Documentation for the Fast DFA Engine

[Adityazzzzz]

I have analyzed and documented the entire dmd.dfa package to make the high-performance DFA engine easier to understand and maintain.
Changes:

• Architecture: Added high-level comments to entry.d and structure.d explaining the O(1) single-pass design and memory model.
• Control Flow: Documented statement.d explaining how branching and "LoopyLabels" are handled without fixed-point iteration.
• Data Flow: Documented expression.d and analysis.d covering Transfer Functions, Confluence (Meet/Join), and Gate logic.
• Reporting: Documented error reporting in report.d.

This should address the "bad at commenting" issue mentioned in the forum/chats!
@rikkimax

[dlang-bot]

Thanks for your pull request and interest in making D better, @Adityazzzzz! We are looking forward to reviewing it, and you should be hearing from a maintainer soon.
Please verify that your PR follows this checklist:

• My PR is fully covered with tests (you can see the coverage diff by visiting the details link of the codecov check)
• My PR is as minimal as possible (smaller, focused PRs are easier to review than big ones)
• I have provided a detailed rationale explaining my changes
• New or modified functions have Ddoc comments (with Params: and Returns:)

Please see CONTRIBUTING.md for more information.

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Testing this PR locally

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dub run digger -- build "master + dmd#22286"

[rikkimax]

Over all some good changes here thanks!

I've add suggestions, only one of which could do with a bit of a rethink.

[Adityazzzzz]

I've applied all the suggested text changes and ran the pre-commit tool to fix the whitespace issues for CI. I also updated the analysis.d comment to clarify that DFAConsequence holds the specific logic.

[rikkimax]

For future reference, rather than using multiple commits, we prefer that there be only one commit per PR.

You can use appending (--ammend) in git, then force push to change the last commit.

We can squash it as part of merge, but it's better commit message wise if we don't need to.

[rikkimax]

Here is the DAutoTest failure:

�[1msrc/dmd/dfa/fast/analysis.d(131): �[1;33mWarning: �[mDdoc: parameter count mismatch, expected 6, got 3
void convergeStatementIf(DFALatticeRef condition, DFAScopeRef scrTrue,

It is expecting all parameters to match 1:1 to the ddoc.

[Adityazzzzz]

I've added the missing parameters (haveFalseBody, unknownBranchTaken, etc.) to the documentation block. Pushed the fix.
@rikkimax

[rikkimax]

�[1msrc/dmd/dfa/fast/expression.d(94): �[1;33mWarning: �[mDdoc: parameter count mismatch, expected 5, got 3
DFALatticeRef seeAssign(DFAVar* assignTo, bool construct, DFALatticeRef lr,

[Adityazzzzz]

Please review

[Adityazzzzz]

@rikkimax can you verify, if everything is alright in this PR, so that it can be merged?.

[Adityazzzzz]

i have updated the changes you mentioned @rikkimax

[Adityazzzzz]

changed to this:

/***********************************************************
 * The collection of values and facts known about a variable.
 *
 * A DFALattice contains one or more `DFAConsequence` nodes.
 * Each `DFAConsequence` represents the state of a variable at the current
 * point in time.
 */