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


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(-)

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;
 	}
 


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