Stabilize saturating_abs and saturating_neg

Stabilizes the following signed integer functions with saturation mechanics:
 * saturating_abs()
 * saturating_neg()

Closes rust-lang#59983

correctly handle uninferred consts

fixes the ICE mentioned in rust-lang#70507 (comment)

I originally tried to generalize `need_type_info_err` to also work with consts which was not as much fun as I hoped 😅

It might be easier to have some duplication here and handle consts separately.

r? @varkor

Ignore arguments when looking for `IndexMut` for subsequent `mut` obligation

Given code like `v[&field].boo();` where `field: String` and
`.boo(&mut self)`, typeck will have decided that `v` is accessed using
`Index`, but when `boo` adds a new `mut` obligation,
`convert_place_op_to_mutable` is called. When this happens, for *some
reason* the arguments' dereference adjustments are completely ignored
causing an error saying that `IndexMut` is not satisfied:

```
error[E0596]: cannot borrow data in an index of `Indexable` as mutable
  --> src/main.rs:30:5
   |
30 |     v[&field].boo();
   |     ^^^^^^^^^ cannot borrow as mutable
   |
   = help: trait `IndexMut` is required to modify indexed content, but it is not implemented for `Indexable`
```

This is not true, but by changing `try_overloaded_place_op` to retry
when given `Needs::MutPlace` without passing the argument types, the
example successfully compiles.

I believe there might be more appropriate ways to deal with this.

Fix rust-lang#72002.

…c-morse

Fix ICE in -Zsave-analysis

Puts a short-circuit in to avoid an ICE in `-Zsave-analysis`.

r? @ecstatic-morse

Resolves rust-lang#72267

Assert doc wording

The current wording implies unsafe code is dependent on assert:

https://users.rust-lang.org/t/are-assert-statements-included-in-unsafe-blocks/42865

Rollup of 5 pull requests

Successful merges:

 - rust-lang#71886 (Stabilize saturating_abs and saturating_neg)
 - rust-lang#72066 (correctly handle uninferred consts)
 - rust-lang#72068 (Ignore arguments when looking for `IndexMut` for subsequent `mut` obligation)
 - rust-lang#72338 (Fix ICE in -Zsave-analysis)
 - rust-lang#72344 (Assert doc wording)

Failed merges:

r? @ghost

…nieu

Tiny Vecs are dumb.

Currently, if you repeatedly push to an empty vector, the capacity
growth sequence is 0, 1, 2, 4, 8, 16, etc. This commit changes the
relevant code (the "amortized" growth strategy) to skip 1 and 2, instead
using 0, 4, 8, 16, etc. (You can still get a capacity of 1 or 2 using
the "exact" growth strategy, e.g. via `reserve_exact()`.)

This idea (along with the phrase "tiny Vecs are dumb") comes from the
"doubling" growth strategy that was removed from `RawVec` in rust-lang#72013.
That strategy was barely ever used -- only when a `VecDeque` was grown,
oddly enough -- which is why it was removed in rust-lang#72013.

(Fun fact: until just a few days ago, I thought the "doubling" strategy
was used for repeated push case. In other words, this commit makes
`Vec`s behave the way I always thought they behaved.)

This change reduces the number of allocations done by rustc itself by
10% or more. It speeds up rustc, and will also speed up any other Rust
program that uses `Vec`s a lot.

In theory, the change could increase memory usage, but in practice it
doesn't. It would be an unusual program where very small `Vec`s having a
capacity of 4 rather than 1 or 2 would make a difference. You'd need a
*lot* of very small `Vec`s, and/or some very small `Vec`s with very
large elements.

r? @Amanieu

Implement new asm! syntax from RFC 2850

This PR implements the new `asm!` syntax proposed in rust-lang/rfcs#2850.

