Emulate MMX vec_dupv2si with SSE.  Add the "Yw" constraint to allow
broadcast from integer register for AVX512BW with TARGET_AVX512VL.
Only SSE register source operand is allowed.

	PR target/89021
	* config/i386/constraints.md (Yw): New constraint.
	* config/i386/mmx.md (*vec_dupv2si): Changed to
	define_insn_and_split and also allow TARGET_MMX_WITH_SSE to
	support SSE emulation.

From-SVN: r271225

Emulate MMX mmx_eq/mmx_gt<mode>3 with SSE.  Only SSE register source
operand is allowed.

	PR target/89021
	* config/i386/mmx.md (mmx_eq<mode>3): Also allow
	TARGET_MMX_WITH_SSE.
	(*mmx_eq<mode>3): Also allow TARGET_MMX_WITH_SSE.  Add SSE
	support.
	(mmx_gt<mode>3): Likewise.

From-SVN: r271224

Emulate MMX mmx_andnot<mode>3 with SSE.  Only SSE register source operand
is allowed.

	PR target/89021
	* config/i386/mmx.md (mmx_andnot<mode>3): Also allow
	TARGET_MMX_WITH_SSE.  Add SSE support.

From-SVN: r271223

Emulate MMX <any_logic><mode>3 with SSE.  Only SSE register source
operand is allowed.

	PR target/89021
	* config/i386/mmx.md (any_logic:mmx_<code><mode>3): Also allow
	TARGET_MMX_WITH_SSE.
	(any_logic:<code><mode>3): New.
	(any_logic:*mmx_<code><mode>3): Also allow TARGET_MMX_WITH_SSE.
	Add SSE support.

From-SVN: r271222

Emulate MMX ashr<mode>3/<shift_insn><mode>3 with SSE.  Only SSE register
source operand is allowed.

	PR target/89021
	* config/i386/mmx.md (mmx_ashr<mode>3): Also allow
	TARGET_MMX_WITH_SSE.  Add SSE emulation.
	(mmx_<shift_insn><mode>3): Likewise.
	(ashr<mode>3): New.
	(<shift_insn><mode>3): Likewise.

From-SVN: r271221

Emulate MMX pmaddwd with SSE.  Only SSE register source operand is
allowed.

	PR target/89021
	* config/i386/mmx.md (mmx_pmaddwd): Also allow TARGET_MMX_WITH_SSE.
	(*mmx_pmaddwd): Also allow TARGET_MMX_WITH_SSE.  Add SSE support.

From-SVN: r271220

Emulate MMX mulv4hi3 with SSE.  Only SSE register source operand is
allowed.

	PR target/89021
	* config/i386/mmx.md (mmx_smulv4hi3_highpart): Also allow
	TARGET_MMX_WITH_SSE.
	(*mmx_smulv4hi3_highpart): Also allow TARGET_MMX_WITH_SSE. Add
	SSE support.

From-SVN: r271219

Emulate MMX mulv4hi3 with SSE.  Only SSE register source operand is
allowed.

	PR target/89021
	* config/i386/mmx.md (mmx_mulv4hi3): Also allow
	TARGET_MMX_WITH_SSE.
	(mulv4hi3): New.
	(*mmx_mulv4hi3): Also allow TARGET_MMX_WITH_SSE.  Add SSE
	support.

From-SVN: r271218

Emulate MMX plusminus/sat_plusminus with SSE.  Only SSE register source
operand is allowed.

	PR target/89021
	* config/i386/mmx.md (MMXMODEI8): Require TARGET_SSE2 for V1DI.
	(plusminus:mmx_<plusminus_insn><mode>3): Check
	TARGET_MMX_WITH_SSE.
	(sat_plusminus:mmx_<plusminus_insn><mode>3): Likewise.
	(<plusminus_insn><mode>3): New.
	(*mmx_<plusminus_insn><mode>3): Add SSE emulation.
	(*mmx_<plusminus_insn><mode>3): Likewise.

From-SVN: r271217

Emulate MMX punpcklXX/punpckhXX with SSE punpcklXX.  For MMX punpckhXX,
move bits 64:127 to bits 0:63 in SSE register.  Only SSE register source
operand is allowed.

