Fixes an execution failure in testcase gfortran.dg/assumed_rank_1.f90.

2020-01-30  Andrew Stubbs  <ams@codesourcery.com>

	gcc/
	* config/gcn/gcn-valu.md (gather<mode>_exec): Move contents ...
	(mask_gather_load<mode>): ... here, and zero-initialize the
	destination.
	(maskload<mode>di): Zero-initialize the destination.
	* config/gcn/gcn.c:

gcc/analyzer/ChangeLog:
	* program-state.cc (extrinsic_state::dump_to_pp): New.
	(extrinsic_state::dump_to_file): New.
	(extrinsic_state::dump): New.
	* program-state.h (extrinsic_state::dump_to_pp): New decl.
	(extrinsic_state::dump_to_file): New decl.
	(extrinsic_state::dump): New decl.
	* sm.cc: Include "pretty-print.h".
	(state_machine::dump_to_pp): New.
	* sm.h (state_machine::dump_to_pp): New decl.

gcc/analyzer/ChangeLog:
	* diagnostic-manager.cc (for_each_state_change): Use
	extrinsic_state::get_num_checkers rather than accessing m_checkers
	directly.
	* program-state.cc (program_state::program_state): Likewise.
	* program-state.h (extrinsic_state::m_checkers): Make private.

This test assumes that memset and strlen have been marked with
__attribute__((nonnull)), which isn't necessarily the case for an
arbitrary <string.h>.  This likely explains these failures:
  FAIL: gcc.dg/analyzer/malloc-1.c  (test for warnings, line 417)
  FAIL: gcc.dg/analyzer/malloc-1.c  (test for warnings, line 418)
  FAIL: gcc.dg/analyzer/malloc-1.c  (test for warnings, line 425)
  FAIL: gcc.dg/analyzer/malloc-1.c  (test for warnings, line 429)
seen in https://gcc.gnu.org/ml/gcc-testresults/2020-01/msg01608.html
on x86_64-apple-darwin18.

Fix it by using the __builtin_ forms.

gcc/testsuite/ChangeLog:
	* gcc.dg/analyzer/malloc-1.c: Remove include of <string.h>.
	Use __builtin_ forms of memset and strlen throughout.

gcc/testsuite/ChangeLog:
	* gcc.dg/analyzer/conditionals-2.c: Move to...
	* gcc.dg/analyzer/torture/conditionals-2.c: ...here, converting
	to a torture test.  Remove redundant include.

PR analyzer/93356 reports an ICE handling __builtin_isnan due to a
failing assertion:
  674     gcc_assert (lhs_ec_id != rhs_ec_id);
with op=UNORDERED_EXPR.
when attempting to add an UNORDERED_EXPR constraint.

This is an overzealous assertion, but underlying it are various forms of
sloppiness regarding NaN within the analyzer:

  (a) the assumption in the constraint_manager that equivalence classes
  are reflexive (X == X), which isn't the case for NaN.

  (b) Hardcoding the "honor_nans" param to false when calling
  invert_tree_comparison throughout the analyzer.

  (c) Ignoring ORDERED_EXPR, UNORDERED_EXPR, and the UN-prefixed
  comparison codes.

I wrote a patch for this which tracks the NaN-ness of floating-point
values and uses this to address all of the above.

However, to minimize changes in gcc 10 stage 4, here's a simpler patch
which rejects attempts to query or add constraints on floating-point
values, instead treating any floating-point comparison as "unknown", and
silently dropping the constraints at edges.

gcc/analyzer/ChangeLog:
	PR analyzer/93356
	* region-model.cc (region_model::eval_condition): In both
	overloads, bail out immediately on floating-point types.
	(region_model::eval_condition_without_cm): Likewise.
	(region_model::add_constraint): Likewise.

gcc/testsuite/ChangeLog:
	PR analyzer/93356
	* gcc.dg/analyzer/conditionals-notrans.c (test_float_selfcmp):
	Add.
	* gcc.dg/analyzer/conditionals-trans.c: Mark floating point
	comparison test as failing.
	(test_float_selfcmp): Add.
	* gcc.dg/analyzer/data-model-1.c: Mark floating point comparison
	tests as failing.
	* gcc.dg/analyzer/torture/pr93356.c: New test.

gcc/ChangeLog:
	PR analyzer/93356
	* doc/analyzer.texi (Limitations): Note that constraints on
	floating-point values are currently ignored.

