[debug] Add -gdescribe-dies

Message ID 20180824153819.GA18240@delia
State New
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  • [debug] Add -gdescribe-dies
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Tom de Vries Aug. 24, 2018, 3:38 p.m.
[ was: Re: [PATCH][debug] Add -gdescriptive-dies ]
On Fri, Aug 24, 2018 at 12:44:38PM +0200, Richard Biener wrote:
> On Wed, 22 Aug 2018, Tom de Vries wrote:

> 

> > [ was: Re: [PATCH][debug] Add -gforce-named-dies ]

> > 

> > On 08/22/2018 11:46 AM, Tom de Vries wrote:

> > > On 08/22/2018 08:56 AM, Tom de Vries wrote:

> > >> This is an undocumented developer-only option, because using this option may

> > >> change behaviour of dwarf consumers, f.i., gdb shows the artificial variables:

> > >> ...

> > >> (gdb) info locals

> > >> a = 0x7fffffffda90 "\005"

> > >> D.4278 = <optimized out>

> > >> ...

> > > I just found in the dwarf 5 spec the attribute DW_AT_description

> > > (present since version 3):

> > > ...

> > > 2.20 Entity Descriptions

> > > Some debugging information entries may describe entities in the program

> > > that are artificial, or which otherwise have a “name” that is not a

> > > valid identifier in the programming language.

> > > 

> > > This attribute provides a means for the producer to indicate the purpose

> > > or usage of the containing debugging infor

> > > 

> > > Generally, any debugging information entry that has, or may have, a

> > > DW_AT_name attribute, may also have a DW_AT_description attribute whose

> > > value is a null-terminated string providing a description of the entity.

> > > 

> > > It is expected that a debugger will display these descriptions as part

> > > of displaying other properties of an entity.

> > > ...

> > > 

> > > AFAICT, gdb currently does not explicitly handle this attribute, which I

> > > think means it's ignored.

> > > 

> > > It seems applicable to use DW_AT_description at least for the artificial

> > > decls.

> > > 

> > > Perhaps even for all cases that are added by the patch?

> > > 

> > 

> > I've chosen for this option. Using DW_AT_desciption instead of

> > DW_AT_name should minimize difference in gdb behaviour with and without

> > -gdescriptive-dies.

> 

> -gdescribe-dies?

>


Done.

> > > I'll rewrite the patch.

> > 

> > OK for trunk?

> 

> Few comments:

> 

> +static void

> +add_desc_attribute (dw_die_ref die, tree decl)

> +{

> +  tree decl_name;

> +

> +  if (!flag_descriptive_dies || dwarf_version < 3)

> +    return;

> +

> 

> you said this is a DWARF5 "feature",


No, it's a DWARF3 "feature". I copied the text from the DWARF5 spec.

> I'd suggest changing the

> check to

> 

>   if (!flag_desctiprive_dies || (dwarf_version < 5 && dwarf_strict))

> 

> given -gdescribe-dies is enough of a user request to enable the

> feature.


Done.

> Not sure if we should warn about -gstrict-dwarf

> combination with it and -gdwarf-N < 5.

>


Not sure either, left it out.

> +  else if (TREE_CODE (decl) == VAR_DECL || TREE_CODE (decl) == 

> CONST_DECL)

> +    {

> +      char buf[32];

> +      char decl_letter = TREE_CODE (decl) == CONST_DECL ? 'C' : 'D';

> +      sprintf (buf, "%c.%u", decl_letter, DECL_UID (decl));

> +      add_desc_attribute (die, buf);

> +    }

> 

> I wondered before if we can use pretty-printing of decl here.  At

> least I wouldn't restrict it to VAR_DECLs, FUNCTION_DECLs can

> certainly appear here I think.

>


Done.

> +@item -gdescriptive-dies

> +@opindex gdescriptive-dies

> +Add description attribute to DWARF DIEs that have no name attribute.

> +

> 

> Either "description attributes" or "a description attribute", not

> 100% sure being a non-native speaker.

>


Went for "description attributes".

> Otherwise the patch looks OK to me but please leave Jason time

> to comment.

>


Will do.

Untested patch attached.

Thanks,
- Tom

[debug] Add -gdescribe-dies

This patch adds option -gdescribe-dies.  It sets the DW_AT_description
attribute of dies that do not get a DW_AT_name attribute, to make it easier to
figure out what the die is describing.

The option exports the names of artificial variables:
...
 DIE    0: DW_TAG_variable (0x7fa934dd54b0)
+  DW_AT_description: "D.1922"
   DW_AT_type: die -> 0 (0x7fa934dd0d70)
   DW_AT_artificial: 1

...
which can be traced back to gimple dumps:
...
  char a[0:D.1922] [value-expr: *a.0];
...

