL_STOP code
state and call MD_BACKCHAIN_FALLBACK.
gcc/testsuite/ChangeLog:
* gcc.target/powerpc/unwind-backchain.c: New test.
These two symbols have been emitted since 4.8, but were not added
to the Darwin exports, so we have been using the ones from libgcc.a.
Added to libgcc_s now.
Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
libgcc/ChangeLog:
* config/i386/libgcc-darwin.ver: Add Symbols for
__cpu_model, __cpu_indicator_init.
Existing code in the sfp-machine header has been using __MACH__
as a guard for Mach-O, where currently symbols aliases are not
supported.
__MACH__ is not a sufficient guard for this, since the define
is also emitted for HURD, at least.
Fixed by amending the guard to use __APPLE__ instead.
Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
libgcc/ChangeLog:
* config/i386/sfp-machine.h: Guard Mach-O-specific code
using __APPLE__.
These were used on older systems to equate the FAT libgcc_s
library to single-slice equivalents. Unused for any current
system and never emitted by GCC.
Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
libgcc/ChangeLog:
* config/t-slibgcc-darwin: Delete unused code.
This reorganises the Darwin symbol vers files to include
the generic ones at the top level; allowing for arch ports
to override (via either exclusion or inclusion as needed).
We add an X86-specific vers file containing the new HF
symbols. Note that although Darwin does not use ELF-style
symbol versioning - the parser that produces the map can
consume it. Using the ELF-style description will help us
know at which rev the symbols were introduced.
Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
libgcc/ChangeLog:
* config/i386/t-darwin: Add in a vers file for X86-specific
symbols.
* config/t-darwin: Add the generic symbol maps here...
* config/t-slibgcc-darwin: ... removing from here.
* config/i386/libgcc-darwin.ver: New file.
We want to override the libgcc2 generic version of these functions
for X86. First exclude the original and the add in the replacements.
Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
libgcc/ChangeLog:
* config/i386/t-softfp: Exclude libgcc2 versions of __divhc3
and __mulhc3.
We have a small unwinder shim that is only used for Darwin10
(and only then in quite specific cases). To avoid linking
this code for every executable or DSO, we can present the crt
as a convenience library (rather than a .o file).
Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
gcc/ChangeLog:
* config/darwin.h (LINK_COMMAND_SPEC_A): Use Darwin10
unwinder shim as a convenience library.
libgcc/ChangeLog:
* config.host: Use convenience library for Darwin10
unwinder shim.
* config/t-darwin: Build Darwin10 unwinder shim as a
convenience library.
m32r support never made it to glibc and the support for the Linux kernel
was removed with 4.18. It does not remove much but no reason to keep
around a port which never worked or one which the support in other
projects is gone.
OK? Checked to make sure m32r-linux and m32rle-linux were rejected
when building.
contrib/ChangeLog:
* config-list.mk: Remove m32r-linux and m32rle-linux
from the list.
gcc/ChangeLog:
* config.gcc: Add m32r-*-linux* and m32rle-*-linux*
to the Unsupported targets list.
Remove support for m32r-*-linux* and m32rle-*-linux*.
* config/m32r/linux.h: Removed.
* config/m32r/t-linux: Removed.
libgcc/ChangeLog:
* config.host: Remove m32r-*-linux* and m32rle-*-linux*.
* config/m32r/libgcc-glibc.ver: Removed.
* config/m32r/t-linux: Removed.
The following patch exports it for Linux from config/i386/*.ver where it
IMNSHO belongs, aarch64 already exports some of those at GCC_11* and other
targets might add them at completely different gcc versions.
2021-09-08 Jakub Jelinek <jakub@redhat.com>
Iain Sandoe <iain@sandoe.co.uk>
* config/i386/libgcc-glibc.ver: Add %inherit GCC_12.0.0 GCC_7.0.0
and export *hf* and *hc* functions at GCC_12.0.0.
For 32-bit libgcc configure w/o sse2, there's would be an error since
GCC only support _Float16 under sse2. Explicitly add -msse2 for those
HF related libgcc functions, so users can still link them w/ the
upper configuration.
libgcc/ChangeLog:
* Makefile.in: Adjust to support specific CFLAGS for each
libgcc source file.
* config/i386/64/t-softfp: Explicitly add -msse2 for HF
related libgcc source files.
* config/i386/t-softfp: Ditto.
* config/i386/_divhc3.c: New file.
* config/i386/_mulhc3.c: New file.
Darwin does not support strong symbol aliases and a work-
around is provided in sfp-machine.h where a second function
is created that simply calls the original. However this
needs the arguments to the synthesized function to track
the mode of the original function.
So the fix here is to match known floating point modes from
the incoming function and apply the one found to the new
function args.
The matching is highly specific to the current set of modes
and will need adjusting should more cases be added.
Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
libgcc/ChangeLog:
* config/i386/sfp-machine.h (alias_HFtype, alias_SFtype
alias_DFtype, alias_TFtype): New.
(ALIAS_SELECTOR): New.
(strong_alias): Use __typeof and a _Generic selector to
provide the type to the synthesized function.
Quoting from https://gcc.gnu.org/pipermail/gcc/2021-July/236716.html:
--------------------------------------------------------------------
It was pointed out to me off-list that config/aarch64/value-unwind.h
is missing the runtime exception. It looks like a few other files
are too; a fuller list is:
libgcc/config/aarch64/value-unwind.h
libgcc/config/frv/frv-abi.h
libgcc/config/i386/value-unwind.h
libgcc/config/pa/pa64-hpux-lib.h
Certainly for the aarch64 file this was simply a mistake;
it seems to have been copied from the i386 version, both of which
reference the runtime exception but don't actually include it.
