ITE and binary relations are constant when all operands are constants

[tautschnig]

This expands the definition of is_constantt to cover if-then-else as well as binary relations. In many, but not, cases the simplifier will have turned these into simpler constants. The included regression test is derived from Rust code, where the intermediate representation (together with constant propagation) will yield such comparisons.

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[peterschrammel]

Does the same reasoning also apply to further operators such as bitwise and boolean operators?

[tautschnig]

Does the same reasoning also apply to further operators such as bitwise and boolean operators?

Good call. Doing something like ptr & 0xF for alignment checks would be such an example that we can safely constant-propagate (once ptr is found to be &object by other constant propagation). Added.

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.10 🎉

Comparison is base (e024ecb) 78.39% compared to head (0289d31) 78.50%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #7569      +/-   ##
===========================================
+ Coverage    78.39%   78.50%   +0.10%     
===========================================
  Files         1670     1670              
  Lines       191760   191764       +4     
===========================================
+ Hits        150337   150544     +207     
+ Misses       41423    41220     -203     

Impacted Files	Coverage Δ
src/util/expr_util.cpp	91.20% <100.00%> (+0.19%)	⬆️
src/util/bitvector_expr.h	97.41% <0.00%> (+0.46%)	⬆️
src/util/symbol_table.cpp	91.30% <0.00%> (+6.52%)	⬆️
src/util/type.h	100.00% <0.00%> (+7.46%)	⬆️
src/util/string_container.h	100.00% <0.00%> (+9.09%)	⬆️
src/util/ssa_expr.h	100.00% <0.00%> (+11.36%)	⬆️
src/util/validate_expressions.cpp	93.75% <0.00%> (+18.75%)	⬆️
src/big-int/bigint.cc	89.00% <0.00%> (+20.50%)	⬆️
src/util/validate_helpers.h	100.00% <0.00%> (+22.22%)	⬆️
src/util/string_container.cpp	51.85% <0.00%> (+27.77%)	⬆️
... and 3 more

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