# Design

A large part of this PR revolves around taking an `asm!` macro invocation and plumbing it through all of the compiler layers down to LLVM codegen. Throughout the various stages, an `InlineAsm` generally consists of 3 components:

- The template string, which is stored as an array of `InlineAsmTemplatePiece`. Each piece represents either a literal or a placeholder for an operand (just like format strings).
```rust
pub enum InlineAsmTemplatePiece {
    String(String),
    Placeholder { operand_idx: usize, modifier: Option<char>, span: Span },
}
```

- The list of operands to the `asm!` (`in`, `[late]out`, `in[late]out`, `sym`, `const`). These are represented differently at each stage of lowering, but follow a common pattern:
  - `in`, `out` and `inout` all have an associated register class (`reg`) or explicit register (`"eax"`).
  - `inout` has 2 forms: one with a single expression that is both read from and written to, and one with two separate expressions for the input and output parts.
  - `out` and `inout` have a `late` flag (`lateout` / `inlateout`) to indicate that the register allocator is allowed to reuse an input register for this output.
  - `out` and the split variant of `inout` allow `_` to be specified for an output, which means that the output is discarded. This is used to allocate scratch registers for assembly code.
  - `sym` is a bit special since it only accepts a path expression, which must point to a `static` or a `fn`.

- The options set at the end of the `asm!` macro. The only one that is particularly of interest to rustc is `NORETURN` which makes `asm!` return `!` instead of `()`.
```rust
bitflags::bitflags! {
    pub struct InlineAsmOptions: u8 {
        const PURE = 1 << 0;
        const NOMEM = 1 << 1;
        const READONLY = 1 << 2;
        const PRESERVES_FLAGS = 1 << 3;
        const NORETURN = 1 << 4;
        const NOSTACK = 1 << 5;
    }
}
```

## AST

`InlineAsm` is represented as an expression in the AST:

```rust
pub struct InlineAsm {
    pub template: Vec<InlineAsmTemplatePiece>,
    pub operands: Vec<(InlineAsmOperand, Span)>,
    pub options: InlineAsmOptions,
}

pub enum InlineAsmRegOrRegClass {
    Reg(Symbol),
    RegClass(Symbol),
}

pub enum InlineAsmOperand {
    In {
        reg: InlineAsmRegOrRegClass,
        expr: P<Expr>,
    },
    Out {
        reg: InlineAsmRegOrRegClass,
        late: bool,
        expr: Option<P<Expr>>,
    },
    InOut {
        reg: InlineAsmRegOrRegClass,
        late: bool,
        expr: P<Expr>,
    },
    SplitInOut {
        reg: InlineAsmRegOrRegClass,
        late: bool,
        in_expr: P<Expr>,
        out_expr: Option<P<Expr>>,
    },
    Const {
        expr: P<Expr>,
    },
    Sym {
        expr: P<Expr>,
    },
}
```

The `asm!` macro is implemented in librustc_builtin_macros and outputs an `InlineAsm` AST node. The template string is parsed using libfmt_macros, positional and named operands are resolved to explicit operand indicies. Since target information is not available to macro invocations, validation of the registers and register classes is deferred to AST lowering.

## HIR

`InlineAsm` is represented as an expression in the HIR:

```rust
pub struct InlineAsm<'hir> {
    pub template: &'hir [InlineAsmTemplatePiece],
    pub operands: &'hir [InlineAsmOperand<'hir>],
    pub options: InlineAsmOptions,
}

pub enum InlineAsmRegOrRegClass {
    Reg(InlineAsmReg),
    RegClass(InlineAsmRegClass),
}

pub enum InlineAsmOperand<'hir> {
    In {
        reg: InlineAsmRegOrRegClass,
        expr: Expr<'hir>,
    },
    Out {
        reg: InlineAsmRegOrRegClass,
        late: bool,
        expr: Option<Expr<'hir>>,
    },
    InOut {
        reg: InlineAsmRegOrRegClass,
        late: bool,
        expr: Expr<'hir>,
    },
    SplitInOut {
        reg: InlineAsmRegOrRegClass,
        late: bool,
        in_expr: Expr<'hir>,
        out_expr: Option<Expr<'hir>>,
    },
    Const {
        expr: Expr<'hir>,
    },
    Sym {
        expr: Expr<'hir>,
    },
}
```

AST lowering is where `InlineAsmRegOrRegClass` is converted from `Symbol`s to an actual register or register class. If any modifiers are specified for a template string placeholder, these are validated against the set allowed for that operand type. Finally, explicit registers for inputs and outputs are checked for conflicts (same register used for different operands).