--------------------------------------------------------------------
Similarly, frv-abi.h referenced the exception but didn't include it.
pa64-hpux-lib.h was missing any reference to the exception.
The decision was that this was simply a mistake
[https://gcc.gnu.org/pipermail/gcc/2021-July/236717.html]:
--------------------------------------------------------------------
[…] It generally is
considered a textual omission. The runtime library components of GCC
are intended to be licensed under the runtime exception, which was
granted and approved at the time of introduction.
--------------------------------------------------------------------
and that we should simply change all of the files above
[https://gcc.gnu.org/pipermail/gcc/2021-July/236719.html]:
--------------------------------------------------------------------
Please correct the text in the files. The files in libgcc used in the
GCC runtime are intended to be licensed with the runtime exception and
GCC previously was granted approval for that licensing and purpose.
[…]
The runtime exception explicitly was intended for this purpose and
usage at the time that GCC received approval to apply the exception.
--------------------------------------------------------------------
libgcc/
* config/aarch64/value-unwind.h: Add missing runtime exception
paragraph.
* config/frv/frv-abi.h: Likewise.
* config/i386/value-unwind.h: Likewise.
* config/pa/pa64-hpux-lib.h: Likewise.
While performing some tests of IEEE 128 float for PPC64LE, Michael
Meissner noticed that __gcc_qsub is substantially slower than
__gcc_qadd. __gcc_qsub calls __gcc_add with the second operand
negated. Because the functions normally are invoked through
libgcc shared object, the extra PLT overhead has a large impact
on the overall time of the function. This patch converts
__gcc_qadd to a static inline function invoked by __gcc_qadd
and __gcc_qsub.
libgcc/ChangeLog:
* config/rs6000/ibm-ldouble.c (ldouble_qadd_internal): Rename from
__gcc_qadd.
(__gcc_qadd): Call ldouble_qadd_internal.
(__gcc_qsub): Call ldouble_qadd_internal with second long double
argument negated.
Add the recommended erratum mitigation sequence to
__gnu_cmse_nonsecure_call for use on Armv8-m.main devices. Since this
is in the library code we cannot know in advance whether the core we
are running on will be affected by this, so always enable it.
libgcc:
PR target/102035
* config/arm/cmse_nonsecure_call.S (__gnu_cmse_nonsecure_call):
Add vlldm erratum work-around.
When linking gcc runtime objects into large binaries the link may fail
with the below errors. This will happen even if we are building with
-mcmodel=large.
/home/shorne/work/openrisc/output/host/lib/gcc/or1k-buildroot-linux-uclibc/10.3.0/crtbeginS.o: in function `deregister_tm_clones':
crtstuff.c:(.text+0x3c): relocation truncated to fit: R_OR1K_GOT16 against undefined symbol `_ITM_deregisterTMCloneTable'
/home/shorne/work/openrisc/output/host/lib/gcc/or1k-buildroot-linux-uclibc/10.3.0/crtbeginS.o: in function `register_tm_clones':
crtstuff.c:(.text+0xc0): relocation truncated to fit: R_OR1K_GOT16 against undefined symbol `_ITM_registerTMCloneTable'
This patch builds the gcc crtstuff binaries always with the
-mcmodel=large option to ensure they can be linked into large binaries.
libgcc/ChangeLog:
PR target/99783
* config.host (or1k-*, tmake_file): Add or1k/t-crtstuff.
* config/or1k/t-crtstuff: New file.
When building gcc with some specific LDFLAGS_FOR_TARGET, e.g.
LDFLAGS_FOR_TARGET=-Wl,-z,relro,-z,now
those flags propagate info linking of target shared libraries,
e.g. lib{ubsan,tsan,stdc++,quadmath,objc,lsan,itm,gphobos,gdruntime,gomp,go,gfortran,atomic,asan}.so.*
but there is one important exception, libgcc_s.so.* linking ignores it.
The following patch fixes that.
Bootstrapped/regtested on x86_64-linux with LDFLAGS_FOR_TARGET=-Wl,-z,relro,-z,now
and verified that libgcc_s.so.* is BIND_NOW when it previously wasn't, and
without any LDFLAGS_FOR_TARGET on x86_64-linux and i686-linux.
There on x86_64-linux I've verified that the libgcc_s.so.1 linking command
line for -m64 is identical except for whitespace to one without the patch,
and for -m32 multilib $(LDFLAGS) actually do supply there an extra -m32
that also repeats later in the @multilib_flags@, which should be harmless.
2021-08-04 Jakub Jelinek <jakub@redhat.com>
* config/t-slibgcc (SHLIB_LINK): Add $(LDFLAGS).
* config/t-slibgcc-darwin (SHLIB_LINK): Likewise.
* config/t-slibgcc-vms (SHLIB_LINK): Likewise.
* config/t-slibgcc-fuchsia (SHLIB_LDFLAGS): Remove $(LDFLAGS).
The file has two identical halves, seems like twice applied patch.
2021-08-04 Jakub Jelinek <jakub@redhat.com>
* config/t-slibgcc-fuchsia: Undo doubly applied patch.
