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Optimize VecDeque::drain
for (half-)open ranges
#118264
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r? @thomcc (rustbot has picked a reviewer for you, use r? to override) |
@AngelicosPhosphoros This PR is about |
Oh, sorry, missed that. |
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Ping @thomcc this PR is waiting for your review. |
r? @the8472 |
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The implementation looks ok. But I think readability has suffered.
Perhaps things can be shuffled around a bit to recover some of that.
if new_len == 0 { | ||
source_deque.head = 0; | ||
} else if head_len < tail_len { | ||
source_deque.head = source_deque.to_physical_idx(drain_len); | ||
} | ||
source_deque.len = new_len; |
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I think the match was easier to read and grouped things more nicely. Now it's somewhat scattered across this block and the outlined function.
I'm not sure what to do about that. Maybe some comments how there can only be 4 cases and how the control flow handles some cases jointly.
source_deque.len = new_len; | ||
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#[cold] | ||
fn copy_data<T, A: Allocator>( |
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Maybe it could be called shift_blocks
or restore_wrapping
or something that describes its purpose rather than what it does internally?
It may copy the bits (in the ptr::copy
sense, including potential overlap), but logically we don't want a copy, we want to shift the parts to restore deque invariants.
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Thanks for the detailed documentation. @bors r+ |
…he8472 Optimize `VecDeque::drain` for (half-)open ranges The most common use cases of `VecDeque::drain` consume either the entire queue or elements from the front or back.[^1] This PR makes these operations faster by optimizing the generated code of the destructor of the drain: * `.drain(..)` is now the same as `.clear()`. * `.drain(n..)` is now (almost[^2]) the same as `.truncate(n)`. * `.drain(..n)` is now an efficient "advance" function. This operation is not provided by a dedicated function and optimizing it is my main motivation for this PR. Previously, all of these cases generated a function call to the destructor of the `DropGuard`, emitting a lot of unused machine code as well as unnecessary branches and loads/stores of stack variables. There are no algorithmic changes in this PR, but it simplifies the code enough to allow LLVM to recognize the special cases and optimize accordingly. Most notably, it allows elimination of the rather large [`wrap_copy`] function. Some [rudimentary microbenchmarks][benches] show a performance improvement of **~3x-4x** on my machine for the special cases and roughly equal performance for the general case. Best reviewed commit by commit. [^1]: source: GitHub code search: [full range `drain(..)` = 7.5k results][full], [from front `drain(..n)` = 3.2k results][front], [from back `drain(n..)` = 1.6k results][back], [from middle `drain(n..m)` = <500 results][middle] [^2]: `.drain(0..)` and `.clear()` reset the head to 0, but `.truncate(0)` does not. [full]: https://github.com/search?type=code&q=%2FVecDeque%28.%7C%5Cn%29%2B%5C.drain%5C%280%3F%5C.%5C.%5C%29%2F+lang%3ARust [front]: https://github.com/search?type=code&q=%2FVecDeque%28.%7C%5Cn%29%2B%5C.drain%5C%280%3F%5C.%5C.%5B%5E%29%5D.*%5C%29%2F+lang%3ARust [back]: https://github.com/search?type=code&q=%2FVecDeque%28.%7C%5Cn%29%2B%5C.drain%5C%28%5B%5E0%5D.*%5C.%5C.%5C%29%2F+lang%3ARust [middle]: https://github.com/search?type=code&q=%2FVecDeque%28.%7C%5Cn%29%2B%5C.drain%5C%28%5B%5E0%5D.*%5C.%5C.%5B%5E%29%5D.*%5C%29%2F+lang%3ARust [`wrap_copy`]: https://github.com/rust-lang/rust/blob/4fd68eb47bad1c121417ac4450b2f0456150db86/library/alloc/src/collections/vec_deque/mod.rs#L262-L391 [benches]: https://gist.github.com/lukas-code/c97bd707d074c4cc31f241edbc7fd2a2 <details> <summary>generated assembly</summary> before: ```asm clear: sub rsp, 40 mov rax, qword ptr [rdi + 24] mov qword ptr [rdi + 24], 0 mov qword ptr [rsp], rdi mov qword ptr [rsp + 8], rax xorps xmm0, xmm0 movups xmmword ptr [rsp + 16], xmm0 mov qword ptr [rsp + 32], rax test rax, rax je .LBB1_2 mov rcx, qword ptr [rdi] mov rdx, qword ptr [rdi + 16] xor esi, esi cmp rdx, rcx cmovae rsi, rcx sub rdx, rsi mov rsi, rcx sub rsi, rdx lea rdi, [rdx + rax] cmp rsi, rax cmovb rdi, rcx sub rdi, rdx mov qword ptr [rsp + 16], rdi mov qword ptr [rsp + 32], 0 .LBB1_2: mov rdi, rsp call core::ptr::drop_in_place<<alloc::collections::vec_deque::drain::Drain<T,A> as core::ops::drop::Drop>::drop::DropGuard<i32,alloc::alloc::Global>> add rsp, 40 ret truncate: mov rax, qword ptr [rdi + 24] sub rax, rsi jbe .LBB2_2 sub rsp, 40 mov qword ptr [rdi + 24], rsi mov qword ptr [rsp], rdi mov qword ptr [rsp + 8], rax mov rcx, qword ptr [rdi] mov rdx, qword ptr [rdi + 16] add rdx, rsi xor edi, edi cmp rdx, rcx cmovae rdi, rcx mov qword ptr [rsp + 24], 0 sub rdx, rdi mov rdi, rcx sub rdi, rdx lea r8, [rdx + rax] cmp rdi, rax cmovb r8, rcx sub rsi, rdx add rsi, r8 mov qword ptr [rsp + 16], rsi mov qword ptr [rsp + 32], 0 mov rdi, rsp call core::ptr::drop_in_place<<alloc::collections::vec_deque::drain::Drain<T,A> as core::ops::drop::Drop>::drop::DropGuard<i32,alloc::alloc::Global>> add rsp, 40 advance: mov rcx, qword ptr [rdi + 24] mov rax, rcx sub rax, rsi jbe .LBB3_1 sub rsp, 40 mov qword ptr [rdi + 24], 0 mov qword ptr [rsp], rdi mov qword ptr [rsp + 8], rsi mov qword ptr [rsp + 16], 0 mov qword ptr [rsp + 24], rax mov qword ptr [rsp + 32], rsi test rsi, rsi je .LBB3_6 mov rax, qword ptr [rdi] mov rcx, qword ptr [rdi + 16] xor edx, edx cmp rcx, rax cmovae rdx, rax sub rcx, rdx mov rdx, rax sub rdx, rcx lea rdi, [rcx + rsi] cmp rdx, rsi cmovb rdi, rax sub rdi, rcx mov qword ptr [rsp + 16], rdi mov qword ptr [rsp + 32], 0 .LBB3_6: mov rdi, rsp call core::ptr::drop_in_place<<alloc::collections::vec_deque::drain::Drain<T,A> as core::ops::drop::Drop>::drop::DropGuard<i32,alloc::alloc::Global>> add rsp, 40 ret .LBB3_1: test rcx, rcx je .LBB3_3 mov qword ptr [rdi + 24], 0 .LBB3_3: mov qword ptr [rdi + 16], 0 ret remove: sub rsp, 40 cmp rdx, rsi jb .LBB4_5 mov rax, qword ptr [rdi + 24] mov rcx, rax sub rcx, rdx jb .LBB4_6 mov qword ptr [rdi + 24], rsi mov qword ptr [rsp], rdi sub rdx, rsi mov qword ptr [rsp + 8], rdx mov qword ptr [rsp + 16], rsi mov qword ptr [rsp + 24], rcx mov qword ptr [rsp + 32], rdx je .LBB4_4 mov rax, qword ptr [rdi] mov rcx, qword ptr [rdi + 16] add rcx, rsi xor edi, edi cmp rcx, rax cmovae rdi, rax sub rcx, rdi mov rdi, rax sub rdi, rcx lea r8, [rcx + rdx] cmp rdi, rdx cmovb r8, rax sub rsi, rcx add rsi, r8 mov qword ptr [rsp + 16], rsi mov qword ptr [rsp + 32], 0 .LBB4_4: mov rdi, rsp call core::ptr::drop_in_place<<alloc::collections::vec_deque::drain::Drain<T,A> as core::ops::drop::Drop>::drop::DropGuard<i32,alloc::alloc::Global>> add rsp, 40 ret .LBB4_5: lea rax, [rip + .L__unnamed_2] mov rdi, rsi mov rsi, rdx mov rdx, rax call qword ptr [rip + core::slice::index::slice_index_order_fail@GOTPCREL] .LBB4_6: lea rcx, [rip + .L__unnamed_2] mov rdi, rdx mov rsi, rax mov rdx, rcx call qword ptr [rip + core::slice::index::slice_end_index_len_fail@GOTPCREL] core::ptr::drop_in_place<<alloc::collections::vec_deque::drain::Drain<T,A> as core::ops::drop::Drop>::drop::DropGuard<i32,alloc::alloc::Global>>: push rbp push r15 push r14 push r13 push r12 push rbx sub rsp, 24 mov rsi, qword ptr [rdi + 32] test rsi, rsi je .LBB0_2 mov rax, qword ptr [rdi + 16] add rsi, rax jb .LBB0_45 .LBB0_2: mov r13, qword ptr [rdi] mov rbp, qword ptr [rdi + 8] mov rbx, qword ptr [r13 + 24] lea r12, [rbx + rbp] mov r15, qword ptr [rdi + 24] lea rsi, [r15 + r12] test rbx, rbx je .LBB0_10 test r15, r15 je .LBB0_42 cmp rbx, r15 jbe .LBB0_12 mov r14, qword ptr [r13] mov rax, qword ptr [r13 + 16] add r12, rax xor ecx, ecx cmp r12, r14 mov rdx, r14 cmovb rdx, rcx sub r12, rdx add rbx, rax cmp rbx, r14 cmovae rcx, r14 sub rbx, rcx mov rcx, rbx sub rcx, r12 je .LBB0_42 mov rdi, qword ptr [r13 + 8] mov rax, rcx add rax, r14 cmovae rax, rcx mov r8, r14 sub r8, r12 mov rcx, r14 sub rcx, rbx mov rdx, r15 sub rdx, r8 mov qword ptr [rsp + 16], rsi jbe .LBB0_18 cmp rax, r15 jae .LBB0_24 mov rdx, r15 sub rdx, r8 shl rdx, 2 cmp r15, rcx jbe .LBB0_30 sub r8, rcx mov qword ptr [rsp], rdi mov rax, qword ptr [rsp] lea rdi, [rax + 4*r8] mov rsi, qword ptr [rsp] mov qword ptr [rsp + 8], rcx mov r15, r8 call qword ptr [rip + memmove@GOTPCREL] sub r14, r15 mov rax, qword ptr [rsp] lea rsi, [rax + 4*r14] shl r15, 2 mov rdi, qword ptr [rsp] mov rdx, r15 call qword ptr [rip + memmove@GOTPCREL] mov rdi, qword ptr [rsp] lea rsi, [rdi + 4*r12] lea