Hi,
this patchlet makes it possible to get rid of useless EH cleanups generated at
-O0 in Ada for simple constructs involving VLAs:
declare
S : String (1 .. N);
begin
...
end;
by duplicating finally blocks that contain only a stack restore. Then the EH
optimization machinery (which is also run at -O0) can remove the cleanups.
Tested on x86_64-suse-linux, OK for the mainline?
2015-09-14 Eric Botcazou <ebotca...@adacore.com>
* tree-eh.c (lower_try_finally_dup_block): Clear location information
on stack restore statements.
(decide_copy_try_finally): Do not consider a stack restore statement as
coming from sources.
2015-09-14 Eric Botcazou <ebotca...@adacore.com>
* gnat.dg/array24.adb: New test.
--
Eric Botcazou
Index: tree-eh.c
===================================================================
--- tree-eh.c (revision 227729)
+++ tree-eh.c (working copy)
@@ -915,7 +915,12 @@ lower_try_finally_dup_block (gimple_seq
for (gsi = gsi_start (new_seq); !gsi_end_p (gsi); gsi_next (&gsi))
{
gimple stmt = gsi_stmt (gsi);
- if (LOCATION_LOCUS (gimple_location (stmt)) == UNKNOWN_LOCATION)
+ /* We duplicate __builtin_stack_restore at -O0 in the hope of eliminating
+ it on the EH paths. When it is not eliminated, make it transparent in
+ the debug info. */
+ if (gimple_call_builtin_p (stmt, BUILT_IN_STACK_RESTORE))
+ gimple_set_location (stmt, UNKNOWN_LOCATION);
+ else if (LOCATION_LOCUS (gimple_location (stmt)) == UNKNOWN_LOCATION)
{
tree block = gimple_block (stmt);
gimple_set_location (stmt, loc);
@@ -1604,8 +1609,12 @@ decide_copy_try_finally (int ndests, boo
for (gsi = gsi_start (finally); !gsi_end_p (gsi); gsi_next (&gsi))
{
+ /* Duplicate __builtin_stack_restore in the hope of eliminating it
+ on the EH paths and, consequently, useless cleanups. */
gimple stmt = gsi_stmt (gsi);
- if (!is_gimple_debug (stmt) && !gimple_clobber_p (stmt))
+ if (!is_gimple_debug (stmt)
+ && !gimple_clobber_p (stmt)
+ && !gimple_call_builtin_p (stmt, BUILT_IN_STACK_RESTORE))
return false;
}
return true;
-- { dg-do compile }
-- { dg-options "-fdump-tree-optimized" }
procedure Array24 (N : Natural) is
S : String (1 .. N);
pragma Volatile (S);
begin
S := (others => '0');
end;
-- { dg-final { scan-tree-dump-not "builtin_unwind_resume" "optimized" } }