Compiling gcc/testsuite/gcc.dg/split-*.c and others with -mcpu=power10
and linking with a non-pcrel libgcc results in crashes due to the
power10 pcrel code not having r2 set for the generic-morestack.c
functions called from __morestack. There is also a problem when
non-pcrel code calls a pcrel libgcc. See the patch comments.
A similar situation theoretically occurs with ELFv1 multi-toc
executables, when __morestack might be located in a different toc
group to its caller. This patch makes no attempt to fix that, since
the gold linker does not support multi-toc (gold is needed for proper
support of -fsplit-stack code) nor does gcc emit __morestack calls
that support multi-toc.
* config/rs6000/morestack.S (R2_SAVE): Define.
(__morestack): Save and restore r2. Set up r2 for called
functions.
This patch enables support for TImode for AMD GCN, the lack of which
is currently causing a number of test failures for the target and which
is also needed to support "omp_depend_kind" for OpenMP 5.0, since that
is implemented as a 128-bit integer.
Several libgcc support routines are built by default for the "word size"
of a machine, and also for "2 * word size" of the machine. The libgcc
build for AMD GCN is changed so that it builds for a "word size" of 64
bits, in order to better match the (64-bit) host compiler. However it
isn't really true that we have 64-bit words -- GCN has 32-bit registers,
so changing UNITS_PER_WORD unconditionally would be the wrong thing to do.
Changing this setting for libgcc (only) means that support routines
are built for "single word" operations that are DImode (64 bits), and
those for "double word" operations are built for TImode (128 bits).
That leaves some gaps regarding previous operations that were built
for a "single word" size of 32 bits and a "double word" size of 64 bits
(generic code doesn't cover both alternatives for all operations that
might be needed). Those gaps are filled in by this patch, or by the
preceding patches in the series.
2021-06-18 Julian Brown <julian@codesourcery.com>
gcc/
* config/gcn/gcn.c (gcn_init_libfuncs): New function.
(TARGET_INIT_LIBFUNCS): Define target hook using above function.
* config/gcn/gcn.h (UNITS_PER_WORD): Define to 8 for IN_LIBGCC2, 4
otherwise.
(LIBGCC2_UNITS_PER_WORD, BITS_PER_WORD): Remove definitions.
(MAX_FIXED_MODE_SIZE): Change to 128.
libgcc/
* config/gcn/lib2-bswapti2.c: New file.
* config/gcn/lib2-divmod-di.c: New file.
* config/gcn/lib2-gcn.h (DItype, UDItype, TItype, UTItype): Add
typedefs.
(__divdi3, __moddi3, __udivdi3, __umoddi3): Add prototypes.
* config/gcn/t-amdgcn (LIB2ADD): Add lib2-divmod-di.c and
lib2-bswapti2.c.
This patch changes the argument and return types for the libgcc __udivsi3
and __umodsi3 helper functions for GCN to USItype instead of SItype.
This is probably just cosmetic in practice.
2021-06-18 Julian Brown <julian@codesourcery.com>
libgcc/
* config/gcn/lib2-divmod.c (__udivsi3, __umodsi3): Change argument and
return types to USItype.
* config/gcn/lib2-gcn.h (__udivsi3, __umodsi3): Update prototypes.
The recent float128 ISA3.1 support (r12-1340) has some typos,
it makes the libgcc build fail if it's with one binutils
(assembler) which doesn't support Power10 insns. The error
looks like:
Error: invalid switch -mpower10
Error: unrecognized option -mpower10
... [...libgcc/shared-object.mk:14: float128-p10.o] Error 1
What this patch does are:
- fix test target typo libgcc_cv_powerpc_3_1_float128_hw
(written wrongly as libgcc_cv_powerpc_float128_hw, so it's
going to build ISA3.1 stuffs just when detecting ISA3.0).
- fix test used for libgcc_cv_powerpc_3_1_float128_hw check.
- fix test option used for libgcc_cv_powerpc_3_1_float128_hw
check.
- remove the ISA3.1 related contents from t-float128-hw.
- add new macro FLOAT128_HW_INSNS_ISA3_1 to differentiate
ISA3.1 content from ISA3.0 part in ifunc support.
Bootstrapped/regtested on:
- powerpc64le-linux-gnu P10
- powerpc64le-linux-gnu P9 (w/i and w/o p10 supported as)
- powerpc64-linux-gnu P8 (w/i and w/o p10 supported as)
libgcc/ChangeLog:
* configure: Regenerate.
* configure.ac (test for libgcc_cv_powerpc_3_1_float128_hw): Fix
typos among the name, CFLAGS and the test.
* config/rs6000/t-float128-hw (fp128_3_1_hw_funcs, fp128_3_1_hw_src,
fp128_3_1_hw_static_obj, fp128_3_1_hw_shared_obj, fp128_3_1_hw_obj):
Remove.
* config/rs6000/t-float128-p10-hw (FLOAT128_HW_INSNS): Append
macro FLOAT128_HW_INSNS_ISA3_1.
(FP128_3_1_CFLAGS_HW): Fix option typo.
* config/rs6000/float128-ifunc.c (SW_OR_HW_ISA3_1): Guard this with
FLOAT128_HW_INSNS_ISA3_1.
(__floattikf_resolve): Likewise.
(__floatuntikf_resolve): Likewise.
(__fixkfti_resolve): Likewise.
(__fixunskfti_resolve): Likewise.
(__floattikf): Likewise.
(__floatuntikf): Likewise.
(__fixkfti): Likewise.