rdi, [rdi + 4*rbx] mov r15, qword ptr [rsp + 8] jmp .LBB0_36 .LBB0_10: test r15, r15 je .LBB0_17 mov rax, qword ptr [r13] sub rsi, rbp add rbp, qword ptr [r13 + 16] xor ecx, ecx cmp rbp, rax cmovae rcx, rax sub rbp, rcx mov qword ptr [r13 + 16], rbp jmp .LBB0_43 .LBB0_12: mov rdx, qword ptr [r13 + 16] mov r15, qword ptr [r13] lea rax, [rdx + rbp] xor ecx, ecx cmp rax, r15 cmovae rcx, r15 mov r12, rax sub r12, rcx mov rcx, r12 sub rcx, rdx je .LBB0_41 mov rdi, qword ptr [r13 + 8] mov rax, rcx add rax, r15 cmovae rax, rcx mov r8, r15 sub r8, rdx mov rcx, r15 sub rcx, r12 mov r14, rbx sub r14, r8 mov qword ptr [rsp + 16], rsi jbe .LBB0_21 cmp rax, rbx jae .LBB0_26 mov qword ptr [rsp], rdx mov rdx, rbx sub rdx, r8 shl rdx, 2 cmp rbx, rcx jbe .LBB0_32 sub r8, rcx mov rbx, rdi lea rdi, [rdi + 4*r8] mov rsi, rbx mov qword ptr [rsp + 8], rcx mov r14, r8 call qword ptr [rip + memmove@GOTPCREL] sub r15, r14 lea rsi, [rbx + 4*r15] shl r14, 2 mov rdi, rbx mov rdx, r14 call qword ptr [rip + memmove@GOTPCREL] mov rdi, rbx mov rax, qword ptr [rsp] lea rsi, [rbx + 4*rax] lea rdi, [rbx + 4*r12] mov rbx, qword ptr [rsp + 8] jmp .LBB0_40 .LBB0_17: xorps xmm0, xmm0 movups xmmword ptr [r13 + 16], xmm0 jmp .LBB0_44 .LBB0_18: mov r14, r15 sub r14, rcx jbe .LBB0_28 cmp rax, r15 jae .LBB0_33 lea rax, [rcx + r12] sub r15, rcx lea rsi, [rdi + 4*rax] shl r15, 2 mov r14, rdi mov rdx, r15 mov r15, rcx jmp .LBB0_31 .LBB0_21: mov r14, rbx sub r14, rcx jbe .LBB0_29 cmp rax, rbx jae .LBB0_34 lea rax, [rcx + rdx] sub rbx, rcx lea rsi, [rdi + 4*rax] shl rbx, 2 mov r14, rdi mov r15, rdx mov rdx, rbx mov rbx, rcx call qword ptr [rip + memmove@GOTPCREL] mov rdi, r14 lea rsi, [r14 + 4*r15] lea rdi, [r14 + 4*r12] jmp .LBB0_40 .LBB0_24: sub r15, rcx jbe .LBB0_35 sub rcx, r8 mov qword ptr [rsp + 8], rcx lea rsi, [rdi + 4*r12] mov r12, rdi lea rdi, [rdi + 4*rbx] lea rdx, [4*r8] mov r14, r8 call qword ptr [rip + memmove@GOTPCREL] add r14, rbx lea rdi, [r12 + 4*r14] mov rbx, qword ptr [rsp + 8] lea rdx, [4*rbx] mov rsi, r12 call qword ptr [rip + memmove@GOTPCREL] mov rdi, r12 lea rsi, [r12 + 4*rbx] jmp .LBB0_36 .LBB0_26: sub rbx, rcx jbe .LBB0_37 sub rcx, r8 lea rsi, [rdi + 4*rdx] mov r15, rdi lea rdi, [rdi + 4*r12] lea rdx, [4*r8] mov r14, rcx mov qword ptr [rsp], r8 call qword ptr [rip + memmove@GOTPCREL] add r12, qword ptr [rsp] lea rdi, [r15 + 4*r12] lea rdx, [4*r14] mov rsi, r15 call qword ptr [rip + memmove@GOTPCREL] mov rdi, r15 lea rsi, [r15 + 4*r14] jmp .LBB0_40 .LBB0_28: lea rsi, [rdi + 4*r12] lea rdi, [rdi + 4*rbx] jmp .LBB0_36 .LBB0_29: lea rsi, [rdi + 4*rdx] lea rdi, [rdi + 4*r12] jmp .LBB0_40 .LBB0_30: lea rax, [r8 + rbx] mov r14, rdi lea rdi, [rdi + 4*rax] mov rsi, r14 mov r15, r8 .LBB0_31: call qword ptr [rip + memmove@GOTPCREL] mov rdi, r14 lea rsi, [r14 + 4*r12] lea rdi, [r14 + 4*rbx] jmp .LBB0_36 .LBB0_32: lea rax, [r12 + r8] mov rbx, rdi lea rdi, [rdi + 4*rax] mov rsi, rbx mov r14, r8 call qword ptr [rip + memmove@GOTPCREL] mov rdi, rbx mov rax, qword ptr [rsp] lea rsi, [rbx + 4*rax] jmp .LBB0_38 .LBB0_33: lea rsi, [rdi + 4*r12] mov r15, rdi lea rdi, [rdi + 4*rbx] lea rdx, [4*rcx] mov rbx, rcx call qword ptr [rip + memmove@GOTPCREL] mov rdi, r15 add rbx, r12 lea rsi, [r15 + 4*rbx] mov r15, r14 jmp .LBB0_36 .LBB0_34: lea rsi, [rdi + 4*rdx] mov rbx, rdi lea rdi, [rdi + 4*r12] mov r15, rdx lea rdx, [4*rcx] mov r12, rcx call qword ptr [rip + memmove@GOTPCREL] mov rdi, rbx add r12, r15 lea rsi, [rbx + 4*r12] jmp .LBB0_39 .LBB0_35: lea rsi, [rdi + 4*r12] mov r14, rdi lea rdi, [rdi + 4*rbx] mov r12, rdx lea rdx, [4*r8] mov r15, r8 call qword ptr [rip + memmove@GOTPCREL] add r15, rbx mov rsi, r14 lea rdi, [r14 + 4*r15] mov r15, r12 .LBB0_36: shl r15, 2 mov rdx, r15 call qword ptr [rip + memmove@GOTPCREL] mov rsi, qword ptr [rsp + 16] jmp .LBB0_42 .LBB0_37: lea rsi, [rdi + 4*rdx] mov rbx, rdi lea rdi, [rdi + 4*r12] lea rdx, [4*r8] mov r15, r8 call qword ptr [rip + memmove@GOTPCREL] add r12, r15 mov rsi, rbx .LBB0_38: lea rdi, [rbx + 4*r12] .LBB0_39: mov rbx, r14 .LBB0_40: shl rbx, 2 mov rdx, rbx call qword ptr [rip + memmove@GOTPCREL] mov r15, qword ptr [r13] mov rax, qword ptr [r13 + 16] add rax, rbp mov rsi, qword ptr [rsp + 16] .LBB0_41: xor ecx, ecx cmp rax, r15 cmovae rcx, r15 sub rax, rcx mov qword ptr [r13 + 16], rax .LBB0_42: sub rsi, rbp .LBB0_43: mov qword ptr [r13 + 24], rsi .LBB0_44: add rsp, 24 pop rbx pop r12 pop r13 pop r14 pop r15 pop rbp ret .LBB0_45: lea rdx, [rip + .L__unnamed_1] mov rdi, rax call qword ptr [rip + core::slice::index::slice_index_order_fail@GOTPCREL] ``` after: ```asm clear: movups xmmword ptr [rdi + 16], xmm0 ret truncate: cmp qword ptr [rdi + 24], rsi jbe .LBB2_4 test rsi, rsi jne .LBB2_3 mov qword ptr [rdi + 16], 0 .LBB2_3: mov qword ptr [rdi + 24], rsi .LBB2_4: ret advance: mov rcx, qword ptr [rdi + 24] mov rax, rcx sub rax, rsi jbe .LBB3_1 mov rcx, qword ptr [rdi] add rsi, qword ptr [rdi + 16] xor edx, edx cmp rsi, rcx cmovae rdx, rcx sub rsi, rdx mov qword ptr [rdi + 16], rsi mov qword ptr [rdi + 24], rax ret .LBB3_1: test rcx, rcx je .LBB3_3 mov qword ptr [rdi + 24], 0 .LBB3_3: mov qword ptr [rdi + 16], 0 ret remove: push rbp push r15 push r14 push r13 push r12 push rbx push rax mov r15, rsi mov r14, rdx sub r14, rsi jb .LBB4_9 mov rbx, rdi mov r12, qword ptr [rdi + 24] mov r13, r12 sub r13, rdx jb .LBB4_10 mov qword ptr [rbx + 24], r15 mov rbp, r12 sub rbp, r14 test r15, r15 je .LBB4_4 cmp rbp, r15 jne .LBB4_11 .LBB4_4: cmp r12, r14 jne .LBB4_6 .LBB4_5: mov qword ptr [rbx + 16], 0 jmp .LBB4_8 .LBB4_11: mov rdi, rbx mov rsi, r14 mov rdx, r15 mov rcx, r13 call <<alloc::collections::vec_deque::drain::Drain<T,A> as core::ops::drop::Drop>::drop::DropGuard<T,A> as core::ops::drop::Drop>::drop::copy_data cmp r12, r14 je .LBB4_5 .LBB4_6: cmp r13, r15 jbe .LBB4_8 mov rax, qword ptr [rbx] add r14, qword ptr [rbx + 16] xor ecx, ecx cmp r14, rax cmovae rcx, rax sub r14, rcx mov qword ptr [rbx + 16], r14 .LBB4_8: mov qword ptr [rbx + 24], rbp add rsp, 8 pop rbx pop r12 pop r13 pop r14 pop r15 pop rbp ret .LBB4_9: lea rax, [rip + .L__unnamed_1] mov rdi, r15 mov rsi, rdx mov rdx, rax call qword ptr [rip + core::slice::index::slice_index_order_fail@GOTPCREL] .LBB4_10: lea rax, [rip + .L__unnamed_1] mov rdi, rdx mov rsi, r12 mov rdx, rax call qword ptr [rip + core::slice::index::slice_end_index_len_fail@GOTPCREL] <<alloc::collections::vec_deque::drain::Drain<T,A> as core::ops::drop::Drop>::drop::DropGuard<T,A> as core::ops::drop::Drop>::drop::copy_data: push rbp push r15 push r14 push r13 push r12 push rbx push rax mov r14, rsi cmp rdx, rcx jae .LBB0_1 mov r12, qword ptr [rdi] mov rax, qword ptr [rdi + 16] add r14, rax xor ecx, ecx cmp r14, r12 cmovae rcx, r12 sub r14, rcx mov r15, rdx mov r13, r14 mov r14, rax mov rcx, r13 sub rcx, r14 je .LBB0_18 .LBB0_4: mov rdi, qword ptr [rdi + 8] mov rax, rcx add rax, r12 cmovae rax, rcx mov rbx, r12 sub rbx, r14 mov rcx, r12 sub rcx, r13 mov rbp, r15 sub rbp, rbx jbe .LBB0_5 cmp rax, r15 jae .LBB0_12 mov rdx, r15 sub rdx, rbx shl rdx, 2 cmp r15, rcx jbe .LBB0_16 sub rbx, rcx mov rbp, rdi lea rdi, [rdi + 4*rbx] mov r15, qword ptr [rip + memmove@GOTPCREL] mov rsi, rbp mov qword ptr [rsp], rcx call r15 sub r12, rbx lea rsi, [4*r12] add rsi, rbp shl rbx, 2 mov rdi, rbp mov rdx, rbx call r15 mov rdi, rbp lea rsi, [4*r14] add rsi, rbp lea rdi, [4*r13] add rdi, rbp mov r15, qword ptr [rsp] jmp .LBB0_7 .LBB0_1: mov r15, rcx add r14, rdx mov r12, qword ptr [rdi] mov r13, qword ptr [rdi + 16] add r14, r13 xor eax, eax cmp r14, r12 mov rcx, r12 cmovb rcx, rax sub r14, rcx add r13, rdx cmp r13, r12 cmovae rax, r12 sub r13, rax mov rcx, r13 sub rcx, r14 jne .LBB0_4 .LBB0_18: add rsp, 8 pop rbx pop r12 pop r13 pop r14 pop r15 pop rbp ret .LBB0_5: mov rbx, r15 sub rbx, rcx jbe .LBB0_6 cmp rax, r15 jae .LBB0_9 lea rax, [rcx + r14] sub r15, rcx lea rsi, [rdi + 4*rax] shl r15, 2 mov rbx, rdi mov rdx, r15 mov r15, rcx call qword ptr [rip + memmove@GOTPCREL] mov rdi, rbx lea rsi, [rbx + 4*r14] lea rdi, [rbx + 4*r13] jmp .LBB0_7 .LBB0_12: sub r15, rcx jbe .LBB0_13 sub rcx, rbx lea rsi, [rdi + 4*r14] mov r12, rdi lea rdi, [rdi + 4*r13] lea rdx, [4*rbx] mov r14, qword ptr [rip + memmove@GOTPCREL] mov rbp, rcx call r14 add rbx, r13 lea rdi, [r12 + 4*rbx] lea rdx, [4*rbp] mov rsi, r12 call r14 mov rdi, r12 lea rsi, [r12 + 4*rbp] jmp .LBB0_7 .LBB0_6: lea rsi, [rdi + 4*r14] lea rdi, [rdi + 4*r13] jmp .LBB0_7 .LBB0_16: lea rax, [rbx + r13] mov r15, rdi lea rdi, [rdi + 4*rax] mov rsi, r15 call qword ptr [rip + memmove@GOTPCREL] mov rdi, r15 lea rsi, [r15 + 4*r14] lea rdi, [r15 + 4*r13] mov r15, rbx jmp .LBB0_7 .LBB0_9: lea rsi, [rdi + 4*r14] mov r15, rdi lea rdi, [rdi + 4*r13] lea rdx, [4*rcx] mov r12, rcx call qword ptr [rip + memmove@GOTPCREL] mov rdi, r15 add r12, r14 lea rsi, [r15 + 4*r12] mov r15, rbx jmp .LBB0_7 .LBB0_13: lea rsi, [rdi + 4*r14] mov r14, rdi lea rdi, [rdi + 4*r13] lea rdx, [4*rbx] call qword ptr [rip + memmove@GOTPCREL] add rbx, r13 mov rsi, r14 lea rdi, [r14 + 4*rbx] mov r15, rbp .LBB0_7: shl r15, 2 mov rdx, r15 add rsp, 8 pop rbx pop r12 pop r13 pop r14 pop r15 pop rbp jmp qword ptr [rip + memmove@GOTPCREL] ``` </details>
