[debug] Reuse debug exprs generated in remap_ssa_name

Message ID 20180708092725.c7ahp6ggfh6d3mqz@delia
State New
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  • [debug] Reuse debug exprs generated in remap_ssa_name
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Commit Message

Tom de Vries July 8, 2018, 9:27 a.m.
On Sun, Jul 08, 2018 at 11:22:41AM +0200, Tom de Vries wrote:
> On Fri, Jul 06, 2018 at 04:38:50PM +0200, Richard Biener wrote:
> > On Fri, Jul 6, 2018 at 12:47 PM Tom de Vries <tdevries@suse.de> wrote:
> > > On 07/05/2018 01:39 PM, Richard Biener wrote:
> 
> <SNIP>
> 
> > I now also spotted the code in remap_ssa_name that is supposed to handle
> > this it seems and for the testcase we only give up because the PARM_DECL is
> > remapped to a VAR_DECL.  So I suppose it is to be handled via the
> > debug-args stuff
> > which probably lacks in the area of versioning.
> > 
> > Your patch feels like it adds stuff ontop of existing mechanisms that
> > should "just work"
> > with the correct setup at the correct places...
> > 
> 
> Hmm, I realized that I may be complicating things, by trying to do an
> optimal fix in a single patch, so I decided to write two patches, one
> with a fix, and then one improving the fix to be more optimal.
> 
> Also, I suspect that the "just work" approach is this:
> ...
>        # DEBUG D#8 s=> iD.1900
>        # DEBUG iD.1949 => D#8
>        # DEBUG D#6 s=> iD.1949
> ...
> whereas previously I tried to map 'D#6' on iD.1900 directly.
> 

Second patch OK for trunk?

Thanks,
- Tom

[debug] Reuse debug exprs generated in remap_ssa_name

When compiling gcc.dg/vla-1.c with -O3 -g, vla a and b in f1 are optimized
away, and f1 is cloned to a version f1.constprop with no parameters, eliminating
parameter i.  Debug info is generated to describe the sizes of a and b, but
that process generates debug expressions that are not reused.

Fix the duplication by saving and reusing the generated debug expressions in
remap_ssa_name.  Concretely: reuse D#7 here instead of generating D#8:
...
 __attribute__((noinline))
 f1.constprop ()
 {
   intD.6 iD.1935;

   <bb 3>
   # DEBUG D#10 s=> iD.1897
   # DEBUG iD.1935 => D#10

   <bb 2>
-  # DEBUG D#8 s=> iD.1935
   # DEBUG D#7 s=> iD.1935
   saved_stack.2_1 = __builtin_stack_save ();
   # DEBUG BEGIN_STMT
   # DEBUG D#6 => D#7 + 1
   # DEBUG D#5 => (long intD.8) D#6
   # DEBUG D#4 => D#5 + -1
   # DEBUG D.1937 => (sizetype) D#4
   # DEBUG a.0D.1942 => NULL
   # DEBUG BEGIN_STMT
-  # DEBUG D#3 => D#8 + 2
+  # DEBUG D#3 => D#7 + 2
   # DEBUG D#2 => (long intD.8) D#3
   # DEBUG D#1 => D#2 + -1
   # DEBUG D.1944 => (sizetype) D#1
   # DEBUG b.1D.1949 => NULL
...

Bootstrapped and reg-tested on x86_64.

2018-07-07  Tom de Vries  <tdevries@suse.de>

	* tree-inline.c (remap_ssa_name): Save and reuse debug exprs generated
	in remap_ssa_name.

	* gcc.dg/vla-1.c: Update.

---
 gcc/testsuite/gcc.dg/vla-1.c | 5 +++--
 gcc/tree-inline.c            | 4 ++++
 2 files changed, 7 insertions(+), 2 deletions(-)

Comments

Richard Biener July 9, 2018, 12:43 p.m. | #1
On Sun, Jul 8, 2018 at 11:27 AM Tom de Vries <tdevries@suse.de> wrote:
>
> On Sun, Jul 08, 2018 at 11:22:41AM +0200, Tom de Vries wrote:
> > On Fri, Jul 06, 2018 at 04:38:50PM +0200, Richard Biener wrote:
> > > On Fri, Jul 6, 2018 at 12:47 PM Tom de Vries <tdevries@suse.de> wrote:
> > > > On 07/05/2018 01:39 PM, Richard Biener wrote:
> >
> > <SNIP>
> >
> > > I now also spotted the code in remap_ssa_name that is supposed to handle
> > > this it seems and for the testcase we only give up because the PARM_DECL is
> > > remapped to a VAR_DECL.  So I suppose it is to be handled via the
> > > debug-args stuff
> > > which probably lacks in the area of versioning.
> > >
> > > Your patch feels like it adds stuff ontop of existing mechanisms that
> > > should "just work"
> > > with the correct setup at the correct places...
> > >
> >
> > Hmm, I realized that I may be complicating things, by trying to do an
> > optimal fix in a single patch, so I decided to write two patches, one
> > with a fix, and then one improving the fix to be more optimal.
> >
> > Also, I suspect that the "just work" approach is this:
> > ...
> >        # DEBUG D#8 s=> iD.1900
> >        # DEBUG iD.1949 => D#8
> >        # DEBUG D#6 s=> iD.1949
> > ...
> > whereas previously I tried to map 'D#6' on iD.1900 directly.
> >
>
> Second patch OK for trunk?