        PR c/88660
        * c-parser.c (c_parser_switch_statement): Make sure to request
        marking the switch expr as used.

        PR c/88660
        * gcc.dg/pr88660.c: New test.

The following testcase FAILs on powerpc64le-linux with assembler errors, as we
emit a call to bar.localalias, then .set bar.localalias, bar twice and then
another call to bar.localalias.  The problem is that bar.localalias can be created
at various stages and e.g. ipa-pure-const can slightly adjust the original decl,
so that the existing bar.localalias isn't considered usable (different
flags_from_decl_or_type).  In that case, we'd create another bar.localalias, which
clashes with the existing name.

Fixed by retrying with another name if it is already present.  The various localalias
aliases shouldn't be that many, from different partitions they would be lto_priv
suffixed and in most cases they would already have the same type/flags/attributes.

2020-01-30  Jakub Jelinek  <jakub@redhat.com>

	PR lto/93384
	* symtab.c (symtab_node::noninterposable_alias): If localalias
	already exists, but is not usable, append numbers after it until
	a unique name is found.  Formatting fix.

	* gcc.dg/lto/pr93384_0.c: New test.
	* gcc.dg/lto/pr93384_1.c: New file.

What happens on this testcase is with the out of bounds rotate we get:
Trying 13 -> 16:
   13: r129:SI=r132:DI#0<-<0x20
      REG_DEAD r132:DI
   16: r123:DI=r129:SI<0
      REG_DEAD r129:SI
Successfully matched this instruction:
(set (reg/v:DI 123 [ <retval> ])
    (const_int 0 [0]))
during combine.  So, perhaps we could also change simplify-rtx.c to punt
if it is out of bounds rather than trying to optimize anything.
Or, but probably GCC11 material, if we decide that ROTATE/ROTATERT doesn't
have out of bounds counts or introduce targetm.rotate_truncation_mask,
we should truncate the argument instead of punting.
Punting is better for backports though.

2020-01-30  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/93505
	* combine.c (simplify_comparison) <case ROTATE>: Punt on out of range
	rotate counts.

	* gcc.c-torture/compile/pr93505.c: New test.

When instantiating a template tsubst_copy_and_build suppresses -Wtype-limits
warnings about e.g. == always being false because it might not always be
false for an instantiation with other template arguments.  But we should
warn if the operands don't depend on template arguments.

	PR c++/82521
	* pt.c (tsubst_copy_and_build) [EQ_EXPR]: Only suppress warnings if
	the expression was dependent before substitution.

        PR fortran/87103
        * expr.c (gfc_check_conformance): Check vsnprintf for truncation.
        * iresolve.c (gfc_get_string): Likewise.
        * symbol.c (gfc_new_symbol): Remove check for maximum symbol
        name length.  Remove redundant 0 setting of new calloc()ed
        gfc_symbol.

Fixes ICE in testcase gcc.dg/pr81228.c

2020-01-30  Andrew Stubbs  <ams@codesourcery.com>

	gcc/
	* config/gcn/gcn.c (print_operand): Handle LTGT.
	* config/gcn/predicates.md (gcn_fp_compare_operator): Allow ltgt.

	* gcc.dg/tree-ssa/ssa-dse-26.c: Make existing dg-final scan
	conditional on !c6x.  Add dg-final scan pattern for c6x.

gcc/testsuite/ChangeLog:
	* gcc.dg/Warray-bounds-57.c: New test.