…he8472 Optimize `VecDeque::drain` for (half-)open ranges The most common use cases of `VecDeque::drain` consume either the entire queue or elements from the front or back.[^1] This PR makes these operations faster by optimizing the generated code of the destructor of the drain: * `.drain(..)` is now the same as `.clear()`. * `.drain(n..)` is now (almost[^2]) the same as `.truncate(n)`. * `.drain(..n)` is now an efficient "advance" function. This operation is not provided by a dedicated function and optimizing it is my main motivation for this PR. Previously, all of these cases generated a function call to the destructor of the `DropGuard`, emitting a lot of unused machine code as well as unnecessary branches and loads/stores of stack variables. There are no algorithmic changes in this PR, but it simplifies the code enough to allow LLVM to recognize the special cases and optimize accordingly. Most notably, it allows elimination of the rather large [`wrap_copy`] function. Some [rudimentary microbenchmarks][benches] show a performance improvement of **~3x-4x** on my machine for the special cases and roughly equal performance for the general case. Best reviewed commit by commit. [^1]: source: GitHub code search: [full range `drain(..)` = 7.5k results][full], [from front `drain(..n)` = 3.2k results][front], [from back `drain(n..)` = 1.6k results][back], [from middle `drain(n..m)` = <500 results][middle] [^2]: `.drain(0..)` and `.clear()` reset the head to 0, but `.truncate(0)` does not. [full]: https://github.com/search?type=code&q=%2FVecDeque%28.%7C%5Cn%29%2B%5C.drain%5C%280%3F%5C.%5C.%5C%29%2F+lang%3ARust [front]: https://github.com/search?type=code&q=%2FVecDeque%28.%7C%5Cn%29%2B%5C.drain%5C%280%3F%5C.%5C.%5B%5E%29%5D.*%5C%29%2F+lang%3ARust [back]: https://github.com/search?type=code&q=%2FVecDeque%28.%7C%5Cn%29%2B%5C.drain%5C%28%5B%5E0%5D.*%5C.%5C.%5C%29%2F+lang%3ARust [middle]: https://github.com/search?type=code&q=%2FVecDeque%28.%7C%5Cn%29%2B%5C.drain%5C%28%5B%5E0%5D.*%5C.%5C.%5B%5E%29%5D.*%5C%29%2F+lang%3ARust [`wrap_copy`]: https://github.com/rust-lang/rust/blob/4fd68eb47bad1c121417ac4450b2f0456150db86/library/alloc/src/collections/vec_deque/mod.rs#L262-L391 [benches]: https://gist.github.com/lukas-code/c97bd707d074c4cc31f241edbc7fd2a2 <details> <summary>generated assembly</summary> before: ```asm clear: sub rsp, 40 mov rax, qword ptr [rdi + 24] mov qword ptr [rdi + 24], 0 mov qword ptr [rsp], rdi mov qword ptr [rsp + 8], rax xorps xmm0, xmm0 movups xmmword ptr [rsp + 16], xmm0 mov qword ptr [rsp + 32], rax test rax, rax je .LBB1_2 mov rcx, qword ptr [rdi] mov rdx, qword ptr [rdi + 16] xor esi, esi cmp rdx, rcx cmovae rsi, rcx sub rdx, rsi mov rsi, rcx sub rsi, rdx lea rdi, [rdx + rax] cmp rsi, rax cmovb rdi, rcx sub rdi, rdx mov qword ptr [rsp + 16], rdi mov qword ptr [rsp + 32], 0 .LBB1_2: mov rdi, rsp call core::ptr::drop_in_place<<alloc::collections::vec_deque::drain::Drain<T,A> as core::ops::drop::Drop>::drop::DropGuard<i32,alloc::alloc::Global>> add rsp, 40 ret truncate: mov rax, qword ptr [rdi + 24] sub rax, rsi jbe .LBB2_2 sub rsp, 40 mov qword ptr [rdi + 24], rsi mov qword ptr [rsp], rdi mov qword ptr [rsp + 8], rax mov rcx, qword ptr [rdi] mov rdx, qword ptr [rdi + 16] add rdx, rsi xor edi, edi cmp rdx, rcx cmovae rdi, rcx mov qword ptr [rsp + 24], 0 sub rdx, rdi mov rdi, rcx sub rdi, rdx lea r8, [rdx + rax] cmp rdi, rax cmovb r8, rcx sub rsi, rdx add rsi, r8 mov qword ptr [rsp + 16], rsi mov qword ptr [rsp + 32], 0 mov rdi, rsp call core::ptr::drop_in_place<<alloc::collections::vec_deque::drain::Drain<T,A> as core::ops::drop::Drop>::drop::DropGuard<i32,alloc::alloc::Global>> add rsp, 40 advance: mov rcx, qword ptr [rdi + 24] mov rax, rcx sub rax, rsi jbe .LBB3_1 sub rsp, 40 mov qword ptr [rdi + 24], 0 mov qword ptr [rsp], rdi mov qword ptr [rsp + 8], rsi mov qword ptr [rsp + 16], 0 mov qword ptr [rsp + 24], rax mov qword ptr [rsp + 32], rsi test rsi, rsi je .LBB3_6 mov rax, qword ptr [rdi] mov rcx, qword ptr [rdi + 16] xor edx, edx cmp rcx, rax cmovae rdx, rax sub rcx, rdx mov rdx, rax sub rdx, rcx lea rdi, [rcx + rsi] cmp rdx, rsi cmovb rdi, rax sub rdi, rcx mov qword ptr [rsp + 16], rdi mov qword ptr [rsp + 32], 0 .LBB3_6: mov rdi, rsp call core::ptr::drop_in_place<<alloc::collections::vec_deque::drain::Drain<T,A> as core::ops::drop::Drop>::drop::DropGuard<i32,alloc::alloc::Global>> add rsp, 40 ret .LBB3_1: test rcx, rcx je .LBB3_3 mov qword ptr [rdi + 24], 0 .LBB3_3: mov qword ptr [rdi + 16], 0 ret remove: sub rsp, 40 cmp rdx, rsi jb .LBB4_5 mov rax, qword ptr [rdi + 24] mov rcx, rax sub rcx, rdx jb .LBB4_6 mov qword ptr [rdi + 24], rsi mov qword ptr [rsp], rdi sub rdx, rsi mov qword ptr [rsp + 8], rdx mov qword ptr [rsp + 16], rsi mov qword ptr [rsp + 24], rcx mov qword ptr [rsp + 32], rdx je .LBB4_4 mov rax, qword ptr [rdi] mov rcx, qword ptr [rdi + 16] add rcx, rsi xor edi, edi cmp rcx, rax cmovae rdi, rax sub rcx, rdi mov rdi, rax sub rdi, rcx lea r8, [rcx + rdx] cmp rdi, rdx cmovb r8, rax sub rsi, rcx add rsi, r8 mov qword ptr [rsp + 16], rsi mov qword ptr [rsp + 32], 0 .LBB4_4: mov rdi, rsp call core::ptr::drop_in_place<<alloc::collections::vec_deque::drain::Drain<T,A> as core::ops::drop::Drop>::drop::DropGuard<i32,alloc::alloc::Global>> add rsp, 40 ret .LBB4_5: lea rax, [rip + .L__unnamed_2] mov rdi, rsi mov rsi, rdx mov rdx, rax call qword ptr [rip + core::slice::index::slice_index_order_fail@GOTPCREL] .LBB4_6: lea rcx, [rip + .L__unnamed_2] mov rdi, rdx mov rsi, rax mov rdx, rcx call qword ptr [rip + core::slice::index::slice_end_index_len_fail@GOTPCREL] core::ptr::drop_in_place<<alloc::collections::vec_deque::drain::Drain<T,A> as core::ops::drop::Drop>::drop::DropGuard<i32,alloc::alloc::Global>>: push rbp push r15 push r14 push r13 push r12 push rbx sub rsp, 24 mov rsi, qword ptr [rdi + 32] test rsi, rsi je .LBB0_2 mov rax, qword ptr [rdi + 16] add rsi, rax jb .LBB0_45 .LBB0_2: mov r13, qword ptr [rdi] mov rbp, qword ptr [rdi + 8] mov rbx, qword ptr [r13 + 24] lea r12, [rbx + rbp] mov r15, qword ptr [rdi + 24] lea rsi, [r15 + r12] test rbx, rbx je .LBB0_10 test r15, r15 je .LBB0_42 cmp rbx, r15 jbe .LBB0_12 mov r14, qword ptr [r13] mov rax, qword ptr [r13 + 16] add r12, rax xor ecx, ecx cmp r12, r14 mov rdx, r14 cmovb rdx, rcx sub r12, rdx add rbx, rax cmp rbx, r14 cmovae rcx, r14 sub rbx, rcx mov rcx, rbx sub rcx, r12 je .LBB0_42 mov rdi, qword ptr [r13 + 8] mov rax, rcx add rax, r14 cmovae rax, rcx mov r8, r14 sub r8, r12 mov rcx, r14 sub rcx, rbx mov rdx, r15 sub rdx, r8 mov qword ptr [rsp + 16], rsi jbe .LBB0_18 cmp rax, r15 jae .LBB0_24 mov rdx, r15 sub rdx, r8 shl rdx, 2 cmp r15, rcx jbe .LBB0_30 sub r8, rcx mov qword ptr [rsp], rdi mov rax, qword ptr [rsp] lea rdi, [rax + 4*r8] mov rsi, qword ptr [rsp] mov qword ptr [rsp + 8], rcx mov r15, r8 call qword ptr [rip + memmove@GOTPCREL] sub r14, r15 mov rax, qword ptr [rsp] lea rsi, [rax + 4*r14] shl r15, 2 mov rdi, qword ptr [rsp] mov rdx, r15 call qword ptr [rip + memmove@GOTPCREL] mov rdi, qword ptr [rsp] lea rsi, [rdi + 4*r12] lea rdi, [rdi + 4*rbx] mov r15, qword ptr [rsp + 8] jmp .LBB0_36 .LBB0_10: test r15, r15 je .LBB0_17 mov rax, qword ptr [r13] sub rsi, rbp add rbp, qword ptr [r13 + 16] xor ecx, ecx cmp rbp, rax cmovae rcx, rax sub rbp, rcx mov qword ptr [r13 + 16], rbp jmp .LBB0_43 .LBB0_12: mov rdx, qword ptr [r13 + 16] mov r15, qword ptr [r13] lea rax, [rdx + rbp] xor ecx, ecx cmp rax, r15 cmovae rcx, r15 mov r12, rax sub r12, rcx mov rcx, r12 sub rcx, rdx je .LBB0_41 mov rdi, qword ptr [r13 + 8] mov rax, rcx add rax, r15 cmovae rax, rcx mov r8, r15 sub r8, rdx mov rcx, r15 sub rcx, r12 mov r14, rbx sub r14, r8 mov qword ptr [rsp + 16], rsi jbe .LBB0_21 cmp rax, rbx jae .LBB0_26 mov qword ptr [rsp], rdx mov rdx, rbx sub rdx, r8 shl rdx, 2 cmp rbx, rcx jbe .LBB0_32 sub r8, rcx mov rbx, rdi lea rdi, [rdi + 4*r8] mov rsi, rbx mov qword ptr [rsp + 8], rcx mov r14, r8 call qword ptr [rip + memmove@GOTPCREL] sub r15, r14 lea rsi, [rbx + 4*r15] shl r14, 2 mov rdi, rbx mov rdx, r14 call qword ptr [rip + memmove@GOTPCREL] mov rdi, rbx mov rax, qword ptr [rsp] lea rsi, [rbx + 4*rax] lea rdi, [rbx + 4*r12] mov rbx, qword ptr [rsp + 8] jmp .LBB0_40 .LBB0_17: xorps xmm0, xmm0 movups xmmword ptr [r13 + 16], xmm0 jmp .LBB0_44 .LBB0_18: mov r14, r15 sub r14, rcx jbe .LBB0_28 cmp rax, r15 jae .LBB0_33 lea rax, [rcx + r12] sub r15, rcx lea rsi, [rdi + 4*rax] shl r15, 2 mov r14, rdi mov