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Re: [c++] typeinfo for target types

Marc Glisse wrote:

On Thu, 24 Apr 2014, Ramana Radhakrishnan wrote:


On Wed, Apr 23, 2014 at 8:43 PM, Marc Glisse <marc.glisse@inria.fr> wrote:

On Wed, 23 Apr 2014, Richard Henderson wrote:


On 04/13/2014 01:41 AM, Marc Glisse wrote:

Hello,

this patch generates typeinfo for target types. On x86_64, it adds these
6
lines to nm -C libsupc++.a. A follow-up patch will be needed to export
and
version those in the shared library.

+0000000000000000 V typeinfo for __float128
+0000000000000000 V typeinfo for __float128 const*
+0000000000000000 V typeinfo for __float128*
+0000000000000000 V typeinfo name for __float128
+0000000000000000 V typeinfo name for __float128 const*
+0000000000000000 V typeinfo name for __float128*

Bootstrap and testsuite on x86_64-linux-gnu (a bit of noise in
tsan/tls_race.c).

2014-04-13  Marc Glisse  <marc.glisse@inria.fr>

    PR libstdc++/43622
gcc/c-family/
    * c-common.c (registered_builtin_types): Make non-static.
    * c-common.h (registered_builtin_types): Declare.
gcc/cp/
    * rtti.c (emit_support_tinfo_1): New function, extracted from
    emit_support_tinfos.
    (emit_support_tinfos): Call it and iterate on
registered_builtin_types.


This is causing aarch64 builds to break.


If it is causing too much trouble, we could ifdef out the last 2 lines of
emit_support_tinfos and revert the libstdc++ changes (or even revert the
whole thing).



Any c++ compilation aborts at


That's surprising, the code I touched is only ever supposed to run while
compiling one file in libsupc++, if I understand correctly.



#0  fancy_abort (file=0x14195c8 "../../git-rh/gcc/cp/mangle.c", line=2303,
   function=0x1419ff8 <write_builtin_type(tree_node*)::__FUNCTION__>
   "write_builtin_type") at ../../git-rh/gcc/diagnostic.c:1190
#1  0x00000000007ce2b4 in write_builtin_type (
   type=<real_type 0x7fb1653540 __builtin_aarch64_simd_df>)
   at ../../git-rh/gcc/cp/mangle.c:2303
#2  0x00000000007cc85c in write_type (
   type=<real_type 0x7fb1653540 __builtin_aarch64_simd_df>)
   at ../../git-rh/gcc/cp/mangle.c:1969
#3  0x00000000007d4d98 in mangle_special_for_type (
   type=<real_type 0x7fb1653540 __builtin_aarch64_simd_df>,
   code=0x1419a98 "TI") at ../../git-rh/gcc/cp/mangle.c:3569
#4  0x00000000007d4dcc in mangle_typeinfo_for_type (
   type=<real_type 0x7fb1653540 __builtin_aarch64_simd_df>)
   at ../../git-rh/gcc/cp/mangle.c:3585
#5  0x000000000070618c in get_tinfo_decl (
   type=<real_type 0x7fb1653540 __builtin_aarch64_simd_df>)
   at ../../git-rh/gcc/cp/rtti.c:422
#6  0x0000000000709ff0 in emit_support_tinfo_1 (
   bltn=<real_type 0x7fb1653540 __builtin_aarch64_simd_df>)
   at ../../git-rh/gcc/cp/rtti.c:1485
#7  0x000000000070a344 in emit_support_tinfos ()
   at ../../git-rh/gcc/cp/rtti.c:1550

Presumably the backend needs to grow some mangling support for its
builtins,


aarch64 has complicated builtins... __builtin_aarch64_simd_df uses
double_aarch64_type_node which is not the same as double_type_node. I mostly
looked at the x86 backend, so I didn't notice that aarch64 registers a lot
more builtins.



but in the meantime can we do something less drastic than abort?


Sounds good, but I am not sure how exactly. We could use a separate hook
(register_builtin_type_for_typeinfo?) so back-ends have to explicitly say
they want typeinfo, but it is ugly having to register types multiple times.
We could add a parameter to the existing register_builtin_type saying
whether we want typeinfo, but that means updating all back-ends.
We could also make typeinfo_in_lib_p more strict so for REAL_TYPE it only returns true for the types listed in fundamentals. 


Well some of these scalar types are not really user visible which is
where I believe the problem is coming from and prima-facie I don't
think we should be inventing mangling for some of these "internal"
types.
If the types are not user-visible, it is not clear to me why they need to be registered with the front-end...
That's probably because of the way they are used in typedefs in arm_neon.h to build vector types and also them being used as internal base-type names to look up the mangling table.
Perhaps a cleaner solution is to build only the vector types in terms of standard base-types and not have to define back-end-specific scalar types just to build their vector types. That will also mean changing how the mangling names are looked up ARM/AArch64 backend... 

Tejas.




 We could
get the mangling functions to take a parameter that says whether errors
should be fatal and skip generating the typeinfo when we can't mangle, but
there is no convenient way to communicate this mangling failure (0 bytes
written?).

Would mangling the aarch64 builtins be a lot of work? Did other platforms
break as well?

It's not a lot of work but I'd like to make sure we're doing the right
thing on both AArch32 and AArch64. So, for now can we just revert this
till the thing is sorted out.
Ok, I'll commit the attached as soon as I've checked it isn't too broken. It is not a complete revert: splitting the rtti function is still cleaner, and the int128 symbols are still there. 

2014-04-24  Marc Glisse  <marc.glisse@inria.fr>

         PR libstdc++/43622
gcc/cp/
 	* rtti.c (emit_support_tinfos): Do not iterate on
 	registered_builtin_types (partial revert).
libstdc++/
 	* config/abi/pre/gnu.ver (CXXABI_1.3.9): Remove __float128 symbols.
 	* config/abi/pre/gnu-versioned-namespace.ver: Likewise.
 	* config/abi/post/x86_64-linux-gnu/baseline_symbols.txt: Update.
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