Add test for #18908
Special-case transmute for primitive, SIMD & pointer types.

This detects (a subset of) the cases when `transmute::<T, U>(x)` can be
lowered to a direct `bitcast T x to U` in LLVM. This assists with
efficiently handling a SIMD vector as multiple different types,
e.g. swapping bytes/words/double words around inside some larger vector
type.

C compilers like GCC and Clang handle integer vector types as `__m128i`
for all widths, and implicitly insert bitcasts as required. This patch
allows Rust to express this, even if it takes a bit of `unsafe`, whereas
previously it was impossible to do at all without inline assembly.

Example:

    pub fn reverse_u32s(u: u64x2) -> u64x2 {
        unsafe {
            let tmp = mem::transmute::<_, u32x4>(u);
            let swapped = u32x4(tmp.3, tmp.2, tmp.1, tmp.0);
            mem::transmute::<_, u64x2>(swapped)
        }
    }

Compiling with `--opt-level=3` gives:

Before

    define <2 x i64> @_ZN12reverse_u32s20hbdb206aba18a03d8tbaE(<2 x i64>) unnamed_addr #0 {
    entry-block:
      %1 = bitcast <2 x i64> %0 to i128
      %u.0.extract.trunc = trunc i128 %1 to i32
      %u.4.extract.shift = lshr i128 %1, 32
      %u.4.extract.trunc = trunc i128 %u.4.extract.shift to i32
      %u.8.extract.shift = lshr i128 %1, 64
      %u.8.extract.trunc = trunc i128 %u.8.extract.shift to i32
      %u.12.extract.shift = lshr i128 %1, 96
      %u.12.extract.trunc = trunc i128 %u.12.extract.shift to i32
      %2 = insertelement <4 x i32> undef, i32 %u.12.extract.trunc, i64 0
      %3 = insertelement <4 x i32> %2, i32 %u.8.extract.trunc, i64 1
      %4 = insertelement <4 x i32> %3, i32 %u.4.extract.trunc, i64 2
      %5 = insertelement <4 x i32> %4, i32 %u.0.extract.trunc, i64 3
      %6 = bitcast <4 x i32> %5 to <2 x i64>
      ret <2 x i64> %6
    }

    _ZN12reverse_u32s20hbdb206aba18a03d8tbaE:
    	.cfi_startproc
    	movd	%xmm0, %rax
    	punpckhqdq	%xmm0, %xmm0
    	movd	%xmm0, %rcx
    	movq	%rcx, %rdx
    	shrq	$32, %rdx
    	movq	%rax, %rsi
    	shrq	$32, %rsi
    	movd	%eax, %xmm0
    	movd	%ecx, %xmm1
    	punpckldq	%xmm0, %xmm1
    	movd	%esi, %xmm2
    	movd	%edx, %xmm0
    	punpckldq	%xmm2, %xmm0
    	punpckldq	%xmm1, %xmm0
    	retq

After

    define <2 x i64> @_ZN12reverse_u32s20hbdb206aba18a03d8tbaE(<2 x i64>) unnamed_addr #0 {
    entry-block:
      %1 = bitcast <2 x i64> %0 to <4 x i32>
      %2 = shufflevector <4 x i32> %1, <4 x i32> undef, <4 x i32> <i32 3, i32 2, i32 1, i32 0>
      %3 = bitcast <4 x i32> %2 to <2 x i64>
      ret <2 x i64> %3
    }

    _ZN12reverse_u32s20hbdb206aba18a03d8tbaE:
    	.cfi_startproc
    	pshufd	$27, %xmm0, %xmm0
    	retq
libcore: Fix `Sized` bounds on overloaded function traits.

