C++ PATCH for target/54908 (thread_local vs emutls)
Jack Howarth
howarth@bromo.med.uc.edu
Sat Jan 19 02:20:00 GMT 2013
On Fri, Jan 18, 2013 at 05:29:02PM -0500, Jason Merrill wrote:
> I've been thinking about how to deal with the problems with calling
> initialization functions in another translation unit; namely, that it's
> significant overhead even for cases where it isn't useful, and that it
> requires alias and weak reference support. This patch introduces a new
> flag -fno-extern-tls-init that allows the user to disable support for
> calling a lazy initialization function in a different translation unit
> to avoid the overhead. It also disables it by default for targets
> without support for aliases or weak references.
>
> Tested x86_64-pc-linux-gnu. Jack, does this fix the thread_local tests
> on Darwin?
Jason,
The proposed patch eliminates all of the previous failures from PR54908
at both -m32/-m64 on x86_64-apple-darwin12 but seems to introduce a new set of
failures...
FAIL: g++.dg/tls/thread_local-wrap3.C scan-assembler _ZTH1i
FAIL: g++.dg/gomp/tls-wrap3.C -std=c++98 scan-assembler _ZTH1i
FAIL: g++.dg/gomp/tls-wrap3.C -std=c++11 scan-assembler _ZTH1i
at both -m32 and -m64. The thread_local-wrap3.s generated with...
/sw/src/fink.build/gcc48-4.8.0-1000/darwin_objdir/gcc/testsuite/g++/../../xg++ -B/sw/src/fink.build/gcc48-4.8.0-1000/darwin_objdir/gcc/testsuite/g++/../../ /sw/src/fink.build/gcc48-4.8.0-1000/gcc-4.8-20130118/gcc/testsuite/g++.dg/tls/thread_local-wrap3.C -fno-diagnostics-show-caret -nostdinc++ -I/sw/src/fink.build/gcc48-4.8.0-1000/darwin_objdir/x86_64-apple-darwin12.2.0/libstdc++-v3/include/x86_64-apple-darwin12.2.0 -I/sw/src/fink.build/gcc48-4.8.0-1000/darwin_objdir/x86_64-apple-darwin12.2.0/libstdc++-v3/include -I/sw/src/fink.build/gcc48-4.8.0-1000/gcc-4.8-20130118/libstdc++-v3/libsupc++ -I/sw/src/fink.build/gcc48-4.8.0-1000/gcc-4.8-20130118/libstdc++-v3/include/backward -I/sw/src/fink.build/gcc48-4.8.0-1000/gcc-4.8-20130118/libstdc++-v3/testsuite/util -fmessage-length=0 -std=c++11 -S -m64 -o thread_local-wrap3.s
is attached. Recompiling the testcase with -fextern-tls-init doesn't produce the missing _ZTH1i.
Jack
ps I'll post full regression results tomorrow.
> commit b3cf0f73d853bb9f0d5bfde22995eafc244210d3
> Author: Jason Merrill <jason@redhat.com>
> Date: Thu Jan 17 06:15:22 2013 -0500
>
> PR target/54908
> c-family/
> * c.opt (-fextern-tls-init): New.
> * c-opts.c (c_common_post_options): Handle it.
> cp/
> * decl2.c (get_local_tls_init_fn): New.
> (get_tls_init_fn): Handle flag_extern_tls_init. Don't bother
> with aliases for internal variables. Don't use weakrefs if
> the variable needs destruction.
> (generate_tls_wrapper): Mark the wrapper as const if no
> initialization is needed.
> (handle_tls_init): Don't require aliases.
