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bors 1df18ff1a5 Auto merge of - jwong101:inplacecollect, r=jhpratt
optimize inplace collection of Vec

This PR has the following changes:

1. Using `usize::unchecked_mul` in 79424056b0/library/alloc/src/vec/in_place_collect.rs (L262) as LLVM, does not know that the operation can't wrap, since that's the size of the original allocation.

Given the following:

```rust

pub struct Foo([usize; 3]);

pub fn unwrap_copy(v: Vec<Foo>) -> Vec<[usize; 3]> {
    v.into_iter().map(|f| f.0).collect()
}
```

<details>
<summary>Before this commit:</summary>

```llvm
define void `@unwrap_copy(ptr` noalias nocapture noundef writeonly sret([24 x i8]) align 8 dereferenceable(24) %_0, ptr noalias nocapture noundef readonly align 8 dereferenceable(24) %iter) {
start:
  %me.sroa.0.0.copyload.i = load i64, ptr %iter, align 8
  %me.sroa.4.0.self.sroa_idx.i = getelementptr inbounds i8, ptr %iter, i64 8
  %me.sroa.4.0.copyload.i = load ptr, ptr %me.sroa.4.0.self.sroa_idx.i, align 8
  %me.sroa.5.0.self.sroa_idx.i = getelementptr inbounds i8, ptr %iter, i64 16
  %me.sroa.5.0.copyload.i = load i64, ptr %me.sroa.5.0.self.sroa_idx.i, align 8
  %_19.i.idx = mul nsw i64 %me.sroa.5.0.copyload.i, 24
  %0 = udiv i64 %_19.i.idx, 24

; Unnecessary calculation
  %_16.i.i = mul i64 %me.sroa.0.0.copyload.i, 24
  %dst_cap.i.i = udiv i64 %_16.i.i, 24

  store i64 %dst_cap.i.i, ptr %_0, align 8
  %1 = getelementptr inbounds i8, ptr %_0, i64 8
  store ptr %me.sroa.4.0.copyload.i, ptr %1, align 8
  %2 = getelementptr inbounds i8, ptr %_0, i64 16
  store i64 %0, ptr %2, align 8
  ret void
}
```
</details>

<details>
<summary>After:</summary>

```llvm
define void `@unwrap_copy(ptr` noalias nocapture noundef writeonly sret([24 x i8]) align 8 dereferenceable(24) %_0, ptr noalias nocapture noundef readonly align 8 dereferenceable(24) %iter) {
start:
  %me.sroa.0.0.copyload.i = load i64, ptr %iter, align 8
  %me.sroa.4.0.self.sroa_idx.i = getelementptr inbounds i8, ptr %iter, i64 8
  %me.sroa.4.0.copyload.i = load ptr, ptr %me.sroa.4.0.self.sroa_idx.i, align 8
  %me.sroa.5.0.self.sroa_idx.i = getelementptr inbounds i8, ptr %iter, i64 16
  %me.sroa.5.0.copyload.i = load i64, ptr %me.sroa.5.0.self.sroa_idx.i, align 8
  %_19.i.idx = mul nsw i64 %me.sroa.5.0.copyload.i, 24
  %0 = udiv i64 %_19.i.idx, 24
  store i64 %me.sroa.0.0.copyload.i, ptr %_0, align 8
  %1 = getelementptr inbounds i8, ptr %_0, i64 8
  store ptr %me.sroa.4.0.copyload.i, ptr %1, align 8
  %2 = getelementptr inbounds i8, ptr %_0, i64 16
  store i64 %0, ptr %2, align 8, !alias.scope , !noalias 
  ret void
}
```
</details>

Note that there is still one more `mul,udiv` pair that I couldn't get
rid of. The root cause is the same issue as https://github.com/rust-lang/rust/issues/121239, the `nuw` gets
stripped off of `ptr::sub_ptr`.

2.

`Iterator::try_fold` gets called on the underlying Iterator in
`SpecInPlaceCollect::collect_in_place` whenever it does not implement
`TrustedRandomAccess`. For types that impl `Drop`, LLVM currently can't
tell that the drop can never occur, when using the default
`Iterator::try_fold` implementation.

