More comprehensive update for variable updates in static exprs

[Stefan J. Wernli (swernli)]

This adds code that better propagates variable values (including known literal values) back and forth across the hybrid and classical maps when partial eval invokes the regular evaluator for static sub-expressions.

Fixes #3801

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[Andrew Casey (amcasey)]

@EntryPoint(Adaptive)
operation Main() : Int {
    use (q1, q2) = (Qubit(), Qubit());

    mutable a = MResetZ(q1) == One ? 1 | 2;
    mutable b = MResetZ(q2) == One ? 3 | 4;
    mutable temporary = 0;

    if true {
        set temporary = a;
        set a = b;
        set b = temporary;
    }

    b
}

This should return 2, but I'm getting 0. Copilot thinks it's because we're updating the map in hash order, rather than assignment order. (Since it's hash-based, it seems possible that you won't see it on your mac.)

[Andrew Casey (amcasey)]

operation Main() : (Result, Result) {
    use (a, b) = (Qubit(), Qubit());
    X(b);

    mutable x = a;
    let snapshot = x;
    set x = b;

    let before = M(snapshot);
    let after = M(x);
    Reset(snapshot);
    Reset(x);
    (before, after)
}

Expected: (0, 1) / Actual: (1, 1)

It's measuring b twice:

  call void @__quantum__qis__m__body(%Qubit* inttoptr (i64 1 to %Qubit*), %Result* inttoptr (i64 0 to %Result*))
  call void @__quantum__qis__m__body(%Qubit* inttoptr (i64 1 to %Qubit*), %Result* inttoptr (i64 1 to %Result*))

Copilot's guess:

The new pre-sync in lib.rs:1266 copies hybrid values into the classical environment.

For mutable x:

env[x]         = Qubit(a)
hybrid_vars[x] = Var(rir_x)
static_vars[x] = Literal::Qubit(0)

The synchronization helper in evaluation_context.rs:239 tries to convert the static RIR literal back into an evaluator value. But map_rir_literal_to_eval_value in lib.rs:5403 does not convert Literal::Qubit; it returns None.

It therefore falls back to:

env[x] = Var(rir_x)

[Stefan J. Wernli (swernli)]

@EntryPoint(Adaptive)
operation Main() : Int {
    use (q1, q2) = (Qubit(), Qubit());

    mutable a = MResetZ(q1) == One ? 1 | 2;
    mutable b = MResetZ(q2) == One ? 3 | 4;
    mutable temporary = 0;

    if true {
        set temporary = a;
        set a = b;
        set b = temporary;
    }

    b
}

This should return 2, but I'm getting 0. Copilot thinks it's because we're updating the map in hash order, rather than assignment order. (Since it's hash-based, it seems possible that you won't see it on your mac.)

Can you confirm if you are getting 0 for all the compatible profiles or just for Adaptive Profile? On my system, only Adaptive is returning 0, and that issue is fixed by the (current) top of the stack, #3941. The ordering could still be problem, but I tried artificially rotating the returned vector of updates and it had no effect on the behavior.

[Stefan J. Wernli (swernli)]

operation Main() : (Result, Result) {
    use (a, b) = (Qubit(), Qubit());
    X(b);

    mutable x = a;
    let snapshot = x;
    set x = b;

    let before = M(snapshot);
    let after = M(x);
    Reset(snapshot);
    Reset(x);
    (before, after)
}

Expected: (0, 1) / Actual: (1, 1)

It's measuring b twice:

  call void @__quantum__qis__m__body(%Qubit* inttoptr (i64 1 to %Qubit*), %Result* inttoptr (i64 0 to %Result*))
  call void @__quantum__qis__m__body(%Qubit* inttoptr (i64 1 to %Qubit*), %Result* inttoptr (i64 1 to %Result*))

Copilot's guess:

The new pre-sync in lib.rs:1266 copies hybrid values into the classical environment.

For mutable x:

env[x]         = Qubit(a)
hybrid_vars[x] = Var(rir_x)
static_vars[x] = Literal::Qubit(0)

The synchronization helper in evaluation_context.rs:239 tries to convert the static RIR literal back into an evaluator value. But map_rir_literal_to_eval_value in lib.rs:5403 does not convert Literal::Qubit; it returns None.

It therefore falls back to:

env[x] = Var(rir_x)

This is fixed by fifth entry in the stack, #3901