## Type checking

Each register class has a whitelist of types that it may be used with. After the types of all operands have been determined, the `intrinsicck` pass will check that these types are in the whitelist. It also checks that split `inout` operands have compatible types and that `const` operands are integers or floats. Suggestions are emitted where needed if a template modifier should be used for an operand based on the type that was passed into it.

## HAIR

`InlineAsm` is represented as an expression in the HAIR:

```rust
crate enum ExprKind<'tcx> {
    // [..]
    InlineAsm {
        template: &'tcx [InlineAsmTemplatePiece],
        operands: Vec<InlineAsmOperand<'tcx>>,
        options: InlineAsmOptions,
    },
}
crate enum InlineAsmOperand<'tcx> {
    In {
        reg: InlineAsmRegOrRegClass,
        expr: ExprRef<'tcx>,
    },
    Out {
        reg: InlineAsmRegOrRegClass,
        late: bool,
        expr: Option<ExprRef<'tcx>>,
    },
    InOut {
        reg: InlineAsmRegOrRegClass,
        late: bool,
        expr: ExprRef<'tcx>,
    },
    SplitInOut {
        reg: InlineAsmRegOrRegClass,
        late: bool,
        in_expr: ExprRef<'tcx>,
        out_expr: Option<ExprRef<'tcx>>,
    },
    Const {
        expr: ExprRef<'tcx>,
    },
    SymFn {
        expr: ExprRef<'tcx>,
    },
    SymStatic {
        expr: ExprRef<'tcx>,
    },
}
```

The only significant change compared to HIR is that `Sym` has been lowered to either a `SymFn` whose `expr` is a `Literal` ZST of the `fn`, or a `SymStatic` whose `expr` is a `StaticRef`.

## MIR

`InlineAsm` is represented as a `Terminator` in the MIR:

```rust
pub enum TerminatorKind<'tcx> {
    // [..]

    /// Block ends with an inline assembly block. This is a terminator since
    /// inline assembly is allowed to diverge.
    InlineAsm {
        /// The template for the inline assembly, with placeholders.
        template: &'tcx [InlineAsmTemplatePiece],

        /// The operands for the inline assembly, as `Operand`s or `Place`s.
        operands: Vec<InlineAsmOperand<'tcx>>,

        /// Miscellaneous options for the inline assembly.
        options: InlineAsmOptions,

        /// Destination block after the inline assembly returns, unless it is
        /// diverging (InlineAsmOptions::NORETURN).
        destination: Option<BasicBlock>,
    },
}

pub enum InlineAsmOperand<'tcx> {
    In {
        reg: InlineAsmRegOrRegClass,
        value: Operand<'tcx>,
    },
    Out {
        reg: InlineAsmRegOrRegClass,
        late: bool,
        place: Option<Place<'tcx>>,
    },
    InOut {
        reg: InlineAsmRegOrRegClass,
        late: bool,
        in_value: Operand<'tcx>,
        out_place: Option<Place<'tcx>>,
    },
    Const {
        value: Operand<'tcx>,
    },
    SymFn {
        value: Box<Constant<'tcx>>,
    },
    SymStatic {
        value: Box<Constant<'tcx>>,
    },
}
```

As part of HAIR lowering, `InOut` and `SplitInOut` operands are lowered to a split form with a separate `in_value` and `out_place`.

Semantically, the `InlineAsm` terminator is similar to the `Call` terminator except that it has multiple output places where a `Call` only has a single return place output.

The constant promotion pass is used to ensure that `const` operands are actually constants (using the same logic as `#[rustc_args_required_const]`).