OK, though I wonder how it doesn't fail with that testcase with
the mismatching type where the removed param-decl is mapped
to a local var-decl.

Richard.

> Thanks,
> - Tom
>
> [debug] Reuse debug exprs generated in remap_ssa_name
>
> When compiling gcc.dg/vla-1.c with -O3 -g, vla a and b in f1 are optimized
> away, and f1 is cloned to a version f1.constprop with no parameters, eliminating
> parameter i.  Debug info is generated to describe the sizes of a and b, but
> that process generates debug expressions that are not reused.
>
> Fix the duplication by saving and reusing the generated debug expressions in
> remap_ssa_name.  Concretely: reuse D#7 here instead of generating D#8:
> ...
>  __attribute__((noinline))
>  f1.constprop ()
>  {
>    intD.6 iD.1935;
>
>    <bb 3>
>    # DEBUG D#10 s=> iD.1897
>    # DEBUG iD.1935 => D#10
>
>    <bb 2>
> -  # DEBUG D#8 s=> iD.1935
>    # DEBUG D#7 s=> iD.1935
>    saved_stack.2_1 = __builtin_stack_save ();
>    # DEBUG BEGIN_STMT
>    # DEBUG D#6 => D#7 + 1
>    # DEBUG D#5 => (long intD.8) D#6
>    # DEBUG D#4 => D#5 + -1
>    # DEBUG D.1937 => (sizetype) D#4
>    # DEBUG a.0D.1942 => NULL
>    # DEBUG BEGIN_STMT
> -  # DEBUG D#3 => D#8 + 2
> +  # DEBUG D#3 => D#7 + 2
>    # DEBUG D#2 => (long intD.8) D#3
>    # DEBUG D#1 => D#2 + -1
>    # DEBUG D.1944 => (sizetype) D#1
>    # DEBUG b.1D.1949 => NULL
> ...
>
> Bootstrapped and reg-tested on x86_64.
>
> 2018-07-07  Tom de Vries  <tdevries@suse.de>
>
>         * tree-inline.c (remap_ssa_name): Save and reuse debug exprs generated
>         in remap_ssa_name.
>
>         * gcc.dg/vla-1.c: Update.
>
> ---
>  gcc/testsuite/gcc.dg/vla-1.c | 5 +++--
>  gcc/tree-inline.c            | 4 ++++
>  2 files changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/gcc/testsuite/gcc.dg/vla-1.c b/gcc/testsuite/gcc.dg/vla-1.c
> index 0c19feffd2b..94db23d1336 100644
> --- a/gcc/testsuite/gcc.dg/vla-1.c
> +++ b/gcc/testsuite/gcc.dg/vla-1.c
> @@ -20,6 +20,7 @@ main ()
>    return 0;
>  }
>
> -/* One debug source bind is generated for the parameter, and two to describe the
> +/* One debug source bind is generated for the parameter, and one to describe the
>     sizes of a and b.  */
> -/* { dg-final { scan-tree-dump-times " s=> i" 3 "optimized" } } */
> +/* { dg-final { scan-tree-dump-times " s=> i" 2 "optimized" } } */
> +
> diff --git a/gcc/tree-inline.c b/gcc/tree-inline.c
> index 6fbd8c3ca61..164c7fff710 100644
> --- a/gcc/tree-inline.c
> +++ b/gcc/tree-inline.c
> @@ -215,12 +215,16 @@ remap_ssa_name (tree name, copy_body_data *id)
>               processing_debug_stmt = -1;
>               return name;
>             }
> +         n = id->decl_map->get (val);
> +         if (n && TREE_CODE (*n) == DEBUG_EXPR_DECL)
> +           return *n;
>           def_temp = gimple_build_debug_source_bind (vexpr, val, NULL);
>           DECL_ARTIFICIAL (vexpr) = 1;
>           TREE_TYPE (vexpr) = TREE_TYPE (name);
>           SET_DECL_MODE (vexpr, DECL_MODE (SSA_NAME_VAR (name)));
>           gsi = gsi_after_labels (single_succ (ENTRY_BLOCK_PTR_FOR_FN (cfun)));
>           gsi_insert_before (&gsi, def_temp, GSI_SAME_STMT);
> +         insert_decl_map (id, val, vexpr);
>           return vexpr;
>         }
>
>
Tom de Vries July 13, 2018, 10:09 a.m. | #2
On 07/09/2018 02:43 PM, Richard Biener wrote:
> On Sun, Jul 8, 2018 at 11:27 AM Tom de Vries <tdevries@suse.de> wrote:
>>
>> On Sun, Jul 08, 2018 at 11:22:41AM +0200, Tom de Vries wrote:
>>> On Fri, Jul 06, 2018 at 04:38:50PM +0200, Richard Biener wrote:
>>>> On Fri, Jul 6, 2018 at 12:47 PM Tom de Vries <tdevries@suse.de> wrote:
>>>>> On 07/05/2018 01:39 PM, Richard Biener wrote:
>>>
>>> <SNIP>
>>>
>>>> I now also spotted the code in remap_ssa_name that is supposed to handle
>>>> this it seems and for the testcase we only give up because the PARM_DECL is
>>>> remapped to a VAR_DECL.  So I suppose it is to be handled via the
>>>> debug-args stuff
>>>> which probably lacks in the area of versioning.
>>>>
>>>> Your patch feels like it adds stuff ontop of existing mechanisms that
>>>> should "just work"
>>>> with the correct setup at the correct places...
>>>>
>>>
>>> Hmm, I realized that I may be complicating things, by trying to do an
>>> optimal fix in a single patch, so I decided to write two patches, one
>>> with a fix, and then one improving the fix to be more optimal.
>>>
>>> Also, I suspect that the "just work" approach is this:
>>> ...
>>>        # DEBUG D#8 s=> iD.1900
>>>        # DEBUG iD.1949 => D#8
>>>        # DEBUG D#6 s=> iD.1949
>>> ...
>>> whereas previously I tried to map 'D#6' on iD.1900 directly.
>>>
>>
>> Second patch OK for trunk?
> 
> OK, though I wonder how it doesn't fail with that testcase with
> the mismatching type where the removed param-decl is mapped
> to a local var-decl.

