Here is a complete patch to add std::bfloat16_t support on
x86 (AArch64 and ARM left for later). Almost no BFmode optabs
are added by the patch, so for binops/unops it extends to SFmode
first and then truncates back to BFmode.
For {HF,SF,DF,XF,TF}mode -> BFmode conversions libgcc has implementations
of all those conversions so that we avoid double rounding, for
BFmode -> {DF,XF,TF}mode conversions to avoid growing libgcc too much
it emits BFmode -> SFmode conversion first and then converts to the even
wider mode, neither step should be imprecise.
For BFmode -> HFmode, it first emits a precise BFmode -> SFmode conversion
and then SFmode -> HFmode, because neither format is subset or superset
of the other, while SFmode is superset of both.
expr.cc then contains a -ffast-math optimization of the BF -> SF and
SF -> BF conversions if we don't optimize for space (and for the latter
if -frounding-math isn't enabled either).
For x86, perhaps truncsfbf2 optab could be defined for TARGET_AVX512BF16
but IMNSHO should FAIL if !flag_finite_math || flag_rounding_math
|| !flag_unsafe_math_optimizations, because I think the insn doesn't
raise on sNaNs, hardcodes round to nearest and flushes denormals to zero.
By default (unless x86 -fexcess-precision=16) we use float excess
precision for BFmode, so truncate only on explicit casts and assignments.
The patch introduces a single __bf16 builtin - __builtin_nansf16b,
because (__bf16) __builtin_nansf ("") will drop the sNaN into qNaN,
and uses f16b suffix instead of bf16 because there would be ambiguity on
log vs. logb - __builtin_logbf16 could be either log with bf16 suffix
or logb with f16 suffix. In other cases libstdc++ should mostly use
__builtin_*f for std::bfloat16_t overloads (we have a problem with
std::nextafter though but that one we have also for std::float16_t).
2022-10-14 Jakub Jelinek <jakub@redhat.com>
gcc/
* tree-core.h (enum tree_index): Add TI_BFLOAT16_TYPE.
* tree.h (bfloat16_type_node): Define.
* tree.cc (excess_precision_type): Promote bfloat16_type_mode
like float16_type_mode.
(build_common_tree_nodes): Initialize bfloat16_type_node if
BFmode is supported.
* expmed.h (maybe_expand_shift): Declare.
* expmed.cc (maybe_expand_shift): No longer static.
* expr.cc (convert_mode_scalar): Don't ICE on BF -> HF or HF -> BF
conversions. If there is no optab, handle BF -> {DF,XF,TF,HF}
conversions as separate BF -> SF -> {DF,XF,TF,HF} conversions, add
-ffast-math generic implementation for BF -> SF and SF -> BF
conversions.
* builtin-types.def (BT_BFLOAT16, BT_FN_BFLOAT16_CONST_STRING): New.
* builtins.def (BUILT_IN_NANSF16B): New builtin.
* fold-const-call.cc (fold_const_call): Handle CFN_BUILT_IN_NANSF16B.
* config/i386/i386.cc (classify_argument): Handle E_BCmode.
(ix86_libgcc_floating_mode_supported_p): Also return true for BFmode
for -msse2.
(ix86_mangle_type): Mangle BFmode as DF16b.
(ix86_invalid_conversion, ix86_invalid_unary_op,
ix86_invalid_binary_op): Remove.
(TARGET_INVALID_CONVERSION, TARGET_INVALID_UNARY_OP,
TARGET_INVALID_BINARY_OP): Don't redefine.
* config/i386/i386-builtins.cc (ix86_bf16_type_node): Remove.
(ix86_register_bf16_builtin_type): Use bfloat16_type_node rather than
ix86_bf16_type_node, only create it if still NULL.
* config/i386/i386-builtin-types.def (BFLOAT16): Likewise.
* config/i386/i386.md (cbranchbf4, cstorebf4): New expanders.
gcc/c-family/
* c-cppbuiltin.cc (c_cpp_builtins): If bfloat16_type_node,
predefine __BFLT16_*__ macros and for C++23 also
__STDCPP_BFLOAT16_T__. Predefine bfloat16_type_node related
macros for -fbuilding-libgcc.
* c-lex.cc (interpret_float): Handle CPP_N_BFLOAT16.
gcc/c/
* c-typeck.cc (convert_arguments): Don't promote __bf16 to
double.
gcc/cp/
* cp-tree.h (extended_float_type_p): Return true for
bfloat16_type_node.
* typeck.cc (cp_compare_floating_point_conversion_ranks): Set
extended{1,2} if mv{1,2} is bfloat16_type_node. Adjust comment.
gcc/testsuite/
* lib/target-supports.exp (check_effective_target_bfloat16,
check_effective_target_bfloat16_runtime, add_options_for_bfloat16):
New.
* gcc.dg/torture/bfloat16-basic.c: New test.
* gcc.dg/torture/bfloat16-builtin.c: New test.
