By putting an "unreachable" instruction into the default arm of a switch
instruction we can let LLVM know that the match is exhaustive, allowing
for better optimizations.
For example, this match:
```rust
pub enum Enum {
One,
Two,
Three,
}
impl Enum {
pub fn get_disc(self) -> u8 {
match self {
Enum::One => 0,
Enum::Two => 1,
Enum::Three => 2,
}
}
}
```
Currently compiles to this on x86_64:
```asm
.cfi_startproc
movzbl %dil, %ecx
cmpl $1, %ecx
setne %al
testb %cl, %cl
je .LBB0_2
incb %al
movb %al, %dil
.LBB0_2:
movb %dil, %al
retq
.Lfunc_end0:
```
But with this change we get:
```asm
.cfi_startproc
movb %dil, %al
retq
.Lfunc_end0:
```
This was non-obvious to me: with no example, I assumed `Electron {}` and
didn't know what else to try when it didn't work. The correct form is
weird because it looks like you're assigning the struct name rather than
an instance of the struct.
r? @steveklabnik
the example for `find` was misleading in that it fails to mention the result is either `None` or `Some` containing only the first match. Further confusing the issue is the `println!` statement, "We got some numbers!"
As discussed in the referenced issues, this PR makes rustc emit `__imp_<symbol>` stubs for all public static data to ensure smooth linking in on `-windows-msvc` targets.
Resolves#26591, cc #27438
This commit updates the `MatchIndices` and `RMatchIndices` iterators to follow
the same pattern as the `chars` and `char_indices` iterators. The `matches`
iterator currently yield `&str` elements, so the `MatchIndices` iterator now
yields the index of the match as well as the `&str` that matched (instead of
start/end indexes).
cc #27743
This wasn't complete (you need a `./configure`), and it is already
documented well in the main README.
Also adds a reference to the books that this also generates.
This was non-obvious to me: with no example, I assumed `Electron {}` and
didn't know what else to try when it didn't work. The correct form is
weird because it looks like you're assigning the struct name rather than
an instance of the struct.
This adds a new target, `x86_64-rumprun-netbsd`, and related changes to `std`.
Rumprun is a unikernel platform that provides a POSIX-y interface. For the most part, rumprun uses NetBSD's libc and drivers, therefore `target_os` is `netbsd`. However, being a unikernel, rumprun does not support process management, signals or virtual memory, so related functions might fail at runtime. For this reason, stack guards are disabled in `std`.
To support conditional compilation, `target_env` is set to `rumprun`. Maybe `target_vendor` would be technically more fitting, but it doesn't seem to be worth the hassle.
Code for rumprun is always cross-compiled, it uses always static linking and needs a custom linker. The target makes use of the newly introduced `no_default_libs` flag, as the rumprun linker will otherwise not use the correct search path.
Because of type inference, duplicate obligations exist and cause duplicate
errors. To avoid this, only display the first error for each (predicate,span).
The inclusion of the span is somewhat bikesheddy, but *is* the more
conservative option (it does not remove some instability, as duplicate
obligations are ignored by `duplicate_set` under some inference conditions).
Fixes#28098
cc #21528 (is it a dupe?)
the example for `find` was misleading in that it fails to mention the result is either `None` or `Some` containing only the first match. Further confusing the issue is the `println!` statement, "We got some numbers!"
This PR removes random remaining `Ident`s outside of libsyntax and performs general cleanup
In particular, interfaces of `Name` and `Ident` are tidied up, `Name`s and `Ident`s being small `Copy` aggregates are always passed to functions by value, and `Ident`s are never used as keys in maps, because `Ident` comparisons are tricky.
Although this PR closes https://github.com/rust-lang/rust/issues/6993 there's still work related to it:
- `Name` can be made `NonZero` to compress numerous `Option<Name>`s and `Option<Ident>`s but it requires const unsafe functions.
- Implementation of `PartialEq` on `Ident` should be eliminated and replaced with explicit hygienic, non-hygienic or member-wise comparisons.
- Finally, large parts of AST can potentially be converted to `Name`s in the same way as HIR to clearly separate identifiers used in hygienic and non-hygienic contexts.
r? @nrc
For most parts, rumprun currently looks like NetBSD, as they share the same
libc and drivers. However, being a unikernel, rumprun does not support
process management, signals or virtual memory, so related functions
might fail at runtime. Stack guards are disabled exactly for this reason.
Code for rumprun is always cross-compiled, it uses always static
linking and needs a custom linker.
This is mainly to avoid infinite recursion and make debugging more convenient in the anomalous case in which `on_panic` panics.
I encountered such issues while changing libstd to debug/fix part of #28129.
While writing this I was wondering about which functions belong to `panicking` and which to `unwind`.
I placed them in this way mostly because of convenience, but I would strongly appreciate guidance.
This adds a new target property, `target_vendor`. It is to be be used as a matcher for conditional compilation. The vendor is part of the [autoconf target triple](http://llvm.org/docs/doxygen/html/classllvm_1_1Triple.html#details): `<arch><sub>-<vendor>-<os>-<env>`. `arch`, `target_os` and `target_env` are already supported by Rust.
This change was suggested in PR #28593. It enables conditional compilation based on the vendor. This is needed for the rumprun target, which needs to match against both, target_os and target_vendor.
The default value for `target_vendor` is "unknown", "apple" and "pc" are other common values.
Matching against the `target_vendor` is introduced behind the feature gate `#![feature(cfg_target_vendor)]`.
This is the first time I messed around with rustc internals. I just added the my code where I found the existing `target_*` variables, hopefully I haven't missed anything. Please review with care. :)
r? @alexcrichton