This wraps { ... } in _Literal (type) for consumption by the GIMPLE FE.

2020-01-30  Richard Biener  <rguenther@suse.de>

	* tree-pretty-print.c (dump_generic_node): Wrap VECTOR_CST
	and CONSTRUCTOR in _Literal (type) with TDF_GIMPLE.

PR analyzer/93450 reports an ICE trying to fold an EQ_EXPR comparison
of (int)0 with (float)Inf.

Most comparisons inside the analyzer come from gimple conditions, for
which the necessary casts have already been added.

This one is done inside constant_svalue::eval_condition as part of
purging sm-state for an unknown function call, and fails to check
the types being compared, leading to the ICE.

sm_state_map::set_state calls region_model::eval_condition_without_cm in
order to handle pointer equality (so that e.g. (void *)&r and (foo *)&r
transition together), which leads to this code generating a bogus query
to see if the two constants are equal.

This patch fixes the ICE in two ways:

- It avoids generating comparisons within
  constant_svalue::eval_condition unless the types are equal (thus for
  constants, but not for pointer values, which are handled by
  region_svalue).

- It updates sm_state_map::set_state to bail immediately if the new
  state is the same as the old one, thus avoiding the above for the
  common case where an svalue_id has no sm-state (such as for the int
  and float constants in the reproducer), for which the above becomes a
  no-op.

gcc/analyzer/ChangeLog:
	PR analyzer/93450
	* program-state.cc (sm_state_map::set_state): For the overload
	taking an svalue_id, bail out if the set_state on the ec does
	nothing.  Convert the latter's return type from void to bool,
	returning true if anything changed.
	(sm_state_map::impl_set_state): Convert the return type from void
	to bool, returning true if the state changed.
	* program-state.h (sm_state_map::set_state): Convert return type
	from void to bool.
	(sm_state_map::impl_set_state): Likewise.
	* region-model.cc (constant_svalue::eval_condition): Only call
	fold_build2 if the types are the same.

gcc/testsuite/ChangeLog:
	PR analyzer/93450
	* gcc.dg/analyzer/torture/pr93450.c: New test.

	2020-01-30  John David Anglin  <danglin@gcc.gnu.org>

	* config/pa/pa.c (pa_elf_select_rtx_section): Place function pointers
	without a DECL in .data.rel.ro.local.

uaddvdi4 expander has an optimization for the low 32-bits of the 2nd input
operand known to be 0.  Unfortunately, in that case it only emits copying of
the low 32 bits to the low 32 bits of the destination, but doesn't emit the
addition with overflow detection for the high 64 bits.
Well, to be precise, it emits it, but into an RTL sequence returned by
gen_uaddvsi4, but that sequence isn't emitted anywhere.

2020-01-30  Jakub Jelinek  <jakub@redhat.com>

	PR target/93494
	* config/arm/arm.md (uaddvdi4): Actually emit what gen_uaddvsi4
	returned.

	* gcc.c-torture/execute/pr93494.c: New test.

        PR bootstrap/93409
        * plugin/configfrag.ac (enable_offload_targets): Skip
        HSA and GCN plugin besides -m32 also for -mx32.
        * configure: Regenerate.

	PR c++/90338
	* g++.dg/pr90338.C: New.

Some time ago, patterns were added to optimize move mask followed by zero
extension from 32 bits to 64 bit.  As the testcase shows, the intrinsics
actually return int, not unsigned int, so it will happen quite often that
one actually needs sign extension instead of zero extension.  Except for
vpmovmskb with 256-bit operand, sign vs. zero extension doesn't make a
difference, as we know the bit 31 will not be set (the source will have 2 or
4 doubles, 4 or 8 floats or 16 or 32 chars).
So, for the floating point patterns, this patch just uses a code iterator
so that we handle both zero extend and sign extend, and for the byte one
adds a separate pattern for the 128-bit operand.