(__fixunskfti): Likewise.
The current CMSE support in the multilib build for
"-march=armv8.1-m.main+mve -mfloat-abi=hard -mfpu=auto" is broken
as specified in PR99939 and this patch fixes the issue.
gcc/testsuite/ChangeLog:
2021-06-11 Srinath Parvathaneni <srinath.parvathaneni@arm.com>
PR target/99939
* gcc.target/arm/cmse/cmse-18.c: Add separate scan-assembler
directives check for target is v8.1-m.main+mve or not before
comparing the assembly output.
* gcc.target/arm/cmse/cmse-20.c: New test.
libgcc/ChangeLog:
2021-06-11 Srinath Parvathaneni <srinath.parvathaneni@arm.com>
PR target/99939
* config/arm/cmse_nonsecure_call.S: Add __ARM_FEATURE_MVE
macro.
* config/arm/t-arm: To link cmse.o and cmse_nonsecure_call.o
on passing -mcmse option.
The *TItype_ppc definitions are guarded by _ARCH_PPC64, so all
declarations using it should do so as well.
2021-06-10 Segher Boessenkool <segher@kernel.crashing.org>
libgcc/
* config/rs6000/quad-float128.h: Guard all uses of [U]TItype_ppc by
_ARCH_PPC64 .
The files fixkfti-sw.c and fixunskfti-sw.c are renamed versions of
fixkfti.c and fixunskfti.c respectively to do the conversions in software.
The function names in the files were updated with the rename as well as
some white spaces fixes. The file float128-p10.c contains the functions
for using the ISA 3.1 hardware instructions to perform the conversions.
2021-06-08 Carl Love <cel@us.ibm.com>
gcc/ChangeLog
* config/rs6000/rs6000.c (__fixkfti, __fixunskfti, __floattikf,
__floatuntikf): Names changed to __fixkfti_sw, __fixunskfti_sw,
__floattikf_sw, __floatuntikf_sw respectively.
* config/rs6000/rs6000.md (floatti<mode>2, floatunsti<mode>2,
fix_trunc<mode>ti2, fixuns_trunc<mode>ti2): Add
define_insn for mode IEEE 128.
gcc/testsuite/ChangeLog
* gcc.target/powerpc/fp128_conversions.c: New file.
* gcc.target/powerpc/int_128bit-runnable.c(vextsd2q,
vcmpuq, vcmpsq, vcmpequq, vcmpequq., vcmpgtsq, vcmpgtsq.
vcmpgtuq, vcmpgtuq.): Update scan-assembler-times.
(ppc_native_128bit): Remove dg-require-effective-target.
libgcc/ChangeLog
* config.host: Add if test and set for
libgcc_cv_powerpc_3_1_float128_hw.
* config/rs6000/fixkfti.c: Renamed to fixkfti-sw.c.
Change calls of __fixkfti to __fixkfti_sw.
* config/rs6000/fixunskfti.c: Renamed to fixunskfti-sw.c.
Change calls of __fixunskfti to __fixunskfti_sw.
* config/rs6000/float128-p10.c (__floattikf_hw,
__floatuntikf_hw, __fixkfti_hw, __fixunskfti_hw): New file.
* config/rs6000/float128-ifunc.c (SW_OR_HW_ISA3_1): New macro.
(__floattikf_resolve, __floatuntikf_resolve, __fixkfti_resolve,
__fixunskfti_resolve): Add resolve functions.
(__floattikf, __floatuntikf, __fixkfti, __fixunskfti): New functions.
* config/rs6000/float128-sed (floattitf, __floatuntitf,
__fixtfti, __fixunstfti): Add editor commands to change names.
* config/rs6000/float128-sed-hw (__floattitf,
__floatuntitf, __fixtfti, __fixunstfti): Add editor commands to
change names.
* config/rs6000/floattikf.c: Renamed to floattikf-sw.c.
* config/rs6000/floatuntikf.c: Renamed to floatuntikf-sw.c.
* config/rs6000/quad-float128.h (__floattikf_sw,
__floatuntikf_sw, __fixkfti_sw, __fixunskfti_sw, __floattikf_hw,
__floatuntikf_hw, __fixkfti_hw, __fixunskfti_hw, __floattikf,
__floatuntikf, __fixkfti, __fixunskfti): New extern declarations.
* config/rs6000/t-float128 (floattikf, floatuntikf,
fixkfti, fixunskfti): Remove file names from fp128_ppc_funcs.
(floattikf-sw, floatuntikf-sw, fixkfti-sw, fixunskfti-sw): Add
file names to fp128_ppc_funcs.
* config/rs6000/t-float128-hw(fp128_3_1_hw_funcs,
fp128_3_1_hw_src, fp128_3_1_hw_static_obj, fp128_3_1_hw_shared_obj,
fp128_3_1_hw_obj): Add variables for ISA 3.1 support.
* config/rs6000/t-float128-p10-hw: New file.
* configure: Update script for isa 3.1 128-bit float support.
* configure.ac: Add check for 128-bit float hardware support.
This should help LD's --gc-sections feature to reduce final ELF size.
libgcc/ChangeLog:
* config/pru/mpyll.S (__pruabi_mpyll): Place into own section.
