[Relay] softmax, max_pool2d, conv2d, fix 4D memory connections (WIP)

[cgyurgyik]

Overview

• nn.max_pool2d implementation with test.
• nn.conv2d implementation with test.
• Fixes to 4D to actually hook in all the appropriate addresses. This includes a runt test, since I missed this bug in an earlier PR.
• Fixes [fud] Add named components for Dahlia lowering to fud, FuTIL passes. #274 .
• Improves modularity. Everything that deals with Relay function call -> Dahlia function -> FuTIL lowering is done in a single file dahlia_lowering.py now.
• Allows for lowering of VGG Net from Relay IR to FuTIL, i.e. python3 example.py vgg_net. This is by no means fast; lowering MLP Net is faster given the smaller number of instructions. I've also verified the FuTIL output lowers to Verilog in both cases.

TODOs Left

• Need to improve nn.softmax to avoid integer underflow for fixed point. Currently, this includes a std_exp operator, however, this operator rounds to the nearest integer because of the following:

            /* verilator lint_off REALCVT */
            out = 2.718281 ** exponent;

Ideally, we'd like that not to occur. I mention this in #299 , though I'm not sure I'll have time to work on this more before Tuesday. I believe this will be easy to do once we can support generalized functions with invoke.

[cgyurgyik]

The TODOs left for VGG Net lowering are discussed explicitly in #276. This includes updating nn.softmax to use invoke and adding the correct types rather than defaulting to unsigned. Currently, VGG Net lowers to Verilog. While not a measure of correctness or completeness, it is progress.

[cgyurgyik]

@rachitnigam I've removed the unnecessary additions to the primitives library and marked softmax as unimplemented for now. This CL is already pretty large, so I can finish the rest in a follow-up CL.

[rachitnigam]

Are there any tests you want to enable by default in the top-level runt.toml?

[cgyurgyik]

Are there any tests you want to enable by default in the top-level runt.toml?

At this time, no. Perhaps after the dat rehaul is finished, or I find that more people are committing. Thanks for the review.