- Remove the `for Sized?` bound on `core::ops::FnOnce`, as it takes
  `self` by value and can never be implemented by an unsized type.
- Add a missing `Sized?` bound to the blanket `core::ops::FnMut` impl,
  as both `Fn` and `FnMut` are `for Sized?`.
rustc: Prepend a length to all metadata

One of the causes of #19501 was that the metadata on OSX was getting corrupted.
For any one particular invocation of the compiler the metadata file inside of an
rlib archive would have extra bytes appended to the end of it. These extra bytes
end up confusing rbml and have it run off the end of the array (resulting in the
out of bounds detected).

This commit prepends the length of metadata to the start of the metadata to
ensure that we always slice the precise amount that we want, and it also
un-ignores the test from #19502.

Closes #19501
Change 'Example' to 'Examples' throughout collections' rustdocs.
Delete the outdated source layout README
Add a doctest for the std::string::as_string method.

Change Example to Examples.

Add a doctest that better demonstrates the utility of as_string.

Update the doctest example to use String instead of &String.
Clean up `libcollections::VecMap`

- Introduce a named type for the return type of `VecMap::move_iter`
- Rename all type parameters to `V` for "Value".
- Remove unnecessary call to an `Option::unwrap`, use pattern matching instead.
- Remove incorrect `Hash` implementation which took the `VecMap`'s capacity
  into account.

This is a [breaking-change], however whoever used the `Hash` implementation
relied on an incorrect implementation.
Add a proper `Hash` implementation for `VecMap`

Also re-add the previously deleted test with an additional test that would have
failed before, when the hash function depended on the capacity.
auto merge of #19563 : alexcrichton/rust/issue-19501, r=pnkfelix

One of the causes of #19501 was that the metadata on OSX was getting corrupted.
For any one particular invocation of the compiler the metadata file inside of an
rlib archive would have extra bytes appended to the end of it. These extra bytes
end up confusing rbml and have it run off the end of the array (resulting in the
out of bounds detected).

This commit prepends the length of metadata to the start of the metadata to
ensure that we always slice the precise amount that we want, and it also
un-ignores the test from #19502.

Closes #19501
auto merge of #19573 : apasel422/rust/sized_fn_once, r=alexcrichton

- Remove the `for Sized?` bound on `core::ops::FnOnce`, as it takes `self` by value and can never be implemented by an unsized type.
- Add a missing `Sized?` bound to the blanket `core::ops::FnMut` impl, as both `Fn` and `FnMut` are `for Sized?`.
typeck: Make the supplied parameters to be a tuple

When a type error occurs, check_method_argument_types() tries to provide
arguments filled with ty::mk_err(). However, if a function takes the
parameters as a tuple, the arguments should be converted to a tuple
before being passed to check_argument_types().

Fixes #19521.
auto merge of #19648 : mquandalle/rust/patch-1, r=alexcrichton
auto merge of #19628 : jbranchaud/rust/add-string-as-string-doctest, r=steveklabnik
auto merge of #19638 : barosl/rust/typeck-tupled-arguments-ice, r=jakub

When a type error occurs, `check_method_argument_types()` tries to provide arguments filled with `ty::mk_err()`. However, if a function takes the parameters as a tuple, the arguments should be converted to a tuple before passing it to `check_argument_types()`.

Fixes #19521.
auto merge of #19655 : jbranchaud/rust/change-example-to-examples, r=steveklabnik

@steveklabnik I got a start on this.
auto merge of #19663 : tbu-/rust/pr_fix_vecmap, r=Gankro

- Introduce a named type for the return type of `VecMap::move_iter`
- Rename all type parameters to `V` for "Value".
- Remove unnecessary call to an `Option::unwrap`, use pattern matching instead.
- Remove incorrect `Hash` implementation which took the `VecMap`'s capacity
  into account.

This is a [breaking-change], however whoever used the `Hash` implementation
relied on an incorrect implementation.
rustc: Fix `make install`

Move a few docblocks from 'ignore' to something that's not rust (e.g. 'text').

Closes #19678
Don't try to dist src/README.md which does not exist
auto merge of #19705 : brson/rust/fix-install, r=alexcrichton