On Wed, Apr 26, 2017 at 6:58 AM, Martin Liška <mli...@suse.cz> wrote:
> On 04/25/2017 01:58 PM, Jakub Jelinek wrote:
>> On Tue, Apr 25, 2017 at 01:48:05PM +0200, Martin Liška wrote:
>>> Hello.
>>>
>>> This is patch that was originally installed by Jason and later reverted due
>>> to PR70422.
>>> In the later PR Richi suggested a fix for that and Segher verified that it
>>> helped him
>>> to survive regression tests. That's reason why I'm resending that.
>>>
>>> Patch can bootstrap on ppc64le-redhat-linux and survives regression tests.
>>>
>>> Ready to be installed?
>>> Martin
>>
>>> >From a34ce0ef37ae00609c9f3ff98a9cb0b7db6a8bd0 Mon Sep 17 00:00:00 2001
>>> From: marxin <mli...@suse.cz>
>>> Date: Thu, 20 Apr 2017 14:56:30 +0200
>>> Subject: [PATCH] Make __FUNCTION__ a mergeable string and do not generate
>>> symbol entry.
>>>
>>> gcc/cp/ChangeLog:
>>>
>>> 2017-04-20 Jason Merrill <ja...@redhat.com>
>>> Martin Liska <mli...@suse.cz>
>>> Segher Boessenkool <seg...@kernel.crashing.org>
>>>
>>> PR c++/64266
>>> PR c++/70353
>>> PR bootstrap/70422
>>> Core issue 1962
>>> * decl.c (cp_fname_init): Decay the initializer to pointer.
>>> (cp_make_fname_decl): Set DECL_DECLARED_CONSTEXPR_P,
>>> * pt.c (tsubst_expr) [DECL_EXPR]: Set DECL_VALUE_EXPR,
>>> DECL_INITIALIZED_BY_CONSTANT_EXPRESSION_P and
>>> DECL_IGNORED_P. Don't call cp_finish_decl.
>>
>> If we don't emit those into the debug info, will the debugger be
>> able to handle __FUNCTION__ etc. properly?
>
> No, debugger with the patch can't handled these. Similar to how clang
> behaves currently. Maybe it can be conditionally enabled with -g3, or -g?
>
>> Admittedly, right now we emit it into debug info only if those decls
>> are actually used, say on:
>> const char * foo () { return __FUNCTION__; }
>> const char * bar () { return ""; }
>> we'd emit foo::__FUNCTION__, but not bar::__FUNCTION__, so the debugger
>> has to have some handling of it anyway. But while in functions
>> that don't refer to __FUNCTION__ it is always the debugger that needs
>> to synthetize those and thus they will be always pointer-equal,
>> if there are some uses of it and for other uses the debugger would
>> synthetize it, there is the possibility that the debugger synthetized
>> string will not be the same object as actually used in the function.
>
> You're right, currently one has to use a special function to be able to
> print it in debugger. I believe we've already discussed that, according
> to spec, the strings don't have to point to a same string.
>
> Suggestions what we should do with the patch?
We need to emit debug information for these variables. From Jim's
description in 70422 it seems that the problem is that the reference
to the string from the debug information is breaking
function_mergeable_rodata_prefix, which relies on
current_function_decl. It seems to me that its callers should pass
along their decl parameter so that f_m_r_p can use the decl's
DECL_CONTEXT rather than rely on current_function_decl being set
properly.
Jason