	PR target/89021
	* config/i386/i386-expand.c (ix86_split_mmx_punpck): New function.
	* config/i386/i386-protos.h (ix86_split_mmx_punpck): New
	prototype.
	* config/i386/mmx.m (mmx_punpckhbw): Changed to
	define_insn_and_split to support SSE emulation.
	(mmx_punpcklbw): Likewise.
	(mmx_punpckhwd): Likewise.
	(mmx_punpcklwd): Likewise.
	(mmx_punpckhdq): Likewise.
	(mmx_punpckldq): Likewise.

From-SVN: r271216

Emulate MMX packsswb/packssdw/packuswb with SSE packsswb/packssdw/packuswb
plus moving bits 64:95 to bits 32:63 in SSE register.  Only SSE register
source operand is allowed.

	PR target/89021
	* config/i386/i386-expand.c (ix86_move_vector_high_sse_to_mmx):
	New function.
	(ix86_split_mmx_pack): Likewise.
	* config/i386/i386-protos.h (ix86_move_vector_high_sse_to_mmx):
	New prototype.
	(ix86_split_mmx_pack): Likewise.
	* config/i386/i386.md (mmx_isa): New.
	(enabled): Also check mmx_isa.
	* config/i386/mmx.md (any_s_truncate): New code iterator.
	(s_trunsuffix): New code attr.
	(mmx_packsswb): Removed.
	(mmx_packssdw): Likewise.
	(mmx_packuswb): Likewise.
	(mmx_pack<s_trunsuffix>swb): New define_insn_and_split to emulate
	MMX packsswb/packuswb with SSE2.
	(mmx_packssdw): Likewise.
	* config/i386/predicates.md (register_mmxmem_operand): New.

Co-Authored-By: Uros Bizjak <ubizjak@gmail.com>

From-SVN: r271215

In 64-bit mode, SSE2 can be used to emulate MMX instructions without
3DNOW.  We can use SSE2 to support MMX register modes.

	PR target/89021
	* config/i386/i386-c.c (ix86_target_macros_internal): Define
	__MMX_WITH_SSE__ for TARGET_MMX_WITH_SSE.
	* config/i386/i386.c (ix86_set_reg_reg_cost): Add support for
	TARGET_MMX_WITH_SSE with VALID_MMX_REG_MODE.
	(ix86_vector_mode_supported_p): Likewise.
	* config/i386/i386.h (TARGET_MMX_WITH_SSE): New.

From-SVN: r271213

2019-05-15  Iain Sandoe  <iain@sandoe.co.uk>

	* lto-plugin.c (cleanup_handler): Remove unused var.

From-SVN: r271212

2019-05-15  Paolo Carlini  <paolo.carlini@oracle.com>

	* call.c (perform_overload_resolution, build_new_method_call_1):
	Use OVL_P; remove redundant TEMPLATE_DECL checks.
	* decl.c (grokfndecl): Likewise.
	* mangle.c (write_expression): Likewise.
	* parser.c (cp_parser_template_id): Likewise.
	* pt.c (resolve_overloaded_unification, type_dependent_expression_p):
	Likewise.
	* search.c (build_baselink): Likewise.
	* tree.c (is_overloaded_fn, dependent_name, maybe_get_fns): Likewise.

From-SVN: r271211

2019-05-15  Martin Liska  <mliska@suse.cz>

	PR middle-end/90478
	* tree-switch-conversion.c (jump_table_cluster::can_be_handled):
	Check for overflow.
2019-05-15  Martin Liska  <mliska@suse.cz>

	PR middle-end/90478
	* gcc.dg/tree-ssa/pr90478-2.c: New test.
	* gcc.dg/tree-ssa/pr90478.c: New test.

From-SVN: r271210

2019-05-15  Richard Biener  <rguenther@suse.de>

	* tree-into-ssa.c (pass_build_ssa::execute): Run
	update_address_taken before going into SSA.

From-SVN: r271209

2019-05-15  Richard Biener  <rguenther@suse.de>

	c/
	* gimple-parser.c (c_parser_gimple_postfix_expression): Handle
	__BIT_FIELD_REF.

	* tree-pretty-print.c (dump_generic_node): Dump BIT_FIELD_REF
	as __BIT_FIELD_REF with type with -gimple.

	* gcc.dg/gimplefe-40.c: Amend.

From-SVN: r271208

2019-05-15  Vladislav Ivanishin  <vlad@ispras.ru>

	* tree-ssa-uninit.c (is_value_included_in): Remove is_unsigned and merge
	semantically equivalent branches (left over after prior refactorings).

