Re: [PATCH] Make SRA tolerate most throwing statements

[Martin Jambor <mjambor at suse dot cz>]

On Wed, Apr 16, 2014 at 11:22:28AM +0200, Richard Biener wrote:
> On Tue, 15 Apr 2014, Martin Jambor wrote:
> 
> > Hi,
> > 
> > back in January in
> > http://gcc.gnu.org/ml/gcc-patches/2014-01/msg00848.html Eric pointed
> > out a testcase where the problem was SRA not scalarizing an aggregate
> > because it was involved in a throwing statement.  The reason is that
> > SRA is likely to need to append new statements after each one where a
> > replaced aggregate is present, but throwing statements must end their
> > BBs.  This patch comes up with a fix for most such situations by
> > adding these new statements onto a single successor non-EH edge, if
> > there is one and only one such edge.
> > 
> > I have bootstrapped and tested a very similar version on x86_64-linux,
> > bootstrap and testing of this exact one is currently underway.  OK for
> > trunk?  Eric, if and once this gets in, can you please add the
> > testcase from your original post to the suite?
> > 
> > Thanks,
> > 
> > Martin
> > 
> > 
> > 2014-04-15  Martin Jambor  <mjambor@suse.cz>
> > 
> > 	* tree-sra.c (single_non_eh_succ): New function.
> > 	(disqualify_ops_if_throwing_stmt): Renamed to
> > 	disqualify_if_bad_bb_terminating_stmt.  Allow throwing statements
> > 	having one non-EH successor BB.
> > 	(gsi_for_eh_followups): New function.
> > 	(sra_modify_expr): If stmt ends bb, use single non-EH successor to
> > 	generate loads into replacements.
> > 	(sra_modify_assign): Likewise and and also use the simple path for
> > 	such statements.
> > 	(sra_modify_function_body): Iterate safely over BBs.
> > 

...

> > @@ -2734,6 +2758,19 @@ get_access_for_expr (tree expr)
> >    return get_var_base_offset_size_access (base, offset, max_size);
> >  }
> >  
> > +/* Split the single non-EH successor edge from BB (there must be exactly one)
> > +   and return a gimple iterator to the new block.  */
> > +
> > +static gimple_stmt_iterator
> > +gsi_for_eh_followups (basic_block bb)
> > +{
> > +  edge e = single_non_eh_succ (bb);
> > +  gcc_assert (e);
> > +
> > +  basic_block new_bb = split_edge (e);
> > +  return gsi_start_bb (new_bb);
> > +}
> > +
> >  /* Replace the expression EXPR with a scalar replacement if there is one and
> >     generate other statements to do type conversion or subtree copying if
> >     necessary.  GSI is used to place newly created statements, WRITE is true if
> > @@ -2763,6 +2800,13 @@ sra_modify_expr (tree *expr, gimple_stmt_iterator *gsi, bool write)
> >    type = TREE_TYPE (*expr);
> >  
> >    loc = gimple_location (gsi_stmt (*gsi));
> > +  gimple_stmt_iterator alt_gsi = gsi_none ();
> > +  if (write && stmt_ends_bb_p (gsi_stmt (*gsi)))
> > +    {
> > +      alt_gsi = gsi_for_eh_followups (gsi_bb (*gsi));
> > +      gsi = &alt_gsi;
> 
> I think you should try to either use gsi_insert_on_edge_immediate
> (yeah, bad we can't build a gsi_for_edge_insert ()) or add
> a gsi_for_edge_insert () building on gimple_find_edge_insert_loc
> (note the before/after flag that returns - gsi_insert_* variants
> that take a flag specifying after/before would come handy here).
> You could also add a flag to gimple_find_edge_insert_loc whether
> it always should be possible to use gsi_insert_after and split
> the block in some more cases (or split it if both after and
> before inserts should be valid, but that would not split in
> the very rare case of an empty successor only).
> 
> Basically usually you can avoid splitting the edge.

The following patch adds gsi_start_edge for that purpose and uses it
together with gsi_commit_edge_inserts from within SRA.

I did not make it an inline static function in the header like the
other gsi initializing functions because that would make
gimple-iterator.h depend on tree-cfg.h and with our current flat
includes that triggered changes of includes in half a gazillion
unrelated c files (I have that patch too because I was apparently too
lazy to think before the third coffee yesterday but I do not think it
is worth it).

Bootstrapped and tested on x86_64-linux, this time it also includes
Eric's testcase.  OK for trunk?

