From b8b3e29e4cceae2bab6e0774b1af994dbe713d97 Mon Sep 17 00:00:00 2001
From: zhanghaijian <[email protected]>
Date: Thu, 15 Jul 2021 09:13:11 +0800
Subject: [PATCH 10/13] [Backport]tree-optimization/94963 - avoid bogus uninit
 warning with store-motion

Reference: https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=371905d12259c180efb9b1f1b5716e969feb60f9

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.

diff --git a/gcc/testsuite/gcc.dg/pr94963.c b/gcc/testsuite/gcc.dg/pr94963.c
new file mode 100644
index 00000000000..09c0524fb3a
--- /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 8c33735b1fa..d74a46ef352 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)
     {
-- 
2.21.0.windows.1