Re: [PR58315] reset inlined debug vars at return-to point

[Alexandre Oliva <aoliva@redhat.com>]

On Feb 25, 2015, Alexandre Oliva <aoliva@redhat.com> wrote:

> This patch fixes a problem that has been with us for several years.
> Variable tracking has no idea about the end of the lifetime of inlined
> variables, so it keeps on computing locations for them over and over,
> even though the computed locations make no sense whatsoever because the
> variable can't even be accessed any more.

> With this patch, we unbind all inlined variables at the point the
> inlined function returns to, so that the locations for those variables
> will not be touched any further.

> In theory, we could do something similar to non-inlined auto variables,
> when they go out of scope, but their decls apply to the entire function
> and I'm told gdb sort-of expects the variables to be accessible
> throughout the function, so I'm not tackling that in this patch, for I'm
> happy enough with what this patch gets us:

> - almost 99% reduction in the output asm for the PR testcase

> - more than 90% reduction in the peak memory use compiling that testcase

> - 63% reduction in the compile time for that testcase

> What's scary is that the testcase is not particularly pathological.  Any
> function that calls a longish sequence of inlined functions, that in
> turn call other inline functions, and so on, something that's not
> particularly unusual in C++, will likely observe significant
> improvement, as we won't see growing sequences of var_location notes
> after each call or so, as var-tracking computes a new in-stack location
> for the implicit this argument of each previously-inlined function.

> Regstrapped on x86_64-linux-gnu and i686-linux-gnu.  Ok to install?

Ping?

for  gcc/ChangeLog

	PR debug/58315
	* tree-inline.c (reset_debug_binding): New.
	(reset_debug_bindings): Likewise.
	(expand_call_inline): Call it.
---
 gcc/tree-inline.c |   56 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 56 insertions(+)

diff --git a/gcc/tree-inline.c b/gcc/tree-inline.c
index 71d75d9..c1578e5 100644
--- a/gcc/tree-inline.c
+++ b/gcc/tree-inline.c
@@ -4346,6 +4346,60 @@ add_local_variables (struct function *callee, struct function *caller,
       }
 }
 
+/* Add to BINDINGS a debug stmt resetting SRCVAR if inlining might
+   have brought in or introduced any debug stmts for SRCVAR.  */
+
+static inline void
+reset_debug_binding (copy_body_data *id, tree srcvar, gimple_seq *bindings)
+{
+  tree *remappedvarp = id->decl_map->get (srcvar);
+
+  if (!remappedvarp)
+    return;
+
+  if (TREE_CODE (*remappedvarp) != VAR_DECL)
+    return;
+
+  if (*remappedvarp == id->retvar || *remappedvarp == id->retbnd)
+    return;
+
+  tree tvar = target_for_debug_bind (*remappedvarp);
+  if (!tvar)
+    return;
+
+  gdebug *stmt = gimple_build_debug_bind (tvar, NULL_TREE,
+					  id->call_stmt);
+  gimple_seq_add_stmt (bindings, stmt);
+}
+
+/* For each inlined variable for which we may have debug bind stmts,
+   add before GSI a final debug stmt resetting it, marking the end of
+   its life, so that var-tracking knows it doesn't have to compute
+   further locations for it.  */
+
+static inline void
+reset_debug_bindings (copy_body_data *id, gimple_stmt_iterator gsi)
+{
+  tree var;
+  unsigned ix;
+  gimple_seq bindings = NULL;
+
+  if (!gimple_in_ssa_p (id->src_cfun))
+    return;
+
+  if (!opt_for_fn (id->dst_fn, flag_var_tracking_assignments))
+    return;
+
+  for (var = DECL_ARGUMENTS (id->src_fn);
+       var; var = DECL_CHAIN (var))
+    reset_debug_binding (id, var, &bindings);
+
+  FOR_EACH_LOCAL_DECL (id->src_cfun, ix, var)
+    reset_debug_binding (id, var, &bindings);
+
+  gsi_insert_seq_before_without_update (&gsi, bindings, GSI_SAME_STMT);
+}
+
 /* If STMT is a GIMPLE_CALL, replace it with its inline expansion.  */
 
 static bool
@@ -4659,6 +4713,8 @@ expand_call_inline (basic_block bb, gimple stmt, copy_body_data *id)
   	     GCOV_COMPUTE_SCALE (cg_edge->frequency, CGRAPH_FREQ_BASE),
 	     bb, return_block, NULL);
 
+  reset_debug_bindings (id, stmt_gsi);
+
   /* Reset the escaped solution.  */
   if (cfun->gimple_df)
     pt_solution_reset (&cfun->gimple_df->escaped);


-- 
Alexandre Oliva, freedom fighter    http://FSFLA.org/~lxoliva/
You must be the change you wish to see in the world. -- Gandhi
Be Free! -- http://FSFLA.org/   FSF Latin America board member
Free Software Evangelist|Red Hat Brasil GNU Toolchain Engineer