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Re: [PATCH] Fix missed debug PR77692
- From: Richard Biener <rguenther at suse dot de>
- To: gcc-patches at gcc dot gnu dot org
- Date: Mon, 26 Sep 2016 09:33:37 +0200 (CEST)
- Subject: Re: [PATCH] Fix missed debug PR77692
- Authentication-results: sourceware.org; auth=none
- References: <alpine.LSU.2.11.1609231441580.26629@t29.fhfr.qr>
On Fri, 23 Sep 2016, Richard Biener wrote:
>
> I am testing the following patch which re-instantiates behavior
> to emit DW_AT_const_value attributes for optimized out non-readonly
> global statics. Those are readonly by means of the ability to
> remove them early (before any optimization such as removing stores
> to write-only global vars). Before my change to make the
> late_global_decl debug hook not go via
> add_location_or_const_value_attribute but only
> tree_add_const_value_attribute_for_decl during the early debug phase
> the former function ran into rtl_for_decl_location doing
>
> /* A variable with no DECL_RTL but a DECL_INITIAL is a compile-time
> constant,
> and will have been substituted directly into all expressions that use
> it.
> C does not have such a concept, but C++ and other languages do. */
> if (!rtl && TREE_CODE (decl) == VAR_DECL && DECL_INITIAL (decl))
> rtl = rtl_for_decl_init (DECL_INITIAL (decl), TREE_TYPE (decl));
>
> where obviously at this point of the compilation no DECL_RTL was
> created yet (the above code looks fishy to me --
> tree_add_const_value_attribute_for_decl checks for TREE_READONLY on
> the decl).
>
> Anyway, bootstrapping and regtesting the following on
> x86_64-unknown-linux-gnu (it makes gcc.dg/debug/dwarf2/const-2b.c PASS
> again).
>
> Comments welcome.
Applied as r240483.
Richard.
> Richard.
>
> 2016-09-23 Richard Biener <rguenther@suse.de>
>
> PR debug/77692
> * cgraphunit.c (analyze_functions): Before early removing
> global vars calls the late_global_decl debug handler mark
> the variable as readonly.
>
> Index: gcc/cgraphunit.c
> ===================================================================
> --- gcc/cgraphunit.c (revision 240388)
> +++ gcc/cgraphunit.c (working copy)
> @@ -1194,8 +1194,15 @@ analyze_functions (bool first_time)
> at looking at optimized away DECLs, since
> late_global_decl will subsequently be called from the
> contents of the now pruned symbol table. */
> - if (!decl_function_context (node->decl))
> - (*debug_hooks->late_global_decl) (node->decl);
> + if (TREE_CODE (node->decl) == VAR_DECL
> + && !decl_function_context (node->decl))
> + {
> + /* We are reclaiming totally unreachable code and variables
> + so they effectively appear as readonly. Show that to
> + the debug machinery. */
> + TREE_READONLY (node->decl) = 1;
> + (*debug_hooks->late_global_decl) (node->decl);
> + }
>
> node->remove ();
> continue;
>
>
--
Richard Biener <rguenther@suse.de>
SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nuernberg)