Thanks,

Martin


2014-04-16  Martin Jambor  <mjambor@suse.cz>

	* gimple-iterator.c (gsi_start_edge): New function.
	* gimple-iterator.h (gsi_start_edge): Declare.
	* tree-sra.c (single_non_eh_succ): New function.
	(disqualify_ops_if_throwing_stmt): Renamed to
	disqualify_if_bad_bb_terminating_stmt.  Allow throwing statements
	having one non-EH successor BB.
	(sra_modify_expr): If stmt ends bb, use single non-EH successor to
	generate loads into replacements.
	(sra_modify_assign): Likewise and and also use the simple path for
	such statements.
	(sra_modify_function_body): Commit statements on edges.

testsuite/
	* gnat.dg/opt34.adb: New.
	* gnat.dg/opt34_pkg.ads: Likewise.

diff --git a/gcc/gimple-iterator.c b/gcc/gimple-iterator.c
index 1cfeb73..8a1ec53 100644
--- a/gcc/gimple-iterator.c
+++ b/gcc/gimple-iterator.c
@@ -689,6 +689,15 @@ gsi_insert_seq_on_edge (edge e, gimple_seq seq)
   gimple_seq_add_seq (&PENDING_STMT (e), seq);
 }
 
+/* Return a new iterator pointing to the first statement in sequence of
+   statements on edge E.  Such statements need to be subsequently moved into a
+   basic block by calling gsi_commit_edge_inserts.  */
+
+gimple_stmt_iterator
+gsi_start_edge (edge e)
+{
+  return gsi_start (PENDING_STMT (e));
+}
 
 /* Insert the statement pointed-to by GSI into edge E.  Every attempt
    is made to place the statement in an existing basic block, but
diff --git a/gcc/gimple-iterator.h b/gcc/gimple-iterator.h
index c35dc81..909d58b 100644
--- a/gcc/gimple-iterator.h
+++ b/gcc/gimple-iterator.h
@@ -123,6 +123,8 @@ gsi_start_bb (basic_block bb)
   return i;
 }
 
+gimple_stmt_iterator gsi_start_edge (edge e);
+
 /* Return a new iterator initially pointing to GIMPLE_SEQ's last statement.  */
 
 static inline gimple_stmt_iterator
diff --git a/gcc/testsuite/gnat.dg/opt34.adb b/gcc/testsuite/gnat.dg/opt34.adb
new file mode 100644
index 0000000..a5d0ab6
--- /dev/null
+++ b/gcc/testsuite/gnat.dg/opt34.adb
@@ -0,0 +1,29 @@
+-- { dg-do compile }
+-- { dg-options "-O -fdump-tree-esra" }
+
+with Opt34_Pkg; use Opt34_Pkg;
+
+procedure Opt34 is
+
+   function Local_Fun (Arg : T_Private) return T_Private is
+      Result : T_Private;
+   begin
+
+      case Get_Integer (Arg) is
+         when 1 =>
+            Result := Get_Private (100);
+         when 2 =>
+            Result := T_Private_Zero;
+         when others =>
+            null;
+      end case;
+
+      return Result;
+   end Local_Fun;
+
+begin
+   Assert (Get_Integer (Local_Fun (Get_Private (1))) = 100);
+end;
+
+-- { dg-final { scan-tree-dump "Created a replacement for result" "esra" } }
+-- { dg-final { cleanup-tree-dump "esra" } }
diff --git a/gcc/testsuite/gnat.dg/opt34_pkg.ads b/gcc/testsuite/gnat.dg/opt34_pkg.ads
new file mode 100644
index 0000000..83ecb49
--- /dev/null
+++ b/gcc/testsuite/gnat.dg/opt34_pkg.ads
@@ -0,0 +1,14 @@
+package Opt34_Pkg is
+
+   type T_Private is record
+      I : Integer := 0;
+   end record;
+
+   T_Private_Zero : constant T_Private := (I => 0);
+
+   function Get_Private (I : Integer) return T_Private;
+   function Get_Integer (X : T_Private) return Integer;
+
+   procedure Assert (Cond : Boolean);
+
+end Opt34_Pkg;
diff --git a/gcc/tree-sra.c b/gcc/tree-sra.c
index ffef13d..73e681d 100644
--- a/gcc/tree-sra.c
+++ b/gcc/tree-sra.c
@@ -1142,17 +1142,41 @@ build_access_from_expr (tree expr, gimple stmt, bool write)
   return false;
 }
 