Signed-off-by: Dimitar Dimitrov <dimitar@dinux.eu>
Correctness and performance test programs used during development of
this project may be found in the attachment to:
https://www.mail-archive.com/gcc-patches@gcc.gnu.org/msg254210.html
Summary of Purpose
This patch to libgcc/libgcc2.c __divdc3 provides an
opportunity to gain important improvements to the quality of answers
for the default complex divide routine (half, float, double, extended,
long double precisions) when dealing with very large or very small exponents.
The current code correctly implements Smith's method (1962) [2]
further modified by c99's requirements for dealing with NaN (not a
number) results. When working with input values where the exponents
are greater than *_MAX_EXP/2 or less than -(*_MAX_EXP)/2, results are
substantially different from the answers provided by quad precision
more than 1% of the time. This error rate may be unacceptable for many
applications that cannot a priori restrict their computations to the
safe range. The proposed method reduces the frequency of
"substantially different" answers by more than 99% for double
precision at a modest cost of performance.
Differences between current gcc methods and the new method will be
described. Then accuracy and performance differences will be discussed.
Background
This project started with an investigation related to
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59714. Study of Beebe[1]
provided an overview of past and recent practice for computing complex
divide. The current glibc implementation is based on Robert Smith's
algorithm [2] from 1962. A google search found the paper by Baudin
and Smith [3] (same Robert Smith) published in 2012. Elen Kalda's
proposed patch [4] is based on that paper.
I developed two sets of test data by randomly distributing values over
a restricted range and the full range of input values. The current
complex divide handled the restricted range well enough, but failed on
the full range more than 1% of the time. Baudin and Smith's primary
test for "ratio" equals zero reduced the cases with 16 or more error
bits by a factor of 5, but still left too many flawed answers. Adding
debug print out to cases with substantial errors allowed me to see the
intermediate calculations for test values that failed. I noted that
for many of the failures, "ratio" was a subnormal. Changing the
"ratio" test from check for zero to check for subnormal reduced the 16
bit error rate by another factor of 12. This single modified test
provides the greatest benefit for the least cost, but the percentage
of cases with greater than 16 bit errors (double precision data) is
still greater than 0.027% (2.7 in 10,000).
Continued examination of remaining errors and their intermediate
computations led to the various tests of input value tests and scaling
to avoid under/overflow. The current patch does not handle some of the
rare and most extreme combinations of input values, but the random
test data is only showing 1 case in 10 million that has an error of
greater than 12 bits. That case has 18 bits of error and is due to
subtraction cancellation. These results are significantly better
than the results reported by Baudin and Smith.
Support for half, float, double, extended, and long double precision
is included as all are handled with suitable preprocessor symbols in a
single source routine. Since half precision is computed with float
precision as per current libgcc practice, the enhanced algorithm
provides no benefit for half precision and would cost performance.
Further investigation showed changing the half precision algorithm
to use the simple formula (real=a*c+b*d imag=b*c-a*d) caused no
loss of precision and modest improvement in performance.
The existing constants for each precision:
float: FLT_MAX, FLT_MIN;
double: DBL_MAX, DBL_MIN;
extended and/or long double: LDBL_MAX, LDBL_MIN
are used for avoiding the more common overflow/underflow cases. This
use is made generic by defining appropriate __LIBGCC2_* macros in
c-cppbuiltin.c.
Tests are added for when both parts of the denominator have exponents
small enough to allow shifting any subnormal values to normal values
all input values could be scaled up without risking overflow. That
gained a clear improvement in accuracy. Similarly, when either
numerator was subnormal and the other numerator and both denominator
values were not too large, scaling could be used to reduce risk of
computing with subnormals. The test and scaling values used all fit
within the allowed exponent range for each precision required by the C
standard.
Float precision has more difficulty with getting correct answers than
double precision. When hardware for double precision floating point
operations is available, float precision is now handled in double
precision intermediate calculations with the simple algorithm the same
as the half-precision method of using float precision for intermediate
calculations. Using the higher precision yields exact results for all
tested input values (64-bit double, 32-bit float) with the only
performance cost being the requirement to convert the four input
values from float to double. If double precision hardware is not
available, then float complex divide will use the same improved
algorithm as the other precisions with similar change in performance.
Further Improvement
The most common remaining substantial errors are due to accuracy loss
when subtracting nearly equal values. This patch makes no attempt to
improve that situation.
NOTATION
For all of the following, the notation is:
Input complex values:
a+bi (a= real part, b= imaginary part)
c+di
Output complex value:
e+fi = (a+bi)/(c+di)
For the result tables:
current = current method (SMITH)
b1div = method proposed by Elen Kalda
b2div = alternate method considered by Elen Kalda
new = new method proposed by this patch
DESCRIPTIONS of different complex divide methods:
NAIVE COMPUTATION (-fcx-limited-range):
e = (a*c + b*d)/(c*c + d*d)
f = (b*c - a*d)/(c*c + d*d)
Note that c*c and d*d will overflow or underflow if either
c or d is outside the range 2^-538 to 2^512.
This method is available in gcc when the switch -fcx-limited-range is
used. That switch is also enabled by -ffast-math. Only one who has a
clear understanding of the maximum range of all intermediate values
generated by an application should consider using this switch.
SMITH's METHOD (current libgcc):
if(fabs(c)<fabs(d) {
r = c/d;
denom = (c*r) + d;
e = (a*r + b) / denom;
f = (b*r - a) / denom;
} else {
r = d/c;
denom = c + (d*r);
e = (a + b*r) / denom;
f = (b - a*r) / denom;
}
Smith's method is the current default method available with __divdc3.
