synth: Add yosys-slang option; demonstrate on Ibex

[povik]

Demonstrate integrating yosys-slang for direct read-in of SV sources

Cc @jeffng-or

[povik]

I've converted nangate45/ibex to use this option. I've kept Ibex at the same version (from Nov 2020) but replaced the pre-processed Verilog sources with the SystemVerilog originals

[povik]

Leaving a note to update the bazel file for Ibex, I'm guessing it will now be

filegroup(
    name = "verilog",
    srcs = glob(include = ["*.v", "*.sv"]),
    visibility = ["//visibility:public"],
)

which will pick up both .v and .sv files, inclusive of subdirectories (until now it only had to pick up .v)

[maliberty]

@oharboe see note about bazel

[oharboe]

Nice!

Requests for change:

1. rename variable to use SYNTH_ prefix, e.g. SYNTH_SLANG, for consistency
2. add SYNTH_SLANG to flow/scripts/variables.yaml

Once this is in master, I'll do a round to clean up the bazel BUILD scripts.

For now, I maintain the ORFS bazel scripts outside of CI, we'll see what happens down the road.

[oharboe]

@maliberty @povik Has it been decided to ship the slang binary in the ORFS docker image?

If ORFS is to contain a test-case for slang and to offer a way to test slang, then I'm thinking that ./build_openroad.sh would need to support building slang for docker and local.

[povik]

If ORFS is to contain a test-case for slang and to offer a way to test slang, then I'm thinking that ./build_openroad.sh would need to support building slang for docker and local.

Yes, if we go ahead with this we need to add yosys-slang to build_openroad.sh, the documentation, and other places.

[maliberty]

I was thinking it would be a dependency installer addition. Do you think we need to put it in the ORFS build?

[oharboe]

I was thinking it would be a dependency installer addition. Do you think we need to put it in the ORFS build?

Will it get into the official ORFS docker image?

[povik]

I was thinking it would be a dependency installer addition. Do you think we need to put it in the ORFS build?

I haven't realized it until now but we need to because it depends on Yosys, and Yosys is built as part of ORFS

[maliberty]

Is slang separate from yosys-slang? Wondering if slang would be a dependency.

[povik]

Yosys-slang compiles against a specific slang vesion and sometimes I have to do patches. It's a pinned submodule somewhat like openroad and opensta

[povik]

To get a sense of the compilation runtime I compared it against Yosys just now:

Yosys

real	3m13.631s
user	21m27.703s
sys	0m45.744s

yosys-slang (inclusive of slang)

real	1m22.555s
user	6m57.400s
sys	0m20.017s

[jeffng-or]

@povik , how do I pass additional options to yosys-slang? When I ran it standalone, I included -Wno-index-oob --ignore-assertions to get mempool_group to go through.