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collect stats on bool ops and negations in an expression

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This commit is contained in:
Oliver Schneider 2016-03-24 15:37:17 +01:00
parent 0f92f84f16
commit dd6bee3b3f
2 changed files with 61 additions and 38 deletions
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89
src/booleans.rs
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@ -180,19 +180,35 @@ fn simple_negate(b: Bool) -> Bool {
}
}
fn terminal_stats(b: &Bool) -> [usize; 32] {
fn recurse(b: &Bool, stats: &mut [usize; 32]) {
#[derive(Default)]
struct Stats {
terminals: [usize; 32],
negations: usize,
ops: usize,
}
fn terminal_stats(b: &Bool) -> Stats {
fn recurse(b: &Bool, stats: &mut Stats) {
match *b {
True | False => {},
Not(ref inner) => recurse(inner, stats),
And(ref v) | Or(ref v) => for inner in v {
recurse(inner, stats)
True | False => stats.ops += 1,
Not(ref inner) => {
match **inner {
And(_) | Or(_) => stats.ops += 1, // brackets are also operations
_ => stats.negations += 1,
}
recurse(inner, stats);
},
Term(n) => stats[n as usize] += 1,
And(ref v) | Or(ref v) => {
stats.ops += v.len() - 1;
for inner in v {
recurse(inner, stats);
}
},
Term(n) => stats.terminals[n as usize] += 1,
}
}
use quine_mc_cluskey::Bool::*;
let mut stats = [0; 32];
let mut stats = Stats::default();
recurse(b, &mut stats);
stats
}
@ -217,40 +233,39 @@ impl<'a, 'tcx> NonminimalBoolVisitor<'a, 'tcx> {
}
simplified.push(simple_negated);
}
if !simplified.iter().any(|s| *s == expr) {
let mut improvements = Vec::new();
'simplified: for suggestion in &simplified {
let simplified_stats = terminal_stats(&suggestion);
let mut improvement = false;
for i in 0..32 {
// ignore any "simplifications" that end up requiring a terminal more often than in the original expression
if stats[i] < simplified_stats[i] {
continue 'simplified;
}
// if the number of occurrences of a terminal doesn't increase, this expression is a candidate for improvement
improvement = true;
if stats[i] != 0 && simplified_stats[i] == 0 {
span_lint_and_then(self.0, LOGIC_BUG, e.span, "this boolean expression contains a logic bug", |db| {
db.span_help(h2q.terminals[i].span, "this expression can be optimized out by applying boolean operations to the outer expression");
db.span_suggestion(e.span, "it would look like the following", suggest(self.0, suggestion, &h2q.terminals));
});
// don't also lint `NONMINIMAL_BOOL`
improvements.clear();
break 'simplified;
}
let mut improvements = Vec::new();
'simplified: for suggestion in &simplified {
let simplified_stats = terminal_stats(&suggestion);
let mut improvement = false;
for i in 0..32 {
// ignore any "simplifications" that end up requiring a terminal more often than in the original expression
if stats.terminals[i] < simplified_stats.terminals[i] {
continue 'simplified;
}
if improvement {
improvements.push(suggestion);
if stats.terminals[i] != 0 && simplified_stats.terminals[i] == 0 {
span_lint_and_then(self.0, LOGIC_BUG, e.span, "this boolean expression contains a logic bug", |db| {
db.span_help(h2q.terminals[i].span, "this expression can be optimized out by applying boolean operations to the outer expression");
db.span_suggestion(e.span, "it would look like the following", suggest(self.0, suggestion, &h2q.terminals));
});
// don't also lint `NONMINIMAL_BOOL`
return;
}
// if the number of occurrences of a terminal decreases or any of the stats decreases while none increases
improvement = (stats.terminals[i] > simplified_stats.terminals[i]) ||
(stats.negations > simplified_stats.negations && stats.ops == simplified_stats.ops) ||
(stats.ops > simplified_stats.ops && stats.negations == simplified_stats.negations);
}
if !improvements.is_empty() {
span_lint_and_then(self.0, NONMINIMAL_BOOL, e.span, "this boolean expression can be simplified", |db| {
for suggestion in &improvements {
db.span_suggestion(e.span, "try", suggest(self.0, suggestion, &h2q.terminals));
}
});
if improvement {
improvements.push(suggestion);
}
}
if !improvements.is_empty() {
span_lint_and_then(self.0, NONMINIMAL_BOOL, e.span, "this boolean expression can be simplified", |db| {
for suggestion in &improvements {
db.span_suggestion(e.span, "try", suggest(self.0, suggestion, &h2q.terminals));
}
});
}
}
}
}