rdx, r15 mov r15, rcx jmp .LBB0_31 .LBB0_21: mov r14, rbx sub r14, rcx jbe .LBB0_29 cmp rax, rbx jae .LBB0_34 lea rax, [rcx + rdx] sub rbx, rcx lea rsi, [rdi + 4*rax] shl rbx, 2 mov r14, rdi mov r15, rdx mov rdx, rbx mov rbx, rcx call qword ptr [rip + memmove@GOTPCREL] mov rdi, r14 lea rsi, [r14 + 4*r15] lea rdi, [r14 + 4*r12] jmp .LBB0_40 .LBB0_24: sub r15, rcx jbe .LBB0_35 sub rcx, r8 mov qword ptr [rsp + 8], rcx lea rsi, [rdi + 4*r12] mov r12, rdi lea rdi, [rdi + 4*rbx] lea rdx, [4*r8] mov r14, r8 call qword ptr [rip + memmove@GOTPCREL] add r14, rbx lea rdi, [r12 + 4*r14] mov rbx, qword ptr [rsp + 8] lea rdx, [4*rbx] mov rsi, r12 call qword ptr [rip + memmove@GOTPCREL] mov rdi, r12 lea rsi, [r12 + 4*rbx] jmp .LBB0_36 .LBB0_26: sub rbx, rcx jbe .LBB0_37 sub rcx, r8 lea rsi, [rdi + 4*rdx] mov r15, rdi lea rdi, [rdi + 4*r12] lea rdx, [4*r8] mov r14, rcx mov qword ptr [rsp], r8 call qword ptr [rip + memmove@GOTPCREL] add r12, qword ptr [rsp] lea rdi, [r15 + 4*r12] lea rdx, [4*r14] mov rsi, r15 call qword ptr [rip + memmove@GOTPCREL] mov rdi, r15 lea rsi, [r15 + 4*r14] jmp .LBB0_40 .LBB0_28: lea rsi, [rdi + 4*r12] lea rdi, [rdi + 4*rbx] jmp .LBB0_36 .LBB0_29: lea rsi, [rdi + 4*rdx] lea rdi, [rdi + 4*r12] jmp .LBB0_40 .LBB0_30: lea rax, [r8 + rbx] mov r14, rdi lea rdi, [rdi + 4*rax] mov rsi, r14 mov r15, r8 .LBB0_31: call qword ptr [rip + memmove@GOTPCREL] mov rdi, r14 lea rsi, [r14 + 4*r12] lea rdi, [r14 + 4*rbx] jmp .LBB0_36 .LBB0_32: lea rax, [r12 + r8] mov rbx, rdi lea rdi, [rdi + 4*rax] mov rsi, rbx mov r14, r8 call qword ptr [rip + memmove@GOTPCREL] mov rdi, rbx mov rax, qword ptr [rsp] lea rsi, [rbx + 4*rax] jmp .LBB0_38 .LBB0_33: lea rsi, [rdi + 4*r12] mov r15, rdi lea rdi, [rdi + 4*rbx] lea rdx, [4*rcx] mov rbx, rcx call qword ptr [rip + memmove@GOTPCREL] mov rdi, r15 add rbx, r12 lea rsi, [r15 + 4*rbx] mov r15, r14 jmp .LBB0_36 .LBB0_34: lea rsi, [rdi + 4*rdx] mov rbx, rdi lea rdi, [rdi + 4*r12] mov r15, rdx lea rdx, [4*rcx] mov r12, rcx call qword ptr [rip + memmove@GOTPCREL] mov rdi, rbx add r12, r15 lea rsi, [rbx + 4*r12] jmp .LBB0_39 .LBB0_35: lea rsi, [rdi + 4*r12] mov r14, rdi lea rdi, [rdi + 4*rbx] mov r12, rdx lea rdx, [4*r8] mov r15, r8 call qword ptr [rip + memmove@GOTPCREL] add r15, rbx mov rsi, r14 lea rdi, [r14 + 4*r15] mov r15, r12 .LBB0_36: shl r15, 2 mov rdx, r15 call qword ptr [rip + memmove@GOTPCREL] mov rsi, qword ptr [rsp + 16] jmp .LBB0_42 .LBB0_37: lea rsi, [rdi + 4*rdx] mov rbx, rdi lea rdi, [rdi + 4*r12] lea rdx, [4*r8] mov r15, r8 call qword ptr [rip + memmove@GOTPCREL] add r12, r15 mov rsi, rbx .LBB0_38: lea rdi, [rbx + 4*r12] .LBB0_39: mov rbx, r14 .LBB0_40: shl rbx, 2 mov rdx, rbx call qword ptr [rip + memmove@GOTPCREL] mov r15, qword ptr [r13] mov rax, qword ptr [r13 + 16] add rax, rbp mov rsi, qword ptr [rsp + 16] .LBB0_41: xor ecx, ecx cmp rax, r15 cmovae rcx, r15 sub rax, rcx mov qword ptr [r13 + 16], rax .LBB0_42: sub rsi, rbp .LBB0_43: mov qword ptr [r13 + 24], rsi .LBB0_44: add rsp, 24 pop rbx pop r12 pop r13 pop r14 pop r15 pop rbp ret .LBB0_45: lea rdx, [rip + .L__unnamed_1] mov rdi, rax call qword ptr [rip + core::slice::index::slice_index_order_fail@GOTPCREL] ``` after: ```asm clear: movups xmmword ptr [rdi + 16], xmm0 ret truncate: cmp qword ptr [rdi + 24], rsi jbe .LBB2_4 test rsi, rsi jne .LBB2_3 mov qword ptr [rdi + 16], 0 .LBB2_3: mov qword ptr [rdi + 24], rsi .LBB2_4: ret advance: mov rcx, qword ptr [rdi + 24] mov rax, rcx sub rax, rsi jbe .LBB3_1 mov rcx, qword ptr [rdi] add rsi, qword ptr [rdi + 16] xor edx, edx cmp rsi, rcx cmovae rdx, rcx sub rsi, rdx mov qword ptr [rdi + 16], rsi mov qword ptr [rdi + 24], rax ret .LBB3_1: test rcx, rcx je .LBB3_3 mov qword ptr [rdi + 24], 0 .LBB3_3: mov qword ptr [rdi + 16], 0 ret remove: push rbp push r15 push r14 push r13 push r12 push rbx push rax mov r15, rsi mov r14, rdx sub r14, rsi jb .LBB4_9 mov rbx, rdi mov r12, qword ptr [rdi + 24] mov r13, r12 sub r13, rdx jb .LBB4_10 mov qword ptr [rbx + 24], r15 mov rbp, r12 sub rbp, r14 test r15, r15 je .LBB4_4 cmp rbp, r15 jne .LBB4_11 .LBB4_4: cmp r12, r14 jne .LBB4_6 .LBB4_5: mov qword ptr [rbx + 16], 0 jmp .LBB4_8 .LBB4_11: mov rdi, rbx mov rsi, r14 mov rdx, r15 mov rcx, r13 call <<alloc::collections::vec_deque::drain::Drain<T,A> as core::ops::drop::Drop>::drop::DropGuard<T,A> as core::ops::drop::Drop>::drop::copy_data cmp r12, r14 je .LBB4_5 .LBB4_6: cmp r13, r15 jbe .LBB4_8 mov rax, qword ptr [rbx] add r14, qword ptr [rbx + 16] xor ecx, ecx cmp r14, rax cmovae rcx, rax sub r14, rcx mov qword ptr [rbx + 16], r14 .LBB4_8: mov qword ptr [rbx + 24], rbp add rsp, 8 pop rbx pop r12 pop r13 pop r14 pop r15 pop rbp ret .LBB4_9: lea rax, [rip + .L__unnamed_1] mov rdi, r15 mov rsi, rdx mov rdx, rax call qword ptr [rip + core::slice::index::slice_index_order_fail@GOTPCREL] .LBB4_10: lea rax, [rip + .L__unnamed_1] mov rdi, rdx mov rsi, r12 mov rdx, rax call qword ptr [rip + core::slice::index::slice_end_index_len_fail@GOTPCREL] <<alloc::collections::vec_deque::drain::Drain<T,A> as core::ops::drop::Drop>::drop::DropGuard<T,A> as core::ops::drop::Drop>::drop::copy_data: push rbp push r15 push r14 push r13 push r12 push rbx push rax mov r14, rsi cmp rdx, rcx jae .LBB0_1 mov r12, qword ptr [rdi] mov rax, qword ptr [rdi + 16] add r14, rax xor ecx, ecx cmp r14, r12 cmovae rcx, r12 sub r14, rcx mov r15, rdx mov r13, r14 mov r14, rax mov rcx, r13 sub rcx, r14 je .LBB0_18 .LBB0_4: mov rdi, qword ptr [rdi + 8] mov rax, rcx add rax, r12 cmovae rax, rcx mov rbx, r12 sub rbx, r14 mov rcx, r12 sub rcx, r13 mov rbp, r15 sub rbp, rbx jbe .LBB0_5 cmp rax, r15 jae .LBB0_12 mov rdx, r15 sub rdx, rbx shl rdx, 2 cmp r15, rcx jbe .LBB0_16 sub rbx, rcx mov rbp, rdi lea rdi, [rdi + 4*rbx] mov r15, qword ptr [rip + memmove@GOTPCREL] mov rsi, rbp mov qword ptr [rsp], rcx call r15 sub r12, rbx lea rsi, [4*r12] add rsi, rbp shl rbx, 2 mov rdi, rbp mov rdx, rbx call r15 mov rdi, rbp lea rsi, [4*r14] add rsi, rbp lea rdi, [4*r13] add rdi, rbp mov r15, qword ptr [rsp] jmp .LBB0_7 .LBB0_1: mov r15, rcx add r14, rdx mov r12, qword ptr [rdi] mov r13, qword ptr [rdi + 16] add r14, r13 xor eax, eax cmp r14, r12 mov rcx, r12 cmovb rcx, rax sub r14, rcx add r13, rdx cmp r13, r12 cmovae rax, r12 sub r13, rax mov rcx, r13 sub rcx, r14 jne .LBB0_4 .LBB0_18: add rsp, 8 pop rbx pop r12 pop r13 pop r14 pop r15 pop rbp ret .LBB0_5: mov rbx, r15 sub rbx, rcx jbe .LBB0_6 cmp rax, r15 jae .LBB0_9 lea rax, [rcx + r14] sub r15, rcx lea rsi, [rdi + 4*rax] shl r15, 2 mov rbx, rdi mov rdx, r15 mov r15, rcx call qword ptr [rip + memmove@GOTPCREL] mov rdi, rbx lea rsi, [rbx + 4*r14] lea rdi, [rbx + 4*r13] jmp .LBB0_7 .LBB0_12: sub r15, rcx jbe .LBB0_13 sub rcx, rbx lea rsi, [rdi + 4*r14] mov r12, rdi lea rdi, [rdi + 4*r13] lea rdx, [4*rbx] mov r14, qword ptr [rip + memmove@GOTPCREL] mov rbp, rcx call r14 add rbx, r13 lea rdi, [r12 + 4*rbx] lea rdx, [4*rbp] mov rsi, r12 call r14 mov rdi, r12 lea rsi, [r12 + 4*rbp] jmp .LBB0_7 .LBB0_6: lea rsi, [rdi + 4*r14] lea rdi, [rdi + 4*r13] jmp .LBB0_7 .LBB0_16: lea rax, [rbx + r13] mov r15, rdi lea rdi, [rdi + 4*rax] mov rsi, r15 call qword ptr [rip + memmove@GOTPCREL] mov rdi, r15 lea rsi, [r15 + 4*r14] lea rdi, [r15 + 4*r13] mov r15, rbx jmp .LBB0_7 .LBB0_9: lea rsi, [rdi + 4*r14] mov r15, rdi lea rdi, [rdi + 4*r13] lea rdx, [4*rcx] mov r12, rcx call qword ptr [rip + memmove@GOTPCREL] mov rdi, r15 add r12, r14 lea rsi, [r15 + 4*r12] mov r15, rbx jmp .LBB0_7 .LBB0_13: lea rsi, [rdi + 4*r14] mov r14, rdi lea rdi, [rdi + 4*r13] lea rdx, [4*rbx] call qword ptr [rip + memmove@GOTPCREL] add rbx, r13 mov rsi, r14 lea rdi, [r14 + 4*rbx] mov r15, rbp .LBB0_7: shl r15, 2 mov rdx, r15 add rsp, 8 pop rbx pop r12 pop r13 pop r14 pop r15 pop rbp jmp qword ptr [rip + memmove@GOTPCREL] ``` </details>
…llaumeGomez Rollup of 13 pull requests Successful merges: - rust-lang#118264 (Optimize `VecDeque::drain` for (half-)open ranges) - rust-lang#120741 (Make `io::BorrowedCursor::advance` safe) - rust-lang#120777 (Bump Unicode to version 15.1.0, regenerate tables) - rust-lang#120971 (Fix comment in core/src/str/validations.rs) - rust-lang#121034 (Improve wording of `static_mut_ref`) - rust-lang#121095 (Add extra indent spaces for rust-playground link) - rust-lang#121109 (Add an ErrorGuaranteed to ast::TyKind::Err (attempt 2)) - rust-lang#121119 (Make `async Fn` trait kind errors better) - rust-lang#121141 (Fix closure kind docs) - rust-lang#121145 (Update aarch64 target feature docs to match LLVM) - rust-lang#121146 (Only point out non-diverging arms for match suggestions) - rust-lang#121147 (Avoid debug logging entire MIR body) - rust-lang#121155 (doc: add note about panicking examples for strict_overflow_ops) r? `@ghost` `@rustbot` modify labels: rollup
