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Auto merge of #123441 - saethlin:fixed-len-file-names, r=oli-obk

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Stabilize the size of incr comp object file names

The current implementation does not produce stable-length paths, and we create the paths in a way that makes our allocation behavior is nondeterministic. I think `@eddyb` fixed a number of other cases like this in the past, and this PR fixes another one. Whether that actually matters I have no idea, but we still have bimodal behavior in rustc-perf and the non-uniformity in `find` and `ls` was bothering me.

I've also removed the truncation of the mangled CGU names. Before this PR incr comp paths look like this:
```
target/debug/incremental/scratch-38izrrq90cex7/s-gux6gz0ow8-1ph76gg-ewe1xj434l26w9up5bedsojpd/261xgo1oqnd90ry5.o
```
And after, they look like this:
```
target/debug/incremental/scratch-035omutqbfkbw/s-gux6borni0-16r3v1j-6n64tmwqzchtgqzwwim5amuga/55v2re42sztc8je9bva6g8ft3.o
```

On the one hand, I'm sure this will break some people's builds because they're on Windows and only a few bytes from the path length limit. But if we're that seriously worried about the length of our file names, I have some other ideas on how to make them smaller. And last time I deleted some hash truncations from the compiler, there was a huge drop in the number if incremental compilation ICEs that were reported: https://github.com/rust-lang/rust/pull/110367https://github.com/rust-lang/rust/pull/110367

---

Upon further reading, this PR actually fixes a bug. This comment says the CGU names are supposed to be a fixed-length hash, and before this PR they aren't: ca7d34efa9/compiler/rustc_monomorphize/src/partitioning.rs (L445-L448)
This commit is contained in:
bors 2024-05-03 17:41:48 +00:00
commit 0d7b2fb797
9 changed files with 146 additions and 71 deletions
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11
compiler/rustc_middle/src/mir/mono.rs
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@ -1,7 +1,9 @@
use crate::dep_graph::{DepNode, WorkProduct, WorkProductId};
use crate::ty::{GenericArgs, Instance, InstanceDef, SymbolName, TyCtxt};
use rustc_attr::InlineAttr;
use rustc_data_structures::base_n;
use rustc_data_structures::base_n::BaseNString;
use rustc_data_structures::base_n::ToBaseN;
use rustc_data_structures::base_n::CASE_INSENSITIVE;
use rustc_data_structures::fingerprint::Fingerprint;
use rustc_data_structures::fx::FxHashMap;
use rustc_data_structures::fx::FxIndexMap;
@ -337,14 +339,11 @@ impl<'tcx> CodegenUnit<'tcx> {
self.is_code_coverage_dead_code_cgu = true;
}
pub fn mangle_name(human_readable_name: &str) -> String {
// We generate a 80 bit hash from the name. This should be enough to
// avoid collisions and is still reasonably short for filenames.
pub fn mangle_name(human_readable_name: &str) -> BaseNString {
let mut hasher = StableHasher::new();
human_readable_name.hash(&mut hasher);
let hash: Hash128 = hasher.finish();
let hash = hash.as_u128() & ((1u128 << 80) - 1);
base_n::encode(hash, base_n::CASE_INSENSITIVE)
hash.as_u128().to_base_fixed_len(CASE_INSENSITIVE)
}
pub fn compute_size_estimate(&mut self) {