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From: "law at redhat dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/80635] [8/9/10/11 regression] std::optional
 and bogus -Wmaybe-uninitialized warning
Date: Thu, 18 Feb 2021 21:05:03 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D80635

--- Comment #57 from Jeffrey A. Law <law at redhat dot com> ---
Below is a POC for improving the uninit analysis to handle this kind of cas=
e.=20
It's not complete.  In particular it does not ensure that the we have the s=
ame
result on the RHS and LHS of the V_C_E.  Basically I'm just showing where/h=
ow
we could look through a V_C_E to determine that the use is properly guarded.

+      /* If FLAG_DEF is a V_C_E, then we can look through it.
+        The trick is to know when the V_C_E doesn't change the
+        value, which isn't validated yet.  */
+      if (is_gimple_assign (*flag_def)
+         && gimple_assign_rhs_code (*flag_def) =3D=3D VIEW_CONVERT_EXPR)
+       {
+         tree rhs =3D gimple_assign_rhs1 (*flag_def);
+         rhs =3D TREE_OPERAND (rhs, 0);
+         if (TREE_CODE (rhs) =3D=3D SSA_NAME)
+           {
+             if ((*flag_def =3D SSA_NAME_DEF_STMT (rhs)) =3D=3D NULL)
+               continue;
+           }
+       }=