Re: [PATCH][debug] Reuse debug exprs generated in remap_ssa_name

[Richard Biener <richard dot guenther at gmail dot com>]

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;
>         }
>
>