Previously I mapped the default def ssa-name onto the debug expression,
which meant I had to add special handling at the start of
remap_ssa_name, where already mapped ssa-names are handled, for the
mismatched argument/parameter type case.

Now I map the local var-decl onto the debug expression, and the code
that is added to look it up is already guarded with processing_debug_stmt.

Thanks,
- Tom

>> diff --git a/gcc/tree-inline.c b/gcc/tree-inline.c
>> index 6fbd8c3ca61..164c7fff710 100644
>> --- a/gcc/tree-inline.c
>> +++ b/gcc/tree-inline.c
>> @@ -215,12 +215,16 @@ remap_ssa_name (tree name, copy_body_data *id)
>>               processing_debug_stmt = -1;
>>               return name;
>>             }
>> +         n = id->decl_map->get (val);
>> +         if (n && TREE_CODE (*n) == DEBUG_EXPR_DECL)
>> +           return *n;
>>           def_temp = gimple_build_debug_source_bind (vexpr, val, NULL);
>>           DECL_ARTIFICIAL (vexpr) = 1;
>>           TREE_TYPE (vexpr) = TREE_TYPE (name);
>>           SET_DECL_MODE (vexpr, DECL_MODE (SSA_NAME_VAR (name)));
>>           gsi = gsi_after_labels (single_succ (ENTRY_BLOCK_PTR_FOR_FN (cfun)));
>>           gsi_insert_before (&gsi, def_temp, GSI_SAME_STMT);
>> +         insert_decl_map (id, val, vexpr);
>>           return vexpr;
>>         }
>>
>>
Richard Biener July 13, 2018, 11:10 a.m. | #3
On Fri, Jul 13, 2018 at 12:09 PM Tom de Vries <tdevries@suse.de> wrote:
>
> On 07/09/2018 02:43 PM, Richard Biener wrote:
> > On Sun, Jul 8, 2018 at 11:27 AM Tom de Vries <tdevries@suse.de> wrote:
> >>
> >> On Sun, Jul 08, 2018 at 11:22:41AM +0200, Tom de Vries wrote:
> >>> On Fri, Jul 06, 2018 at 04:38:50PM +0200, Richard Biener wrote:
> >>>> On Fri, Jul 6, 2018 at 12:47 PM Tom de Vries <tdevries@suse.de> wrote:
> >>>>> On 07/05/2018 01:39 PM, Richard Biener wrote:
> >>>
> >>> <SNIP>
> >>>
> >>>> I now also spotted the code in remap_ssa_name that is supposed to handle
> >>>> this it seems and for the testcase we only give up because the PARM_DECL is
> >>>> remapped to a VAR_DECL.  So I suppose it is to be handled via the
> >>>> debug-args stuff
> >>>> which probably lacks in the area of versioning.
> >>>>
> >>>> Your patch feels like it adds stuff ontop of existing mechanisms that
> >>>> should "just work"
> >>>> with the correct setup at the correct places...
> >>>>
> >>>
> >>> Hmm, I realized that I may be complicating things, by trying to do an
> >>> optimal fix in a single patch, so I decided to write two patches, one
> >>> with a fix, and then one improving the fix to be more optimal.
> >>>
> >>> Also, I suspect that the "just work" approach is this:
> >>> ...
> >>>        # DEBUG D#8 s=> iD.1900
> >>>        # DEBUG iD.1949 => D#8
> >>>        # DEBUG D#6 s=> iD.1949
> >>> ...
> >>> whereas previously I tried to map 'D#6' on iD.1900 directly.
> >>>
> >>
> >> Second patch OK for trunk?
> >
> > OK, though I wonder how it doesn't fail with that testcase with
> > the mismatching type where the removed param-decl is mapped
> > to a local var-decl.
>
> Previously I mapped the default def ssa-name onto the debug expression,
> which meant I had to add special handling at the start of
> remap_ssa_name, where already mapped ssa-names are handled, for the
> mismatched argument/parameter type case.
>
> Now I map the local var-decl onto the debug expression, and the code
> that is added to look it up is already guarded with processing_debug_stmt.

