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Keep dead EBB arguments around in LiveValueTracker::ebb_top().

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Provide a drop_dead_args() function which deletes them instead.

We still need to assign a register to dead EBB arguments, so they can't
just be ignored.
This commit is contained in:
Jakob Stoklund Olesen
2017-05-11 11:25:35 -07:00
parent 2c0d4136b0
commit 94944d2057
3 changed files with 46 additions and 12 deletions
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40
lib/cretonne/src/regalloc/live_value_tracker.rs
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@@ -7,7 +7,7 @@
use dominator_tree::DominatorTree;
use entity_list::{EntityList, ListPool};
use ir::instructions::BranchInfo;
use ir::{Inst, Ebb, Value, DataFlowGraph, ProgramOrder, ExpandedProgramPoint};
use ir::{Inst, Ebb, Value, DataFlowGraph, Layout, ExpandedProgramPoint};
use partition_slice::partition_slice;
use regalloc::affinity::Affinity;
use regalloc::liveness::Liveness;
@@ -116,6 +116,12 @@ impl LiveValueVec {
let keep = self.live_after(next_inst);
self.values.truncate(keep);
}
/// Remove any dead values.
fn remove_dead_values(&mut self) {
self.values.retain(|v| !v.is_dead);
self.live_prefix = None;
}
}
impl LiveValueTracker {
@@ -150,14 +156,15 @@ impl LiveValueTracker {
///
/// Returns `(liveins, args)` as a pair of slices. The first slice is the set of live-in values
/// from the immediate dominator. The second slice is the set of `ebb` arguments that are live.
/// Dead arguments with no uses are ignored and not added to the set.
pub fn ebb_top<PO: ProgramOrder>(&mut self,
ebb: Ebb,
dfg: &DataFlowGraph,
liveness: &Liveness,
program_order: &PO,
domtree: &DominatorTree)
-> (&[LiveValue], &[LiveValue]) {
///
/// Dead arguments with no uses are included in `args`. Call `drop_dead_args()` to remove them.
pub fn ebb_top(&mut self,
ebb: Ebb,
dfg: &DataFlowGraph,
liveness: &Liveness,
layout: &Layout,
domtree: &DominatorTree)
-> (&[LiveValue], &[LiveValue]) {
// Start over, compute the set of live values at the top of the EBB from two sources:
//
// 1. Values that were live before `ebb`'s immediate dominator, filtered for those that are
@@ -183,7 +190,7 @@ impl LiveValueTracker {
.expect("Immediate dominator value has no live range");
// Check if this value is live-in here.
if let Some(endpoint) = lr.livein_local_end(ebb, program_order) {
if let Some(endpoint) = lr.livein_local_end(ebb, layout) {
self.live.push(value, endpoint, lr);
}
}
@@ -202,10 +209,14 @@ impl LiveValueTracker {
}
ExpandedProgramPoint::Ebb(local_ebb) => {
// This is a dead EBB argument which is not even live into the first
// instruction in the EBB. We can ignore it.
// instruction in the EBB.
assert_eq!(local_ebb,
ebb,
"EBB argument live range ends at wrong EBB header");
// Give this value a fake endpoint that is the first instruction in the EBB.
// We expect it to be removed by calling `drop_dead_args()`.
self.live
.push(value, layout.first_inst(ebb).expect("Empty EBB"), lr);
}
}
}
@@ -281,6 +292,13 @@ impl LiveValueTracker {
self.live.remove_kill_values(inst);
}
/// Drop any values that are marked as `is_dead`.
///
/// Use this after calling `ebb_top` to clean out dead EBB arguments.
pub fn drop_dead_args(&mut self) {
self.live.remove_dead_values();
}
/// Save the current set of live values so it is associated with `idom`.
fn save_idom_live_set(&mut self, idom: Inst) {
let values = self.live.values.iter().map(|lv| lv.value);