Furthermore, it adds names to external references:
...
 DIE    0: DW_TAG_subprogram (0x7fa88b9650f0)
+DW_AT_description: "main"
 DW_AT_abstract_origin: die -> label: vla_1.c.6719312a + 29 (0x7fa88b965140)
...

2018-08-15  Tom de Vries  <tdevries@suse.de>

	* common.opt (gdescribe-dies): Add option.
	* dwarf2out.c (add_name_and_src_coords_attributes): Add description
	attribute for artifical and nameless decls.
	(dwarf2out_register_external_die): Add description attribute to
	external reference die.
	(add_desc_attribute): New functions.
	(gen_subprogram_die): Add description attribute to
	DW_TAG_call_site_parameter.
	* tree-pretty-print.c (print_generic_expr_to_str): New function.
	* tree-pretty-print.h (print_generic_expr_to_str): Declare.
	* doc/invoke.texi (@item Debugging Options): Add -gdescribe-dies and
	-gno-describe-dies.
	(@item -gdescribe-dies): Add.

---
 gcc/common.opt          |  4 ++++
 gcc/doc/invoke.texi     |  6 +++++-
 gcc/dwarf2out.c         | 57 +++++++++++++++++++++++++++++++++++++++++++++++++
 gcc/tree-pretty-print.c | 10 +++++++++
 gcc/tree-pretty-print.h |  1 +
 5 files changed, 77 insertions(+), 1 deletion(-)

Comments

Jason Merrill Aug. 31, 2018, 9:19 p.m. | #1
On Fri, Aug 24, 2018 at 11:38 AM, Tom de Vries <tdevries@suse.de> wrote:
> [ was: Re: [PATCH][debug] Add -gdescriptive-dies ]

> On Fri, Aug 24, 2018 at 12:44:38PM +0200, Richard Biener wrote:

>> On Wed, 22 Aug 2018, Tom de Vries wrote:

>>

>> > [ was: Re: [PATCH][debug] Add -gforce-named-dies ]

>> >

>> > On 08/22/2018 11:46 AM, Tom de Vries wrote:

>> > > On 08/22/2018 08:56 AM, Tom de Vries wrote:

>> > >> This is an undocumented developer-only option, because using this option may

>> > >> change behaviour of dwarf consumers, f.i., gdb shows the artificial variables:

>> > >> ...

>> > >> (gdb) info locals

>> > >> a = 0x7fffffffda90 "\005"

>> > >> D.4278 = <optimized out>

>> > >> ...

>> > > I just found in the dwarf 5 spec the attribute DW_AT_description

>> > > (present since version 3):

>> > > ...

>> > > 2.20 Entity Descriptions

>> > > Some debugging information entries may describe entities in the program

>> > > that are artificial, or which otherwise have a “name” that is not a

>> > > valid identifier in the programming language.

>> > >

>> > > This attribute provides a means for the producer to indicate the purpose

>> > > or usage of the containing debugging infor

>> > >

>> > > Generally, any debugging information entry that has, or may have, a

>> > > DW_AT_name attribute, may also have a DW_AT_description attribute whose

>> > > value is a null-terminated string providing a description of the entity.

>> > >

>> > > It is expected that a debugger will display these descriptions as part

>> > > of displaying other properties of an entity.

>> > > ...

>> > >

>> > > AFAICT, gdb currently does not explicitly handle this attribute, which I

>> > > think means it's ignored.

>> > >

>> > > It seems applicable to use DW_AT_description at least for the artificial

>> > > decls.

>> > >

>> > > Perhaps even for all cases that are added by the patch?

>> > >

>> >

>> > I've chosen for this option. Using DW_AT_desciption instead of

>> > DW_AT_name should minimize difference in gdb behaviour with and without

>> > -gdescriptive-dies.

>>

>> -gdescribe-dies?

>>

>

> Done.

>

>> > > I'll rewrite the patch.

>> >

>> > OK for trunk?

>>

>> Few comments:

>>

>> +static void

>> +add_desc_attribute (dw_die_ref die, tree decl)

>> +{

>> +  tree decl_name;

>> +

>> +  if (!flag_descriptive_dies || dwarf_version < 3)

>> +    return;

>> +

>>

>> you said this is a DWARF5 "feature",

>

> No, it's a DWARF3 "feature". I copied the text from the DWARF5 spec.

>

>> I'd suggest changing the

>> check to

>>

>>   if (!flag_desctiprive_dies || (dwarf_version < 5 && dwarf_strict))

>>

>> given -gdescribe-dies is enough of a user request to enable the

>> feature.