## Codegen

Operands are lowered one more time before being passed to LLVM codegen:

```rust
pub enum InlineAsmOperandRef<'tcx, B: BackendTypes + ?Sized> {
    In {
        reg: InlineAsmRegOrRegClass,
        value: OperandRef<'tcx, B::Value>,
    },
    Out {
        reg: InlineAsmRegOrRegClass,
        late: bool,
        place: Option<PlaceRef<'tcx, B::Value>>,
    },
    InOut {
        reg: InlineAsmRegOrRegClass,
        late: bool,
        in_value: OperandRef<'tcx, B::Value>,
        out_place: Option<PlaceRef<'tcx, B::Value>>,
    },
    Const {
        string: String,
    },
    SymFn {
        instance: Instance<'tcx>,
    },
    SymStatic {
        def_id: DefId,
    },
}
```

The operands are lowered to LLVM operands and constraint codes as follow:
- `out` and the output part of `inout` operands are added first, as required by LLVM. Late output operands have a `=` prefix added to their constraint code, non-late output operands have a `=&` prefix added to their constraint code.
- `in` operands are added normally.
- `inout` operands are tied to the matching output operand.
- `sym` operands are passed as function pointers or pointers, using the `"s"` constraint.
- `const` operands are formatted to a string and directly inserted in the template string.

The template string is converted to LLVM form:
- `$` characters are escaped as `$$`.
- `const` operands are converted to strings and inserted directly.
- Placeholders are formatted as `${X:M}` where `X` is the operand index and `M` is the modifier character. Modifiers are converted from the Rust form to the LLVM form.

The various options are converted to clobber constraints or LLVM attributes, refer to the [RFC](https://github.com/Amanieu/rfcs/blob/inline-asm/text/0000-inline-asm.md#mapping-to-llvm-ir) for more details.

Note that LLVM is sometimes rather picky about what types it accepts for certain constraint codes so we sometimes need to insert conversions to/from a supported type. See the target-specific ISelLowering.cpp files in LLVM for details.

# Adding support for new architectures

Adding inline assembly support to an architecture is mostly a matter of defining the registers and register classes for that architecture. All the definitions for register classes are located in `src/librustc_target/asm/`.

Additionally you will need to implement lowering of these register classes to LLVM constraint codes in `src/librustc_codegen_llvm/asm.rs`.

Missed in 2a66355.

Fixes rust-lang#68489

When checking two `TokenStreams` to see if they are 'probably equal',
we ignore the `IsJoint` information associated with each `TokenTree`.
However, the `IsJoint` information determines whether adjacent tokens
will be 'glued' (if possible) when construction the `TokenStream` - e.g.
`[Gt Gt]` can be 'glued' to `BinOp(Shr)`.

Since we are ignoring the `IsJoint` information, 'glued' and 'unglued'
tokens are equivalent for determining if two `TokenStreams` are
'probably equal'. Therefore, we need to 'unglue' all tokens in the
stream to avoid false negatives (which cause us to throw out the cached
tokens, losing span information).

Introduce function attribute corresponding to the `const`/`pure`
attributes supported by GCC, clang and other compilers.

Based on the work of gnzlbg <gonzalobg88@gmail.com>.

Based on the work of gnzlbg <gonzalobg88@gmail.com>.

…able book

Based on the work of gnzlbg <gonzalobg88@gmail.com>.

Some tokens need to be broken in a loop until we reach
'unbreakable' tokens.

This was supposed to land as part of rust-lang#72227. (I wish `git push` would
abort when you have uncommited changes.)

Instead of using a bespoke dataflow analysis, `MaybeRequiresStorage`,
for computing locals that need to be stored across yield points and that
have conflicting storage, use a combination of simple, generally
applicable dataflow analyses. In this case, the formula for locals
that are live at a yield point is:

    live_across_yield := (live & init) | (!movable & borrowed)

and the formula for locals that require storage (and thus may conflict
with others) at a given point is:

    requires_storage := init | borrowed

`init` is `MaybeInitializedLocals`, a direct equivalent of
`MaybeInitializedPlaces` that works only on whole `Local`s. `borrowed`
and `live` are the pre-existing `MaybeBorrowedLocals` and
`MaybeLiveLocals` analyses respectively.

