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Missed optimization with mir-opt-level 4 #100408
Description
This code with an inner immediately invoked lambda function:
use std::num::NonZeroI32;
pub fn foo(x: NonZeroI32) -> i32 {
(|x: &NonZeroI32| 33 / x.get())(&x)
}Compiled using:
rustc 1.65.0-nightly (f03ce3096 2022-08-08)
binary: rustc
commit-hash: f03ce30962cf1b2a5158667eabae8bf6e8d1cb03
commit-date: 2022-08-08
host: x86_64-unknown-linux-gnu
release: 1.65.0-nightly
LLVM version: 14.0.6
With arguments:
--edition 2021 -C opt-level=3 -Z mir-opt-level=3
Gives a nice asm:
foo:
mov eax, 33
xor edx, edx
idiv edi
retBut cranking opt up to the 4th level:
--edition 2021 -C opt-level=3 -Z mir-opt-level=4
Gives an asm similar to not using the lambda function at all:
foo:
test edi, edi
je .LBB0_2
mov eax, 33
xor edx, edx
idiv edi
ret
.LBB0_2:
push rax
lea rdi, [rip + str.0]
lea rdx, [rip + .L__unnamed_1]
mov esi, 25
call qword ptr [rip + core::panicking::panic@GOTPCREL]
ud2(Inspired by: https://old.reddit.com/r/rust/comments/wkw55b/help_matching_c_codegen_for_a_small_function/ijr7o5x/ ).
Activity
Noratrieb commentedon Aug 11, 2022
I thought that it might be UnreachablePropagation being broken here, but my fix for that pass still emits the bad assembly, so it's probably not it.
tmiasko commentedon Aug 12, 2022
Looks like SROA drops the load range metadata (similar to what happened with
!nonnullin #37945).joseph-isaacs commentedon Aug 31, 2026
Seems to be fixed in #128371
Regression test here:
https://github.com/joseph-isaacs/rust/tree/ji/issue-100408-closeif required