[MIR] Deaggregate structs to enable further optimizations
Currently, we generate MIR like:
```
tmp0 = ...;
tmp1 = ...;
tmp3 = Foo { a: ..., b: ... };
```
This PR implements "deaggregation," i.e.:
```
tmp3.0 = ...
tmp3.1 = ...
```
Currently, the code only deaggregates structs, not enums. My understanding is that we do not have MIR to set the discriminant of an enum.
Properly enforce the "patterns aren't allowed in foreign functions" rule
Cases like `arg @ PATTERN` or `mut arg` were missing.
Apply the same rule to function pointer types.
Closes https://github.com/rust-lang/rust/issues/35203
[breaking-change], no breakage in sane code is expected though
r? @nikomatsakis
This is somewhat related to https://github.com/rust-lang/rfcs/pull/1685 (cc @matklad).
The goal is to eventually support full pattern syntax where it makes sense (function body may present) and to support *only* the following forms - `TYPE`, `ident: TYPE`, `_: TYPE` - where patterns don't make sense (function body doesn't present), i.e. in foreign functions and function pointer types.
Support removed LLVM intrinsics by invoking its AutoUpgrade mechanism.
Turns out that LLVM sometimes renames platform intrinsics or replaces them with first-class instructions.
For example, signed minimum became `select (icmp SLT, a, b), a, b` where `a` and `b` are vectors.
This is blocking the Servo rustup ([relevant failure](http://build.servo.org/builders/windows-dev/builds/226/steps/compile/logs/stdio)), as they're using a few such intrinsics.
The fix in this PR is to invoke LLVM's own `AutoUpgrade` mechanism to do the replacements.
Add -mrelax-relocations=no hacks to fix musl build
* this is just a start, dunno if it will work, but I'll just push it out to get feedback (my rust is still building 😢)
* I don't know much about rustbuild, so i just added that flag in there. it's a total hack, don't judge me
* I suspect the places in the musl .mk files are sufficient (but we may also need it present when building std), I'm not sure, needs more testing.
core: fix `cargo build` for targets with "max-atomic-width": 0
This crate was failing to compile due to dead_code/unused_imports
warnings. This commits disables these two lints for these targets.
---
r? @alexcrichton
cc @Amanieu is `cfg(target_has_atomic = "8")` the right `cfg` to use? I think that all targets that support some form of atomics will at a minimum support byte level atomics.
FWIW, the only thing that's left in `sync::atomic` for these targets is `Ordering` and the `fence` function.
rustc_trans: don't lose the cross-crate DefId, MIR trans needs it.
We might have been missing out on some issues because MIR trans was never being used cross-crate.
cc @rust-lang/compiler
Switch to MIR-based translation by default.
This patch makes `-Z orbit` default to "on", which means that by default, functions will be translated from Rust to LLVM IR through the upcoming MIR backend, instead of the antiquated AST backend.
This switch is made possible by the recently merged #33622, #33905 and smaller fixes.
If you experience any issues, please file a report for each of them. You can switch to the old backend to work around problems by either setting `RUSTFLAGS="-Zorbit=off"` or by annotating specific functions with `#[rustc_no_mir]` (which requires `#![feature(rustc_attrs)]` at the crate-level).
I would like this PR to get into nightly soon so that we can get early feedback in this release cycle and focus on correctness fixes and performance improvements, with the potential for removing the old backend implementation before beta branches off.
cc @rust-lang/compiler
