From f4dfdd1a39e3300b001d47758fea702499e99426 Mon Sep 17 00:00:00 2001
From: Michael Tautschnig <tautschn@amazon.com>
Date: Wed, 15 Feb 2023 15:25:02 +0000
Subject: [PATCH] unwindset parsing: Work around spurious GCC 12 warning
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

GCC 12 wrongly complains about the use of an uninitialized variable. Work
around by doing a poor man's version of a variable with an accompanying
Boolean.

The build failure was:
```
In file included from /usr/include/c++/12/bits/stl_algobase.h:64,
                 from /usr/include/c++/12/bits/stl_tree.h:63,
                 from /usr/include/c++/12/map:60,
                 from ../util/symbol_table_base.h:9,
                 from ../util/symbol_table.h:9,
                 from ../goto-programs/goto_model.h:15,
                 from unwindset.h:15,
                 from unwindset.cpp:9:
In constructor ‘constexpr std::pair<_T1, _T2>::pair(_U1&&, _U2&&) [with _U1 = std::__cxx11::basic_string<char>&; _U2 = unsigned int&; typename std::enable_if<(std::_PCC<true, _T1, _T2>::_MoveConstructiblePair<_U1, _U2>() && std::_PCC<true, _T1, _T2>::_ImplicitlyMoveConvertiblePair<_U1, _U2>()), bool>::type <anonymous> = true; _T1 = dstringt; _T2 = unsigned int]’,
    inlined from ‘void unwindsett::parse_unwindset_one_loop(std::string, message_handlert&)’ at unwindset.cpp:174:28:
/usr/include/c++/12/bits/stl_pair.h:535:42: error: ‘*(unsigned int*)((char*)&thread_nr + offsetof(nonstd::optional_lite::optionalt<unsigned int>,nonstd::optional_lite::optional<unsigned int>::contained))’ may be used uninitialized [-Werror=maybe-uninitialized]
  535 |         : first(std::forward<_U1>(__x)), second(std::forward<_U2>(__y)) { }
      |                                          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
unwindset.cpp: In member function ‘void unwindsett::parse_unwindset_one_loop(std::string, message_handlert&)’:
unwindset.cpp:39:23: note: ‘*(unsigned int*)((char*)&thread_nr + offsetof(nonstd::optional_lite::optionalt<unsigned int>,nonstd::optional_lite::optional<unsigned int>::contained))’ was declared here
   35 |   optionalt<unsigned> thread_nr;
      |                       ^~~~~~~~~
```
when using GCC 12: g++ (GCC) 12.2.1 20221121 (Red Hat 12.2.1-4)
---
 src/goto-instrument/unwindset.cpp | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/src/goto-instrument/unwindset.cpp b/src/goto-instrument/unwindset.cpp
index eebd8c5682d..95e73247ef4 100644
--- a/src/goto-instrument/unwindset.cpp
+++ b/src/goto-instrument/unwindset.cpp
@@ -36,7 +36,9 @@ void unwindsett::parse_unwindset_one_loop(
   if(val.empty())
     return;
 
-  optionalt<unsigned> thread_nr;
+  // we should use optionalt<unsigned> here, but then GCC 12 wrongly complains that we may be using an uninitialized variable
+  unsigned thread_nr = 0;
+  bool thread_nr_is_set = false;
   if(isdigit(val[0]))
   {
     auto c_pos = val.find(':');
@@ -44,6 +46,7 @@ void unwindsett::parse_unwindset_one_loop(
     {
       std::string nr = val.substr(0, c_pos);
       thread_nr = unsafe_string2unsigned(nr);
+      thread_nr_is_set = true;
       val.erase(0, nr.size() + 1);
     }
   }
@@ -171,8 +174,10 @@ void unwindsett::parse_unwindset_one_loop(
     else
       uw = unsafe_string2unsigned(uw_string);
 
-    if(thread_nr.has_value())
-      thread_loop_map[std::pair<irep_idt, unsigned>(id, *thread_nr)] = uw;
+    if(thread_nr_is_set)
+    {
+      thread_loop_map[std::make_pair(id, thread_nr)] = uw;
+    }
     else
       loop_map[id] = uw;
   }