>

> Done.

>

>> Not sure if we should warn about -gstrict-dwarf

>> combination with it and -gdwarf-N < 5.

>>

>

> Not sure either, left it out.

>

>> +  else if (TREE_CODE (decl) == VAR_DECL || TREE_CODE (decl) ==

>> CONST_DECL)

>> +    {

>> +      char buf[32];

>> +      char decl_letter = TREE_CODE (decl) == CONST_DECL ? 'C' : 'D';

>> +      sprintf (buf, "%c.%u", decl_letter, DECL_UID (decl));

>> +      add_desc_attribute (die, buf);

>> +    }

>>

>> I wondered before if we can use pretty-printing of decl here.  At

>> least I wouldn't restrict it to VAR_DECLs, FUNCTION_DECLs can

>> certainly appear here I think.

>>

>

> Done.

>

>> +@item -gdescriptive-dies

>> +@opindex gdescriptive-dies

>> +Add description attribute to DWARF DIEs that have no name attribute.

>> +

>>

>> Either "description attributes" or "a description attribute", not

>> 100% sure being a non-native speaker.

>>

>

> Went for "description attributes".

>

>> Otherwise the patch looks OK to me but please leave Jason time

>> to comment.

>>

>

> Will do.

>

> Untested patch attached.

>

> Thanks,

> - Tom

>

> [debug] Add -gdescribe-dies

>

> This patch adds option -gdescribe-dies.  It sets the DW_AT_description

> attribute of dies that do not get a DW_AT_name attribute, to make it easier to

> figure out what the die is describing.

>

> The option exports the names of artificial variables:

> ...

>  DIE    0: DW_TAG_variable (0x7fa934dd54b0)

> +  DW_AT_description: "D.1922"

>    DW_AT_type: die -> 0 (0x7fa934dd0d70)

>    DW_AT_artificial: 1

>

> ...

> which can be traced back to gimple dumps:

> ...

>   char a[0:D.1922] [value-expr: *a.0];

> ...

>

> Furthermore, it adds names to external references:

> ...

>  DIE    0: DW_TAG_subprogram (0x7fa88b9650f0)

> +DW_AT_description: "main"

>  DW_AT_abstract_origin: die -> label: vla_1.c.6719312a + 29 (0x7fa88b965140)


Please add more of this description to the one-line documentation
patch you have now; there are many DIEs that have no name because they
don't need one, and this patch doesn't add names to all of them.

These two cases seem like they have very different uses, but I suppose
we don't really need two new options.

Jason
Tom de Vries Sept. 1, 2018, 6:10 p.m. | #2
On 08/31/2018 11:19 PM, Jason Merrill wrote:
> On Fri, Aug 24, 2018 at 11:38 AM, Tom de Vries <tdevries@suse.de> wrote:

>> [ was: Re: [PATCH][debug] Add -gdescriptive-dies ]

>> On Fri, Aug 24, 2018 at 12:44:38PM +0200, Richard Biener wrote:

>>> On Wed, 22 Aug 2018, Tom de Vries wrote:

>>>

>>>> [ was: Re: [PATCH][debug] Add -gforce-named-dies ]

>>>>

>>>> On 08/22/2018 11:46 AM, Tom de Vries wrote:

>>>>> On 08/22/2018 08:56 AM, Tom de Vries wrote:

>>>>>> This is an undocumented developer-only option, because using this option may

>>>>>> change behaviour of dwarf consumers, f.i., gdb shows the artificial variables:

>>>>>> ...

>>>>>> (gdb) info locals

>>>>>> a = 0x7fffffffda90 "\005"

>>>>>> D.4278 = <optimized out>

>>>>>> ...

>>>>> I just found in the dwarf 5 spec the attribute DW_AT_description

>>>>> (present since version 3):

>>>>> ...

>>>>> 2.20 Entity Descriptions

>>>>> Some debugging information entries may describe entities in the program

>>>>> that are artificial, or which otherwise have a “name” that is not a

>>>>> valid identifier in the programming language.

>>>>>

>>>>> This attribute provides a means for the producer to indicate the purpose

>>>>> or usage of the containing debugging infor

>>>>>

>>>>> Generally, any debugging information entry that has, or may have, a

>>>>> DW_AT_name attribute, may also have a DW_AT_description attribute whose

>>>>> value is a null-terminated string providing a description of the entity.

>>>>>

>>>>> It is expected that a debugger will display these descriptions as part

>>>>> of displaying other properties of an entity.

>>>>> ...

>>>>>

>>>>> AFAICT, gdb currently does not explicitly handle this attribute, which I

>>>>> think means it's ignored.