For example, given the following code from 

```rust
#[repr(transparent)]
struct WrappedClone {
    inner: String
}

#[no_mangle]
pub fn unwrap_clone(list: Vec<WrappedClone>) -> Vec<String> {
    list.into_iter().map(|s| s.inner).collect()
}
```

<details>
<summary>The asm for the `unwrap_clone` method is currently:</summary>

```asm
unwrap_clone:
        push    rbp
        push    r15
        push    r14
        push    r13
        push    r12
        push    rbx
        push    rax
        mov     rbx, rdi
        mov     r12, qword ptr [rsi]
        mov     rdi, qword ptr [rsi + 8]
        mov     rax, qword ptr [rsi + 16]
        movabs  rsi, -6148914691236517205
        mov     r14, r12
        test    rax, rax
        je      .LBB0_10
        lea     rcx, [rax + 2*rax]
        lea     r14, [r12 + 8*rcx]
        shl     rax, 3
        lea     rax, [rax + 2*rax]
        xor     ecx, ecx
.LBB0_2:
        cmp     qword ptr [r12 + rcx], 0
        je      .LBB0_4
        add     rcx, 24
        cmp     rax, rcx
        jne     .LBB0_2
        jmp     .LBB0_10
.LBB0_4:
        lea     rdx, [rax - 24]
        lea     r14, [r12 + rcx]
        cmp     rdx, rcx
        je      .LBB0_10
        mov     qword ptr [rsp], rdi
        sub     rax, rcx
        add     rax, -24
        mul     rsi
        mov     r15, rdx
        lea     rbp, [r12 + rcx]
        add     rbp, 32
        shr     r15, 4
        mov     r13, qword ptr [rip + __rust_dealloc@GOTPCREL]
        jmp     .LBB0_6
.LBB0_8:
        add     rbp, 24
        dec     r15
        je      .LBB0_9
.LBB0_6:
        mov     rsi, qword ptr [rbp]
        test    rsi, rsi
        je      .LBB0_8
        mov     rdi, qword ptr [rbp - 8]
        mov     edx, 1
        call    r13
        jmp     .LBB0_8
.LBB0_9:
        mov     rdi, qword ptr [rsp]
        movabs  rsi, -6148914691236517205
.LBB0_10:
        sub     r14, r12
        mov     rax, r14
        mul     rsi
        shr     rdx, 4
        mov     qword ptr [rbx], r12
        mov     qword ptr [rbx + 8], rdi
        mov     qword ptr [rbx + 16], rdx
        mov     rax, rbx
        add     rsp, 8
        pop     rbx
        pop     r12
        pop     r13
        pop     r14
        pop     r15
        pop     rbp
        ret
```
</details>

<details>
<summary>After this PR:</summary>

```asm
unwrap_clone:
	mov	rax, rdi
	movups	xmm0, xmmword ptr [rsi]
	mov	rcx, qword ptr [rsi + 16]
	movups	xmmword ptr [rdi], xmm0
	mov	qword ptr [rdi + 16], rcx
	ret
```
</details>

Fixes https://github.com/rust-lang/rust/issues/120493
2024-05-20 00:51:12 +00:00
.cargo internal: Move ide-assists codegen tests into an xtask codegen command 2024-02-28 16:54:44 +01:00
.github Use actions/cache again in metrics CI 2024-05-15 15:25:58 +02:00
.vscode Spelling 2023-04-19 09:45:55 -04:00
assets Automatically change text color in logo based on dark mode 2022-03-06 23:06:53 +11:00
bench_data Spelling 2023-04-19 09:45:55 -04:00
crates Merge from rust-lang/rust 2024-05-19 11:20:26 +03:00
docs Correct Neovim 0.10 inlay hints config example 2024-05-17 12:42:17 +02:00
editors/code Make term search fuel configurable 2024-05-08 19:46:33 +03:00
lib fix: Report all LSP protocol errors with invalid_data 2024-05-08 16:08:00 -07:00
xtask add no-new-root check to josh pull 2024-04-27 09:02:07 +02:00
.editorconfig add max_line_length to .editorconfig 2024-01-20 17:14:00 +03:00
.git-blame-ignore-revs Show workspace info in the status bar 2024-04-26 11:28:33 +02:00
.gitattributes Fix .gitattributes for test_data 2022-07-24 14:05:35 +02:00
.gitignore internal: add "Shuffle Crate Graph" command 2021-12-07 16:37:19 +01:00
.typos.toml remove ignore-hidden = false 2024-03-05 20:16:32 +08:00
Cargo.lock Bump rustc crates 2024-05-19 11:22:58 +03:00
Cargo.toml Bump rustc crates 2024-05-19 11:22:58 +03:00
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CONTRIBUTING.md Add CONTRIBUTING.md 2024-04-18 10:24:40 +02:00
LICENSE-APACHE Licenses 2018-01-10 22:47:04 +03:00
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triagebot.toml triagebot exclude_labels -> exclude_titles 2023-09-16 10:58:53 -06:00

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