Ah, thanks for the explanation!

Richard.

> Thanks,
> - Tom
>
> >> diff --git a/gcc/tree-inline.c b/gcc/tree-inline.c
> >> index 6fbd8c3ca61..164c7fff710 100644
> >> --- a/gcc/tree-inline.c
> >> +++ b/gcc/tree-inline.c
> >> @@ -215,12 +215,16 @@ remap_ssa_name (tree name, copy_body_data *id)
> >>               processing_debug_stmt = -1;
> >>               return name;
> >>             }
> >> +         n = id->decl_map->get (val);
> >> +         if (n && TREE_CODE (*n) == DEBUG_EXPR_DECL)
> >> +           return *n;
> >>           def_temp = gimple_build_debug_source_bind (vexpr, val, NULL);
> >>           DECL_ARTIFICIAL (vexpr) = 1;
> >>           TREE_TYPE (vexpr) = TREE_TYPE (name);
> >>           SET_DECL_MODE (vexpr, DECL_MODE (SSA_NAME_VAR (name)));
> >>           gsi = gsi_after_labels (single_succ (ENTRY_BLOCK_PTR_FOR_FN (cfun)));
> >>           gsi_insert_before (&gsi, def_temp, GSI_SAME_STMT);
> >> +         insert_decl_map (id, val, vexpr);
> >>           return vexpr;
> >>         }
> >>
> >>

Patch

diff --git a/gcc/testsuite/gcc.dg/vla-1.c b/gcc/testsuite/gcc.dg/vla-1.c
index 0c19feffd2b..94db23d1336 100644
--- a/gcc/testsuite/gcc.dg/vla-1.c
+++ b/gcc/testsuite/gcc.dg/vla-1.c
@@ -20,6 +20,7 @@  main ()
   return 0;
 }
 
-/* One debug source bind is generated for the parameter, and two to describe the
+/* One debug source bind is generated for the parameter, and one to describe the
    sizes of a and b.  */
-/* { dg-final { scan-tree-dump-times " s=> i" 3 "optimized" } } */
+/* { dg-final { scan-tree-dump-times " s=> i" 2 "optimized" } } */
+
diff --git a/gcc/tree-inline.c b/gcc/tree-inline.c
index 6fbd8c3ca61..164c7fff710 100644
--- a/gcc/tree-inline.c
+++ b/gcc/tree-inline.c
@@ -215,12 +215,16 @@  remap_ssa_name (tree name, copy_body_data *id)
 	      processing_debug_stmt = -1;
 	      return name;
 	    }
+	  n = id->decl_map->get (val);
+	  if (n && TREE_CODE (*n) == DEBUG_EXPR_DECL)
+	    return *n;
 	  def_temp = gimple_build_debug_source_bind (vexpr, val, NULL);
 	  DECL_ARTIFICIAL (vexpr) = 1;
 	  TREE_TYPE (vexpr) = TREE_TYPE (name);
 	  SET_DECL_MODE (vexpr, DECL_MODE (SSA_NAME_VAR (name)));
 	  gsi = gsi_after_labels (single_succ (ENTRY_BLOCK_PTR_FOR_FN (cfun)));
 	  gsi_insert_before (&gsi, def_temp, GSI_SAME_STMT);
+	  insert_decl_map (id, val, vexpr);
 	  return vexpr;
 	}