-/* Disqualify LHS and RHS for scalarization if STMT must end its basic block in
-   modes in which it matters, return true iff they have been disqualified.  RHS
-   may be NULL, in that case ignore it.  If we scalarize an aggregate in
-   intra-SRA we may need to add statements after each statement.  This is not
-   possible if a statement unconditionally has to end the basic block.  */
+/* Return the single non-EH successor edge of BB or NULL if there is none or
+   more than one.  */
+
+static edge
+single_non_eh_succ (basic_block bb)
+{
+  edge e, res = NULL;
+  edge_iterator ei;
+
+  FOR_EACH_EDGE (e, ei, bb->succs)
+    if (!(e->flags & EDGE_EH))
+      {
+	if (res)
+	  return NULL;
+	res = e;
+      }
+
+  return res;
+}
+
+/* Disqualify LHS and RHS for scalarization if STMT has to terminate its BB and
+   there is no alternative spot where to put statements SRA might need to
+   generate after it.  The spot we are looking for is an edge leading to a
+   single non-EH successor, if it exists and is indeed single.  RHS may be
+   NULL, in that case ignore it.  */
+
 static bool
-disqualify_ops_if_throwing_stmt (gimple stmt, tree lhs, tree rhs)
+disqualify_if_bad_bb_terminating_stmt (gimple stmt, tree lhs, tree rhs)
 {
   if ((sra_mode == SRA_MODE_EARLY_INTRA || sra_mode == SRA_MODE_INTRA)
-      && (stmt_can_throw_internal (stmt) || stmt_ends_bb_p (stmt)))
+      && stmt_ends_bb_p (stmt))
     {
+      if (single_non_eh_succ (gimple_bb (stmt)))
+	return false;
+
       disqualify_base_of_expr (lhs, "LHS of a throwing stmt.");
       if (rhs)
 	disqualify_base_of_expr (rhs, "RHS of a throwing stmt.");
@@ -1180,7 +1204,7 @@ build_accesses_from_assign (gimple stmt)
   lhs = gimple_assign_lhs (stmt);
   rhs = gimple_assign_rhs1 (stmt);
 
-  if (disqualify_ops_if_throwing_stmt (stmt, lhs, rhs))
+  if (disqualify_if_bad_bb_terminating_stmt (stmt, lhs, rhs))
     return false;
 
   racc = build_access_from_expr_1 (rhs, stmt, false);
@@ -1319,7 +1343,7 @@ scan_function (void)
 		}
 
 	      t = gimple_call_lhs (stmt);
-	      if (t && !disqualify_ops_if_throwing_stmt (stmt, t, NULL))
+	      if (t && !disqualify_if_bad_bb_terminating_stmt (stmt, t, NULL))
 		ret |= build_access_from_expr (t, stmt, true);
 	      break;
 
@@ -2763,6 +2787,13 @@ sra_modify_expr (tree *expr, gimple_stmt_iterator *gsi, bool write)
   type = TREE_TYPE (*expr);
 
   loc = gimple_location (gsi_stmt (*gsi));
+  gimple_stmt_iterator alt_gsi = gsi_none ();
+  if (write && stmt_ends_bb_p (gsi_stmt (*gsi)))
+    {
+      alt_gsi = gsi_start_edge (single_non_eh_succ (gsi_bb (*gsi)));
+      gsi = &alt_gsi;
+    }
+
   if (access->grp_to_be_replaced)
     {
       tree repl = get_access_replacement (access);
@@ -3226,14 +3257,23 @@ sra_modify_assign (gimple *stmt, gimple_stmt_iterator *gsi)
   if (modify_this_stmt
       || gimple_has_volatile_ops (*stmt)
       || contains_vce_or_bfcref_p (rhs)
-      || contains_vce_or_bfcref_p (lhs))
+      || contains_vce_or_bfcref_p (lhs)
+      || stmt_ends_bb_p (*stmt))
     {
       if (access_has_children_p (racc))
 	generate_subtree_copies (racc->first_child, racc->base, 0, 0, 0,
 				 gsi, false, false, loc);
       if (access_has_children_p (lacc))
-	generate_subtree_copies (lacc->first_child, lacc->base, 0, 0, 0,
-				 gsi, true, true, loc);
+	{
+	  gimple_stmt_iterator alt_gsi = gsi_none ();
+	  if (stmt_ends_bb_p (*stmt))
+	    {
+	      alt_gsi = gsi_start_edge (single_non_eh_succ (gsi_bb (*gsi)));
+	      gsi = &alt_gsi;
+	    }
+	  generate_subtree_copies (lacc->first_child, lacc->base, 0, 0, 0,
+				   gsi, true, true, loc);
+	}
       sra_stats.separate_lhs_rhs_handling++;
 
       /* This gimplification must be done after generate_subtree_copies,
@@ -3397,6 +3437,7 @@ sra_modify_function_body (void)
 	}
     }
 
+  gsi_commit_edge_inserts ();
   return cfg_changed;
 }