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Auto merge of #113562 - saethlin:larger-incr-comp-offset, r=nnethercote

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Use u64 for incr comp allocation offsets

Fixes https://github.com/rust-lang/rust/issues/76037
Fixes https://github.com/rust-lang/rust/issues/95780
Fixes https://github.com/rust-lang/rust/issues/111613

These issues are all reporting ICEs caused by using `u32` to store offsets to allocations in the incremental compilation cache. This PR aims to lift that limitation by changing the offset type in question to `u64`.

There are two perf runs in this PR. The first reports a regression, and the second does not. The changes are the same in both. I rebased the PR then did the second perf run because I noticed that the primary regression in it was very commonly seen in spurious regression reports.

I do not know what the perf run will report when this is merged. I would not be surprised to see regression or neutral, but the cachegrind diffs for the regression point at `try_mark_previous_green` which is a common source of inexplicable regressions and I don't think should be perturbed by this PR.

I'm not opposed to adding a regression test such as
```rust
fn main() {
    println!("{}", [37; 1 << 30].len());
}
```
But that program takes 1 minute to compile and consumes 4.6 GB of memory then writes that much to disk. Is that a concerning amount of resource use for a test?

r? `@nnethercote`
This commit is contained in:
bors 2023-07-17 04:45:10 +00:00
commit 6f65ef5717
5 changed files with 9 additions and 6 deletions
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6
compiler/rustc_middle/src/query/on_disk_cache.rs
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@ -104,7 +104,9 @@ struct Footer {
query_result_index: EncodedDepNodeIndex,
side_effects_index: EncodedDepNodeIndex,
// The location of all allocations.
interpret_alloc_index: Vec<u32>,
// Most uses only need values up to u32::MAX, but benchmarking indicates that we can use a u64
// without measurable overhead. This permits larger const allocations without ICEing.
interpret_alloc_index: Vec<u64>,
// See `OnDiskCache.syntax_contexts`
syntax_contexts: FxHashMap<u32, AbsoluteBytePos>,
// See `OnDiskCache.expn_data`
@ -301,7 +303,7 @@ impl<'sess> OnDiskCache<'sess> {
interpret_alloc_index.reserve(new_n - n);
for idx in n..new_n {
let id = encoder.interpret_allocs[idx];
let pos: u32 = encoder.position().try_into().unwrap();
let pos: u64 = encoder.position().try_into().unwrap();
interpret_alloc_index.push(pos);
interpret::specialized_encode_alloc_id(&mut encoder, tcx, id);
}