Improving ASR passes infrastructure

[certik]

Currently one can print all passes using lfortran --pass xx examples/expr2.f90.

High priority:

• printing ASR output after every pass - Support for print ASR after pass. #950
• easier registration of new passes - Simplifying registering passes in pass_manager.h #966, Simplifying registering passes in pass_manager.h lfortran/lfortran#158
• Add an option to skip/ignore a pass in the default pipeline

Low priority:

• figure out how to handle parameters for each pass. Some kind of a map of argument name, type and value; dynamically constructed from the ASR passes cpp files; keep the door open for creating plugins for ASR passes, that are registered at runtime (using a shared library)
• Expose arguments in the driver
• Add lfortran --print-passes which would print all passes, one on each line, with a "name" and a "one line description"
• Add lfortran --print-pass=fma which will print "name", "one line description", "full multi-paragraph description", "all parameters: names, types, default values"
• Add lfortran --print-pass-pipeline --show-llvm examples/expr2.f90 that will print half a page of all the passes in some format such as arr_slice,do_loops,fma[ax=5,b=7],... including all parameters that the LLVM backend (let's say) sets for the given pass (and the given compiler options such as --fast and architecture, for loop unrolling for example).
• Add lfortran --pass="arr_slice,fma[ax=5,b=7]" --show-llvm examples/expr2.f90 that would reproduce the default LLVM pass pipeline; then one can modify it and the command line (add/remove passes, change pass parameters)
• Idea: instead of (or in addition to) --pass="arr_slice,fma[ax=5,b=7]" LFortran could generate (via --print-pass-pipeline) and then the user provide a JSON file

[czgdp1807]

easier registration of new passes

Added to my list. Will work on it.

[redbopo]

I'd like to add on printing ASR output after every pass .