>>>>>

>>>>> It seems applicable to use DW_AT_description at least for the artificial

>>>>> decls.

>>>>>

>>>>> Perhaps even for all cases that are added by the patch?

>>>>>

>>>>

>>>> I've chosen for this option. Using DW_AT_desciption instead of

>>>> DW_AT_name should minimize difference in gdb behaviour with and without

>>>> -gdescriptive-dies.

>>>

>>> -gdescribe-dies?

>>>

>>

>> Done.

>>

>>>>> I'll rewrite the patch.

>>>>

>>>> OK for trunk?

>>>

>>> Few comments:

>>>

>>> +static void

>>> +add_desc_attribute (dw_die_ref die, tree decl)

>>> +{

>>> +  tree decl_name;

>>> +

>>> +  if (!flag_descriptive_dies || dwarf_version < 3)

>>> +    return;

>>> +

>>>

>>> you said this is a DWARF5 "feature",

>>

>> No, it's a DWARF3 "feature". I copied the text from the DWARF5 spec.

>>

>>> I'd suggest changing the

>>> check to

>>>

>>>   if (!flag_desctiprive_dies || (dwarf_version < 5 && dwarf_strict))

>>>

>>> given -gdescribe-dies is enough of a user request to enable the

>>> feature.

>>

>> Done.

>>

>>> Not sure if we should warn about -gstrict-dwarf

>>> combination with it and -gdwarf-N < 5.

>>>

>>

>> Not sure either, left it out.

>>

>>> +  else if (TREE_CODE (decl) == VAR_DECL || TREE_CODE (decl) ==

>>> CONST_DECL)

>>> +    {

>>> +      char buf[32];

>>> +      char decl_letter = TREE_CODE (decl) == CONST_DECL ? 'C' : 'D';

>>> +      sprintf (buf, "%c.%u", decl_letter, DECL_UID (decl));

>>> +      add_desc_attribute (die, buf);

>>> +    }

>>>

>>> I wondered before if we can use pretty-printing of decl here.  At

>>> least I wouldn't restrict it to VAR_DECLs, FUNCTION_DECLs can

>>> certainly appear here I think.

>>>

>>

>> Done.

>>

>>> +@item -gdescriptive-dies

>>> +@opindex gdescriptive-dies

>>> +Add description attribute to DWARF DIEs that have no name attribute.

>>> +

>>>

>>> Either "description attributes" or "a description attribute", not

>>> 100% sure being a non-native speaker.

>>>

>>

>> Went for "description attributes".

>>

>>> Otherwise the patch looks OK to me but please leave Jason time

>>> to comment.

>>>

>>

>> Will do.

>>

>> Untested patch attached.

>>


Now bootstrapped and reg-tested on x86_64.

>> [debug] Add -gdescribe-dies

>>

>> This patch adds option -gdescribe-dies.  It sets the DW_AT_description

>> attribute of dies that do not get a DW_AT_name attribute, to make it easier to

>> figure out what the die is describing.

>>

>> The option exports the names of artificial variables:

>> ...

>>  DIE    0: DW_TAG_variable (0x7fa934dd54b0)

>> +  DW_AT_description: "D.1922"

>>    DW_AT_type: die -> 0 (0x7fa934dd0d70)

>>    DW_AT_artificial: 1

>>

>> ...

>> which can be traced back to gimple dumps:

>> ...

>>   char a[0:D.1922] [value-expr: *a.0];

>> ...

>>

>> Furthermore, it adds names to external references:

>> ...

>>  DIE    0: DW_TAG_subprogram (0x7fa88b9650f0)

>> +DW_AT_description: "main"

>>  DW_AT_abstract_origin: die -> label: vla_1.c.6719312a + 29 (0x7fa88b965140)

> 

> Please add more of this description to the one-line documentation

> patch you have now;


Done.

> there are many DIEs that have no name because they

> don't need one, and this patch doesn't add names to all of them.

> 


I've added the qualification "some" (to both documentation and command
line option description).

> These two cases seem like they have very different uses, but I suppose

> we don't really need two new options.


In both cases we add a description of the DIE. Could you explain what
the difference in usage you refer to is?

Attached patch (which I will merge with the posted patch pre-commit)
fixes up documentation and command line option description.

OK?

Thanks,
- Tom
fixup

---
 gcc/common.opt      | 2 +-
 gcc/doc/invoke.texi | 4 +++-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/gcc/common.opt b/gcc/common.opt
index f41f8f74b30..ef6a63087af 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -2978,7 +2978,7 @@ Don't emit DWARF additions beyond selected version.
 
 gdescribe-dies
 Common Driver Report Var(flag_describe_dies) Init(0)
-Add description attributes to DWARF DIEs that have no name attribute.
+Add description attributes to some DWARF DIEs that have no name attribute.
 
 gtoggle
 Common Driver Report Var(flag_gtoggle)
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index b06189f73ce..d7cf30ad2d1 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -7468,7 +7468,9 @@ files.
 