The generator transform needs to inspect all possible dataflow states.
This can be done with half the number of bitset union operations if we
can assume that the relevant analyses do not use "before" effects.

...when determining what locals are live.

A local cannot be borrowed before it is `storage_live` and
`MaybeBorrowedLocals` already invalidates borrows on `StorageDead`.
Likewise, a local cannot be initialized before it is marked StorageLive
and is marked as uninitialized after `StorageDead`.

Update cargo

9 commits in cb06cb2696df2567ce06d1a39b1b40612a29f853..500b2bd01c958f5a33b6aa3f080bea015877b83c
2020-05-08 21:57:44 +0000 to 2020-05-18 17:12:54 +0000
- Handle LTO with an rlib/cdylib crate type (rust-lang/cargo#8254)
- Gracefully handle errors during a build. (rust-lang/cargo#8247)
- Update `im-rc` to 15.0.0 (rust-lang/cargo#8255)
- Fix `cargo update` with unused patch. (rust-lang/cargo#8243)
- Rephrased error message for disallowed sections in virtual workspace (rust-lang/cargo#8200)
- Ignore broken console output in some situations. (rust-lang/cargo#8236)
- Expand error message to explain that a string was found (rust-lang/cargo#8235)
- Add context to some fs errors. (rust-lang/cargo#8232)
- Move SipHasher to an isolated module. (rust-lang/cargo#8233)

linker: More systematic handling of CRT objects

Document which kinds of `crt0.o`-like objects we link and in which cases, discovering bugs in process.
`src/librustc_target/spec/crt_objects.rs` is the place to start reading from.

This PR also automatically contains half of the `-static-pie` support (rust-lang#70740), because that's one of the six cases that we need to consider when linking CRT objects.

This is a breaking change for custom target specifications that specify CRT objects.

Closes rust-lang#30868

Check non-Send/Sync upvars captured by generator

Closes rust-lang#70818
r? @tmandry

Suggest fixes and add error recovery for `use foo::self`

Fixes rust-lang#63741.
I have implemented 2 suggestions on how to fix a `use foo::self` import, however I feel like showing them both might be too verbose.

Additionally, I have also implemented error recovery as [menitoned](rust-lang#63741 (comment)) by @comex.

I believe r? @estebank deals with diagnostics.

Make `fold` standalone.

`fold` is currently implemented via `try_fold`, but implementing it
directly results in slightly less LLVM IR being generated, speeding up
compilation of some benchmarks.

r? @cuviper

…static-morse

Continue lowering for unsupported async generator instead of returning an error.

This way the hir is "valid" and we can remove one more call to
`opt_node_id_to_hir_id` but an error is still emitted.

This is another partial fix for rust-lang#71104

r? @eddyb

…king_issue, r=shepmaster

split_inclusive: add tracking issue number (72360)

Adds tracking issue number ( rust-lang#72360 ) to the unstable feature attributes.

…ulacrum

Remove unused dependencies

Remove some unused dependencies found while while working on rust-lang#72342.

…owup, r=Amanieu

Adjust the zero check in `RawVec::grow`.

This was supposed to land as part of rust-lang#72227. (I wish `git push` would
abort when you have uncommited changes.)

r? @Amanieu

When MSVC's `link.exe` wasn't found but another `link.exe` was, the error message given can be impenetrable to many users. The usual suspect is GNU's `link` tool. In this case, inform the user that they may need to install VS build tools.

This only applies when Microsoft's link tool is expected. Not `lld-link` or other MSVC compatible linkers.

