Dirty locals copied across threads require program-order constraints

[tautschnig]

We previously lacked SHARED_WRITE events in program order in a newly-spawned
thread for dirty locals being copied from the spawning thread. This resulted in
spurious failures as reading from initial values seemed possible, when the
from-read constraint should have prevented such reads.

Also, replace the variable "t" by the more descriptive "new_thread_nr."

• Each commit message has a non-empty body, explaining why the change was made.
• n/a Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
• n/a The feature or user visible behaviour I have added or modified has been documented in the User Guide in doc/cprover-manual/
• Regression or unit tests are included, or existing tests cover the modified code (in this case I have detailed which ones those are in the commit message).
• n/a My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• n/a White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[codecov]

Codecov Report

Merging #6122 (fa14bb5) into develop (1154f13) will increase coverage by 0.17%.
The diff coverage is 88.81%.

@@             Coverage Diff             @@
##           develop    #6122      +/-   ##
===========================================
+ Coverage    76.92%   77.10%   +0.17%     
===========================================
  Files         1583     1582       -1     
  Lines       183314   182642     -672     
===========================================
- Hits        141018   140829     -189     
+ Misses       42296    41813     -483     

Impacted Files	Coverage Δ
src/cpp/cpp_typecheck_conversions.cpp	85.14% <0.00%> (+0.10%)	⬆️
src/goto-instrument/dump_c.cpp	80.49% <0.00%> (+0.28%)	⬆️
src/goto-instrument/dump_c_class.h	100.00% <ø> (ø)
src/goto-instrument/goto_program2code.cpp	68.84% <0.00%> (+0.06%)	⬆️
src/goto-programs/xml_expr.cpp	51.21% <0.00%> (ø)
src/util/expr_util.h	100.00% <ø> (ø)
src/util/pointer_predicates.cpp	93.10% <ø> (-0.45%)	⬇️
src/util/pointer_predicates.h	66.66% <ø> (ø)
src/analyses/custom_bitvector_analysis.cpp	55.96% <44.44%> (+0.07%)	⬆️
src/solvers/smt2/smt2_conv.cpp	67.57% <66.66%> (-0.04%)	⬇️
... and 33 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 352be59...fa14bb5. Read the comment docs.