 @item -gdescribe-dies
 @opindex gdescribe-dies
-Add description attributes to DWARF DIEs that have no name attribute.
+Add description attributes to some DWARF DIEs that have no name attribute,
+such as artificial variables, external references and call site
+parameter DIEs.
 
 @item -gpubnames
 @opindex gpubnames
Tom de Vries Sept. 11, 2018, 3:32 p.m. | #3
On 09/01/2018 08:10 PM, Tom de Vries wrote:
>> Please add more of this description to the one-line documentation

>> patch you have now;

> Done.

> 

>> there are many DIEs that have no name because they

>> don't need one, and this patch doesn't add names to all of them.

>>

> I've added the qualification "some" (to both documentation and command

> line option description).

> 

>> These two cases seem like they have very different uses, but I suppose

>> we don't really need two new options.

> In both cases we add a description of the DIE. Could you explain what

> the difference in usage you refer to is?

> 

> Attached patch (which I will merge with the posted patch pre-commit)

> fixes up documentation and command line option description.

> 

> OK?

> 


Ping.

Thanks,
- Tom
> 

> 

> 0002-fixup.patch

> 

> 

> fixup

> 

> ---

>  gcc/common.opt      | 2 +-

>  gcc/doc/invoke.texi | 4 +++-

>  2 files changed, 4 insertions(+), 2 deletions(-)

> 

> diff --git a/gcc/common.opt b/gcc/common.opt

> index f41f8f74b30..ef6a63087af 100644

> --- a/gcc/common.opt

> +++ b/gcc/common.opt

> @@ -2978,7 +2978,7 @@ Don't emit DWARF additions beyond selected version.

>  

>  gdescribe-dies

>  Common Driver Report Var(flag_describe_dies) Init(0)

> -Add description attributes to DWARF DIEs that have no name attribute.

> +Add description attributes to some DWARF DIEs that have no name attribute.

>  

>  gtoggle

>  Common Driver Report Var(flag_gtoggle)

> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi

> index b06189f73ce..d7cf30ad2d1 100644

> --- a/gcc/doc/invoke.texi

> +++ b/gcc/doc/invoke.texi

> @@ -7468,7 +7468,9 @@ files.

>  

>  @item -gdescribe-dies

>  @opindex gdescribe-dies

> -Add description attributes to DWARF DIEs that have no name attribute.

> +Add description attributes to some DWARF DIEs that have no name attribute,

> +such as artificial variables, external references and call site

> +parameter DIEs.

>  

>  @item -gpubnames

>  @opindex gpubnames
Jason Merrill Sept. 11, 2018, 4:16 p.m. | #4
On Sat, Sep 1, 2018 at 7:10 PM, Tom de Vries <tdevries@suse.de> wrote:
> On 08/31/2018 11:19 PM, Jason Merrill wrote:

>> On Fri, Aug 24, 2018 at 11:38 AM, Tom de Vries <tdevries@suse.de> wrote:

>>> [ was: Re: [PATCH][debug] Add -gdescriptive-dies ]

>>> On Fri, Aug 24, 2018 at 12:44:38PM +0200, Richard Biener wrote:

>>>> On Wed, 22 Aug 2018, Tom de Vries wrote:

>>>>

>>>>> [ was: Re: [PATCH][debug] Add -gforce-named-dies ]

>>>>>

>>>>> On 08/22/2018 11:46 AM, Tom de Vries wrote:

>>>>>> On 08/22/2018 08:56 AM, Tom de Vries wrote:

>>>>>>> This is an undocumented developer-only option, because using this option may

>>>>>>> change behaviour of dwarf consumers, f.i., gdb shows the artificial variables:

>>>>>>> ...

>>>>>>> (gdb) info locals

>>>>>>> a = 0x7fffffffda90 "\005"

>>>>>>> D.4278 = <optimized out>

>>>>>>> ...

>>>>>> I just found in the dwarf 5 spec the attribute DW_AT_description

>>>>>> (present since version 3):

>>>>>> ...

>>>>>> 2.20 Entity Descriptions

>>>>>> Some debugging information entries may describe entities in the program

>>>>>> that are artificial, or which otherwise have a “name” that is not a

>>>>>> valid identifier in the programming language.

