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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug libstdc++/105562] std::function<bool(char)>::_M_invoker may be
 used uninitialized in std::regex move with -fno-strict-aliasing
Date: Thu, 12 May 2022 09:57:05 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D105562

--- Comment #11 from Richard Biener <rguenth at gcc dot gnu.org> ---
diff --git a/gcc/tree-ssa-sccvn.cc b/gcc/tree-ssa-sccvn.cc
index d4d0aba880c..9f7f12846cb 100644
--- a/gcc/tree-ssa-sccvn.cc
+++ b/gcc/tree-ssa-sccvn.cc
@@ -2593,6 +2593,11 @@ vn_reference_lookup_3 (ao_ref *ref, tree vuse, void
*data_,
   bool lhs_ref_ok =3D false;
   poly_int64 copy_size;

+  /* We can optimistically disambiguate against CLOBBERs, when there
+     is any overlap it would be undefined behavior.  */
+  if (gimple_clobber_p (def_stmt))
+    return NULL;
+
   /* First try to disambiguate after value-replacing in the definitions LH=
S.=20
*/
   if (is_gimple_assign (def_stmt))
     {


avoids the diagnostics.=