From-SVN: r271207

re PR tree-optimization/90474 (ICE: verify_gimple failed (error: DECL_GIMPLE_REG_P set on a variable with address taken; error: invalid address operand in MEM_REF))

2019-05-15  Richard Biener  <rguenther@suse.de>

	PR c/90474
	* c-common.c (c_common_mark_addressable_vec): Also mark
	a COMPOUND_LITERAL_EXPR_DECL addressable similar to
	c_mark_addressable.

From-SVN: r271206

If we build Darwin with a modern assembler, then it might well
recognise insns that cannot be used on current Darwin systems.

The patch augments the tests for feature support for VSX,
power8 and power9 to exclude Darwin even if the assembler can
handle the instructions.

2019-05-15  Iain Sandoe  <iain@sandoe.co.uk>

	* lib/target-supports.exp 
	(check_effective_target_powerpc_p8vector_ok): No support for Darwin.
	(check_effective_target_powerpc_p9vector_ok): Likewise.
	(check_effective_target_powerpc_float128_sw_ok): Likewise.
	(check_effective_target_powerpc_float128_hw_ok): Likewise.
	(check_effective_target_powerpc_vsx_ok): Likewise.
	* gcc.target/powerpc/bfp/bfp.exp: Don't try to run this for Darwin.
	* gcc.target/powerpc/dfp/dfp.exp: Likewise.

From-SVN: r271205

2019-05-15  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/88828
	* tree-ssa-forwprop.c (simplify_vector_constructor): Fix
	bogus check.

From-SVN: r271204

gimple-parser.c (c_parser_gimple_statement): Remove questionable auto-promotion to VIEW_CONVERT_EXPR.

2019-05-14  Richard Biener  <rguenther@suse.de>

	* gimple-parser.c (c_parser_gimple_statement): Remove
	questionable auto-promotion to VIEW_CONVERT_EXPR.
	(c_parser_gimple_typespec): Split out from __MEM parsing.
	(c_parser_gimple_postfix_expression): Handle __VIEW_CONVERT.
	* tree-pretty-print.c (dump_generic_node): Dump VIEW_CONVERT_EXPR
	as __VIEW_CONVERT with -gimple.

	* gcc.dg/gimplefe-40.c: New testcase.

From-SVN: r271203

This patch makes the lto-plugin follow the same approach
to save-temps as collect2. 

-save-temps causes the temp file to be named meaningfully,
and for the relevant input files to be saved in CWD.

-v, —version causes the save actions to be output to stderr.

one can get this to happen by just putting -save-temps, -v on
the regular link line or (for compatibility with the way the
 -debug flag works) by appending -plugin-opt=-save-temps, etc.

lto-plugin/

2019-05-15  Iain Sandoe  <iain@sandoe.co.uk>

	* lto-plugin.c (exec_lto_wrapper): Make the wrapper
	arguments filename more user-friendly.
	(file_exists, maybe_unlink): New.
	(cleanup_handler): Use maybe unlink to handle the
	case when temps should be saved.
	(process_option): Look for -v, —-version, -save-temps.
	(onload): Record the linker output file name.
	Check for -v, —-version, -save-temps in the GCC collect
	options environment.

From-SVN: r271202

From-SVN: r271201

The test fails on PPC Darwin because we emit 
__POWERPC__ instead of __powerpc__ fixed by allowing
for both.

2019-05-15  Iain Sandoe  <iain@sandoe.co.uk>

	* gcc.dg/pr87600.h: Add __POWERPC__ as an alternate test
	for PowerPC platforms.

From-SVN: r271200

These ae test adjustments to the scan assembler strings
mostly just to catch missing __USER_LABEL_PREFIX__s  on
symbols.

2019-05-15  Iain Sandoe  <iain@sandoe.co.uk>

	PR target/82920
	* g++.dg/cet-notrack-1.C: Adjust scan assembler for Darwin.
	* gcc.target/i386/cet-notrack-5a.c: Likewise.
	* gcc.target/i386/cet-notrack-5b.c: Likewise.
	* gcc.target/i386/cet-notrack-6b.c: Likewise.
	* gcc.target/i386/cet-notrack-icf-1.c: Likewise.
	* gcc.target/i386/cet-notrack-icf-2.c: Likewise.
	* gcc.target/i386/cet-notrack-icf-3.c: Likewise.
	* gcc.target/i386/cet-notrack-icf-4.c: Likewise.
	* gcc.target/i386/cet-sjlj-3.c: Likewise.
	* gcc.target/i386/cet-sjlj-5.c: Likewise.