>>>>>>

>>>>>> This attribute provides a means for the producer to indicate the purpose

>>>>>> or usage of the containing debugging infor

>>>>>>

>>>>>> Generally, any debugging information entry that has, or may have, a

>>>>>> DW_AT_name attribute, may also have a DW_AT_description attribute whose

>>>>>> value is a null-terminated string providing a description of the entity.

>>>>>>

>>>>>> It is expected that a debugger will display these descriptions as part

>>>>>> of displaying other properties of an entity.

>>>>>> ...

>>>>>>

>>>>>> AFAICT, gdb currently does not explicitly handle this attribute, which I

>>>>>> think means it's ignored.

>>>>>>

>>>>>> It seems applicable to use DW_AT_description at least for the artificial

>>>>>> decls.

>>>>>>

>>>>>> Perhaps even for all cases that are added by the patch?

>>>>>>

>>>>>

>>>>> I've chosen for this option. Using DW_AT_desciption instead of

>>>>> DW_AT_name should minimize difference in gdb behaviour with and without

>>>>> -gdescriptive-dies.

>>>>

>>>> -gdescribe-dies?

>>>>

>>>

>>> Done.

>>>

>>>>>> I'll rewrite the patch.

>>>>>

>>>>> OK for trunk?

>>>>

>>>> Few comments:

>>>>

>>>> +static void

>>>> +add_desc_attribute (dw_die_ref die, tree decl)

>>>> +{

>>>> +  tree decl_name;

>>>> +

>>>> +  if (!flag_descriptive_dies || dwarf_version < 3)

>>>> +    return;

>>>> +

>>>>

>>>> you said this is a DWARF5 "feature",

>>>

>>> No, it's a DWARF3 "feature". I copied the text from the DWARF5 spec.

>>>

>>>> I'd suggest changing the

>>>> check to

>>>>

>>>>   if (!flag_desctiprive_dies || (dwarf_version < 5 && dwarf_strict))

>>>>

>>>> given -gdescribe-dies is enough of a user request to enable the

>>>> feature.

>>>

>>> Done.

>>>

>>>> Not sure if we should warn about -gstrict-dwarf

>>>> combination with it and -gdwarf-N < 5.

>>>>

>>>

>>> Not sure either, left it out.

>>>

>>>> +  else if (TREE_CODE (decl) == VAR_DECL || TREE_CODE (decl) ==

>>>> CONST_DECL)

>>>> +    {

>>>> +      char buf[32];

>>>> +      char decl_letter = TREE_CODE (decl) == CONST_DECL ? 'C' : 'D';

>>>> +      sprintf (buf, "%c.%u", decl_letter, DECL_UID (decl));

>>>> +      add_desc_attribute (die, buf);

>>>> +    }

>>>>

>>>> I wondered before if we can use pretty-printing of decl here.  At

>>>> least I wouldn't restrict it to VAR_DECLs, FUNCTION_DECLs can

>>>> certainly appear here I think.

>>>>

>>>

>>> Done.

>>>

>>>> +@item -gdescriptive-dies

>>>> +@opindex gdescriptive-dies

>>>> +Add description attribute to DWARF DIEs that have no name attribute.

>>>> +

>>>>

>>>> Either "description attributes" or "a description attribute", not

>>>> 100% sure being a non-native speaker.

>>>>

>>>

>>> Went for "description attributes".

>>>

>>>> Otherwise the patch looks OK to me but please leave Jason time

>>>> to comment.

>>>>

>>>

>>> Will do.

>>>

>>> Untested patch attached.

>>>

>

> Now bootstrapped and reg-tested on x86_64.

>

>>> [debug] Add -gdescribe-dies

>>>

>>> This patch adds option -gdescribe-dies.  It sets the DW_AT_description

>>> attribute of dies that do not get a DW_AT_name attribute, to make it easier to

>>> figure out what the die is describing.

>>>

>>> The option exports the names of artificial variables:

>>> ...

>>>  DIE    0: DW_TAG_variable (0x7fa934dd54b0)

>>> +  DW_AT_description: "D.1922"

>>>    DW_AT_type: die -> 0 (0x7fa934dd0d70)

>>>    DW_AT_artificial: 1

>>>

>>> ...

>>> which can be traced back to gimple dumps:

>>> ...

>>>   char a[0:D.1922] [value-expr: *a.0];

>>> ...

>>>

>>> Furthermore, it adds names to external references:

>>> ...

>>>  DIE    0: DW_TAG_subprogram (0x7fa88b9650f0)

>>> +DW_AT_description: "main"

>>>  DW_AT_abstract_origin: die -> label: vla_1.c.6719312a + 29 (0x7fa88b965140)

>>

>> Please add more of this description to the one-line documentation

>> patch you have now;

>

> Done.

