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nak: Fix repair_ssa() for back-edges

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In the presence of nested loops, there is no guarantee that we can
handle back-edges in a single pass.  Instead, use a bitset as a worlist
and repair until we're out of missing sources.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24998>
This commit is contained in:
Faith Ekstrand 2023-10-08 20:50:29 -05:00 • committed by Marge Bot
parent 5839be3c4d
commit 2ff6a36e2a
1 changed files with 31 additions and 8 deletions
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39
src/nouveau/compiler/nak_repair_ssa.rs
View file

@ -1,6 +1,7 @@
// Copyright © 2023 Collabora, Ltd.
// SPDX-License-Identifier: MIT
use crate::bitset::BitSet;
use crate::nak_ir::*;
use std::cell::RefCell;
@ -24,6 +25,7 @@ fn get_ssa_or_phi(
ssa_alloc: &mut SSAValueAllocator,
phi_alloc: &mut PhiAllocator,
blocks: &[DefTrackerBlock],
needs_src: &mut BitSet,
b_idx: usize,
ssa: SSAValue,
) -> SSAValue {
@ -41,8 +43,9 @@ fn get_ssa_or_phi(
// it later if it's not needed
all_same = false;
} else {
let p_ssa =
get_ssa_or_phi(ssa_alloc, phi_alloc, blocks, *p_idx, ssa);
let p_ssa = get_ssa_or_phi(
ssa_alloc, phi_alloc, blocks, needs_src, *p_idx, ssa,
);
if *pred_ssa.get_or_insert(p_ssa) != p_ssa {
all_same = false;
}
@ -64,6 +67,7 @@ fn get_ssa_or_phi(
};
for p_idx in &b.pred {
if *p_idx >= b_idx {
needs_src.insert(*p_idx);
continue;
}
// The earlier recursive call ensured this exists
@ -164,6 +168,7 @@ impl Function {
let phi_alloc = &mut self.phi_alloc;
let mut blocks = Vec::new();
let mut needs_src = BitSet::new();
for b_idx in 0..cfg.len() {
assert!(blocks.len() == b_idx);
blocks.push(DefTrackerBlock {
@ -177,7 +182,12 @@ impl Function {
instr.for_each_ssa_use_mut(|ssa| {
if num_defs.get(ssa).cloned().unwrap_or(0) > 1 {
*ssa = get_ssa_or_phi(
ssa_alloc, phi_alloc, &blocks, b_idx, *ssa,
ssa_alloc,
phi_alloc,
&blocks,
&mut needs_src,
b_idx,
*ssa,
);
}
});
@ -190,8 +200,15 @@ impl Function {
}
});
}
}
// Populate phi sources for any back-edges
loop {
let Some(b_idx) = needs_src.next_set(0) else {
break;
};
needs_src.remove(b_idx);
// Populate phi sources for any back-edges
for s_idx in &blocks[b_idx].succ {
if *s_idx <= b_idx {
let s = &blocks[*s_idx];
@ -202,10 +219,16 @@ impl Function {
// set for s and so no new phis should need to be added.
// RefCell's dynamic borrow checks will assert this.
for phi in s.phis.borrow_mut().iter_mut() {
let b_ssa = get_ssa_or_phi(
ssa_alloc, phi_alloc, &blocks, b_idx, phi.orig,
);
phi.srcs.insert(b_idx, b_ssa);
phi.srcs.entry(b_idx).or_insert_with(|| {
get_ssa_or_phi(
ssa_alloc,
phi_alloc,
&blocks,
&mut needs_src,
b_idx,
phi.orig,
)
});
}
}
}