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Auto merge of #113166 - moulins:ref-niches-initial, r=oli-obk

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Prototype: Add unstable `-Z reference-niches` option

MCP: rust-lang/compiler-team#641
Relevant RFC: rust-lang/rfcs#3204

This prototype adds a new `-Z reference-niches` option, controlling the range of valid bit-patterns for reference types (`&T` and `&mut T`), thereby enabling new enum niching opportunities. Like `-Z randomize-layout`, this setting is crate-local; as such, references to built-in types (primitives, tuples, ...) are not affected.

The possible settings are (here, `MAX` denotes the all-1 bit-pattern):
| `-Z reference-niches=` | Valid range |
|:---:|:---:|
| `null` (the default) | `1..=MAX` |
| `size` | `1..=(MAX- size)` |
| `align` | `align..=MAX.align_down_to(align)` |
| `size,align` | `align..=(MAX-size).align_down_to(align)` |

------

This is very WIP, and I'm not sure the approach I've taken here is the best one, but stage 1 tests pass locally; I believe this is in a good enough state to unleash this upon unsuspecting 3rd-party code, and see what breaks.
This commit is contained in:
bors 2023-07-21 15:00:36 +00:00
commit 557359f925
48 changed files with 1067 additions and 296 deletions
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2
compiler/rustc_interface/src/tests.rs
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@ -28,6 +28,7 @@ use rustc_span::edition::{Edition, DEFAULT_EDITION};
use rustc_span::symbol::sym;
use rustc_span::FileName;
use rustc_span::SourceFileHashAlgorithm;
use rustc_target::abi::ReferenceNichePolicy;
use rustc_target::spec::{CodeModel, LinkerFlavorCli, MergeFunctions, PanicStrategy, RelocModel};
use rustc_target::spec::{RelroLevel, SanitizerSet, SplitDebuginfo, StackProtector, TlsModel};
@ -820,6 +821,7 @@ fn test_unstable_options_tracking_hash() {
tracked!(profile_emit, Some(PathBuf::from("abc")));
tracked!(profile_sample_use, Some(PathBuf::from("abc")));
tracked!(profiler_runtime, "abc".to_string());
tracked!(reference_niches, Some(ReferenceNichePolicy { size: true, align: false }));
tracked!(relax_elf_relocations, Some(true));
tracked!(relro_level, Some(RelroLevel::Full));
tracked!(remap_cwd_prefix, Some(PathBuf::from("abc")));