2020-01-30  Jakub Jelinek  <jakub@redhat.com>

	PR target/91824
	* config/i386/sse.md
	(*<sse>_movmsk<ssemodesuffix><avxsizesuffix>_zext): Renamed to ...
	(*<sse>_movmsk<ssemodesuffix><avxsizesuffix>_<u>ext): ... this.  Use
	any_extend code iterator instead of always zero_extend.
	(*<sse>_movmsk<ssemodesuffix><avxsizesuffix>_zext_lt): Renamed to ...
	(*<sse>_movmsk<ssemodesuffix><avxsizesuffix>_<u>ext_lt): ... this.
	Use any_extend code iterator instead of always zero_extend.
	(*<sse>_movmsk<ssemodesuffix><avxsizesuffix>_zext_shift): Renamed to ...
	(*<sse>_movmsk<ssemodesuffix><avxsizesuffix>_<u>ext_shift): ... this.
	Use any_extend code iterator instead of always zero_extend.
	(*sse2_pmovmskb_ext): New define_insn.
	(*sse2_pmovmskb_ext_lt): New define_insn_and_split.

	* gcc.target/i386/pr91824-2.c: New test.

Like any other instruction with 32-bit GPR destination operand in 64-bit
mode, popcntl also clears the upper 32 bits of the register (and other bits
too, it can return only 0 to 32 inclusive).

During combine, the zero or sign extensions of it show up as paradoxical
subreg of the popcount & 63, there 63 is the smallest power of two - 1 mask
that can represent all the 0 to 32 inclusive values.

2020-01-30  Jakub Jelinek  <jakub@redhat.com>

	PR target/91824
	* config/i386/i386.md (*popcountsi2_zext): New define_insn_and_split.
	(*popcountsi2_zext_falsedep): New define_insn.

	* gcc.target/i386/pr91824-1.c: New test.

This is something that has been discussed already a few months ago, but
seems to have stalled.  Here is Paul's patch from the PR except for the
TREE_STATIC hunk which is wrong, and does the most conservative fn spec
tweak for the problematic two builtins we are aware of (to repeat what is in
the PR, both .wR and .ww are wrong for these builtins that transform one
layout of an descriptor to another one; while the first pointer is properly
marked that we only store to what it points to, from the second pointer
we copy and reshuffle the content and store into the first one; if there
wouldn't be any pointers, ".wr" would be just fine, but as there is a
pointer and that pointer is copied to the area pointed by first argument,
the pointer effectively leaks that way, so we e.g. can't optimize stores
into what the data pointer in the descriptor points to).  I haven't
analyzed other fn spec attributes in the FE, but think it is better to
fix at least this one we have analyzed.

2020-01-30  Paul Thomas  <pault@gcc.gnu.org>
	    Jakub Jelinek  <jakub@redhat.com>

	PR fortran/92123
	* trans-decl.c (gfc_get_symbol_decl): Call gfc_defer_symbol_init for
	CFI descs.
	(gfc_build_builtin_function_decls): Use ".w." instead of ".ww" or ".wR"
	for gfor_fndecl_{cfi_to_gfc,gfc_to_cfi}.
	(convert_CFI_desc): Handle references to CFI descriptors.

Co-authored-by: Paul Thomas <pault@gcc.gnu.org>

Commit 54b3d52c ("Emit .note.GNU-stack for hard-float linux targets.")
was missing generated files.  Add them now.

gcc/ChangeLog:

2020-01-30  Dragan Mladjenovic  <dmladjenovic@wavecomp.com>

	* config.in: Regenerated.
	* configure: Regenerated.

By standard, coroutine body should be encapsulated in try-catch block
as following:
  try {
    // coroutine body
  } catch(...) {
    promise.unhandled_exception();
  }
Given above try-catch block is implemented in the coroutine actor
function called by coroutine ramp function, so the promise should
be accessed via actor function's coroutine frame pointer argument,
rather than the ramp function's coroutine frame variable.