Elen Kalda's METHOD
Elen Kalda proposed a patch about a year ago, also based on Baudin and
Smith, but not including tests for subnormals:
https://gcc.gnu.org/legacy-ml/gcc-patches/2019-08/msg01629.html [4]
It is compared here for accuracy with this patch.
This method applies the most significant part of the algorithm
proposed by Baudin&Smith (2012) in the paper "A Robust Complex
Division in Scilab" [3]. Elen's method also replaces two divides by
one divide and two multiplies due to the high cost of divide on
aarch64. In the comparison sections, this method will be labeled
b1div. A variation discussed in that patch which does not replace the
two divides will be labeled b2div.
inline void improved_internal (MTYPE a, MTYPE b, MTYPE c, MTYPE d)
{
r = d/c;
t = 1.0 / (c + (d * r));
if (r != 0) {
x = (a + (b * r)) * t;
y = (b - (a * r)) * t;
} else {
/* Changing the order of operations avoids the underflow of r impacting
the result. */
x = (a + (d * (b / c))) * t;
y = (b - (d * (a / c))) * t;
}
}
if (FABS (d) < FABS (c)) {
improved_internal (a, b, c, d);
} else {
improved_internal (b, a, d, c);
y = -y;
}
NEW METHOD (proposed by patch) to replace the current default method:
The proposed method starts with an algorithm proposed by Baudin&Smith
(2012) in the paper "A Robust Complex Division in Scilab" [3]. The
patch makes additional modifications to that method for further
reductions in the error rate. The following code shows the #define
values for double precision. See the patch for #define values used
for other precisions.
#define RBIG ((DBL_MAX)/2.0)
#define RMIN (DBL_MIN)
#define RMIN2 (0x1.0p-53)
#define RMINSCAL (0x1.0p+51)
#define RMAX2 ((RBIG)*(RMIN2))
if (FABS(c) < FABS(d)) {
/* prevent overflow when arguments are near max representable */
if ((FABS (d) > RBIG) || (FABS (a) > RBIG) || (FABS (b) > RBIG) ) {
a = a * 0.5;
b = b * 0.5;
c = c * 0.5;
d = d * 0.5;
}
/* minimize overflow/underflow issues when c and d are small */
else if (FABS (d) < RMIN2) {
a = a * RMINSCAL;
b = b * RMINSCAL;
c = c * RMINSCAL;
d = d * RMINSCAL;
}
else {
if(((FABS (a) < RMIN) && (FABS (b) < RMAX2) && (FABS (d) < RMAX2)) ||
((FABS (b) < RMIN) && (FABS (a) < RMAX2) && (FABS (d) < RMAX2))) {
a = a * RMINSCAL;
b = b * RMINSCAL;
c = c * RMINSCAL;
d = d * RMINSCAL;
}
}
r = c/d; denom = (c*r) + d;
if( r > RMIN ) {
e = (a*r + b) / denom ;
f = (b*r - a) / denom
} else {
e = (c * (a/d) + b) / denom;
f = (c * (b/d) - a) / denom;
}
}
[ only presenting the fabs(c) < fabs(d) case here, full code in patch. ]
Before any computation of the answer, the code checks for any input
values near maximum to allow down scaling to avoid overflow. These
scalings almost never harm the accuracy since they are by 2. Values that
are over RBIG are relatively rare but it is easy to test for them and
allow aviodance of overflows.
Testing for RMIN2 reveals when both c and d are less than [FLT|DBL]_EPSILON.
By scaling all values by 1/EPSILON, the code converts subnormals to normals,
avoids loss of accuracy and underflows in intermediate computations
that otherwise might occur. If scaling a and b by 1/EPSILON causes either
to overflow, then the computation will overflow whatever method is used.
Finally, we test for either a or b being subnormal (RMIN) and if so,
for the other three values being small enough to allow scaling. We
only need to test a single denominator value since we have already
determined which of c and d is larger.
Next, r (the ratio of c to d) is checked for being near zero. Baudin
and Smith checked r for zero. This code improves that approach by
checking for values less than DBL_MIN (subnormal) covers roughly 12
times as many cases and substantially improves overall accuracy. If r
is too small, then when it is used in a multiplication, there is a
high chance that the result will underflow to zero, losing significant
accuracy. That underflow is avoided by reordering the computation.
When r is subnormal, the code replaces a*r (= a*(c/d)) with ((a/d)*c)
which is mathematically the same but avoids the unnecessary underflow.
TEST Data
Two sets of data are presented to test these methods. Both sets
contain 10 million pairs of complex values. The exponents and
mantissas are generated using multiple calls to random() and then
combining the results. Only values which give results to complex
divide that are representable in the appropriate precision after
being computed in quad precision are used.
The first data set is labeled "moderate exponents".
The exponent range is limited to -DBL_MAX_EXP/2 to DBL_MAX_EXP/2
for Double Precision (use FLT_MAX_EXP or LDBL_MAX_EXP for the
appropriate precisions.
The second data set is labeled "full exponents".
The exponent range for these cases is the full exponent range
including subnormals for a given precision.
ACCURACY Test results:
Note: The following accuracy tests are based on IEEE-754 arithmetic.
Note: All results reporteed are based on use of fused multiply-add. If
fused multiply-add is not used, the error rate increases, giving more
1 and 2 bit errors for both current and new complex divide.
Differences between using fused multiply and not using it that are
greater than 2 bits are less than 1 in a million.
