[PATCH] tree-optimization/94963 - avoid bogus uninit warning with store-motion

[PATCH] tree-optimization/94963 - avoid bogus uninit warning with store-motion

[Richard Biener]

Eliding the load for store-motion causes an uninitialized variable
flowing into the loop, conditionally initialized and used.  The
uninit warning cannot relate the flag used to guard the initialization
and use with the actual initialization so the following robustifies
the previous approach of marking the conditional store as not to
be warned on by instead initializing the variable on loop entry
from an uninitialized variable we mark as not to be warned for.

Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed.

Richard.

2020-05-06  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/94963
	* tree-ssa-loop-im.c (execute_sm_if_changed): Remove
	no-warning marking of the conditional store.
	(execute_sm): Instead mark the uninitialized state
	on loop entry to be not warned about.

	* gcc.dg/pr94963.c: New testcase.
---
 gcc/testsuite/gcc.dg/pr94963.c | 35 +++++++++++++++++++++++++++++++++++
 gcc/tree-ssa-loop-im.c         | 18 +++++++++++-------
 2 files changed, 46 insertions(+), 7 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/pr94963.c

diff --git a/gcc/testsuite/gcc.dg/pr94963.c b/gcc/testsuite/gcc.dg/pr94963.c
new file mode 100644
index 00000000000..aca9e161301
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr94963.c
@@ -0,0 +1,35 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -Wall" } */
+
+typedef struct
+{
+  int p1;
+  int p2;
+  int p3;
+} P;
+struct S
+{
+  int field;
+};
+extern int v2;
+extern void foo (struct S *map);
+static struct S var;
+const P *pv;
+int ps;
+void
+f (void)
+{
+  if (pv != 0)
+    for (const P *ph = pv; ph < &pv[ps]; ++ph)
+      switch (ph->p1)
+	{
+	case 1:
+	v2 = ph->p2;
+	break;
+	case 2:
+	var.field = ph->p3;
+	break;
+	}
+  if (var.field != 0) /* { dg-bogus "uninitialized" } */
+    foo (&var);
+}
diff --git a/gcc/tree-ssa-loop-im.c b/gcc/tree-ssa-loop-im.c
index 554dd4be5bb..3056b4bfed2 100644
--- a/gcc/tree-ssa-loop-im.c
+++ b/gcc/tree-ssa-loop-im.c
@@ -1994,8 +1994,6 @@ execute_sm_if_changed (edge ex, tree mem, tree tmp_var, tree flag,
   gsi = gsi_start_bb (then_bb);
   /* Insert actual store.  */
   stmt = gimple_build_assign (unshare_expr (mem), tmp_var);
-  /* Make sure to not warn about maybe-uninit uses of tmp_var here.  */
-  gimple_set_no_warning (stmt, true);
   gsi_insert_after (&gsi, stmt, GSI_CONTINUE_LINKING);
 
   edge e1 = single_succ_edge (new_bb);
@@ -2149,13 +2147,19 @@ execute_sm (class loop *loop, vec<edge> exits, im_mem_ref *ref)
      store then.  */
   if ((!always_stored && !multi_threaded_model_p)
       || (ref->loaded && bitmap_bit_p (ref->loaded, loop->num)))
+    load = gimple_build_assign (tmp_var, unshare_expr (ref->mem.ref));
+  else
     {
-      load = gimple_build_assign (tmp_var, unshare_expr (ref->mem.ref));
-      lim_data = init_lim_data (load);
-      lim_data->max_loop = loop;
-      lim_data->tgt_loop = loop;
-      gsi_insert_before (&gsi, load, GSI_SAME_STMT);
+      /* If not emitting a load mark the uninitialized state on the
+	 loop entry as not to be warned for.  */
+      tree uninit = create_tmp_reg (TREE_TYPE (tmp_var));
+      TREE_NO_WARNING (uninit) = 1;
+      load = gimple_build_assign (tmp_var, uninit);
     }
+  lim_data = init_lim_data (load);
+  lim_data->max_loop = loop;
+  lim_data->tgt_loop = loop;
+  gsi_insert_before (&gsi, load, GSI_SAME_STMT);
 
   if (multi_threaded_model_p)
     {
-- 
2.12.3