From-SVN: r271199

From-SVN: r271197

	PR c++/68918
	* g++.dg/cpp0x/decltype71.C: New test.

From-SVN: r271193

	PR c++/70156
	* g++.dg/init/static5.C: New test.

From-SVN: r271192

Darwin doesn't support mx32, and some tests were
failing because it was trying to do them.  When we
disable this it turns out that quite a few tests
requiring mx32 support were not guarded.

gcc/

2019-05-14  Iain Sandoe  <iain@sandoe.co.uk>

	PR target/82920
	* config/i386/darwin.h (CC1_SPEC): Report -mx32 as an error for
	Darwin.

gcc/testsuite/

2019-05-14  Iain Sandoe  <iain@sandoe.co.uk>

	PR target/82920
	* gcc.target/i386/cet-sjlj-6b.c: Require effective target x32.
	* gcc.target/i386/pr52146.c: Likewise.
	* gcc.target/i386/pr52698.c: Likewise.
	* gcc.target/i386/pr52857-1.c: Likewise.
	* gcc.target/i386/pr52857-2.c: Likewise.
	* gcc.target/i386/pr52876.c: Likewise.
	* gcc.target/i386/pr53698.c: Likewise.
	* gcc.target/i386/pr54157.c: Likewise.
	* gcc.target/i386/pr55049-1.c: Likewise.
	* gcc.target/i386/pr55093.c: Likewise.
	* gcc.target/i386/pr55116-1.c: Likewise.
	* gcc.target/i386/pr55116-2.c: Likewise.
	* gcc.target/i386/pr55597.c: Likewise.
	* gcc.target/i386/pr59929.c: Likewise.
	* gcc.target/i386/pr66470.c: Likewise.

From-SVN: r271190

	* testsuite/util/testsuite_allocator.h (NullablePointer::operator bool):
	Fix return value.

From-SVN: r271189

	* config/rs6000/rs6000.md (eh_set_lr_<mode>): Merge with following
	define_split to become a define_insn_and_split.

From-SVN: r271185

We currently call rs6000_emit_epilogue with a boolean parameter saying
if this is for a sibcall.  We also need to create epilogues for
eh_return.  This isn't yet indicated directly: instead, we get an
eh_return epilogue if crtl->calls_eh_return and this is not a sibcall.

This patch changes things so there is a three-way enum argument.

What is called "normal" now can still actually be "eh_return".  The
rs6000_emit_epilogue function still uses an "int sibcall" variable
internally.


	* config/rs6000/rs6000-protos.h (rs6000_emit_epilogue): Change
	arguments.
	* config/rs6000/rs6000.c (rs6000_emit_epilogue): Change arguments.
	* config/rs6000/rs6000.md (epilogue_type): New define_enum.
	(sibcall_epilogue): Adjust.
	(epilogue): Adjust.

From-SVN: r271184

	libstdc++-v3:
	* config/os/solaris/solaris2.10: Move to ...
	* config/os/solaris: ... this.
	* configure.host (os_include_dir): Adapt.
	(abi_baseline_pair): Remove Solaris 10 handling.
	* config/abi/post/i386-solaris2.10: Remove.
	* config/abi/post/sparc-solaris2.10: Remove.
	* config/abi/post/i386-solaris2.11: Rename to ...
	* config/abi/post/i386-solaris: ... this.
	* config/abi/post/sparc-solaris2.11: Rename to ...
	* config/abi/post/sparc-solaris: ... this.

	* libsupc++/new_opa.cc [_GLIBCXX_HAVE_MEMALIGN] [__sun]: Remove
	workaround.

	* testsuite/ext/enc_filebuf/char/13598.cc: Remove *-*-solaris2.10
	xfail.

	libsanitizer:
	* configure.ac (have_dl_iterate_phdr): Remove *-*-solaris2.10*
	handling.
	* configure: Regenerate.

	libgcc:
	* config.host: Simplify various *-*-solaris2.1[0-9]* to
	*-*-solaris2*.
	* configure.ac: Likewise.
	* configure: Regenerate.