The complex divide methods are evaluated by determining the percentage
of values that exceed differences in low order bits. If a "2 bit"
test results show 1%, that would mean that 1% of 10,000,000 values
(100,000) have either a real or imaginary part that differs from the
quad precision result by more than the last 2 bits.
Results are reported for differences greater than or equal to 1 bit, 2
bits, 8 bits, 16 bits, 24 bits, and 52 bits for double precision. Even
when the patch avoids overflows and underflows, some input values are
expected to have errors due to the potential for catastrophic roundoff
from floating point subtraction. For example, when b*c and a*d are
nearly equal, the result of subtraction may lose several places of
accuracy. This patch does not attempt to detect or minimize this type
of error, but neither does it increase them.
I only show the results for Elen Kalda's method (with both 1 and
2 divides) and the new method for only 1 divide in the double
precision table.
In the following charts, lower values are better.
current - current complex divide in libgcc
b1div - Elen Kalda's method from Baudin & Smith with one divide
b2div - Elen Kalda's method from Baudin & Smith with two divides
new - This patch which uses 2 divides
===================================================
Errors Moderate Dataset
gtr eq current b1div b2div new
====== ======== ======== ======== ========
1 bit 0.24707% 0.92986% 0.24707% 0.24707%
2 bits 0.01762% 0.01770% 0.01762% 0.01762%
8 bits 0.00026% 0.00026% 0.00026% 0.00026%
16 bits 0.00000% 0.00000% 0.00000% 0.00000%
24 bits 0% 0% 0% 0%
52 bits 0% 0% 0% 0%
===================================================
Table 1: Errors with Moderate Dataset (Double Precision)
Note in Table 1 that both the old and new methods give identical error
rates for data with moderate exponents. Errors exceeding 16 bits are
exceedingly rare. There are substantial increases in the 1 bit error
rates for b1div (the 1 divide/2 multiplys method) as compared to b2div
(the 2 divides method). These differences are minimal for 2 bits and
larger error measurements.
===================================================
Errors Full Dataset
gtr eq current b1div b2div new
====== ======== ======== ======== ========
1 bit 2.05% 1.23842% 0.67130% 0.16664%
2 bits 1.88% 0.51615% 0.50354% 0.00900%
8 bits 1.77% 0.42856% 0.42168% 0.00011%
16 bits 1.63% 0.33840% 0.32879% 0.00001%
24 bits 1.51% 0.25583% 0.24405% 0.00000%
52 bits 1.13% 0.01886% 0.00350% 0.00000%
===================================================
Table 2: Errors with Full Dataset (Double Precision)
Table 2 shows significant differences in error rates. First, the
difference between b1div and b2div show a significantly higher error
rate for the b1div method both for single bit errros and well
beyond. Even for 52 bits, we see the b1div method gets completely
wrong answers more than 5 times as often as b2div. To retain
comparable accuracy with current complex divide results for small
exponents and due to the increase in errors for large exponents, I
choose to use the more accurate method of two divides.
The current method has more 1.6% of cases where it is getting results
where the low 24 bits of the mantissa differ from the correct
answer. More than 1.1% of cases where the answer is completely wrong.
The new method shows less than one case in 10,000 with greater than
two bits of error and only one case in 10 million with greater than
16 bits of errors. The new patch reduces 8 bit errors by
a factor of 16,000 and virtually eliminates completely wrong
answers.
As noted above, for architectures with double precision
hardware, the new method uses that hardware for the
intermediate calculations before returning the
result in float precision. Testing of the new patch
has shown zero errors found as seen in Tables 3 and 4.
Correctness for float
=============================
Errors Moderate Dataset
gtr eq current new
====== ======== ========
1 bit 28.68070% 0%
2 bits 0.64386% 0%
8 bits 0.00401% 0%
16 bits 0.00001% 0%
24 bits 0% 0%
=============================
Table 3: Errors with Moderate Dataset (float)
=============================
Errors Full Dataset
gtr eq current new
====== ======== ========
1 bit 19.98% 0%
2 bits 3.20% 0%
8 bits 1.97% 0%
16 bits 1.08% 0%
24 bits 0.55% 0%
=============================
Table 4: Errors with Full Dataset (float)
As before, the current method shows an troubling rate of extreme
errors.
There very minor changes in accuracy for half-precision since the code
changes from Smith's method to the simple method. 5 out of 1 million
test cases show correct answers instead of 1 or 2 bit errors.
libgcc computes half-precision functions in float precision
allowing the existing methods to avoid overflow/underflow issues
for the allowed range of exponents for half-precision.
Extended precision (using x87 80-bit format on x86) and Long double
(using IEEE-754 128-bit on x86 and aarch64) both have 15-bit exponents
as compared to 11-bit exponents in double precision. We note that the
C standard also allows Long Double to be implemented in the equivalent
range of Double. The RMIN2 and RMINSCAL constants are selected to work
within the Double range as well as with extended and 128-bit ranges.
We will limit our performance and accurancy discussions to the 80-bit
and 128-bit formats as seen on x86 here.
The extended and long double precision investigations were more
limited. Aarch64 does not support extended precision but does support
the software implementation of 128-bit long double precision. For x86,
long double defaults to the 80-bit precision but using the
-mlong-double-128 flag switches to using the software implementation
of 128-bit precision. Both 80-bit and 128-bit precisions have the same
exponent range, with the 128-bit precision has extended mantissas.
