Rework and optimize match MIR generation

[xacrimon]

left to do:

• cleanup
• code comments
• tcx arena strategy
• const eq
• handle non u8 types
• less pricky about prefixes
• also handle slice midsections and suffixes
• probably more?
• tidy
• ci
• tests
• perf improvements?
• handle type changing automatic deref/ref properly
• const eq handling for `user_ty constants in patterns
• more generic const subsequence handling involving bindings or wildcard patterns
• inspect generated mir
• phf? trie? generate an efficient decision tree to decide between patterns?
• and patterns and other things?
• subslicing/indexing bounds & check them so we don't UB
• look at earlier prs?
• reduce code size?
• handle indirect constant patterns
• inspect the mir, are we doing more work than needed? can we generate match trees in a better way? sorting?
• fix duplicated slice eq arms
• tests?

example code:

use std::{num::NonZero, ffi::CStr};constSTANDARD_BASE:&[u8] = b"org.freedesktop.DBus.Error.";#[no_mangle]pub(crate)fnto_errno(s:&CStr) -> Option<NonZero<i32>>{let(pfx, sfx) = s.to_bytes().split_at_checked(STANDARD_BASE.len())?;if pfx != STANDARD_BASE{returnNone;}match sfx {b"NoMemory" => NonZero::new(1),b"ServiceUnknown" | b"UnknownObject" | b"UnknownInterface" | b"UnknownMethod"
| b"UnknownProperty" | b"NameHasNoOwner" => NonZero::new(18),b"AccessDenied" | b"AuthFailed" | b"InteractiveAuthorizationRequired" => {NonZero::new(1245)}b"LimitsExceeded" => NonZero::new(9),b"Timeout" | b"TimedOut" => NonZero::new(420),b"UnixProcessIdUnknown" => NonZero::new(69),b"NotSupported" => NonZero::new(228),b"IOError" | b"NoNetwork" | b"AddressInUse" => NonZero::new(100500),
_ => None,}}

duplicate arms example

#[no_mangle]pub(crate)fnhas_magic(s:&[u8]) -> bool{matches!(
s,[b'm',b'a',b'g',b'i',b'c', ..,b'e',b'n',b'd']
| [b's',b't',b'a',b'r',b't', ..,b'e',b'n',b'd'])}

without this patch: mir and aarch64asm,opt-level=3
with this patch: mir and aarch64asm,opt-level=3

note to self: should probably be looked at by compiler-errors and scottmcm, oli?

[rustbot]

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[xacrimon]

r? @ghost

[rustbot]

Failed to set assignee to ghost: invalid assignee

Note: Only org members with at least the repository "read" role, users with write permissions, or people who have commented on the PR may be assigned.

[bors]

☔ The latest upstream changes (presumably #136227) made this pull request unmergeable. Please resolve the merge conflicts.

[xacrimon]

@rustbot label +S-waiting-on-author -S-waiting-on-review

[rust-log-analyzer]

The job x86_64-gnu-tools failed! Check out the build log: (web)(plain)

Click to see the possible cause of the failure (guessed by this bot)

 Compiling rustc_codegen_llvm v0.0.0 (/checkout/compiler/rustc_codegen_llvm)
error[E0023]: this pattern has 2 fields, but the corresponding tuple variant has 1 field
--> compiler/rustc_mir_build/src/builder/matches/match_pair.rs:170:41
|
170 | && let ty::ConstKind::Value(_, valtree) = const_.kind()
| ^ ^^^^^^^ expected 1 field, found 2
::: /checkout/compiler/rustc_type_ir/src/const_kind.rs:34:11
|
34 | Value(I::ValueConst),
| ------------- tuple variant has 1 field
| ------------- tuple variant has 1 field
error[E0023]: this pattern has 2 fields, but the corresponding tuple variant has 1 field
--> compiler/rustc_mir_build/src/builder/matches/match_pair.rs:182:41
|
182 | && let ty::ConstKind::Value(_, valtree) = const_.kind()
| ^ ^^^^^^^ expected 1 field, found 2
::: /checkout/compiler/rustc_type_ir/src/const_kind.rs:34:11
|
34 | Value(I::ValueConst),
| ------------- tuple variant has 1 field
| ------------- tuple variant has 1 field
error[E0061]: this enum variant takes 1 argument but 2 arguments were supplied
--> compiler/rustc_mir_build/src/builder/matches/match_pair.rs:214:44
|
214 | let ty_const = ty::Const::new(tcx, ty::ConstKind::Value(const_ty, valtree));
| ^^^^^^^^^^^^^^^^^^^^ -------- ------- unexpected argument #2 of type `ValTree<'tcx>`
| expected `Value<'_>`, found `Ty<'_>`
|
note: tuple variant defined here
--> /checkout/compiler/rustc_type_ir/src/const_kind.rs:34:5
--> /checkout/compiler/rustc_type_ir/src/const_kind.rs:34:5
|
34 | Value(I::ValueConst),
| ^^^^^
help: remove the extra argument
|
214 - let ty_const = ty::Const::new(tcx, ty::ConstKind::Value(const_ty, valtree));
214 + let ty_const = ty::Const::new(tcx, ty::ConstKind::Value(/* rustc_middle::ty::Value<'_> */));
Some errors have detailed explanations: E0023, E0061.
For more information about an error, try `rustc --explain E0023`.
error: could not compile `rustc_mir_build` (lib) due to 3 previous errors

[xacrimon]

Closing in favour of #136417