This patch cleans code a bit to make fix easy.

gcc/cp
    * coroutines.cc (act_des_fn): New.
    (morph_fn_to_coro): Call act_des_fn to build actor/destroy decls.
    Access promise via actor function's frame pointer argument.
    (build_actor_fn, build_destroy_fn): Use frame pointer argument.

Function co_await_expander expands CO_AWAIT_EXPR and inserts expanded
code before result of co_await is used, however, it doesn't cover the
type conversion case and leads to gimplify ICE.  This patch fixes it.

gcc/cp
    * coroutines.cc (co_await_expander): Handle type conversion case.

gcc/testsuite
    * g++.dg/coroutines/co-await-syntax-09-convert.C: New test.

Patch by Svante Signell.

Updates PR go/93468

Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/216959

Patch from Svante Signell.

Updates PR go/93468

Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/216958

Since expand_stack_vars and such know how to deal with variables aligned
beyond MAX_SUPPORTED_STACK_ALIGNMENT, we shouldn't reject alignas of large
alignments.  And if we don't do that, there's no point in having
check_cxx_fundamental_alignment_constraints at all, since
check_user_alignment already enforces MAX_OFILE_ALIGNMENT.

	PR c++/89357
	* c-attribs.c (check_cxx_fundamental_alignment_constraints): Remove.

The test uses __int128_t, so won't work on targets that don't support it.

2020-01-30  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/92706
	* gcc.dg/tree-ssa/pr92706-1.c: Require int128 effective target.

My fix for 60503 fixed handling of C++11 attributes following the
lambda-declarator.  My patch for 89640 re-added support for GNU attributes,
but attributes after the trailing return type were parsed as applying to the
return type rather than to the function.  This patch adjusts parsing of a
trailing-return-type to ignore GNU attributes at the end of the declaration
so that they will be applied to the declaration as a whole.

I also considered parsing the attributes between the closing paren and the
trailing-return-type, and tried a variety of approaches to implementing
that, but I think it's better to stick with the documented rule that "An
attribute specifier list may appear immediately before the comma, '=' or
semicolon terminating the declaration of an identifier...."  Anyone
disagree?

Meanwhile, C++ committee discussion about the lack of any way to apply
attributes to a lambda op() seems to have concluded that they should go
between the introducer and declarator, so I've implemented that as well.

	PR c++/90333
	PR c++/89640
	PR c++/60503
	* parser.c (cp_parser_type_specifier_seq): Don't parse attributes in
	a trailing return type.
	(cp_parser_lambda_declarator_opt): Parse C++11 attributes before
	parens.

        PR bootstrap/93409
        * config/gcn/gcn-hsa.h (ASM_SPEC): Add -mattr=-code-object-v3 as
        LLVM's assembler changed the default in version 9.

This test got fixed by r10-1976-gdaaa6fcc
so let's add it to the testsuite.

	PR c++/88092
	* g++.dg/cpp2a/nontype-class31.C: New test.

Improve DSE which in turn eliminates the need for jump threading and block duplication for the original testcase in pr89689 which in turn eliminates the false positive -Warray-bounds warning for the original testcase.

	PR tree-optimization/89689
	* builtins.def (BUILT_IN_OBJECT_SIZE): Make it const rather than pure.

	PR tree-optimization/89689
	* gcc.dg/pr89689.c: New test.

The patch caused regressions in gcc.target/sh/pr64345-1.c on
sh3-linux-gnu and gcc.target/m68k/pr39726.c on m68k-linux-gnu.
It didn't look like they would be fixable in an acceptably
non-invasive and unhacky way, so punting till future releases.

2020-01-29  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	Revert:

	2020-01-28  Richard Sandiford  <richard.sandiford@arm.com>

	PR rtl-optimization/87763
	* simplify-rtx.c (simplify_truncation): Extend sign/zero_extract
	simplification to handle subregs as well as bare regs.
	* config/i386/i386.md (*testqi_ext_3): Match QI extracts too.

