PR middle-end/53590

	* common.opt (-fdelete-dead-exceptions): New switch.
	* doc/invoke.texi (Code Gen Options): Document it.
	* cse.c (count_reg_usage) <CALL_INSN>: Use !insn_nothrow_p in lieu of
	insn_could_throw_p predicate.  Do not skip an insn that could throw
	if dead exceptions can be deleted.
	(insn_live_p): Likewise, do not return true in that case.
	* dce.c (can_alter_cfg): New flag.
	(deletable_insn_p): Do not return false for an insn that can throw if
	the CFG can be altered and dead exceptions can be deleted.
	(init_dce): Set can_alter_cfg to false for fast DCE, true otherwise.
	* dse.c (scan_insn): Use !insn_nothrow_p in lieu of insn_could_throw_
	predicate. Do not preserve an insn that could throw if dead exceptions
	can be deleted.
	* function.h (struct function): Add can_delete_dead_exceptions flag.
	* function.c (allocate_struct_function): Set it.
	* lto-streamer-in.c (input_struct_function_base): Stream it.
	* lto-streamer-out.c (input_struct_function_base): Likewise.
	* tree-ssa-dce.c (mark_stmt_if_obviously_necessary): Do not mark a
	statement that could throw as necessary if dead exceptions can be
	deleted.
ada/
	* gcc-interface/misc.c (gnat_init_options_struct): Set
	opts->x_flag_delete_dead_exceptions to 1.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@188651 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 9 insertions, 2 deletions

diff --git a/gcc/dce.c b/gcc/dce.c
index 86edea11c55..8954d5c0c01 100644
--- a/gcc/dce.c
+++ b/gcc/dce.c
@@ -47,6 +47,9 @@ along with GCC; see the file COPYING3.  If not see
    we don't want to reenter it.  */
 static bool df_in_progress = false;
 
+/* True if we are allowed to alter the CFG in this pass.  */
+static bool can_alter_cfg = false;
+
 /* Instructions that have been marked but whose dependencies have not
    yet been processed.  */
 static VEC(rtx,heap) *worklist;
@@ -113,8 +116,9 @@ deletable_insn_p (rtx insn, bool fast, bitmap arg_stores)
   if (!NONJUMP_INSN_P (insn))
     return false;
 
-  /* Don't delete insns that can throw.  */
-  if (!insn_nothrow_p (insn))
+  /* Don't delete insns that may throw if we cannot do so.  */
+  if (!(cfun->can_delete_dead_exceptions && can_alter_cfg)
+      && !insn_nothrow_p (insn))
     return false;
 
   body = PATTERN (insn);
@@ -711,7 +715,10 @@ init_dce (bool fast)
     {
       bitmap_obstack_initialize (&dce_blocks_bitmap_obstack);
       bitmap_obstack_initialize (&dce_tmp_bitmap_obstack);
+      can_alter_cfg = false;
     }
+  else
+    can_alter_cfg = true;
 
   marked = sbitmap_alloc (get_max_uid () + 1);
   sbitmap_zero (marked);