…8472 Optimize `VecDeque::drain` for (half-)open ranges The most common use cases of `VecDeque::drain` consume either the entire queue or elements from the front or back.[^1] This PR makes these operations faster by optimizing the generated code of the destructor of the drain: * `.drain(..)` is now the same as `.clear()`. * `.drain(n..)` is now (almost[^2]) the same as `.truncate(n)`. * `.drain(..n)` is now an efficient "advance" function. This operation is not provided by a dedicated function and optimizing it is my main motivation for this PR. Previously, all of these cases generated a function call to the destructor of the `DropGuard`, emitting a lot of unused machine code as well as unnecessary branches and loads/stores of stack variables. There are no algorithmic changes in this PR, but it simplifies the code enough to allow LLVM to recognize the special cases and optimize accordingly. Most notably, it allows elimination of the rather large [`wrap_copy`] function. Some [rudimentary microbenchmarks][benches] show a performance improvement of **~3x-4x** on my machine for the special cases and roughly equal performance for the general case. Best reviewed commit by commit. [^1]: source: GitHub code search: [full range `drain(..)` = 7.5k results][full], [from front `drain(..n)` = 3.2k results][front], [from back `drain(n..)` = 1.6k results][back], [from middle `drain(n..m)` = <500 results][middle] [^2]: `.drain(0..)` and `.clear()` reset the head to 0, but `.truncate(0)` does not. [full]: https://github.com/search?type=code&q=%2FVecDeque%28.%7C%5Cn%29%2B%5C.drain%5C%280%3F%5C.%5C.%5C%29%2F+lang%3ARust [front]: https://github.com/search?type=code&q=%2FVecDeque%28.%7C%5Cn%29%2B%5C.drain%5C%280%3F%5C.%5C.%5B%5E%29%5D.*%5C%29%2F+lang%3ARust [back]: https://github.com/search?type=code&q=%2FVecDeque%28.%7C%5Cn%29%2B%5C.drain%5C%28%5B%5E0%5D.*%5C.%5C.%5C%29%2F+lang%3ARust [middle]: https://github.com/search?type=code&q=%2FVecDeque%28.%7C%5Cn%29%2B%5C.drain%5C%28%5B%5E0%5D.*%5C.%5C.%5B%5E%29%5D.*%5C%29%2F+lang%3ARust [`wrap_copy`]: https://github.com/rust-lang/rust/blob/4fd68eb47bad1c121417ac4450b2f0456150db86/library/alloc/src/collections/vec_deque/mod.rs#L262-L391 [benches]: https://gist.github.com/lukas-code/c97bd707d074c4cc31f241edbc7fd2a2 <details> <summary>generated assembly</summary> before: ```asm clear: sub rsp, 40 mov rax, qword ptr [rdi + 24] mov qword ptr [rdi + 24], 0 mov qword ptr [rsp], rdi mov qword ptr [rsp + 8], rax xorps xmm0, xmm0 movups xmmword ptr [rsp + 16], xmm0 mov qword ptr [rsp + 32], rax test rax, rax je .LBB1_2 mov rcx, qword ptr [rdi] mov rdx, qword ptr [rdi + 16] xor esi, esi cmp rdx, rcx cmovae rsi, rcx sub rdx, rsi mov rsi, rcx sub rsi, rdx lea rdi, [rdx + rax] cmp rsi, rax cmovb rdi, rcx sub rdi, rdx mov qword ptr [rsp + 16], rdi mov qword ptr [rsp + 32], 0 .LBB1_2: mov rdi, rsp call core::ptr::drop_in_place<<alloc::collections::vec_deque::drain::Drain<T,A> as core::ops::drop::Drop>::drop::DropGuard<i32,alloc::alloc::Global>> add rsp, 40 ret truncate: mov rax, qword ptr [rdi + 24] sub rax, rsi jbe .LBB2_2 sub rsp, 40 mov qword ptr [rdi + 24], rsi mov qword ptr [rsp], rdi mov qword ptr [rsp + 8], rax mov rcx, qword ptr [rdi] mov rdx, qword ptr [rdi + 16] add rdx, rsi xor edi, edi cmp rdx, rcx cmovae rdi, rcx mov qword ptr [rsp + 24], 0 sub rdx, rdi mov rdi, rcx sub rdi, rdx lea r8, [rdx + rax] cmp rdi, rax cmovb r8, rcx sub rsi, rdx add rsi, r8 mov qword ptr [rsp + 16], rsi mov qword ptr [rsp + 32], 0 mov rdi, rsp call core::ptr::drop_in_place<<alloc::collections::vec_deque::drain::Drain<T,A> as core::ops::drop::Drop>::drop::DropGuard<i32,alloc::alloc::Global>> add rsp, 40 advance: mov rcx, qword ptr [rdi + 24] mov rax, rcx sub rax, rsi jbe .LBB3_1 sub rsp, 40 mov qword ptr [rdi + 24], 0 mov qword ptr [rsp], rdi mov qword ptr [rsp + 8], rsi mov qword ptr [rsp + 16], 0 mov qword ptr [rsp + 24], rax mov qword ptr [rsp + 32], rsi test rsi, rsi je .LBB3_6 mov rax, qword ptr [rdi] mov rcx, qword ptr [rdi + 16] xor edx, edx cmp rcx, rax cmovae rdx, rax sub rcx, rdx mov rdx, rax sub rdx, rcx lea rdi, [rcx + rsi] cmp rdx, rsi cmovb rdi, rax sub rdi, rcx mov qword ptr [rsp + 16], rdi mov qword ptr [rsp + 32], 0 .LBB3_6: mov rdi, rsp call core::ptr::drop_in_place<<alloc::collections::vec_deque::drain::Drain<T,A> as core::ops::drop::Drop>::drop::DropGuard<i32,alloc::alloc::Global>> add rsp, 40 ret .LBB3_1: test rcx, rcx je .LBB3_3 mov qword ptr [rdi + 24], 0 .LBB3_3: mov qword ptr [rdi + 16], 0 ret remove: sub rsp, 40 cmp rdx, rsi jb .LBB4_5 mov rax, qword ptr [rdi + 24] mov rcx, rax sub rcx, rdx jb .LBB4_6 mov qword ptr [rdi + 24], rsi mov qword ptr [rsp], rdi sub rdx, rsi mov qword ptr [rsp + 8], rdx mov qword ptr [rsp + 16], rsi mov qword ptr [rsp + 24], rcx mov qword ptr [rsp + 32], rdx je .LBB4_4 mov rax, qword ptr [rdi] mov rcx, qword ptr [rdi + 16] add rcx, rsi xor edi, edi cmp rcx, rax cmovae rdi, rax sub rcx, rdi mov rdi, rax sub rdi, rcx lea r8, [rcx + rdx] cmp rdi, rdx cmovb r8, rax sub rsi, rcx add rsi, r8 mov qword ptr [rsp + 16], rsi mov qword ptr [rsp + 32], 0 .LBB4_4: mov rdi, rsp call core::ptr::drop_in_place<<alloc::collections::vec_deque::drain::Drain<T,A> as core::ops::drop::Drop>::drop::DropGuard<i32,alloc::alloc::Global>> add rsp, 40 ret .LBB4_5: lea rax, [rip + .L__unnamed_2] mov rdi, rsi mov rsi, rdx mov rdx, rax call qword ptr [rip + core::slice::index::slice_index_order_fail@GOTPCREL] .LBB4_6: lea rcx, [rip + .L__unnamed_2] mov rdi, rdx mov rsi, rax mov rdx, rcx call qword ptr [rip + core::slice::index::slice_end_index_len_fail@GOTPCREL] core::ptr::drop_in_place<<alloc::collections::vec_deque::drain::Drain<T,A> as core::ops::drop::Drop>::drop::DropGuard<i32,alloc::alloc::Global>>: push rbp push r15 push r14 push r13 push r12 push rbx sub rsp, 24 mov rsi, qword ptr [rdi + 32] test rsi, rsi je .LBB0_2 mov rax, qword ptr [rdi + 16] add rsi, rax jb .LBB0_45 .LBB0_2: mov r13, qword ptr [rdi] mov rbp, qword ptr [rdi + 8] mov rbx, qword ptr [r13 + 24] lea r12, [rbx + rbp] mov r15, qword ptr [rdi + 24] lea rsi, [r15 + r12] test rbx, rbx je .LBB0_10 test r15, r15 je .LBB0_42 cmp rbx, r15 jbe .LBB0_12 mov r14, qword ptr [r13] mov rax, qword ptr [r13 + 16] add r12, rax xor ecx, ecx cmp r12, r14 mov rdx, r14 cmovb rdx, rcx sub r12, rdx add rbx, rax cmp rbx, r14 cmovae rcx, r14 sub rbx, rcx mov rcx, rbx sub rcx, r12 je .LBB0_42 mov rdi, qword ptr [r13 + 8] mov rax, rcx add rax, r14 cmovae rax, rcx mov r8, r14 sub r8, r12 mov rcx, r14 sub rcx, rbx mov rdx, r15 sub rdx, r8 mov qword ptr [rsp + 16], rsi jbe .LBB0_18 cmp rax, r15 jae .LBB0_24 mov rdx, r15 sub rdx, r8 shl rdx, 2 cmp r15, rcx jbe .LBB0_30 sub r8, rcx mov qword ptr [rsp], rdi mov rax, qword ptr [rsp] lea rdi, [rax + 4*r8] mov rsi, qword ptr [rsp] mov qword ptr [rsp + 8], rcx mov r15, r8 call qword ptr [rip + memmove@GOTPCREL] sub r14, r15 mov rax, qword ptr [rsp] lea rsi, [rax + 4*r14] shl r15, 2 mov rdi, qword ptr [rsp] mov rdx, r15 call qword ptr [rip + memmove@GOTPCREL] mov rdi, qword ptr [rsp] lea rsi, [rdi + 4*r12] lea rdi, [rdi + 4*rbx] mov r15, qword ptr [rsp + 8] jmp .LBB0_36 .LBB0_10: test r15, r15 je .LBB0_17 mov rax, qword ptr [r13] sub rsi, rbp add rbp, qword ptr [r13 + 16] xor ecx, ecx cmp rbp, rax cmovae rcx, rax sub rbp, rcx mov qword ptr [r13 + 16], rbp jmp .LBB0_43 .LBB0_12: mov rdx, qword ptr [r13 + 16] mov r15, qword ptr [r13] lea rax, [rdx + rbp] xor ecx, ecx cmp rax, r15 cmovae rcx, r15 mov r12, rax sub r12, rcx mov rcx, r12 sub rcx, rdx je .LBB0_41 mov rdi, qword ptr [r13 + 8] mov rax, rcx add rax, r15 cmovae rax, rcx mov r8, r15 sub r8, rdx mov rcx, r15 sub rcx, r12 mov r14, rbx sub r14, r8 mov qword ptr [rsp + 16], rsi jbe .LBB0_21 cmp rax, rbx jae .LBB0_26 mov qword ptr [rsp], rdx mov rdx, rbx sub rdx, r8 shl rdx, 2 cmp rbx, rcx jbe .LBB0_32 sub r8, rcx mov rbx, rdi lea rdi, [rdi + 4*r8] mov rsi, rbx mov qword ptr [rsp + 8], rcx mov r14, r8 call qword ptr [rip + memmove@GOTPCREL] sub r15, r14 lea rsi, [rbx + 4*r15] shl r14, 2 mov rdi, rbx mov rdx, r14 call qword ptr [rip + memmove@GOTPCREL] mov rdi, rbx mov rax, qword ptr [rsp] lea rsi, [rbx + 4*rax] lea rdi, [rbx + 4*r12] mov rbx, qword ptr [rsp + 8] jmp .LBB0_40 .LBB0_17: xorps xmm0, xmm0 movups xmmword ptr [r13 + 16], xmm0 jmp .LBB0_44 .LBB0_18: mov r14, r15 sub r14, rcx jbe .LBB0_28 cmp rax, r15 jae .LBB0_33 lea rax, [rcx + r12] sub r15, rcx lea rsi, [rdi + 4*rax] shl r15, 2 mov r14, rdi mov rdx, r15 mov r15, rcx jmp .LBB0_31 .LBB0_21: mov r14, rbx sub r14, rcx jbe .LBB0_29 cmp rax, rbx jae .LBB0_34 lea rax, [rcx + rdx] sub rbx, rcx lea rsi, [rdi + 4*rax] shl rbx, 2 mov r14, rdi mov r15, rdx mov rdx, rbx mov rbx, rcx call qword ptr [rip + memmove@GOTPCREL] mov rdi, r14 lea rsi, [r14 + 4*r15] lea rdi, [r14 + 4*r12] jmp .LBB0_40 .LBB0_24: sub r15, rcx jbe .LBB0_35 sub rcx, r8 mov qword ptr [rsp + 