* gcc.dg/torture/bfloat16-builtin-issignaling-1.c: New test.
* gcc.dg/torture/bfloat16-complex.c: New test.
* gcc.dg/torture/builtin-issignaling-1.c: Allow to be includable
from bfloat16-builtin-issignaling-1.c.
* gcc.dg/torture/floatn-basic.h: Allow to be includable from
bfloat16-basic.c.
* gcc.target/i386/vect-bfloat16-typecheck_2.c: Adjust expected
diagnostics.
* gcc.target/i386/sse2-bfloat16-scalar-typecheck.c: Likewise.
* gcc.target/i386/vect-bfloat16-typecheck_1.c: Likewise.
* g++.target/i386/bfloat_cpp_typecheck.C: Likewise.
libcpp/
* include/cpplib.h (CPP_N_BFLOAT16): Define.
* expr.cc (interpret_float_suffix): Handle bf16 and BF16 suffixes for
C++.
libgcc/
* config/i386/t-softfp (softfp_extensions): Add bfsf.
(softfp_truncations): Add tfbf xfbf dfbf sfbf hfbf.
(CFLAGS-extendbfsf2.c, CFLAGS-truncsfbf2.c, CFLAGS-truncdfbf2.c,
CFLAGS-truncxfbf2.c, CFLAGS-trunctfbf2.c, CFLAGS-trunchfbf2.c): Add
-msse2.
* config/i386/libgcc-glibc.ver (GCC_13.0.0): Export
__extendbfsf2 and __trunc{s,d,x,t,h}fbf2.
* config/i386/sfp-machine.h (_FP_NANSIGN_B): Define.
* config/i386/64/sfp-machine.h (_FP_NANFRAC_B): Define.
* config/i386/32/sfp-machine.h (_FP_NANFRAC_B): Define.
* soft-fp/brain.h: New file.
* soft-fp/truncsfbf2.c: New file.
* soft-fp/truncdfbf2.c: New file.
* soft-fp/truncxfbf2.c: New file.
* soft-fp/trunctfbf2.c: New file.
* soft-fp/trunchfbf2.c: New file.
* soft-fp/truncbfhf2.c: New file.
* soft-fp/extendbfsf2.c: New file.
libiberty/
* cp-demangle.h (D_BUILTIN_TYPE_COUNT): Increment.
* cp-demangle.c (cplus_demangle_builtin_types): Add std::bfloat16_t
entry.
(cplus_demangle_type): Demangle DF16b.
* testsuite/demangle-expected (_Z3xxxDF16b): New test.
This directory contains the -liberty library of free software.
It is a collection of subroutines used by various GNU programs.
Current members include:
getopt -- get options from command line
obstack -- stacks of arbitrarily-sized objects
strerror -- error message strings corresponding to errno
strtol -- string-to-long conversion
strtoul -- string-to-unsigned-long conversion
We expect many of the GNU subroutines that are floating around to
eventually arrive here.
The library must be configured from the top source directory. Don't
try to run configure in this directory. Follow the configuration
instructions in ../README.
Please report bugs to https://gcc.gnu.org/bugzilla/ and send fixes to
"gcc-patches@gcc.gnu.org". Thank you.
ADDING A NEW FILE
=================
There are two sets of files: Those that are "required" will be
included in the library for all configurations, while those
that are "optional" will be included in the library only if "needed."
To add a new required file, edit Makefile.in to add the source file
name to CFILES and the object file to REQUIRED_OFILES.
To add a new optional file, it must provide a single function, and the
name of the function must be the same as the name of the file.
* Add the source file name to CFILES in Makefile.in and the object
file to CONFIGURED_OFILES.
* Add the function to name to the funcs shell variable in
configure.ac.
* Add the function to the AC_CHECK_FUNCS lists just after the
setting of the funcs shell variable. These AC_CHECK_FUNCS calls
are never executed; they are there to make autoheader work
better.
* Consider the special cases of building libiberty; as of this
writing, the special cases are newlib and VxWorks. If a
particular special case provides the function, you do not need
to do anything. If it does not provide the function, add the
object file to LIBOBJS, and add the function name to the case
controlling whether to define HAVE_func.
Finally, in the build directory of libiberty, configure with
"--enable-maintainer-mode", run "make maint-deps" to update
Makefile.in, and run 'make stamp-functions' to regenerate
functions.texi.
The optional file you've added (e.g. getcwd.c) should compile and work
on all hosts where it is needed. It does not have to work or even
compile on hosts where it is not needed.
ADDING A NEW CONFIGURATION
==========================
On most hosts you should be able to use the scheme for automatically
figuring out which files are needed. In that case, you probably
don't need a special Makefile stub for that configuration.
If the fully automatic scheme doesn't work, you may be able to get
by with defining EXTRA_OFILES in your Makefile stub. This is
a list of object file names that should be treated as required
for this configuration - they will be included in libiberty.a,
regardless of whatever might be in the C library.
Jakub Jelinek
c2565a31c1