>

>> there are many DIEs that have no name because they

>> don't need one, and this patch doesn't add names to all of them.

>>

>

> I've added the qualification "some" (to both documentation and command

> line option description).

>

>> These two cases seem like they have very different uses, but I suppose

>> we don't really need two new options.

>

> In both cases we add a description of the DIE. Could you explain what

> the difference in usage you refer to is?


I meant when you'd want them.  The artificial decl names are useful
for comparing debug output to optimizer dumps, while the external
reference names can be useful long after the compiler dumps are gone.

> Attached patch (which I will merge with the posted patch pre-commit)

> fixes up documentation and command line option description.

>

> OK?


OK.

Jason

Patch

diff --git a/gcc/common.opt b/gcc/common.opt
index ebc3ef43ce2..f41f8f74b30 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -2976,6 +2976,10 @@  gstrict-dwarf
 Common Driver Report Var(dwarf_strict) Init(0)
 Don't emit DWARF additions beyond selected version.
 
+gdescribe-dies
+Common Driver Report Var(flag_describe_dies) Init(0)
+Add description attributes to DWARF DIEs that have no name attribute.
+
 gtoggle
 Common Driver Report Var(flag_gtoggle)
 Toggle debug information generation.
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 99849ec6467..5b51eeca594 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -372,7 +372,7 @@  Objective-C and Objective-C++ Dialects}.
 -ginternal-reset-location-views  -gno-internal-reset-location-views @gol
 -ginline-points  -gno-inline-points @gol
 -gvms  -gxcoff  -gxcoff+  -gz@r{[}=@var{type}@r{]} @gol
--gsplit-dwarf @gol
+-gsplit-dwarf -gdescribe-dies -gno-describe-dies @gol
 -fdebug-prefix-map=@var{old}=@var{new}  -fdebug-types-section @gol
 -fno-eliminate-unused-debug-types @gol
 -femit-struct-debug-baseonly  -femit-struct-debug-reduced @gol
@@ -7395,6 +7395,10 @@  the build system to avoid linking files with debug information.  To
 be useful, this option requires a debugger capable of reading @file{.dwo}
 files.
 
+@item -gdescribe-dies
+@opindex gdescribe-dies
+Add description attributes to DWARF DIEs that have no name attribute.
+
 @item -gpubnames
 @opindex gpubnames
 Generate DWARF @code{.debug_pubnames} and @code{.debug_pubtypes} sections.
diff --git a/gcc/dwarf2out.c b/gcc/dwarf2out.c
index fb71ff349fa..1fc1dbb3392 100644
--- a/gcc/dwarf2out.c
+++ b/gcc/dwarf2out.c
@@ -3808,6 +3808,7 @@  static bool add_location_or_const_value_attribute (dw_die_ref, tree, bool);
 static bool tree_add_const_value_attribute (dw_die_ref, tree);
 static bool tree_add_const_value_attribute_for_decl (dw_die_ref, tree);
 static void add_name_attribute (dw_die_ref, const char *);
+static void add_desc_attribute (dw_die_ref, tree);
 static void add_gnat_descriptive_type_attribute (dw_die_ref, tree, dw_die_ref);
 static void add_comp_dir_attribute (dw_die_ref);
 static void add_scalar_info (dw_die_ref, enum dwarf_attribute, tree, int,
@@ -6022,6 +6023,8 @@  dwarf2out_register_external_die (tree decl, const char *sym,
   else
     equate_decl_number_to_die (decl, die);
 
+  add_desc_attribute (die, decl);
+
   /* Add a reference to the DIE providing early debug at $sym + off.  */
   add_AT_external_die_ref (die, DW_AT_abstract_origin, sym, off);
 }
@@ -20529,6 +20532,52 @@  add_name_attribute (dw_die_ref die, const char *name_string)
     }
 }
 