8], rcx lea rsi, [rdi + 4*r12] mov r12, rdi lea rdi, [rdi + 4*rbx] lea rdx, [4*r8] mov r14, r8 call qword ptr [rip + memmove@GOTPCREL] add r14, rbx lea rdi, [r12 + 4*r14] mov rbx, qword ptr [rsp + 8] lea rdx, [4*rbx] mov rsi, r12 call qword ptr [rip + memmove@GOTPCREL] mov rdi, r12 lea rsi, [r12 + 4*rbx] jmp .LBB0_36 .LBB0_26: sub rbx, rcx jbe .LBB0_37 sub rcx, r8 lea rsi, [rdi + 4*rdx] mov r15, rdi lea rdi, [rdi + 4*r12] lea rdx, [4*r8] mov r14, rcx mov qword ptr [rsp], r8 call qword ptr [rip + memmove@GOTPCREL] add r12, qword ptr [rsp] lea rdi, [r15 + 4*r12] lea rdx, [4*r14] mov rsi, r15 call qword ptr [rip + memmove@GOTPCREL] mov rdi, r15 lea rsi, [r15 + 4*r14] jmp .LBB0_40 .LBB0_28: lea rsi, [rdi + 4*r12] lea rdi, [rdi + 4*rbx] jmp .LBB0_36 .LBB0_29: lea rsi, [rdi + 4*rdx] lea rdi, [rdi + 4*r12] jmp .LBB0_40 .LBB0_30: lea rax, [r8 + rbx] mov r14, rdi lea rdi, [rdi + 4*rax] mov rsi, r14 mov r15, r8 .LBB0_31: call qword ptr [rip + memmove@GOTPCREL] mov rdi, r14 lea rsi, [r14 + 4*r12] lea rdi, [r14 + 4*rbx] jmp .LBB0_36 .LBB0_32: lea rax, [r12 + r8] mov rbx, rdi lea rdi, [rdi + 4*rax] mov rsi, rbx mov r14, r8 call qword ptr [rip + memmove@GOTPCREL] mov rdi, rbx mov rax, qword ptr [rsp] lea rsi, [rbx + 4*rax] jmp .LBB0_38 .LBB0_33: lea rsi, [rdi + 4*r12] mov r15, rdi lea rdi, [rdi + 4*rbx] lea rdx, [4*rcx] mov rbx, rcx call qword ptr [rip + memmove@GOTPCREL] mov rdi, r15 add rbx, r12 lea rsi, [r15 + 4*rbx] mov r15, r14 jmp .LBB0_36 .LBB0_34: lea rsi, [rdi + 4*rdx] mov rbx, rdi lea rdi, [rdi + 4*r12] mov r15, rdx lea rdx, [4*rcx] mov r12, rcx call qword ptr [rip + memmove@GOTPCREL] mov rdi, rbx add r12, r15 lea rsi, [rbx + 4*r12] jmp .LBB0_39 .LBB0_35: lea rsi, [rdi + 4*r12] mov r14, rdi lea rdi, [rdi + 4*rbx] mov r12, rdx lea rdx, [4*r8] mov r15, r8 call qword ptr [rip + memmove@GOTPCREL] add r15, rbx mov rsi, r14 lea rdi, [r14 + 4*r15] mov r15, r12 .LBB0_36: shl r15, 2 mov rdx, r15 call qword ptr [rip + memmove@GOTPCREL] mov rsi, qword ptr [rsp + 16] jmp .LBB0_42 .LBB0_37: lea rsi, [rdi + 4*rdx] mov rbx, rdi lea rdi, [rdi + 4*r12] lea rdx, [4*r8] mov r15, r8 call qword ptr [rip + memmove@GOTPCREL] add r12, r15 mov rsi, rbx .LBB0_38: lea rdi, [rbx + 4*r12] .LBB0_39: mov rbx, r14 .LBB0_40: shl rbx, 2 mov rdx, rbx call qword ptr [rip + memmove@GOTPCREL] mov r15, qword ptr [r13] mov rax, qword ptr [r13 + 16] add rax, rbp mov rsi, qword ptr [rsp + 16] .LBB0_41: xor ecx, ecx cmp rax, r15 cmovae rcx, r15 sub rax, rcx mov qword ptr [r13 + 16], rax .LBB0_42: sub rsi, rbp .LBB0_43: mov qword ptr [r13 + 24], rsi .LBB0_44: add rsp, 24 pop rbx pop r12 pop r13 pop r14 pop r15 pop rbp ret .LBB0_45: lea rdx, [rip + .L__unnamed_1] mov rdi, rax call qword ptr [rip + core::slice::index::slice_index_order_fail@GOTPCREL] ``` after: ```asm clear: movups xmmword ptr [rdi + 16], xmm0 ret truncate: cmp qword ptr [rdi + 24], rsi jbe .LBB2_4 test rsi, rsi jne .LBB2_3 mov qword ptr [rdi + 16], 0 .LBB2_3: mov qword ptr [rdi + 24], rsi .LBB2_4: ret advance: mov rcx, qword ptr [rdi + 24] mov rax, rcx sub rax, rsi jbe .LBB3_1 mov rcx, qword ptr [rdi] add rsi, qword ptr [rdi + 16] xor edx, edx cmp rsi, rcx cmovae rdx, rcx sub rsi, rdx mov qword ptr [rdi + 16], rsi mov qword ptr [rdi + 24], rax ret .LBB3_1: test rcx, rcx je .LBB3_3 mov qword ptr [rdi + 24], 0 .LBB3_3: mov qword ptr [rdi + 16], 0 ret remove: push rbp push r15 push r14 push r13 push r12 push rbx push rax mov r15, rsi mov r14, rdx sub r14, rsi jb .LBB4_9 mov rbx, rdi mov r12, qword ptr [rdi + 24] mov r13, r12 sub r13, rdx jb .LBB4_10 mov qword ptr [rbx + 24], r15 mov rbp, r12 sub rbp, r14 test r15, r15 je .LBB4_4 cmp rbp, r15 jne .LBB4_11 .LBB4_4: cmp r12, r14 jne .LBB4_6 .LBB4_5: mov qword ptr [rbx + 16], 0 jmp .LBB4_8 .LBB4_11: mov rdi, rbx mov rsi, r14 mov rdx, r15 mov rcx, r13 call <<alloc::collections::vec_deque::drain::Drain<T,A> as core::ops::drop::Drop>::drop::DropGuard<T,A> as core::ops::drop::Drop>::drop::copy_data cmp r12, r14 je .LBB4_5 .LBB4_6: cmp r13, r15 jbe .LBB4_8 mov rax, qword ptr [rbx] add r14, qword ptr [rbx + 16] xor ecx, ecx cmp r14, rax cmovae rcx, rax sub r14, rcx mov qword ptr [rbx + 16], r14 .LBB4_8: mov qword ptr [rbx + 24], rbp add rsp, 8 pop rbx pop r12 pop r13 pop r14 pop r15 pop rbp ret .LBB4_9: lea rax, [rip + .L__unnamed_1] mov rdi, r15 mov rsi, rdx mov rdx, rax call qword ptr [rip + core::slice::index::slice_index_order_fail@GOTPCREL] .LBB4_10: lea rax, [rip + .L__unnamed_1] mov rdi, rdx mov rsi, r12 mov rdx, rax call qword ptr [rip + core::slice::index::slice_end_index_len_fail@GOTPCREL] <<alloc::collections::vec_deque::drain::Drain<T,A> as core::ops::drop::Drop>::drop::DropGuard<T,A> as core::ops::drop::Drop>::drop::copy_data: push rbp push r15 push r14 push r13 push r12 push rbx push rax mov r14, rsi cmp rdx, rcx jae .LBB0_1 mov r12, qword ptr [rdi] mov rax, qword ptr [rdi + 16] add r14, rax xor ecx, ecx cmp r14, r12 cmovae rcx, r12 sub r14, rcx mov r15, rdx mov r13, r14 mov r14, rax mov rcx, r13 sub rcx, r14 je .LBB0_18 .LBB0_4: mov rdi, qword ptr [rdi + 8] mov rax, rcx add rax, r12 cmovae rax, rcx mov rbx, r12 sub rbx, r14 mov rcx, r12 sub rcx, r13 mov rbp, r15 sub rbp, rbx jbe .LBB0_5 cmp rax, r15 jae .LBB0_12 mov rdx, r15 sub rdx, rbx shl rdx, 2 cmp r15, rcx jbe .LBB0_16 sub rbx, rcx mov rbp, rdi lea rdi, [rdi + 4*rbx] mov r15, qword ptr [rip + memmove@GOTPCREL] mov rsi, rbp mov qword ptr [rsp], rcx call r15 sub r12, rbx lea rsi, [4*r12] add rsi, rbp shl rbx, 2 mov rdi, rbp mov rdx, rbx call r15 mov rdi, rbp lea rsi, [4*r14] add rsi, rbp lea rdi, [4*r13] add rdi, rbp mov r15, qword ptr [rsp] jmp .LBB0_7 .LBB0_1: mov r15, rcx add r14, rdx mov r12, qword ptr [rdi] mov r13, qword ptr [rdi + 16] add r14, r13 xor eax, eax cmp r14, r12 mov rcx, r12 cmovb rcx, rax sub r14, rcx add r13, rdx cmp r13, r12 cmovae rax, r12 sub r13, rax mov rcx, r13 sub rcx, r14 jne .LBB0_4 .LBB0_18: add rsp, 8 pop rbx pop r12 pop r13 pop r14 pop r15 pop rbp ret .LBB0_5: mov rbx, r15 sub rbx, rcx jbe .LBB0_6 cmp rax, r15 jae .LBB0_9 lea rax, [rcx + r14] sub r15, rcx lea rsi, [rdi + 4*rax] shl r15, 2 mov rbx, rdi mov rdx, r15 mov r15, rcx call qword ptr [rip + memmove@GOTPCREL] mov rdi, rbx lea rsi, [rbx + 4*r14] lea rdi, [rbx + 4*r13] jmp .LBB0_7 .LBB0_12: sub r15, rcx jbe .LBB0_13 sub rcx, rbx lea rsi, [rdi + 4*r14] mov r12, rdi lea rdi, [rdi + 4*r13] lea rdx, [4*rbx] mov r14, qword ptr [rip + memmove@GOTPCREL] mov rbp, rcx call r14 add rbx, r13 lea rdi, [r12 + 4*rbx] lea rdx, [4*rbp] mov rsi, r12 call r14 mov rdi, r12 lea rsi, [r12 + 4*rbp] jmp .LBB0_7 .LBB0_6: lea rsi, [rdi + 4*r14] lea rdi, [rdi + 4*r13] jmp .LBB0_7 .LBB0_16: lea rax, [rbx + r13] mov r15, rdi lea rdi, [rdi + 4*rax] mov rsi, r15 call qword ptr [rip + memmove@GOTPCREL] mov rdi, r15 lea rsi, [r15 + 4*r14] lea rdi, [r15 + 4*r13] mov r15, rbx jmp .LBB0_7 .LBB0_9: lea rsi, [rdi + 4*r14] mov r15, rdi lea rdi, [rdi + 4*r13] lea rdx, [4*rcx] mov r12, rcx call qword ptr [rip + memmove@GOTPCREL] mov rdi, r15 add r12, r14 lea rsi, [r15 + 4*r12] mov r15, rbx jmp .LBB0_7 .LBB0_13: lea rsi, [rdi + 4*r14] mov r14, rdi lea rdi, [rdi + 4*r13] lea rdx, [4*rbx] call qword ptr [rip + memmove@GOTPCREL] add rbx, r13 mov rsi, r14 lea rdi, [r14 + 4*rbx] mov r15, rbp .LBB0_7: shl r15, 2 mov rdx, r15 add rsp, 8 pop rbx pop r12 pop r13 pop r14 pop r15 pop rbp jmp qword ptr [rip + memmove@GOTPCREL] ``` </details>
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I fixed the codegen test for 32-bit. @rustbot label -A-testsuite -T-infra |
@bors r+ |