	* config/i386/sol2-unwind.h (x86_fallback_frame_state): Remove
	Solaris 10 and Solaris 11 < snv_125 handling.

	libbacktrace:
	* configure.ac (have_dl_iterate_phdr): Remove *-*-solaris2.10*
	handling.
	* configure: Regenerate.

	gcc/testsuite:
	* gcc.dg/atomic/c11-atomic-exec-4.c: Simplify triplet to
	*-*-solaris2*.
	* gcc.dg/atomic/c11-atomic-exec-5.c: Likewise.
	* gcc.dg/c99-math-double-1.c: Likewise.
	* gcc.dg/c99-math-float-1.c: Likewise.
	* gcc.dg/c99-math-long-double-1.c: Likewise.
	* gcc.misc-tests/linkage.exp: Simplify triplet to
	x86_64-*-solaris2*.

	* gcc.target/i386/mcount_pic.c: Remove *-*-solaris2.10* && !gld
	xfail.
	* gcc.target/i386/pr63620.c: Likewise.

	* lib/target-supports.exp (check_sse_os_support_available): Remove
	Solaris 9/x86 workaround.

	gcc:
	* config.gcc: Move *-*-solaris2.10* from obsolete configurations
	to unsupported ones.
	Simplify x86_64-*-solaris2.1[0-9]* to x86_64-*-solaris2*.
	* config.host: Likewise.
	* config/i386/sol2.h (ASM_COMMENT_START): Remove.
	* config/sparc/driver-sparc.c (host_detect_local_cpu) [__sun__ &&
	__svr4__]: Remove "brand" fallback.
	[!KSTAT_DATA_STRING]: Remove.
	* configure.ac (gcc_cv_ld_hidden): Simplify *-*-solaris2.1[0-9]*
	to *-*-solaris2*.
	(comdat_group): Likewise.
	(set_have_as_tls): Likewise.
	(gcc_cv_target_dl_iterate_phdr): Likewise.
	(gcc_cv_as_shf_merge): Remove Solaris 10/x86 workaround.
	(gcc_cv_ld_aligned_shf_merge): Remove Solaris 10/SPARC workaround.
	* configure: Regenerate.
	* doc/install.texi: Simplify Solaris target triplets.
	(Specific, i?86-*-solaris2*): Remove Solaris 10 references.
	(Specific, *-*-solaris2*): Document Solaris 10 removal.
	Remove Solaris 10 references.
	Remove obsolete Solaris bug reference.
	(Specific, sparc-sun-solaris2.10): Remove.

From-SVN: r271183

This change simplifies visitation for variants, by using INVOKE<R> for
the visit<R> form, and explicitly specifying the tag types for raw
visitation, instead of inferring them from the return types of the
lambda functions used as visitors.

	* include/std/variant (__visit_with_index): Remove typedef.
	(__deduce_visit_result): New tag type.
	(__raw_visit, __raw_idx_visit): New helper functions for "raw"
	visitation of possibly-valueless variants, forwarding to __do_visit
	with the relevant tag type.
	(_Variant_storage<false, _Types...>::_M_reset_impl): Use __raw_visit
	and make lambda return void.
	(__variant_construct): Likewise.
	(_Copy_assign_base::operator=, _Move_assign_base::operator=): Use
	__raw_idx_visit and make lambda return void.
	(_Multi_array::__untag_result): Add metafunction to check the function
	pointer type for a tag type that dictates the kind of visitation.
	(_Multi_array<_Ret(*)(_Visitor, _Variants...), __first, __rest...>):
	Use decltype(auto) instead of tagged function pointer type.
	(__gen_vtable_impl): Remove bool non-type parameter and unused
	_Variant_tuple parameter.
	(__gen_vtable_impl::__visit_invoke_impl): Remove.
	(__gen_vtable_impl::__do_visit_invoke): Remove.
	(__gen_vtable_impl::__do_visit_invoke_r): Remove.
	(__gen_vtable_impl::__visit_invoke): Use if-constexpr and __invoke_r
	for the visit<R> case, rather than dispatching to separate functions.
	(_VARIANT_RELATION_FUNCTION_TEMPLATE): Use __raw_idx_visit and make
	lambda return void.
	(variant::swap): Likewise.
	(__do_visit): Replace two non-type template parameters with a single
	type parameter, so that the caller must specify the visitor's return
	type (or one of the tag types).
	(visit): Deduce a return type from the visitor and use the
	__deduce_visit_result tag to enforce that all overloads return the
	same type.
	(visit<R>): Call __do_visit<R> with explicit result type.
	(__variant_hash_call_base_impl::operator()): Use __raw_visit and make
	lambda return void.