Since this change is only aimed at avoiding underflow/overflow for
extreme exponents, I studied the extended precision results on x86 for
100,000 values. The limited exponent dataset showed no differences.
For the dataset with full exponent range, the current and new values
showed major differences (greater than 32 bits) in 567 cases out of
100,000 (0.56%). In every one of these cases, the ratio of c/d or d/c
(as appropriate) was zero or subnormal, indicating the advantage of
the new method and its continued correctness where needed.
PERFORMANCE Test results
In order for a library change to be practical, it is necessary to show
the slowdown is tolerable. The slowdowns observed are much less than
would be seen by (for example) switching from hardware double precison
to a software quad precision, which on the tested machines causes a
slowdown of around 100x).
The actual slowdown depends on the machine architecture. It also
depends on the nature of the input data. If underflow/overflow is
rare, then implementations that have strong branch prediction will
only slowdown by a few cycles. If underflow/overflow is common, then
the branch predictors will be less accurate and the cost will be
higher.
Results from two machines are presented as examples of the overhead
for the new method. The one labeled x86 is a 5 year old Intel x86
processor and the one labeled aarch64 is a 3 year old arm64 processor.
In the following chart, the times are averaged over a one million
value data set. All values are scaled to set the time of the current
method to be 1.0. Lower values are better. A value of less than 1.0
would be faster than the current method and a value greater than 1.0
would be slower than the current method.
================================================
Moderate set full set
x86 aarch64 x86 aarch64
======== =============== ===============
float 0.59 0.79 0.45 0.81
double 1.04 1.24 1.38 1.56
long double 1.13 1.24 1.29 1.25
================================================
Table 5: Performance Comparisons (ratio new/current)
The above tables omit the timing for the 1 divide and 2 multiply
comparison with the 2 divide approach.
The float results show clear performance improvement due to using the
simple method with double precision for intermediate calculations.
The double results with the newer method show less overhead for the
moderate dataset than for the full dataset. That's because the moderate
dataset does not ever take the new branches which protect from
under/overflow. The better the branch predictor, the lower the cost
for these untaken branches. Both platforms are somewhat dated, with
the x86 having a better branch predictor which reduces the cost of the
additional branches in the new code. Of course, the relative slowdown
may be greater for some architectures, especially those with limited
branch prediction combined with a high cost of misprediction.
The long double results are fairly consistent in showing the moderate
additional cost of the extra branches and calculations for all cases.
The observed cost for all precisions is claimed to be tolerable on the
grounds that:
(a) the cost is worthwhile considering the accuracy improvement shown.
(b) most applications will only spend a small fraction of their time
calculating complex divide.
(c) it is much less than the cost of extended precision
(d) users are not forced to use it (as described below)
Those users who find this degree of slowdown unsatisfactory may use
the gcc switch -fcx-fortran-rules which does not use the library
routine, instead inlining Smith's method without the C99 requirement
for dealing with NaN results. The proposed patch for libgcc complex
divide does not affect the code generated by -fcx-fortran-rules.
SUMMARY
When input data to complex divide has exponents whose absolute value
is less than half of *_MAX_EXP, this patch makes no changes in
accuracy and has only a modest effect on performance. When input data
contains values outside those ranges, the patch eliminates more than
99.9% of major errors with a tolerable cost in performance.
In comparison to Elen Kalda's method, this patch introduces more
performance overhead but reduces major errors by a factor of
greater than 4000.
REFERENCES
[1] Nelson H.F. Beebe, "The Mathematical-Function Computation Handbook.
Springer International Publishing AG, 2017.
[2] Robert L. Smith. Algorithm 116: Complex division. Commun. ACM,
5(8):435, 1962.
[3] Michael Baudin and Robert L. Smith. "A robust complex division in
Scilab," October 2012, available at http://arxiv.org/abs/1210.4539.
[4] Elen Kalda: Complex division improvements in libgcc
https://gcc.gnu.org/legacy-ml/gcc-patches/2019-08/msg01629.html
2020-12-08 Patrick McGehearty <patrick.mcgehearty@oracle.com>
gcc/c-family/
* c-cppbuiltin.c (c_cpp_builtins): Add supporting macros for new
complex divide
libgcc/
* libgcc2.c (XMTYPE, XCTYPE, RBIG, RMIN, RMIN2, RMINSCAL, RMAX2):
Define.
(__divsc3, __divdc3, __divxc3, __divtc3): Improve complex divide.
* config/rs6000/_divkc3.c (RBIG, RMIN, RMIN2, RMINSCAL, RMAX2):
Define.
(__divkc3): Improve complex divide.
gcc/testsuite/
* gcc.c-torture/execute/ieee/cdivchkd.c: New test.
* gcc.c-torture/execute/ieee/cdivchkf.c: Likewise.
* gcc.c-torture/execute/ieee/cdivchkld.c: Likewise.
Frederic Konrad
Olivier Hainque
Rasmus Villemoes
Iain Sandoe
Rasmus Villemoes
Nelson Chu
John David Anglin
Raphael Moreira Zinsly
Jakub Jelinek
Stafford Horne
Ian Lance Taylor
Andrew Pinski
liuhongt
Richard Sandiford
David Edelsohn
Jonathan Yong
Richard Earnshaw
Alan Modra
Julian Brown
Kewen Lin
Srinath Parvathaneni
Segher Boessenkool
Carl Love
Dimitar Dimitrov
Patrick McGehearty