…he8472 Optimize `VecDeque::drain` for (half-)open ranges The most common use cases of `VecDeque::drain` consume either the entire queue or elements from the front or back.[^1] This PR makes these operations faster by optimizing the generated code of the destructor of the drain: * `.drain(..)` is now the same as `.clear()`. * `.drain(n..)` is now (almost[^2]) the same as `.truncate(n)`. * `.drain(..n)` is now an efficient "advance" function. This operation is not provided by a dedicated function and optimizing it is my main motivation for this PR. Previously, all of these cases generated a function call to the destructor of the `DropGuard`, emitting a lot of unused machine code as well as unnecessary branches and loads/stores of stack variables. There are no algorithmic changes in this PR, but it simplifies the code enough to allow LLVM to recognize the special cases and optimize accordingly. Most notably, it allows elimination of the rather large [`wrap_copy`] function. Some [rudimentary microbenchmarks][benches] show a performance improvement of **~3x-4x** on my machine for the special cases and roughly equal performance for the general case. Best reviewed commit by commit. [^1]: source: GitHub code search: [full range `drain(..)` = 7.5k results][full], [from front `drain(..n)` = 3.2k results][front], [from back `drain(n..)` = 1.6k results][back], [from middle `drain(n..m)` = <500 results][middle] [^2]: `.drain(0..)` and `.clear()` reset the head to 0, but `.truncate(0)` does not. [full]: https://github.com/search?type=code&q=%2FVecDeque%28.%7C%5Cn%29%2B%5C.drain%5C%280%3F%5C.%5C.%5C%29%2F+lang%3ARust [front]: https://github.com/search?type=code&q=%2FVecDeque%28.%7C%5Cn%29%2B%5C.drain%5C%280%3F%5C.%5C.%5B%5E%29%5D.*%5C%29%2F+lang%3ARust [back]: https://github.com/search?type=code&q=%2FVecDeque%28.%7C%5Cn%29%2B%5C.drain%5C%28%5B%5E0%5D.*%5C.%5C.%5C%29%2F+lang%3ARust [middle]: https://github.com/search?type=code&q=%2FVecDeque%28.%7C%5Cn%29%2B%5C.drain%5C%28%5B%5E0%5D.*%5C.%5C.%5B%5E%29%5D.*%5C%29%2F+lang%3ARust [`wrap_copy`]: https://github.com/rust-lang/rust/blob/4fd68eb47bad1c121417ac4450b2f0456150db86/library/alloc/src/collections/vec_deque/mod.rs#L262-L391 [benches]: https://gist.github.com/lukas-code/c97bd707d074c4cc31f241edbc7fd2a2 <details> <summary>generated assembly</summary> before: ```asm clear: sub rsp, 40 mov rax, qword ptr [rdi + 24] mov qword ptr [rdi + 24], 0 mov qword ptr [rsp], rdi mov qword ptr [rsp + 8], rax xorps xmm0, xmm0 movups xmmword ptr [rsp + 16], xmm0 mov qword ptr [rsp + 32], rax test rax, rax je .LBB1_2 mov rcx, qword ptr [rdi] mov rdx, qword ptr [rdi + 16] xor esi, esi cmp rdx, rcx cmovae rsi, rcx sub rdx, rsi mov rsi, rcx sub rsi, rdx lea rdi, [rdx + rax] cmp rsi, rax cmovb rdi, rcx sub rdi, rdx mov qword ptr [rsp + 16], rdi mov qword ptr [rsp + 32], 0 .LBB1_2: mov rdi, rsp call core::ptr::drop_in_place<<alloc::collections::vec_deque::drain::Drain<T,A> as core::ops::drop::Drop>::drop::DropGuard<i32,alloc::alloc::Global>> add rsp, 40 ret truncate: mov rax, qword ptr [rdi + 24] sub rax, rsi jbe .LBB2_2 sub rsp, 40 mov qword ptr [rdi + 24], rsi mov qword ptr [rsp], rdi mov qword ptr [rsp + 8], rax mov rcx, qword ptr [rdi] mov rdx, qword ptr [rdi + 16] add rdx, rsi xor edi, edi cmp rdx, rcx cmovae rdi, rcx mov qword ptr [rsp + 24], 0 sub rdx, rdi mov rdi, rcx sub rdi, rdx lea r8, [rdx + rax] cmp rdi, rax cmovb r8, rcx sub rsi, rdx add rsi, r8 mov qword ptr [rsp + 16], rsi mov qword ptr [rsp + 32], 0 mov rdi, rsp call core::ptr::drop_in_place<<alloc::collections::vec_deque::drain::Drain<T,A> as core::ops::drop::Drop>::drop::DropGuard<i32,alloc::alloc::Global>> add rsp, 40 advance: mov rcx, qword ptr [rdi + 24] mov rax, rcx sub rax, rsi jbe .LBB3_1 sub rsp, 40 mov qword ptr [rdi + 24], 0 mov qword ptr [rsp], rdi mov qword ptr [rsp + 8], rsi mov qword ptr [rsp + 16], 0 mov qword ptr [rsp + 24], rax mov qword ptr [rsp + 32], rsi test rsi, rsi je .LBB3_6 mov rax, qword ptr [rdi] mov rcx, qword ptr [rdi + 16] xor edx, edx cmp rcx, rax cmovae rdx, rax sub rcx, rdx mov rdx, rax sub rdx, rcx lea rdi, [rcx + rsi] cmp rdx, rsi cmovb rdi, rax sub rdi, rcx mov qword ptr [rsp + 16], rdi mov qword ptr [rsp + 32], 0 .LBB3_6: mov rdi, rsp call core::ptr::drop_in_place<<alloc::collections::vec_deque::drain::Drain<T,A> as core::ops::drop::Drop>::drop::DropGuard<i32,alloc::alloc::Global>> add rsp, 40 ret .LBB3_1: test rcx, rcx je .LBB3_3 mov qword ptr [rdi + 24], 0 .LBB3_3: mov qword ptr [rdi + 16], 0 ret remove: sub rsp, 40 cmp rdx, rsi jb .LBB4_5 mov rax, qword ptr [rdi + 24] mov rcx, rax sub rcx, rdx jb .LBB4_6 mov qword ptr [rdi + 24], rsi mov qword ptr [rsp], rdi sub rdx, rsi mov qword ptr [rsp + 8], rdx mov qword ptr [rsp + 16], rsi mov qword ptr [rsp + 24], rcx mov qword ptr [rsp + 32], rdx je .LBB4_4 mov rax, qword ptr [rdi] mov rcx, qword ptr [rdi + 16] add rcx, rsi xor edi, edi cmp rcx, rax cmovae rdi, rax sub rcx, rdi mov rdi, rax sub rdi, rcx lea r8, [rcx + rdx] cmp rdi, rdx cmovb r8, rax sub rsi, rcx add rsi, r8 mov qword ptr [rsp + 16], rsi mov qword ptr [rsp + 32], 0 .LBB4_4: mov rdi, rsp call core::ptr::drop_in_place<<alloc::collections::vec_deque::drain::Drain<T,A> as core::ops::drop::Drop>::drop::DropGuard<i32,alloc::alloc::Global>> add rsp, 40 ret .LBB4_5: lea rax, [rip + .L__unnamed_2] mov rdi, rsi mov rsi, rdx mov rdx, rax call qword ptr [rip + core::slice::index::slice_index_order_fail@GOTPCREL] .LBB4_6: lea rcx, [rip + .L__unnamed_2] mov rdi, rdx mov rsi, rax mov rdx, rcx call qword ptr [rip + core::slice::index::slice_end_index_len_fail@GOTPCREL] core::ptr::drop_in_place<<alloc::collections::vec_deque::drain::Drain<T,A> as core::ops::drop::Drop>::drop::DropGuard<i32,alloc::alloc::Global>>: push rbp push r15 push r14 push r13 push r12 push rbx sub rsp, 24 mov rsi, qword ptr [rdi + 32] test rsi, rsi je .LBB0_2 mov rax, qword ptr [rdi + 16] add rsi, rax jb .LBB0_45 .LBB0_2: mov r13, qword ptr [rdi] mov rbp, qword ptr [rdi + 8] mov rbx, qword ptr [r13 + 24] lea r12, [rbx + rbp] mov r15, qword ptr [rdi + 24] lea rsi, [r15 + r12] test rbx, rbx je .LBB0_10 test r15, r15 je .LBB0_42 cmp rbx, r15 jbe .LBB0_12 mov r14, qword ptr [r13] mov rax, qword ptr [r13 + 16] add r12, rax xor ecx, ecx cmp r12, r14 mov rdx, r14 cmovb rdx, rcx sub r12, rdx add rbx, rax cmp rbx, r14 cmovae rcx, r14 sub rbx, rcx mov rcx, rbx sub rcx, r12 je .LBB0_42 mov rdi, qword ptr [r13 + 8] mov rax, rcx add rax, r14 cmovae rax, rcx mov r8, r14 sub r8, r12 mov rcx, r14 sub rcx, rbx mov rdx, r15 sub rdx, r8 mov qword ptr [rsp + 16], rsi jbe .LBB0_18 cmp rax, r15 jae .LBB0_24 mov rdx, r15 sub rdx, r8 shl rdx, 2 cmp r15, rcx jbe .LBB0_30 sub r8, rcx mov qword ptr [rsp], rdi mov rax, qword ptr [rsp] lea rdi, [rax + 4*r8] mov rsi, qword ptr [rsp] mov qword ptr [rsp + 8], rcx mov r15, r8 call qword ptr [rip + memmove@GOTPCREL] sub r14, r15 mov rax, qword ptr [rsp] lea rsi, [rax + 4*r14] shl r15, 2 mov rdi, qword ptr [rsp] mov rdx, r15 call qword ptr [rip + memmove@GOTPCREL] mov rdi, qword ptr [rsp] lea rsi, [rdi + 4*r12] lea rdi, [rdi + 4*rbx] mov r15, qword ptr [rsp + 8] jmp .LBB0_36 .LBB0_10: test r15, r15 je .LBB0_17 mov rax, qword ptr [r13] sub rsi, rbp add rbp, qword ptr [r13 + 16] xor ecx, ecx cmp rbp, rax cmovae rcx, rax sub rbp, rcx mov qword ptr [r13 + 16], rbp jmp .LBB0_43 .LBB0_12: mov rdx, qword ptr [r13 + 16] mov r15, qword ptr [r13] lea rax, [rdx + rbp] xor ecx, ecx cmp rax, r15 cmovae rcx, r15 mov r12, rax sub r12, rcx mov rcx, r12 sub rcx, rdx je .LBB0_41 mov rdi, qword ptr [r13 + 8] mov rax, rcx add rax, r15 cmovae rax, rcx mov r8, r15 sub r8, rdx mov rcx, r15 sub rcx, r12 mov r14, rbx sub r14, r8 mov qword ptr [rsp + 16], rsi jbe .LBB0_21 cmp rax, rbx jae .LBB0_26 mov qword ptr [rsp], rdx mov rdx, rbx sub rdx, r8 shl rdx, 2 cmp rbx, rcx jbe .LBB0_32 sub r8, rcx mov rbx, rdi lea rdi, [rdi + 4*r8] mov rsi, rbx mov qword ptr [rsp + 8], rcx mov r14, r8 call qword ptr [rip + memmove@GOTPCREL] sub r15, r14 lea rsi, [rbx + 4*r15] shl r14, 2 mov rdi, rbx mov rdx, r14 call qword ptr [rip + memmove@GOTPCREL] mov rdi, rbx mov rax, qword ptr [rsp] lea rsi, [rbx + 4*rax] lea rdi, [rbx + 4*r12] mov rbx, qword ptr [rsp + 8] jmp .LBB0_40 .LBB0_17: xorps xmm0, xmm0 movups xmmword ptr [r13 + 16], xmm0 jmp .LBB0_44 .LBB0_18: mov r14, r15 sub r14, rcx jbe .LBB0_28 cmp rax, r15 jae .LBB0_33 lea rax, [rcx + r12] sub r15, rcx lea rsi, [rdi + 4*rax] shl r15, 2 mov r14, rdi mov rdx, r15 mov r15, rcx jmp .LBB0_31 .LBB0_21: mov r14, rbx sub r14, rcx jbe .LBB0_29 cmp rax, rbx jae .LBB0_34 lea rax, [rcx + rdx] sub rbx, rcx lea rsi, [rdi + 4*rax] shl rbx, 2 mov r14, rdi mov r15, rdx mov rdx, rbx mov rbx, rcx call qword ptr [rip + memmove@GOTPCREL] mov rdi, r14 lea rsi, [r14 + 4*r15] lea rdi, [r14 + 4*r12] jmp .LBB0_40 .LBB0_24: sub r15, rcx jbe .LBB0_35 sub rcx, r8 mov qword ptr [rsp + 8], rcx lea rsi, [rdi + 4*r12] mov r12, rdi lea rdi, [rdi + 4*rbx] lea rdx, [4*r8] mov r14, r8 call qword ptr [rip + memmove@GOTPCREL] add r14, rbx lea rdi, [r12 + 4*r14] mov rbx, qword ptr [rsp + 8] lea rdx, [4*rbx] mov rsi, r12 call qword ptr [rip + memmove@GOTPCREL] mov rdi, r12 lea rsi, [r12 + 4*rbx] jmp .LBB0_36 .LBB0_26: sub rbx, rcx jbe .LBB0_37 sub rcx, r8 lea rsi, [rdi + 4*rdx] mov r15, rdi lea rdi, [rdi + 4*r12] lea rdx, [4*r8] mov r14, rcx mov qword ptr [rsp], r8 call qword ptr [rip + memmove@GOTPCREL] add r12, qword ptr [rsp] lea rdi, [r15 + 4*r12] lea rdx, [4*r14] mov rsi, r15 call qword ptr [rip + memmove@GOTPCREL] mov rdi, r15 lea rsi, [r15 + 4*r14] jmp .LBB0_40 .LBB0_28: lea rsi, [rdi + 4*r12] lea rdi, [rdi + 4*rbx] jmp .LBB0_36 .LBB0_29: lea rsi, [rdi + 4*rdx] lea rdi, [rdi + 4*r12] jmp .LBB0_40 .LBB0_30: lea rax, [r8 + rbx] mov r14, rdi lea rdi, [rdi + 4*rax] mov rsi, r14 mov r15, r8 .LBB0_31: call qword ptr [rip + memmove@GOTPCREL] mov rdi, r14 lea rsi, [r14 + 4*r12] lea rdi, [r14 + 4*rbx] jmp .LBB0_36 .LBB0_32: lea rax, [r12 + r8] mov rbx, rdi lea rdi, [rdi + 4*rax] mov rsi, rbx mov r14, r8 call qword ptr [rip + memmove@GOTPCREL] mov rdi, rbx mov rax, qword ptr [rsp] lea rsi, [rbx + 4*rax] jmp .LBB0_38 .LBB0_33: lea rsi, [rdi + 4*r12] mov r15, rdi lea rdi, [rdi + 4*rbx] lea rdx, [4*rcx] mov rbx, rcx call qword ptr [rip + memmove@GOTPCREL] mov rdi, r15 add rbx, r12 lea rsi, [r15 + 4*rbx] mov r15, r14 jmp .LBB0_36 .LBB0_34: lea rsi, [rdi + 4*rdx] mov rbx, rdi lea rdi, [rdi + 4*r12] mov r15, rdx lea rdx, [4*rcx] mov r12, rcx call qword ptr [rip + memmove@GOTPCREL] mov rdi, rbx add r12, r15 lea rsi, [rbx + 4*r12] jmp .LBB0_39 .LBB0_35: lea rsi, [rdi + 4*r12] mov r14, rdi lea rdi, [rdi + 4*rbx] mov r12, rdx lea rdx, [4*r8] mov r15, r8 call qword ptr [rip + memmove@GOTPCREL] add r15, rbx mov rsi, r14 lea rdi, [r14 + 4*r15] mov r15, r12 .LBB0_36: shl r15, 2 mov rdx, r15 call qword ptr [rip + memmove@GOTPCREL] mov rsi, qword ptr [rsp + 16] jmp .LBB0_42 .LBB0_37: lea rsi, [rdi + 4*rdx] mov rbx, rdi lea rdi, [rdi + 4*r12] lea rdx, [4*r8] mov r15, r8 call qword ptr [rip + memmove@GOTPCREL] add r12, r15 mov rsi, rbx .LBB0_38: lea rdi, [rbx + 4*r12] .LBB0_39: mov rbx, r14 .LBB0_40: shl rbx, 2 mov rdx, rbx call qword ptr [rip + memmove@GOTPCREL] mov r15, qword ptr [r13] mov rax, qword ptr [r13 + 16] add rax, rbp mov rsi, qword ptr [rsp + 16] .LBB0_41: xor ecx, ecx cmp rax, r15 cmovae rcx, r15 sub rax, rcx mov qword ptr [r13 + 16], rax .LBB0_42: sub rsi, rbp .LBB0_43: mov qword ptr [r13 + 24], rsi .LBB0_44: add rsp, 24 pop rbx pop r12 pop r13 pop r14 pop r15 pop rbp ret .LBB0_45: lea rdx, [rip + .L__unnamed_1] mov rdi, rax call qword ptr [rip + core::slice::index::slice_index_order_fail@GOTPCREL] ``` after: ```asm clear: movups xmmword ptr [rdi + 16], xmm0 ret truncate: cmp qword ptr [rdi + 24], rsi jbe .LBB2_4 test rsi, rsi jne .LBB2_3 mov qword ptr [rdi + 16], 0 .LBB2_3: mov qword ptr [rdi + 24], rsi .LBB2_4: ret advance: mov rcx, qword ptr [rdi + 24] mov rax, rcx sub rax, rsi jbe .LBB3_1 mov rcx, qword ptr [rdi] add rsi, qword ptr [rdi + 16] xor edx, edx cmp rsi, rcx cmovae rdx, rcx sub rsi, rdx mov qword ptr [rdi + 16], rsi mov qword ptr [rdi + 24], rax ret .LBB3_1: test rcx, rcx je .LBB3_3 mov qword ptr [rdi + 24], 0 .LBB3_3: mov qword ptr [rdi + 16], 0 ret remove: push rbp push r15 push r14 push r13 push r12 push rbx push rax mov r15, rsi mov r14, rdx sub r14, rsi jb .LBB4_9 mov rbx, rdi mov r12, qword ptr [rdi + 24] mov r13, r12 sub r13, rdx jb .LBB4_10 mov qword ptr [rbx + 24], r15 mov rbp, r12 sub rbp, r14 test r15, r15 je .LBB4_4 cmp rbp, r15 jne .LBB4_11 .LBB4_4: cmp r12, r14 jne .LBB4_6 .LBB4_5: mov qword ptr [rbx + 16], 0 jmp .LBB4_8 .LBB4_11: mov rdi, rbx mov rsi, r14 mov rdx, r15 mov rcx, r13 call <<alloc::collections::vec_deque::drain::Drain<T,A> as core::ops::drop::Drop>::drop::DropGuard<T,A> as core::ops::drop::Drop>::drop::copy_data cmp r12, r14 je .LBB4_5 .LBB4_6: cmp r13, r15 jbe .LBB4_8 mov rax, qword ptr [rbx] add r14, qword ptr [rbx + 16] xor ecx, ecx cmp r14, rax cmovae rcx, rax sub r14, rcx mov qword ptr [rbx + 16], r14 .LBB4_8: mov qword ptr [rbx + 24], rbp add rsp, 8 pop rbx pop r12 pop r13 pop r14 pop r15 pop rbp ret .LBB4_9: lea rax, [rip + .L__unnamed_1] mov rdi, r15 mov rsi, rdx mov rdx, rax call qword ptr [rip + core::slice::index::slice_index_order_fail@GOTPCREL] .LBB4_10: lea rax, [rip + .L__unnamed_1] mov rdi, rdx mov rsi, r12 mov rdx, rax call qword ptr [rip + core::slice::index::slice_end_index_len_fail@GOTPCREL] <<alloc::collections::vec_deque::drain::Drain<T,A> as core::ops::drop::Drop>::drop::DropGuard<T,A> as core::ops::drop::Drop>::drop::copy_data: push rbp push r15 push r14 push r13 push r12 push rbx push rax mov r14, rsi cmp rdx, rcx jae .LBB0_1 mov r12, qword ptr [rdi] mov rax, qword ptr [rdi + 16] add r14, rax xor ecx, ecx cmp r14, r12 cmovae rcx, r12 sub r14, rcx mov r15, rdx mov r13, r14 mov r14, rax mov rcx, r13 sub rcx, r14 je .LBB0_18 .LBB0_4: mov rdi, qword ptr [rdi + 8] mov rax, rcx add rax, r12 cmovae rax, rcx mov rbx, r12 sub rbx, r14 mov rcx, r12 sub rcx, r13 mov rbp, r15 sub rbp, rbx jbe .LBB0_5 cmp rax, r15 jae .LBB0_12 mov rdx, r15 sub rdx, rbx shl rdx, 2 cmp r15, rcx jbe .LBB0_16 sub rbx, rcx mov rbp, rdi lea rdi, [rdi + 4*rbx] mov r15, qword ptr [rip + memmove@GOTPCREL] mov rsi, rbp mov qword ptr [rsp], rcx call r15 sub r12, rbx lea rsi, [4*r12] add rsi, rbp shl rbx, 2 mov rdi, rbp mov rdx, rbx call r15 mov rdi, rbp lea rsi, [4*r14] add rsi, rbp lea rdi, [4*r13] add rdi, rbp mov r15, qword ptr [rsp] jmp .LBB0_7 .LBB0_1: mov r15, rcx add r14, rdx mov r12, qword ptr [rdi] mov r13, qword ptr [rdi + 16] add r14, r13 xor eax, eax cmp r14, r12 mov rcx, r12 cmovb rcx, rax sub r14, rcx add r13, rdx cmp r13, r12 cmovae rax, r12 sub r13, rax mov rcx, r13 sub rcx, r14 jne .LBB0_4 .LBB0_18: add rsp, 8 pop rbx pop r12 pop r13 pop r14 pop r15 pop rbp ret .LBB0_5: mov rbx, r15 sub rbx, rcx jbe .LBB0_6 cmp rax, r15 jae .LBB0_9 lea rax, [rcx + r14] sub r15, rcx lea rsi, [rdi + 4*rax] shl r15, 2 mov rbx, rdi mov rdx, r15 mov r15, rcx call qword ptr [rip + memmove@GOTPCREL] mov rdi, rbx lea rsi, [rbx + 4*r14] lea rdi, [rbx + 4*r13] jmp .LBB0_7 .LBB0_12: sub r15, rcx jbe .LBB0_13 sub rcx, rbx lea rsi, [rdi + 4*r14] mov r12, rdi lea rdi, [rdi + 4*r13] lea rdx, [4*rbx] mov r14, qword ptr [rip + memmove@GOTPCREL] mov rbp, rcx call r14 add rbx, r13 lea rdi, [r12 + 4*rbx] lea rdx, [4*rbp] mov rsi, r12 call r14 mov rdi, r12 lea rsi, [r12 + 4*rbp] jmp .LBB0_7 .LBB0_6: lea rsi, [rdi + 4*r14] lea rdi, [rdi + 4*r13] jmp .LBB0_7 .LBB0_16: lea rax, [rbx + r13] mov r15, rdi lea rdi, [rdi + 4*rax] mov rsi, r15 call qword ptr [rip + memmove@GOTPCREL] mov rdi, r15 lea rsi, [r15 + 4*r14] lea rdi, [r15 + 4*r13] mov r15, rbx jmp .LBB0_7 .LBB0_9: lea rsi, [rdi + 4*r14] mov r15, rdi lea rdi, [rdi + 4*r13] lea rdx, [4*rcx] mov r12, rcx call qword ptr [rip + memmove@GOTPCREL] mov rdi, r15 add r12, r14 lea rsi, [r15 + 4*r12] mov r15, rbx jmp .LBB0_7 .LBB0_13: lea rsi, [rdi + 4*r14] mov r14, rdi lea rdi, [rdi + 4*r13] lea rdx, [4*rbx] call qword ptr [rip + memmove@GOTPCREL] add rbx, r13 mov rsi, r14 lea rdi, [r14 + 4*rbx] mov r15, rbp .LBB0_7: shl r15, 2 mov rdx, r15 add rsp, 8 pop rbx pop r12 pop r13 pop r14 pop r15 pop rbp jmp qword ptr [rip + memmove@GOTPCREL] ``` </details>
…llaumeGomez Rollup of 7 pull requests Successful merges: - rust-lang#118264 (Optimize `VecDeque::drain` for (half-)open ranges) - rust-lang#121079 (distribute tool documentations and avoid file conflicts on `x install`) - rust-lang#121100 (Detect when method call on argument could be removed to fulfill failed trait bound) - rust-lang#121160 (rustdoc: fix and refactor HTML rendering a bit) - rust-lang#121198 (Add more checks for `unnamed_fields` during HIR analysis) - rust-lang#121221 (AstConv: Refactor lowering of associated item bindings a bit) - rust-lang#121237 (Use better heuristic for printing Cargo specific diagnostics) r? `@ghost` `@rustbot` modify labels: rollup
☀️ Test successful - checks-actions |
Finished benchmarking commit (158f00a): comparison URL. Overall result: ❌✅ regressions and improvements - no action needed@rustbot label: -perf-regression Instruction countThis is a highly reliable metric that was used to determine the overall result at the top of this comment.
Max RSS (memory usage)ResultsThis is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.
CyclesResultsThis is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.
Binary sizeResultsThis is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.
Bootstrap: 641.933s -> 639.353s (-0.40%) |
The most common use cases of
VecDeque::drain
consume either the entire queue or elements from the front or back.1 This PR makes these operations faster by optimizing the generated code of the destructor of the drain:.drain(..)
is now the same as.clear()
..drain(n..)
is now (almost2) the same as.truncate(n)
..drain(..n)
is now an efficient "advance" function. This operation is not provided by a dedicated function and optimizing it is my main motivation for this PR.Previously, all of these cases generated a function call to the destructor of the
DropGuard
, emitting a lot of unused machine code as well as unnecessary branches and loads/stores of stack variables.There are no algorithmic changes in this PR, but it simplifies the code enough to allow LLVM to recognize the special cases and optimize accordingly. Most notably, it allows elimination of the rather large
wrap_copy
function.Some rudimentary microbenchmarks show a performance improvement of ~3x-4x on my machine for the special cases and roughly equal performance for the general case.
Best reviewed commit by commit.
generated assembly
before:
after:
Footnotes
source: GitHub code search: full range
drain(..)
= 7.5k results, from frontdrain(..n)
= 3.2k results, from backdrain(n..)
= 1.6k results, from middledrain(n..m)
= <500 results ↩.drain(0..)
and.clear()
reset the head to 0, but.truncate(0)
does not. ↩