94 lines
No EOL
2.8 KiB
Rust
94 lines
No EOL
2.8 KiB
Rust
/*
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Liveness analysis for protocols. This is useful for a lot of possible
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optimizations.
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This analysis computes the "co-live" relationship between
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states. Co-live is defined inductively as follows.
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1. u is co-live with v if u can transition to v in one message.
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2. u is co-live with v if there exists a w such that u and w are
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co-live, w and v are co-live, and u and w have the same direction.
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This relationship approximates when it is safe to store two states in
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the same memory location. If there is no u such u is co-live with
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itself, then the protocol is bounded.
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(These assertions could use proofs)
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In addition, this analysis does reachability, to warn when we have
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useless states.
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The algorithm is a fixpoint computation. For each state, we initialize
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a bitvector containing whether it is co-live with each other state. At
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first we use rule (1) above to set each vector. Then we iterate
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updating the states using rule (2) until there are no changes.
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*/
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import dvec::extensions;
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import std::bitv::{bitv, methods};
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import proto::methods;
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import ast_builder::empty_span;
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fn analyze(proto: protocol, _cx: ext_ctxt) {
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#debug("initializing colive analysis");
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let num_states = proto.num_states();
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let colive = do (copy proto.states).map_to_vec |state| {
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let bv = bitv(num_states, false);
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for state.reachable |s| {
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bv.set(s.id, true);
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}
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bv
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};
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let mut i = 0;
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let mut changed = true;
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while changed {
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changed = false;
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#debug("colive iteration %?", i);
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for colive.eachi |i, this_colive| {
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let this = proto.get_state_by_id(i);
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for this_colive.ones |j| {
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let next = proto.get_state_by_id(j);
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if this.dir == next.dir {
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changed = changed || this_colive.union(colive[j]);
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}
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}
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}
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i += 1;
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}
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#debug("colive analysis complete");
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// Determine if we're bounded
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let mut self_live = ~[];
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for colive.eachi |i, bv| {
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if bv.get(i) {
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vec::push(self_live, proto.get_state_by_id(i))
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}
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}
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if self_live.len() > 0 {
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let states = str::connect(self_live.map(|s| *s.name), ~" ");
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#debug("protocol %s is unbounded due to loops involving: %s",
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*proto.name, states);
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// Someday this will be configurable with a warning
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//cx.span_warn(empty_span(),
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// #fmt("protocol %s is unbounded due to loops \
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// involving these states: %s",
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// *proto.name,
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// states));
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proto.bounded = some(false);
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}
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else {
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#debug("protocol %s is bounded. yay!", *proto.name);
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proto.bounded = some(true);
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}
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} |