>
> diff --git a/gcc/c-family/c-opts.c b/gcc/c-family/c-opts.c
> index 3fabb36..1a922a8 100644
> --- a/gcc/c-family/c-opts.c
> +++ b/gcc/c-family/c-opts.c
> @@ -901,6 +901,20 @@ c_common_post_options (const char **pfilename)
> else if (warn_narrowing == -1)
> warn_narrowing = 0;
>
> + if (flag_extern_tls_init)
> + {
> +#if !defined (ASM_OUTPUT_DEF) || !SUPPORTS_WEAK
> + /* Lazy TLS initialization for a variable in another TU requires
> + alias and weak reference support. */
> + if (flag_extern_tls_init > 0)
> + sorry ("external TLS initialization functions not supported "
> + "on this target");
> + flag_extern_tls_init = 0;
> +#else
> + flag_extern_tls_init = 1;
> +#endif
> + }
> +
> if (flag_preprocess_only)
> {
> /* Open the output now. We must do so even if flag_no_output is
> diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
> index 187f3be..10ae84d 100644
> --- a/gcc/c-family/c.opt
> +++ b/gcc/c-family/c.opt
> @@ -913,6 +913,9 @@ finput-charset=
> C ObjC C++ ObjC++ Joined RejectNegative
> -finput-charset=<cset> Specify the default character set for source files
>
> +fextern-tls-init
> +C++ ObjC++ Var(flag_extern_tls_init) Init(-1)
> +Support dynamic initialization of thread-local variables in a different translation unit
>
> fexternal-templates
> C++ ObjC++ Ignore Warn(switch %qs is no longer supported)
> diff --git a/gcc/cp/decl2.c b/gcc/cp/decl2.c
> index 619d30d..4496395 100644
> --- a/gcc/cp/decl2.c
> +++ b/gcc/cp/decl2.c
> @@ -2812,6 +2812,28 @@ var_needs_tls_wrapper (tree var)
> && !var_defined_without_dynamic_init (var));
> }
>
> +/* Get the FUNCTION_DECL for the shared TLS init function for this
> + translation unit. */
> +
> +static tree
> +get_local_tls_init_fn (void)
> +{
> + tree sname = get_identifier ("__tls_init");
> + tree fn = IDENTIFIER_GLOBAL_VALUE (sname);
> + if (!fn)
> + {
> + fn = build_lang_decl (FUNCTION_DECL, sname,
> + build_function_type (void_type_node,
> + void_list_node));
> + SET_DECL_LANGUAGE (fn, lang_c);
> + TREE_PUBLIC (fn) = false;
> + DECL_ARTIFICIAL (fn) = true;
> + mark_used (fn);
> + SET_IDENTIFIER_GLOBAL_VALUE (sname, fn);
> + }
> + return fn;
> +}
> +
> /* Get a FUNCTION_DECL for the init function for the thread_local
> variable VAR. The init function will be an alias to the function
> that initializes all the non-local TLS variables in the translation
> @@ -2824,6 +2846,18 @@ get_tls_init_fn (tree var)
> if (!var_needs_tls_wrapper (var))
> return NULL_TREE;
>
> + /* If -fno-extern-tls-init, assume that we don't need to call
> + a tls init function for a variable defined in another TU. */
> + if (!flag_extern_tls_init && DECL_EXTERNAL (var))
> + return NULL_TREE;
> +
> +#ifdef ASM_OUTPUT_DEF
> + /* If the variable is internal, or if we can't generate aliases,
> + call the local init function directly. */
> + if (!TREE_PUBLIC (var))
> +#endif
> + return get_local_tls_init_fn ();
> +
> tree sname = mangle_tls_init_fn (var);
> tree fn = IDENTIFIER_GLOBAL_VALUE (sname);
> if (!fn)
> @@ -2841,11 +2875,12 @@ get_tls_init_fn (tree var)
> if (TREE_PUBLIC (var))
> {
> tree obtype = strip_array_types (non_reference (TREE_TYPE (var)));
> - /* If the variable might have static initialization, make the
> - init function a weak reference. */
> + /* If the variable is defined somewhere else and might have static
> + initialization, make the init function a weak reference. */
> if ((!TYPE_NEEDS_CONSTRUCTING (obtype)
> || TYPE_HAS_CONSTEXPR_CTOR (obtype))
> - && TARGET_SUPPORTS_WEAK)
> + && TYPE_HAS_TRIVIAL_DESTRUCTOR (obtype)
> + && DECL_EXTERNAL (var))
> declare_weak (fn);
> else