Workaround MSYS2/chocolatey issue again

NativeLibrary(Kind) -> NativeLib(Kind)
NativeStatic -> StaticBundle
NativeStaticNobundle -> StaticNoBundle
NativeFramework -> Framework
NativeRawDylib -> RawDylib
NativeUnknown -> Unspecified

Rollup of 6 pull requests

Successful merges:

 - rust-lang#71863 (Suggest fixes and add error recovery for `use foo::self`)
 - rust-lang#72139 (Make `fold` standalone.)
 - rust-lang#72275 (Continue lowering for unsupported async generator instead of returning an error.)
 - rust-lang#72361 (split_inclusive: add tracking issue number (72360))
 - rust-lang#72364 (Remove unused dependencies)
 - rust-lang#72366 (Adjust the zero check in `RawVec::grow`.)

Failed merges:

r? @ghost

Update to LLVM 10

LLVM 10 is going to be branched soon, so it's a good time to start finding all those tasty new miscompiles and performance regressions ;)

Status:

 * Preparation split off into rust-lang#67900.
 * Optimization regressions:
   * [x] https://bugs.llvm.org/show_bug.cgi?id=44419 => https://reviews.llvm.org/D72048 has landed.
   * [x] https://bugs.llvm.org/show_bug.cgi?id=44423 => https://reviews.llvm.org/D72060 has landed.
   * [x] https://reviews.llvm.org/D72169 submitted.
   * [ ] https://bugs.llvm.org/show_bug.cgi?id=44461 reported. https://reviews.llvm.org/D72420 submitted, but unlikely eligible for LLVM 10.
 * Compile-time regressions:
   * [x] GlobalOpt regression identified. ~~fhahn proposed https://reviews.llvm.org/D72214.~~ fhahn has [reverted](llvm/llvm-project@192cce1) the patch.
   * [ ] Even with the revert, there are [large regressions](https://perf.rust-lang.org/compare.html?start=760ce94c69ca510d44087291c311296f6d9ccdf5&end=4e84f97d76e694bb9f59039f5bdeb6d8bca46d14).
 * Assertion failures / infinite loops:
   * [x] https://bugs.llvm.org/show_bug.cgi?id=44600 => https://reviews.llvm.org/D73135, https://reviews.llvm.org/D73854 and https://reviews.llvm.org/D73908 have landed and been cherry-picked to the 10.x branch.
   * [x] https://bugs.llvm.org/show_bug.cgi?id=44835 => https://reviews.llvm.org/D74278 has landed and been cherry-picked.

For running the compiler, we usually only need LLVM from `$sysroot/lib`,
which rustup will make available with `LD_LIBRARY_PATH`. We've also been
shipping LLVM in the `$target/lib` directory, which bloats the download
and installed size. The only times we do need the latter are for the
RPATH of `llvm-tools-preview` binaries, and for linking `rustc-dev`
libraries. We'll move it to the `llvm-tools-preview` component directly,
and `rustc-dev` will have an implicit dependency on it.

Here are the dist sizes that I got before and after this change:

    llvm-tools-1.45.0-dev-x86_64-unknown-linux-gnu.tar.gz     1.3M   24M
    llvm-tools-1.45.0-dev-x86_64-unknown-linux-gnu.tar.xz     748K   17M
    rustc-1.45.0-dev-x86_64-unknown-linux-gnu.tar.gz          83M    61M
    rustc-1.45.0-dev-x86_64-unknown-linux-gnu.tar.xz          56M    41M

The installed size should reduce by exactly one `libLLVM.so` (~70-80M),
unless you also install `llvm-tools`, and then it should be identical.

…akis

Use `T`'s discriminant type in `mem::Discriminant<T>` instead of `u64`.

fixes rust-lang#70509

Adds the lang-item `discriminant_kind`.
Updates the function signature of `intrinsics::discriminant_value`.
Adds the *probably permanently unstable* trait `DiscriminantKind`.
`mem::Discriminant` should now be smaller in some cases.

r? @ghost

Dumb NRVO

This is a very simple version of an NRVO pass, which scans backwards from the `return` terminator to see if there is an an assignment like `_0 = _1`. If a basic block with two or more predecessors is encountered during this scan without first seeing an assignment to the return place, we bail out. This avoids running a full "reaching definitions" dataflow analysis.

