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Rollup of 9 pull requests #78362

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r? @ghost

Jonas Schievink and others added 30 commits October 19, 2020 16:37
This allows us to use the C++ compiler configured via
`CXX_target_triple` env vars
This allows moving a lot of run-make-fulldeps tests to just run-make
tests, and allows running those on target-only platforms
Somewhat hacky to reuse `tools.mk` like this, we should probably migrate
most of them now
Writing any fmt::Arguments would trigger the inclusion of usize
formatting and padding code in the resulting binary, because indexing
used in fmt::write would generate code using panic_bounds_check, which
prints the index and length.

These bounds checks are not necessary, as fmt::Arguments never contains
any out-of-bounds indexes.

This change replaces them with unsafe get_unchecked, to reduce the
amount of generated code, which is especially important for embedded
targets.
It checks that fmt::write by itself doesn't pull in any panicking or
or display code.
Prior to this commit, debuginfo was always generated by mapping a name
to a Place. This has the side-effect that `SimplifyLocals` cannot remove
locals that are only used for debuginfo because their other uses have
been const-propagated.

To allow these locals to be removed, we now allow debuginfo to point to
a constant value. The `ConstProp` pass detects when debuginfo points to
a local with a known constant value and replaces it with the value. This
allows the later `SimplifyLocals` pass to remove the local.
Co-authored-by: BlackHoleFox <blackholefoxdev@gmail.com>
…oli-obk

[mir-opt] Allow debuginfo to be generated for a constant or a Place

Prior to this commit, debuginfo was always generated by mapping a name
to a Place. This has the side-effect that `SimplifyLocals` cannot remove
locals that are only used for debuginfo because their other uses have
been const-propagated.

To allow these locals to be removed, we now allow debuginfo to point to
a constant value. The `ConstProp` pass detects when debuginfo points to
a local with a known constant value and replaces it with the value. This
allows the later `SimplifyLocals` pass to remove the local.
…, r=Mark-Simulacrum

Unignore test for rust-lang#36710 on MUSL

This now works fine thanks to autodetected `-C link-self-contained`.

Closes rust-lang#36710
…bounds-check, r=dtolnay

Avoid panic_bounds_check in fmt::write.

Writing any fmt::Arguments would trigger the inclusion of usize formatting and padding code in the resulting binary, because indexing used in fmt::write would generate code using panic_bounds_check, which prints the index and length.

These bounds checks are not necessary, as fmt::Arguments never contains any out-of-bounds indexes.

This change replaces them with unsafe get_unchecked, to reduce the amount of generated code, which is especially important for embedded targets.

---

Demonstration of the size of and the symbols in a 'hello world' no_std binary:

<details>
<summary>Source code</summary>

```rust
#![feature(lang_items)]
#![feature(start)]
#![no_std]

use core::fmt;
use core::fmt::Write;

#[link(name = "c")]
extern "C" {
    #[allow(improper_ctypes)]
    fn write(fd: i32, s: &str) -> isize;
    fn exit(code: i32) -> !;
}

struct Stdout;

impl fmt::Write for Stdout {
    fn write_str(&mut self, s: &str) -> fmt::Result {
        unsafe { write(1, s) };
        Ok(())
    }
}

#[start]
fn main(_argc: isize, _argv: *const *const u8) -> isize {
    let _ = writeln!(Stdout, "Hello World");
    0
}

#[lang = "eh_personality"]
fn eh_personality() {}

#[panic_handler]
fn panic(_: &core::panic::PanicInfo) -> ! {
    unsafe { exit(1) };
}
```
</details>

Before:
```
   text	   data	    bss	    dec	    hex	filename
   6059	    736	      8	   6803	   1a93	before
```
```
0000000000001e00 T <T as core::any::Any>::type_id
0000000000003dd0 D core::fmt::num::DEC_DIGITS_LUT
0000000000001ce0 T core::fmt::num::imp::<impl core::fmt::Display for u64>::fmt
0000000000001ce0 T core::fmt::num::imp::<impl core::fmt::Display for usize>::fmt
0000000000001370 T core::fmt::write
0000000000001b30 t core::fmt::Formatter::pad_integral::write_prefix
0000000000001660 T core::fmt::Formatter::pad_integral
0000000000001350 T core::ops::function::FnOnce::call_once
0000000000001b80 t core::ptr::drop_in_place
0000000000001120 t core::ptr::drop_in_place
0000000000001c50 t core::iter::adapters::zip::Zip<A,B>::new
0000000000001c90 t core::iter::adapters::zip::Zip<A,B>::new
0000000000001b90 T core::panicking::panic_bounds_check
0000000000001c10 T core::panicking::panic_fmt
0000000000001130 t <&mut W as core::fmt::Write>::write_char
0000000000001200 t <&mut W as core::fmt::Write>::write_fmt
0000000000001250 t <&mut W as core::fmt::Write>::write_str
```

After:
```
   text	   data	    bss	    dec	    hex	filename
   3068	    600	      8	   3676	    e5c	after
```
```
0000000000001360 T core::fmt::write
0000000000001340 T core::ops::function::FnOnce::call_once
0000000000001120 t core::ptr::drop_in_place
0000000000001620 t core::iter::adapters::zip::Zip<A,B>::new
0000000000001660 t core::iter::adapters::zip::Zip<A,B>::new
0000000000001130 t <&mut W as core::fmt::Write>::write_char
0000000000001200 t <&mut W as core::fmt::Write>::write_fmt
0000000000001250 t <&mut W as core::fmt::Write>::write_str
```
Miri engine: entirely skip interning of ZST, and improve some comments

r? `@oli-obk`
Tweak match arm semicolon removal suggestion to account for futures

* Tweak and extend "use `.await`" suggestions
* Suggest removal of semicolon on prior match arm
* Account for `impl Future` when suggesting semicolon removal
* Silence some errors when encountering `await foo()?` as can't be certain what the intent was

*Thanks to https://twitter.com/a_hoverbear/status/1318960787105353728 for pointing this out!*
…, r=m-ou-se

Capture output from threads spawned in tests

This is revival of rust-lang#75172.

Original text:
> Fixes rust-lang#42474.
>
> r? `@dtolnay` since you expressed interest in this, but feel free to redirect if you aren't the right person anymore.

---

Closes rust-lang#75172.
Do not try to report on closures to avoid ICE

Fixes rust-lang#78262
Make some functions private that don't have to be public

r? @GuillaumeGomez
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