> DECL_WEAK (fn) = DECL_WEAK (var);
> @@ -2956,6 +2991,9 @@ generate_tls_wrapper (tree fn)
> finish_if_stmt (if_stmt);
> }
> }
> + else
> + /* If there's no initialization, the wrapper is a constant function. */
> + TREE_READONLY (fn) = true;
> finish_return_stmt (convert_from_reference (var));
> finish_function_body (body);
> expand_or_defer_fn (finish_function (0));
> @@ -3861,15 +3899,6 @@ handle_tls_init (void)
>
> location_t loc = DECL_SOURCE_LOCATION (TREE_VALUE (vars));
>
> - #ifndef ASM_OUTPUT_DEF
> - /* This currently requires alias support. FIXME other targets could use
> - small thunks instead of aliases. */
> - input_location = loc;
> - sorry ("dynamic initialization of non-function-local thread_local "
> - "variables not supported on this target");
> - return;
> - #endif
> -
> write_out_vars (vars);
>
> tree guard = build_decl (loc, VAR_DECL, get_identifier ("__tls_guard"),
> @@ -3882,14 +3911,7 @@ handle_tls_init (void)
> DECL_TLS_MODEL (guard) = decl_default_tls_model (guard);
> pushdecl_top_level_and_finish (guard, NULL_TREE);
>
> - tree fn = build_lang_decl (FUNCTION_DECL,
> - get_identifier ("__tls_init"),
> - build_function_type (void_type_node,
> - void_list_node));
> - SET_DECL_LANGUAGE (fn, lang_c);
> - TREE_PUBLIC (fn) = false;
> - DECL_ARTIFICIAL (fn) = true;
> - mark_used (fn);
> + tree fn = get_local_tls_init_fn ();
> start_preparsed_function (fn, NULL_TREE, SF_PRE_PARSED);
> tree body = begin_function_body ();
> tree if_stmt = begin_if_stmt ();
> @@ -3904,11 +3926,17 @@ handle_tls_init (void)
> tree init = TREE_PURPOSE (vars);
> one_static_initialization_or_destruction (var, init, true);
>
> - tree single_init_fn = get_tls_init_fn (var);
> - cgraph_node *alias
> - = cgraph_same_body_alias (cgraph_get_create_node (fn),
> - single_init_fn, fn);
> - gcc_assert (alias != NULL);
> +#ifdef ASM_OUTPUT_DEF
> + /* Output init aliases even with -fno-extern-tls-init. */
> + if (TREE_PUBLIC (var))
> + {
> + tree single_init_fn = get_tls_init_fn (var);
> + cgraph_node *alias
> + = cgraph_same_body_alias (cgraph_get_create_node (fn),
> + single_init_fn, fn);
> + gcc_assert (alias != NULL);
> + }
> +#endif
> }
>
> finish_then_clause (if_stmt);
> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> index 9ef6c93..48ee779 100644
> --- a/gcc/doc/invoke.texi
> +++ b/gcc/doc/invoke.texi
> @@ -2029,6 +2029,29 @@ exceptions in violation of the exception specifications; the compiler
> still optimizes based on the specifications, so throwing an
> unexpected exception results in undefined behavior at run time.
>
> +@item -fextern-tls-init
> +@itemx -fno-extern-tls-init
> +@opindex fextern-tls-init
> +@opindex fno-extern-tls-init
> +The C++11 and OpenMP standards allow @samp{thread_local} and
> +@samp{threadprivate} variables to have dynamic (runtime)
> +initialization. To support this, any use of such a variable goes
> +through a wrapper function that performs any necessary initialization.
> +When the use and definition of the variable are in the same
> +translation unit, this overhead can be optimized away, but when the
> +use is in a different translation unit there is significant overhead
> +even if the variable doesn't actually need dynamic initialization. If
> +the programmer can be sure that no use of the variable in a
> +non-defining TU needs to trigger dynamic initialization (either
> +because the variable is statically initialized, or a use of the
> +variable in the defining TU will be executed before any uses in
> +another TU), they can avoid this overhead with the
> +@option{-fno-extern-tls-init} option.