I wanted to see how much `rustc` would benefit from even a very limited version of this optimization. We should be able to use this as a point of comparison for more advanced versions that are based on live ranges.

r? @ghost

…ts, r=Amanieu

Make `std::char` functions and constants associated to `char`.

First step to fix rust-lang#71763.

rustc-book: Document `-Z strip=val` option

cc rust-lang#72110

…h-search-behaviour, r=kinnison

Fix going back in history to a search result page on firefox

This bug was actually firefox not re-running JS script when you go back in history. To trigger it on the current docs:

 * Make a search
 * Pick an element (which isn't on the same page as the current element!)
 * Go back in history

Instead of having the search results, you'll see the normal doc page. You can find a small explanation about it [here](http://web.archive.org/web/20100428053932/http://www.firefoxanswer.com/firefox/672-firefoxanswer.html).

r? @kinnison

cc @ollie27

…ochenkov

Suggest installing VS Build Tools in more situations

When MSVC's `link.exe` wasn't found but another `link.exe` was, the error message given can be [impenetrable](https://pastebin.com/MRMCr7HM) to many users. The usual suspect is GNU's `link` tool. In this case, inform the user that they may need to install VS build tools.

This only applies when Microsoft's link tool is expected.

…r=ecstatic-morse

Remove unused `StableHashingContext::node_to_hir_id` method

cc rust-lang#50928

…eklabnik

FIX - Char documentation for unexperienced users

This is my first PR on rust and even if I've read [CONTRIBUTING.md](https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#pull-requests) I'm ensure everything is perfect. Sorry if I didn't follow the exact procedure.

**What it does:**
- Add an example in the char documentation

**Explanation**
Unexperienced users might not know that punctuation is `Case_Ignorable` and not `Uppercase` and `Lowercase` which mean that when checking if a string is uppercase one might be tempted to write:
```rust
my_string.chars().all(char::is_uppercase)
```

However this will return false for `"HELLO WORLD"` which is not intuitive. Since the function `is_case_ignorable` doesn't exists I believe the correct way to check is:
```rust
!my_string.chars().any(char::is_lowercase)
```

The aim of this example is to prevent unexperienced users to make an error which punctuation chars.

llvm: Expose tiny code model to users

This model is relevant to embedded AArch64 targets and was added to LLVM relatively recently (https://reviews.llvm.org/D49673, mid 2018), so rustc frontend didn't provide access to it with `-C code-model`. The gcc analogue is [`-mcmodel=tiny`](https://gcc.gnu.org/onlinedocs/gcc/AArch64-Options.html).
(This is one of the options that are passed directly to LLVM without being interpreted by rustc.)

Follow up to rust-lang#72248.

Rollup of 7 pull requests

Successful merges:

 - rust-lang#71854 (Make `std::char` functions and constants associated to `char`.)
 - rust-lang#72111 (rustc-book: Document `-Z strip=val` option)
 - rust-lang#72272 (Fix going back in history to a search result page on firefox)
 - rust-lang#72296 (Suggest installing VS Build Tools in more situations)
 - rust-lang#72365 (Remove unused `StableHashingContext::node_to_hir_id` method)
 - rust-lang#72371 (FIX - Char documentation for unexperienced users)
 - rust-lang#72397 (llvm: Expose tiny code model to users)

Failed merges:

r? @ghost

Experimentally add `ffi_const` and `ffi_pure` extern fn attributes

Add FFI function attributes corresponding to clang/gcc/... `const` and `pure`.

Rebased version of rust-lang#58327 by @gnzlbg with the following changes:

- Switched back from the `c_ffi_const` and `c_ffi_pure` naming to `ffi_const` and `ffi_pure`, as I agree with rust-lang#58327 (comment) and this nicely aligns with `ffi_returns_twice`
- (Hopefully) took care of all of @hanna-kruppe's change requests in the original PR

r? @hanna-kruppe

…tead of `NodeId`

…of `NodeId`