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//! Performs a simple taint analysis, to find all live ranges that are reftyped.
use crate::data_structures::{
InstPoint, Map, MoveInfo, MoveInfoElem, RangeFrag, RangeFragIx, RangeId, RealRange,
RealRangeIx, Reg, RegClass, RegToRangesMaps, TypedIxVec, VirtualRange, VirtualRangeIx,
VirtualReg,
};
use crate::sparse_set::{SparseSet, SparseSetU};
use log::debug;
use smallvec::SmallVec;
pub fn do_reftypes_analysis(
// From dataflow/liveness analysis. Modified by setting their is_ref bit.
rlr_env: &mut TypedIxVec<RealRangeIx, RealRange>,
vlr_env: &mut TypedIxVec<VirtualRangeIx, VirtualRange>,
// From dataflow analysis
frag_env: &TypedIxVec<RangeFragIx, RangeFrag>,
reg_to_ranges_maps: &RegToRangesMaps,
move_info: &MoveInfo,
// As supplied by the client
reftype_class: RegClass,
reftyped_vregs: &Vec<VirtualReg>,
) {
// Helper: find the RangeId (RealRange or VirtualRange) for a register at an InstPoint.
let find_range_id_for_reg = |pt: InstPoint, reg: Reg| -> RangeId {
if reg.is_real() {
for &rlrix in ®_to_ranges_maps.rreg_to_rlrs_map[reg.get_index() as usize] {
if rlr_env[rlrix].sorted_frags.contains_pt(frag_env, pt) {
return RangeId::new_real(rlrix);
}
}
} else {
for &vlrix in ®_to_ranges_maps.vreg_to_vlrs_map[reg.get_index() as usize] {
if vlr_env[vlrix].sorted_frags.contains_pt(pt) {
return RangeId::new_virtual(vlrix);
}
}
}
panic!("do_reftypes_analysis::find_range_for_reg: can't find range");
};
// The game here is: starting with `reftyped_vregs`, find *all* the VirtualRanges and
// RealRanges to which refness can flow, via instructions which the client's `is_move`
// function considers to be moves.
// This is done in three stages:
//
// (1) Create a mapping from source (virtual or real) ranges to sets of destination ranges.
// We have `move_info`, which tells us which (virtual or real) regs are connected by
// moves. However, that's not directly useful -- we need to know which *ranges* are
// connected by moves. `move_info` as supplied helpfully indicates both source and
// destination regs and ranges, so we can simply use that.
//
// (2) Similarly, convert `reftyped_vregs` into a set of reftyped ranges by consulting
// `reg_to_ranges_maps`.
//
// (3) Compute the transitive closure of (1) starting from the ranges in (2). This is done
// by a depth first search of the graph implied by (1).
// ====== Compute (1) above ======
// Each entry in `succ` maps from `src` to a `SparseSet<dsts>`, so to speak. That is, for
// `d1`, `d2`, etc, in `dsts`, the function contains moves `d1 := src`, `d2 := src`, etc.
let mut succ = Map::<RangeId, SparseSetU<[RangeId; 4]>>::default();
for &MoveInfoElem { dst, src, iix, .. } in &move_info.moves {
// Don't waste time processing moves which can't possibly be of reftyped values.
debug_assert!(dst.get_class() == src.get_class());
if dst.get_class() != reftype_class {
continue;
}
let src_range = find_range_id_for_reg(InstPoint::new_use(iix), src);
let dst_range = find_range_id_for_reg(InstPoint::new_def(iix), dst);
debug!(
"move from {:?} (range {:?}) to {:?} (range {:?}) at inst {:?}",
src, src_range, dst, dst_range, iix
);
match succ.get_mut(&src_range) {
Some(dst_ranges) => dst_ranges.insert(dst_range),
None => {
// Re `; 4`: we expect most copies copy a register to only a few destinations.
let mut dst_ranges = SparseSetU::<[RangeId; 4]>::empty();
dst_ranges.insert(dst_range);
let r = succ.insert(src_range, dst_ranges);
assert!(r.is_none());
}
}
}
// ====== Compute (2) above ======
let mut reftyped_ranges = SparseSet::<RangeId>::empty();
for vreg in reftyped_vregs {
// If this fails, the client has been telling is that some virtual reg is reftyped, yet
// it doesn't belong to the class of regs that it claims can carry refs. So the client
// is buggy.
debug_assert!(vreg.get_class() == reftype_class);
for vlrix in ®_to_ranges_maps.vreg_to_vlrs_map[vreg.get_index()] {
debug!("range {:?} is reffy due to reffy vreg {:?}", vlrix, vreg);
reftyped_ranges.insert(RangeId::new_virtual(*vlrix));
}
}
// ====== Compute (3) above ======
// Almost all chains of copies will be less than 64 long, I would guess.
let mut stack = SmallVec::<[RangeId; 64]>::new();
let mut visited = reftyped_ranges.clone();
for start_point_range in reftyped_ranges.iter() {
// Perform DFS from `start_point_range`.
stack.clear();
stack.push(*start_point_range);
while let Some(src_range) = stack.pop() {
visited.insert(src_range);
if let Some(dst_ranges) = succ.get(&src_range) {
for dst_range in dst_ranges.iter() {
if !visited.contains(*dst_range) {
stack.push(*dst_range);
}
}
}
}
}
// Finally, annotate rlr_env/vlr_env with the results of the analysis. (That was the whole
// point!)
for range in visited.iter() {
if range.is_real() {
let rrange = &mut rlr_env[range.to_real()];
debug_assert!(!rrange.is_ref);
debug!(" -> rrange {:?} is reffy", range.to_real());
rrange.is_ref = true;
} else {
let vrange = &mut vlr_env[range.to_virtual()];
debug_assert!(!vrange.is_ref);
debug!(" -> rrange {:?} is reffy", range.to_virtual());
vrange.is_ref = true;
}
}
}