Here we fail to compile the attached test, stating that the use of
T<s> in T<s>::T() {} is "invalid use of incomplete type".  It is a
function definition so grokdeclarator checks that the qualifying type
is complete.

When we parsed the class T, finish_struct gave the class a non-null
TYPE_SIZE, making it COMPLETE_TYPE_P.  But then we're parsing T<s>,
a TEMPLATE_ID, in

  T<s>::T() {}

so try to lookup_template_class T.  This failed because we couldn't
find such a class: comp_template_args told us that the argument lists
don't match, because one of the args was wrapped in a VIEW_CONVERT_EXPR
to make it look const.  It seems to me that we should see through
these artificial wrappers and consider the args same.

2020-01-29  Marek Polacek  <polacek@redhat.com>

	PR c++/91754 - Fix template arguments comparison with class NTTP.
	* pt.c (class_nttp_const_wrapper_p): New.
	(template_args_equal): See through class_nttp_const_wrapper_p
	arguments.

	* g++.dg/cpp2a/nontype-class30.C: New test.

This PR points out an ICE with an alias template and class NTTP, but I
found that there are more issues.  Trouble arise when we use a
(non-type) template parameter as an argument to the template arg list of
a template that accepts a class NTTP and a conversion to a class is
involved, e.g.

  struct A { A(int) { } };
  template<A a> struct B { };

  template<int X> void fn () {
      B<X> b;
  }

Normally for such a conversion we create a TARGET_EXPR with an
AGGR_INIT_EXPR that calls a __ct_comp with some arguments, but not in
this case: when converting X to type A in convert_nontype_argument we
are in a template and the template parameter 'X' is value-dependent, and
AGGR_INIT_EXPR don't work in templates.  So it just creates a TARGET_EXPR
that contains "A::A(*this, X)", but with that overload resolution fails:
  error: no matching function for call to 'A::A(A*, int)'
That happens because finish_call_expr for a BASELINK creates a dummy
object, so we have 'this' twice.  I thought for the value-dependent case
we could use IMPLICIT_CONV_EXPR, as in the patch below.  Note that I
only do this when we convert to a different type than the type of the
expr.  The point is to avoid the call to a converting ctor.

The second issue was an ICE in tsubst_copy: when there's a conversion
like the above involved then
 /* Wrapper to make a C++20 template parameter object const.  */
  op = tsubst_copy (op, args, complain, in_decl);
might not produce a _ZT... VAR_DECL with const type, so the assert
  gcc_assert (CP_TYPE_CONST_P (TREE_TYPE (op)));
fails.  Allowing IMPLICIT_CONV_EXPR there probably makes sense.

And since convert_nontype_argument uses value_dependent_expression_p
a lot, I used a dedicated bool to speed things up.

2020-01-29  Marek Polacek  <polacek@redhat.com>

	PR c++/92948 - Fix class NTTP with template arguments.
	* pt.c (convert_nontype_argument): Use IMPLICIT_CONV_EXPR when
	converting a value-dependent expression to a class type.
	(tsubst_copy) <case VIEW_CONVERT_EXPR>: Allow IMPLICIT_CONV_EXPR
	as the result of the tsubst_copy call.

	* g++.dg/cpp2a/nontype-class28.C: New test.
	* g++.dg/cpp2a/nontype-class29.C: New test.

Fix synchronization issues in <stop_token>. Replace shared_ptr with
_Stop_state_ref and a reference count embedded in the shared state.
Replace std::mutex with spinlock using one bit of a std::atomic<> that
also tracks whether a stop request has been made and how many
stop_source objects share ownership of the state.

