Taras Tsugrii 6ae2677d72 [rustc_span][perf] Hoist lookup sorted by words out of the loop. ... @lqd commented on https://github.com/rust-lang/rust/pull/114351 asking if `sort_by_words(lookup)` is computed repeatedly. I was assuming that rustc should have no difficulties to hoist it automatically outside of the loop to avoid repeated pure computation, but according to https://godbolt.org/z/frs8Kj1rq it seems like I was wrong: original version seems to have 2 calls per loop iteration ``` .LBB16_3: mov rbx, qword ptr [r13] mov r14, qword ptr [r13 + 8] lea rdi, [rsp + 40] mov rsi, rbx mov rdx, r14 call example::sort_by_words lea rdi, [rsp + 64] mov rsi, qword ptr [rsp + 8] mov rdx, qword ptr [rsp + 16] call example::sort_by_words mov rdi, qword ptr [rsp + 40] mov rdx, qword ptr [rsp + 56] mov rsi, qword ptr [rsp + 64] cmp rdx, qword ptr [rsp + 80] mov qword ptr [rsp + 32], rdi mov qword ptr [rsp + 24], rsi jne .LBB16_5 call qword ptr [rip + bcmp@GOTPCREL] test eax, eax sete al mov dword ptr [rsp + 4], eax mov rsi, qword ptr [rsp + 72] test rsi, rsi jne .LBB16_8 jmp .LBB16_9 ``` but the manually hoisted version just 1: ``` .LBB16_3: mov r13, qword ptr [r15] mov r14, qword ptr [r15 + 8] lea rdi, [rsp + 64] mov rsi, r13 mov rdx, r14 call example::sort_by_words mov rdi, qword ptr [rsp + 64] mov rdx, qword ptr [rsp + 16] cmp qword ptr [rsp + 80], rdx mov qword ptr [rsp + 32], rdi jne .LBB16_5 mov rsi, qword ptr [rsp + 8] call qword ptr [rip + bcmp@GOTPCREL] test eax, eax sete bpl mov rsi, qword ptr [rsp + 72] test rsi, rsi jne .LBB16_8 jmp .LBB16_9 ``` This code is probably not very hot, but there is no reason to leave such a low hanging fruit.		2023-08-02 20:51:16 -07:00
..
src	[rustc_span][perf] Hoist lookup sorted by words out of the loop.	2023-08-02 20:51:16 -07:00
Cargo.toml	Upgrade to indexmap 2.0.0	2023-07-03 13:51:54 -07:00