From-SVN: r271182

	* config/i386/i386.md (any_div): New code iterator.
	(paired_mod): New code attribute.
	(sgnprefix): Handle DIV and UDIV RTXes.
	(u): Ditto.
	(<u>divmod<mode>4): Macroize expander from divmod<mode>4
	and udivmod<mode>4 patterns using any_div code iterator.
	(divmod splitters): Macroize splitters using any_div code iterator.
	(*udivmodsi4_pow2_zext_1): Use exactl_log2 in insn condition.
	(*udivmodsi4_pow2_zext_2): Ditto.
	(*<u>divmod<mode>4_noext): Macroize insn from *divmod<mode>4_noext
	and *udivmod<mode>4_noext patterns using any_div code iterator.
	(*<u>divmod<mode>4_noext_zext_1): Macroize insn from
	*divmod<mode>4_noext_zext_1 and *udivmod<mode>4_noext_zext_1
	patterns using any_div code iterator.
	(*<u>divmod<mode>4_noext_zext_2): Macroize insn from
	*divmod<mode>4_noext_zext_2 and *udivmod<mode>4_noext_zext_2
	patterns using any_div code iterator.
	(<u>divmodhiqi3): Macroize insn from divmodhiqi3 and
	udivmodhiqi3 patterns using any_extend code iterator.

From-SVN: r271179

2019-05-14  Nina Dinka Ranns  <dinka.ranns@gmail.com>

	nonesuch is insufficiently useless (lwg2996)
	* include/std/type_traits (struct __nonesuch): Added private base
	class to make __nonesuch not an aggregate and removed deleted default
	constructor.
	* include/bits/stl_pair.h (struct __nonesuch_no_braces): Removed.
	(operator=(const pair&)): Use __nonesuch instead of
	__nonesuch_no_braces.
	(operator=(pair&&)): Likewise
	* include/std/tuple (operator=(const tuple&)): Use __nonesuch instead
	of __nonesuch_no_braces.
	(operator=(tuple&&)): Likewise
	* include/experimental/type_traits (struct nonesuch): Added private
	base class to make nonesuch not an aggregate and removed deleted
	default constructor.
	* testsuite/20_util/nonesuch/nonesuch.cc: New.
	* testsuite/experimental/type_traits/nonesuch.cc: New.

From-SVN: r271175

As well as simpifying the code by removing duplication, this means that
we only need to touch std::__invoke_r if we need to implement changes to
INVOKE<R>, such as those in P0932R0.

	* include/bits/std_function.h (_Simple_type_wrapper): Remove.
	(_Function_handler): Remove partial specializations for void return
	types and pointers to member.
	(_Function_handler::_M_manager): Adapt to removal of
	_Simple_type_wrapper.
	(_Function_handler::_M_invoke): Use __invoke_r instead of __invoke.
	* include/std/functional (_Bind_result::__enable_if_void)
	(_Bind_result::__disable_if_void): Remove sfinae helpers.
	(_Bind_result::__call): Use __invoke_r and remove overloads for void
	return types.
	* include/std/future (__future_base::_Task_state::_M_run)
	(__future_base::_Task_state::_M_run_delayed): Use __invoke_r and
	change return type of lambda expressions.

From-SVN: r271174

	* include/bits/invoke.h (__invoke_r): Define new function implementing
	the INVOKE<R> pseudo-function.
	* testsuite/20_util/function_objects/invoke/1.cc: Add more tests.
	* testsuite/20_util/function_objects/invoke/2.cc: New test.

From-SVN: r271173

    
    Revise the gccgo version of memory/block/mutex profiling to reduce
    runtime overhead. The main change is to collect raw stack traces while
    the profile is on line, then post-process the stacks just prior to the
    point where we are ready to use the final product. Memory profiling
    (at a very low sampling rate) is enabled by default, and the overhead
    of the symbolization / DWARF-reading from backtrace_full was slowing
    things down relative to the main Go runtime.
    
    Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/171497

From-SVN: r271172