+/* Generate a DW_AT_description attribute given some string value to be included
+   as the value of the attribute.  */
+
+static void
+add_desc_attribute (dw_die_ref die, const char *name_string)
+{
+  if (!flag_describe_dies || (dwarf_version < 3 && dwarf_strict))
+    return;
+
+  if (name_string == NULL || *name_string == 0)
+    return;
+
+  if (demangle_name_func)
+    name_string = (*demangle_name_func) (name_string);
+
+  add_AT_string (die, DW_AT_description, name_string);
+}
+
+/* Generate a DW_AT_description attribute given some decl to be included
+   as the value of the attribute.  */
+
+static void
+add_desc_attribute (dw_die_ref die, tree decl)
+{
+  tree decl_name;
+
+  if (!flag_describe_dies || (dwarf_version < 3 && dwarf_strict))
+    return;
+
+  if (decl == NULL_TREE || !DECL_P (decl))
+    return;
+  decl_name = DECL_NAME (decl);
+
+  if (decl_name != NULL && IDENTIFIER_POINTER (decl_name) != NULL)
+    {
+      const char *name = dwarf2_name (decl, 0);
+      add_desc_attribute (die, name ? name : IDENTIFIER_POINTER (decl_name));
+    }
+  else
+    {
+      char *desc = print_generic_expr_to_str (decl);
+      add_desc_attribute (die, desc);
+      free (desc);
+    }
+}
+
 /* Retrieve the descriptive type of TYPE, if any, make sure it has a
    DIE and attach a DW_AT_GNAT_descriptive_type attribute to the DIE
    of TYPE accordingly.
@@ -21287,12 +21336,17 @@  add_name_and_src_coords_attributes (dw_die_ref die, tree decl,
       const char *name = dwarf2_name (decl, 0);
       if (name)
 	add_name_attribute (die, name);
+      else
+	add_desc_attribute (die, decl);
+
       if (! DECL_ARTIFICIAL (decl))
 	add_src_coords_attributes (die, decl);
 
       if (!no_linkage_name)
 	add_linkage_name (die, decl);
     }
+  else
+    add_desc_attribute (die, decl);
 
 #ifdef VMS_DEBUGGING_INFO
   /* Get the function's name, as described by its RTL.  This may be different
@@ -23265,6 +23319,7 @@  gen_subprogram_die (tree decl, dw_die_ref context_die)
 	      dw_die_ref die = NULL;
 	      rtx tloc = NULL_RTX, tlocc = NULL_RTX;
 	      rtx arg, next_arg;
+	      tree arg_decl = NULL_TREE;
 
 	      for (arg = (ca_loc->call_arg_loc_note != NULL_RTX
 			  ? XEXP (ca_loc->call_arg_loc_note, 0)
@@ -23329,6 +23384,7 @@  gen_subprogram_die (tree decl, dw_die_ref context_die)
 		      tdie = lookup_decl_die (tdecl);
 		      if (tdie == NULL)
 			continue;
+		      arg_decl = tdecl;
 		    }
 		  else
 		    continue;
@@ -23345,6 +23401,7 @@  gen_subprogram_die (tree decl, dw_die_ref context_die)
 		    die = gen_call_site_die (decl, subr_die, ca_loc);
 		  cdie = new_die (dwarf_TAG (DW_TAG_call_site_parameter), die,
 				  NULL_TREE);
+		  add_desc_attribute (cdie, arg_decl);
 		  if (reg != NULL)
 		    add_AT_loc (cdie, DW_AT_location, reg);
 		  else if (tdie != NULL)
diff --git a/gcc/tree-pretty-print.c b/gcc/tree-pretty-print.c
index 627d8d7e2d7..a4489d7f5ab 100644
--- a/gcc/tree-pretty-print.c
+++ b/gcc/tree-pretty-print.c
@@ -162,6 +162,16 @@  print_generic_expr (FILE *file, tree t, dump_flags_t flags)
   pp_flush (tree_pp);
 }
 
+/* Print a single expression T to string, and return it.  */
+
+char *
+print_generic_expr_to_str (tree t)
+{
+  pretty_printer pp;
+  dump_generic_node (&pp, t, 0, TDF_VOPS|TDF_MEMSYMS, false);
+  return xstrdup (pp_formatted_text (&pp));
+}
+
 /* Dump NAME, an IDENTIFIER_POINTER, sanitized so that D<num> sequences
    in it are replaced with Dxxxx, as long as they are at the start or
    preceded by $ and at the end or followed by $.  See make_fancy_name
diff --git a/gcc/tree-pretty-print.h b/gcc/tree-pretty-print.h
index adfc77b29cd..4de0e090cba 100644
--- a/gcc/tree-pretty-print.h
+++ b/gcc/tree-pretty-print.h
@@ -38,6 +38,7 @@  extern void print_generic_decl (FILE *, tree, dump_flags_t);
 extern void print_generic_stmt (FILE *, tree, dump_flags_t = TDF_NONE);
 extern void print_generic_stmt_indented (FILE *, tree, dump_flags_t, int);
 extern void print_generic_expr (FILE *, tree, dump_flags_t = TDF_NONE);
+extern char *print_generic_expr_to_str (tree);
 extern void dump_omp_clauses (pretty_printer *, tree, int, dump_flags_t);
 extern int dump_generic_node (pretty_printer *, tree, int, dump_flags_t, bool);
 extern void print_declaration (pretty_printer *, tree, int, dump_flags_t);