missed optimization: coalesce PathBuf reallocation #127059
Description
compare the following disassemblies:
#![allow(dead_code)] use std::path::{Path, PathBuf}; #[no_mangle] pub fn boxed_path() -> Box<Path> { Path::new("aaa").into() }boxed_path: lea rdi, [rip + .L__unnamed_1] mov esi, 3 jmp qword ptr [rip + std::path::<impl core::convert::From<&std::path::Path> for alloc::boxed::Box<std::path::Path>>::from::hfd2d6fbd02ea1491@GOTPCREL] .L__unnamed_1: .zero 3,97#![allow(dead_code)] use std::path::{Path, PathBuf}; #[no_mangle] pub fn boxed_path() -> Box<Path> { PathBuf::from("aaa").into() }boxed_path: push rbx sub rsp, 32 lea rsi, [rip + .L__unnamed_1] lea rbx, [rsp + 8] mov edx, 3 mov rdi, rbx call qword ptr [rip + std::sys::os_str::bytes::Slice::to_owned::hda0e6bb365f52f1f@GOTPCREL] mov rdi, rbx call qword ptr [rip + std::ffi::os_str::OsString::into_boxed_os_str::haa190229882bb506@GOTPCREL] add rsp, 32 pop rbx ret .L__unnamed_1: .zero 3,97