Experimenting with different adder implementations

[tautschnig]

Depends-on: #8990

The experiments were performed using the following example:

 #ifndef SIZE
 #define SIZE 100
 #endif

 #ifndef UNSAT
 int main()
 {
   int a[SIZE], b[SIZE];
   for(int i=0; i < SIZE; ++i)
     __CPROVER_assert(a[i] + b[i] > a[i], "");
 }
 #else
 #include <limits.h>

 int main()
 {
   int a[SIZE], b[SIZE];
   for(int i=0; i < SIZE; ++i)
   {
     __CPROVER_assert(
       b[i] <= 0 ||
       (a[i] >= (INT_MAX >> 28) || b[i] >= (INT_MAX >> 28)) ||
       (a[i] <= (INT_MIN >> 1) || b[i] <= (INT_MIN >> 1)) ||
       a[i] + b[i] > a[i], "");
   }
 }
 #endif

See https://tinyurl.com/adder-comparison
(https://docs.google.com/spreadsheets/d/1ckrIwxe5QVUu12rs3OaY3o7CQ-UqFnEWvcEOf8cw580/) for results.

• Each commit message has a non-empty body, explaining why the change was made.
• 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).
• 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

❌ Patch coverage is 0.97087% with 306 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.32%. Comparing base (6df204e) to head (1fd90bb).

Files with missing lines	Patch %	Lines
src/solvers/flattening/bv_utils.cpp	0.97%	306 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #7993      +/-   ##
===========================================
- Coverage    80.46%   80.32%   -0.14%     
===========================================
  Files         1704     1704              
  Lines       188665   188973     +308     
  Branches        73       73              
===========================================
- Hits        151805   151801       -4     
- Misses       36860    37172     +312     

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