	PR libstdc++/92895
	* include/std/stop_token (stop_token::stop_possible()): Call new
	_M_stop_possible() function.
	(stop_token::stop_requested()): Do not use stop_possible().
	(stop_token::binary_semaphore): New class, as temporary stand-in for
	std::binary_semaphore.
	(stop_token::_Stop_cb::_M_callback): Add noexcept to type.
	(stop_token::_Stop_cb::_M_destroyed, stop_token::_Stop_cb::_M_done):
	New data members for symchronization with stop_callback destruction.
	(stop_token::_Stop_cb::_Stop_cb): Make non-template.
	(stop_token::_Stop_cb::_M_linked, stop_token::_Stop_cb::_S_execute):
	Remove.
	(stop_token::_Stop_cb::_M_run): New member function.
	(stop_token::_Stop_state::_M_stopped, stop_token::_Stop_state::_M_mtx):
	Remove.
	(stop_token::_Stop_state::_M_owners): New data member to track
	reference count for ownership.
	(stop_token::_Stop_state::_M_value): New data member combining a
	spinlock, the stop requested flag, and the reference count for
	associated stop_source objects.
	(stop_token::_Stop_state::_M_requester): New data member for
	synchronization with stop_callback destruction.
	(stop_token::_Stop_state::_M_stop_possible()): New member function.
	(stop_token::_Stop_state::_M_stop_requested()): Inspect relevant bit
	of _M_value.
	(stop_token::_Stop_state::_M_add_owner)
	(stop_token::_Stop_state::_M_release_ownership)
	(stop_token::_Stop_state::_M_add_ssrc)
	(stop_token::_Stop_state::_M_sub_ssrc): New member functions for
	updating reference counts.
	(stop_token::_Stop_state::_M_lock, stop_token::_Stop_state::_M_unlock)
	(stop_token::_Stop_state::_M_lock, stop_token::_Stop_state::_M_unlock)
	(stop_token::_Stop_state::_M_try_lock)
	(stop_token::_Stop_state::_M_try_lock_and_stop)
	(stop_token::_Stop_state::_M_do_try_lock): New member functions for
	managing spinlock.
	(stop_token::_Stop_state::_M_request_stop): Use atomic operations to
	read and update state. Release lock while running callbacks. Use new
	data members to synchronize with callback destruction.
	(stop_token::_Stop_state::_M_remove_callback): Likewise.
	(stop_token::_Stop_state::_M_register_callback): Use atomic operations
	to read and update state.
	(stop_token::_Stop_state_ref): Handle type to manage _Stop_state,
	replacing shared_ptr.
	(stop_source::stop_source(const stop_source&)): Update reference count.
	(stop_source::operator=(const stop_source&)): Likewise.
	(stop_source::~stop_source()): Likewise.
	(stop_source::stop_source(stop_source&&)): Define as defaulted.
	(stop_source::operator=(stop_source&&)): Establish postcondition on
	parameter.
	(stop_callback): Enforce preconditions on template parameter. Replace
	base class with data member of new _Cb_impl type.
	(stop_callback::stop_callback(const stop_token&, Cb&&))
	(stop_callback::stop_callback(stop_token&&, Cb&&)): Fix TOCTTOU race.
	(stop_callback::_Cb_impl): New type wrapping _Callback member and
	defining the _S_execute member function.
	* testsuite/30_threads/stop_token/stop_callback/deadlock-mt.cc: New
	test.
	* testsuite/30_threads/stop_token/stop_callback/deadlock.cc: New test.
	* testsuite/30_threads/stop_token/stop_callback/destroy.cc: New test.
	* testsuite/30_threads/stop_token/stop_callback/destructible_neg.cc:
	New test.
	* testsuite/30_threads/stop_token/stop_callback/invocable_neg.cc: New
	test.
	* testsuite/30_threads/stop_token/stop_callback/invoke.cc: New test.
	* testsuite/30_threads/stop_token/stop_source/assign.cc: New test.
	* testsuite/30_threads/stop_token/stop_token/stop_possible.cc: New
	test.