llvm / llvm/circt

[FIRRTL] Support read-under-write modifiers on CHIRRTL mem constructs

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enhancement FIRRTL
Dominant language
C++
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Description

CHIRRTL memories were supposed to have an undefined, old, or new read-under-write modifiers after the memory declaration. E.g.:

smem mem1 : UInt<8> [8] old
smem mem2 : UInt<8> [8] new
smem mem3 : UInt<8> [8] undefined

This then should be copied over to the FIRRTL memory that is inferred.

Presently, this modifier was never serialized in the textual format coming out of Chisel. (It was just dropped.)

This will change in the actual release of Chisel 3.6.

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First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Locate the CHIRRTL memory parsing and textual serialization entry points, then trace how inferred FIRRTL memories are produced. Verify the undefined, old, and new modifiers are preserved from declarations through inferred memories, and run the relevant memory-format tests if available.

Written by the indexing model from the issue text.

Assessment

Tech stack
cpp
Domain
compilers
Issue type
Feature
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
45/100

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