Add a pretty printer for irept

[NathanJPhillips]

This is the pretty printer for irept that I use. It works in GDB directly but not in CLion and is therefore not enabled in this PR (users can adjust the load_cbmc_printers function to enable it). @JohnDumbell is planning on doing a full pretty printer for irept soon so having this in the code base may be a useful first step.

• 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.
• 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.
• White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[JohnDumbell]

That's really useful, thanks! Did CLion give anything useful in regards to errors or just not work?

[allredj]

✔️
Passed Diffblue compatibility checks (cbmc commit: e1e5092).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/121127968

[NathanJPhillips]

Example output:

(gdb) p generic_parameters
$1 = std::vector of length 2, capacity 2 = {
  {<reference_typet> = "pointer" = {
      [sub[0]] = "struct_tag" = {
        [named_sub["identifier"]] = "java::java.lang.Object", [named_sub["#base_name"]] = "java.lang.Object", 
        [named_sub["#java_generic_parameter"]] = "1", 
        [named_sub["type_variables"]] = "" = {
          [sub[0]] = "struct_tag" = {
            [named_sub["identifier"]] = "java::com.diffblue.regression.GenericOuter::K"}}}, 
      [named_sub["width"]] = "64", 
      [named_sub["#reference"]] = "1"}, <No data fields>}, {<reference_typet> = "pointer" = {
      [sub[0]] = "struct_tag" = {
        [named_sub["identifier"]] = "java::java.lang.Object", [named_sub["#base_name"]] = "java.lang.Object", 
        [named_sub["#java_generic_parameter"]] = "1", 
        [named_sub["type_variables"]] = "" = {
          [sub[0]] = "struct_tag" = {
            [named_sub["identifier"]] = "java::com.diffblue.regression.GenericOuter$GenericInner::T"}}}, 
      [named_sub["width"]] = "64", 
      [named_sub["#reference"]] = "1"}, <No data fields>}}

[thk123]

This doesn't work correctly in CLion, but it looks to be a CLion bug as using p on gdb directly produces the expected result - nice!

It does however need adding so people get the advantage

[thk123]

⛏️ Probably would have been easier to review if the refactoring of printing dstring was separate to the introduction of irep printing

[NathanJPhillips]

That might be slightly overkill - the changes can be read top-to-bottom - only the last hunk is not related to this refactoring.