make DumpPipe from Tofino available to all

[grg]

Move the DumpPipe inspector from Tofino into the common ir/dump.h

Add a pair of DumpPipe passes to the p4test backend.

[grg]

Usage question for all: because I've placed the preorder implementation in dump.cpp, dumping is enabled via -T dump:1 (or higher number). Let me know if anyone is really attached to -T dump_pipe:1 and I can move the implementation to a separate file.

[fruffy]

I have never actually used this, what is it for?

[grg]

I have never actually used this, what is it for?

It was really useful during Tofino development when trying to see how a pass or set of passes had transformed the IR without having to set breakpoints in a debugger and manually inspect nodes.

There is overlap with the P4 dumping functionality (via --toP4). But dumping the IR tree provides detail that can't always be discerned from a P4 dump. For example, is a headers_t reference a StringLiteral or a Type_Header at a given point in the program execution? Plus it's quite useful in a backend like Tofino that introduces custom IR nodes that don't necessarily have a clean/easy transformation back into P4.

[ChrisDodd]

Usage question for all: because I've placed the preorder implementation in dump.cpp, dumping is enabled via -T dump:1 (or higher number). Let me know if anyone is really attached to -T dump_pipe:1 and I can move the implementation to a separate file.

I think this is fine.

I have never actually used this, what is it for?

The main usage is to have a dump that uses dbprint (at level 1) instead of toP4, mostly for backend-specific stuff that doesn't map well to P4 (and isn't handled by toP4 -- it just gets skipped). Having a level-2 full dump is sometimes useful too (though that is often too verbose).

[grg]

@ChrisDodd Anything else blocking approval of this PR?

[ChrisDodd]

@ChrisDodd Anything else blocking approval of this PR?

Just the one suggestion (moving the #if so as to not visit when the pass is disabled) above.

[grg]

@ChrisDodd Anything else blocking approval of this PR?

Just the one suggestion (moving the #if so as to not visit when the pass is disabled) above.

Whoops -- that's on me 😬 I missed pushing the changes after making them locally.

Thanks for the approval!