tree-optimization/18501

	* tree-optimize.c (init_tree_optimization_passes): Run
	pass_late_warn_uninitialized before the last DCE run.


testsuite/ChangeLog:

	* gcc.dg/pr18501.c: New test.
	* gcc.dg/uninit-5.c: XFAIL.
	* gcc.dg/uninit-9.c: XFAIL.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@92337 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 10 insertions, 1 deletions

diff --git a/gcc/tree-optimize.c b/gcc/tree-optimize.c
index 9f58f533731..eae39df90aa 100644
--- a/gcc/tree-optimize.c
+++ b/gcc/tree-optimize.c
@@ -381,12 +381,21 @@ init_tree_optimization_passes (void)
   NEXT_PASS (pass_loop);
   NEXT_PASS (pass_dominator);
   NEXT_PASS (pass_redundant_phi);
+  /* FIXME: If DCE is not run before checking for uninitialized uses,
+     we may get false warnings (e.g., testsuite/gcc.dg/uninit-5.c).
+     However, this also causes us to misdiagnose cases that should be
+     real warnings (e.g., testsuite/gcc.dg/pr18501.c).
+     
+     To fix the false positives in uninit-5.c, we would have to
+     account for the predicates protecting the set and the use of each
+     variable.  Using a representation like Gated Single Assignment
+     may help.  */
+  NEXT_PASS (pass_late_warn_uninitialized);
   NEXT_PASS (pass_cd_dce);
   NEXT_PASS (pass_dse);
   NEXT_PASS (pass_forwprop);
   NEXT_PASS (pass_phiopt);
   NEXT_PASS (pass_tail_calls);
-  NEXT_PASS (pass_late_warn_uninitialized);
   NEXT_PASS (pass_del_ssa);
   NEXT_PASS (pass_nrv);
   NEXT_PASS (pass_remove_useless_vars);