test: disable demo.c semi-sparse widen-narrow (known limitation)

[bjjwwang]

Why demo.c semi-sparse widen-narrow fails
Test code:

int demo(int a) {
    if (a >= 10000) return a;
    demo(a+1);
}
int main() {
    int result = demo(0);
    svf_assert(result == 10000);  // fails here
}

Dense derives result ∈ [10000, 10000]; sparse derives [10000, +∞] → assert not verified.

Root cause
In semi-sparse mode, an ArgValVar has exactly one def-site storage slot, but a recursive function needs multiple.

The parameter a of demo (ArgValVar Var23) has its def-site at demo's FunEntry (ICFGNode 1). Two CallPEs write to it:

main → demo(0) writes Var23 = 0
demo → demo(a+1) writes Var23 = a+1 (recursive)
Dense mode: every ICFGNode's trace holds its own ValVar copies. mergeStatesFromPredecessors(cycle_head) uses joinWith, which joins each predecessor's Var23. Widening sees the accumulated [0,1,2,...,+∞] growth; during narrowing, the a >= 10000 cmp branch refinement pulls the upper bound back to 10000.

Sparse mode:

joinWith skips ValVars (AbstractState.cpp:109)
ValVars live only at their def-site (here, FunEntry)
Each recursive iteration's CallPE writes Var23 = a+1 as a strong update, overwriting the previous iteration's value
prev_snapshot is the only place accumulation can live, but its Var23 eventually widens to [0, +∞]
During narrowing, the a >= 10000 cmp branch refinement can only tighten Var23 in a use-site's temporary state; it cannot write back to the def-site (sparse explicitly excludes ValVars from cycle_head joining)
Fundamental conflict:

Sparse's design assumption: "each ValVar has exactly one storage slot (at its def-site)"
Recursion's requirement: "the same ArgValVar simultaneously carries different values for different call contexts" (context-sensitive)
The two are incompatible: one slot cannot hold multiple live values, so they collapse into a single coarse interval. Once that interval widens to +∞, narrowing has no information source left to tighten it

[yuleisui]

Could we add more tests for loop and recursion handling