[Synth] Add canonicalization for choice

[uenoku]

Add following canonicalization. Operands of choices can be transitively merged.

%0 = synth.choice %x, %y, %constant
=>
%constant 

%0 = synth.choice %x, %y, %z:
%1 = synth.choice %0, %u:
%2 = synth.choice %z, %v

=> %0 = synth.choice %x, %y, %z, %u, %v

[joaovam]

Hi uenoku! Can I give it a try? 🙂

[uenoku]

Sure!

[AayushMainali-Github]

Add following canonicalization. Operands of choices can be transitively merged.

%0 = synth.choice %x, %y, %constant
=>
%constant
%0 = synth.choice %x, %y, %z:
%1 = synth.choice %0, %u:
%2 = synth.choice %z, %v

=> %0 = synth.choice %x, %y, %z, %u, %v

@uenoku I checked the current implementation and sent a narrow fix for transitive synth.choice flattening/merge, along with focused tests. Could you take a look and see if this matches what you had in mind?

[joaovam]

Hi @uenoku . I've created the PR implementing what you requested. Could you please have a look at it when possible? Thanks in advance!

[uenoku]

Hi thanks both! Since @joaovam volunteered first, let me review @joaovam's PR first