Tier 2 optimizer's abstract interpreter

[Fidget-Spinner]

Linked PRs

• gh-114058: The Tier2 Optimizer #114059
• gh-114058: Foundations of the Tier2 redundancy eliminator #115085
• gh-114058: Fix flaky globals to constant test #115423
• gh-114058: More robust method handling in redundancy eliminator #115779
• gh-114058: Only allow immortal constants in tier 2 #115817
• gh-114058: Improve method information in redundancy eliminator #115848

[markshannon]

We need a lattice of values that embodies type information, NULLness, Noneness, constant values, version numbers, at the least.

The lattice should look something like this:

graph BT;
    t("True");
    f("False");
    bl("bool");
    nnull(not NULL);
    nnone(not None);
    ot(other types);
    oc(other constants);
    b("bottom(unknown)");
    b-->NULL;
    b-->nnull;
    nnull-->nnone;
    nnull-->None;
    nnone-->ot;
    nnone-->bl;
    ot-->oc;
    oc-->top;
    None-->top;
    NULL-->top;
    bl-->t;
    bl-->f;
    t-->top;
    f-->top;

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[markshannon]

There should be edges from all the nodes (except bottom) to top, but I've omitted those to avoid the diagram becoming a mess

[gvanrossum]

There should be edges from all the nodes (except bottom) to top, but I've omitted those to avoid the diagram becoming a mess

Maybe top needn't be part of the diagram at all? It ought to be unreachable (IIUC it represents an impossible condition). Might as well simplify the diagram a bit further.