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Avoid generating consecutive assignments to the same place #12

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Avoid generating consecutive assignments to the same place #12

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26 changes: 23 additions & 3 deletions generate/src/generation/mod.rs
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Original file line number Diff line number Diff line change
@@ -1,5 +1,6 @@
mod intrinsics;

use std::cell::Cell;
use std::cell::RefCell;
use std::rc::Rc;
use std::{cmp, fmt, vec};
Expand Down Expand Up @@ -66,6 +67,7 @@ pub struct GenerationCtx {
saved_ctx: Vec<SavedCtx>,
cursor: Cursor,
config: GenerationConfig,
previous_lhs: Cell<Option<Place>>,
}

// Operand
Expand Down Expand Up @@ -448,21 +450,37 @@ impl GenerationCtx {
// Statement
impl GenerationCtx {
fn generate_assign(&self) -> Result<Statement> {
let (lhs_choices, weights) = PlaceSelector::for_lhs(self.tcx.clone())
let (lhs_choices, mut weights) = PlaceSelector::for_lhs(self.tcx.clone())
.into_weighted(&self.pt)
.ok_or(SelectionError::Exhausted)?;

self.make_choice_weighted(lhs_choices.into_iter(), weights, |ppath| {
if let Some(prev) = self.previous_lhs.take() {
for (i, choice) in lhs_choices.iter().enumerate() {
let choice = choice.to_place(&self.pt);
if choice == prev {
weights
.update_weights(&[(i, &0)])
.map_err(|_| SelectionError::Exhausted)?;
break;
}
}
}

let stmt = self.make_choice_weighted(lhs_choices.into_iter(), weights, |ppath| {
let lhs = ppath.to_place(&self.pt);
trace!(
"generating an assignment statement with lhs {}: {}",
lhs.serialize_place(&self.tcx),
lhs.ty(self.current_decls(), &self.tcx).serialize(&self.tcx)
);

self.previous_lhs.set(Some(lhs.clone()));

let statement = Statement::Assign(lhs.clone(), self.generate_rvalue(&lhs)?);
Ok(statement)
})
});

stmt
}

// Hack to take &self
Expand Down Expand Up @@ -919,6 +937,7 @@ impl GenerationCtx {

/// Terminates the current BB, and moves the generation context to the new BB
fn choose_terminator(&mut self) -> bool {
self.previous_lhs.set(None);
assert!(matches!(self.current_bb().terminator(), Terminator::Hole));
if self.pt.can_return() {
if Place::RETURN_SLOT.complexity(&self.pt) > 10
Expand Down Expand Up @@ -1202,6 +1221,7 @@ impl GenerationCtx {
},
saved_ctx: vec![],
config: config.generation,
previous_lhs: Cell::new(None),
}
}

Expand Down