> +
> +On targets that support symbol aliases, the default is
> +@option{-fextern-tls-init}. On targets that do not support symbol
> +aliases, the default is @option{-fno-extern-tls-init}.
> +
> @item -ffor-scope
> @itemx -fno-for-scope
> @opindex ffor-scope
> diff --git a/libgomp/testsuite/libgomp.c++/pr24455.C b/libgomp/testsuite/libgomp.c++/pr24455.C
> index 3185ca5..8256b66 100644
> --- a/libgomp/testsuite/libgomp.c++/pr24455.C
> +++ b/libgomp/testsuite/libgomp.c++/pr24455.C
> @@ -1,8 +1,7 @@
> // { dg-do run }
> // { dg-additional-sources pr24455-1.C }
> // { dg-require-effective-target tls_runtime }
> -// { dg-options "-Wl,-G" { target powerpc-ibm-aix* } }
> -// { dg-options "-Wl,-undefined,dynamic_lookup" { target *-*-darwin* } }
> +// { dg-options "-fno-extern-tls-init" }
>
> extern "C" void abort (void);
>
-------------- next part --------------
.text
.globl _main
_main:
LFB0:
pushq %rbp
LCFI0:
movq %rsp, %rbp
LCFI1:
call __ZTW1i
movl (%rax), %eax
subl $42, %eax
popq %rbp
LCFI2:
ret
LFE0:
.section __TEXT,__textcoal_nt,coalesced,pure_instructions
.globl __ZTW1i
.weak_definition __ZTW1i
.private_extern __ZTW1i
__ZTW1i:
LFB1:
pushq %rbp
LCFI3:
movq %rsp, %rbp
LCFI4:
movq ___emutls_v.i@GOTPCREL(%rip), %rax
movq %rax, %rdi
call ___emutls_get_address
popq %rbp
LCFI5:
ret
LFE1:
.section __TEXT,__eh_frame,coalesced,no_toc+strip_static_syms+live_support
EH_frame1:
.set L$set$0,LECIE1-LSCIE1
.long L$set$0
LSCIE1:
.long 0
.byte 0x1
.ascii "zR\0"
.byte 0x1
.byte 0x78
.byte 0x10
.byte 0x1
.byte 0x10
.byte 0xc
.byte 0x7
.byte 0x8
.byte 0x90
.byte 0x1
.align 3
LECIE1:
LSFDE1:
.set L$set$1,LEFDE1-LASFDE1
.long L$set$1
LASFDE1:
.long LASFDE1-EH_frame1
.quad LFB0-.
.set L$set$2,LFE0-LFB0
.quad L$set$2
.byte 0
.byte 0x4
.set L$set$3,LCFI0-LFB0
.long L$set$3
.byte 0xe
.byte 0x10
.byte 0x86
.byte 0x2
.byte 0x4
.set L$set$4,LCFI1-LCFI0
.long L$set$4
.byte 0xd
.byte 0x6
.byte 0x4
.set L$set$5,LCFI2-LCFI1
.long L$set$5
.byte 0xc
.byte 0x7
.byte 0x8
.align 3
LEFDE1:
LSFDE3:
.set L$set$6,LEFDE3-LASFDE3
.long L$set$6
LASFDE3:
.long LASFDE3-EH_frame1
.quad LFB1-.
.set L$set$7,LFE1-LFB1
.quad L$set$7
.byte 0
.byte 0x4
.set L$set$8,LCFI3-LFB1
.long L$set$8
.byte 0xe
.byte 0x10
.byte 0x86
.byte 0x2
.byte 0x4
.set L$set$9,LCFI4-LCFI3
.long L$set$9
.byte 0xd
.byte 0x6
.byte 0x4
.set L$set$10,LCFI5-LCFI4
.long L$set$10
.byte 0xc
.byte 0x7
.byte 0x8
.align 3
LEFDE3:
.constructor
.destructor
.align 1
.subsections_via_symbols
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