Release builds using AVX code produce incorrect output

Code

#[cfg(target_arch = "x86_64")]
use std::arch::x86_64::*;

fn main() {
    unsafe {
        let f = _mm256_set_pd(2.0, 2.0, 2.0, 2.0);
        let r = _mm256_mul_pd(f, f);

        println!("{:?}", r);
    }
}

Output

The expected output is

__m256d(4.0, 4.0, 4.0, 4.0)

The actual output is

__m256d(4.0, 4.0, 0.0, 0.0)

Notes

The code built in debug mode produces the expected result. This issue only occurs in a release build.
Using _mm instead of _mm256 results in correct output in both debug and release mode.
Code using only _mm or _mm256 yields the same performance (I have another piece of code for that. I can provide it if needed).

Versions

The issue can be reproduced with 1.30.0-nightly (2018-09-24), 1.30.0-beta.7, 1.29.0.

shouldn‘t be a #[target_feature(enable = "avx2")] in there?

Edit: It works when you add the target feature. playground link

I think the compiler should deny the code from the OP though, instead of producing wrong code.

Looks like a duplicate of #50154 at a glance.

@nicokoch

Yes, I forgot to add #[target_feature(enable = "avx2")]. I agree with @nicokoch. The code should not compile. I think that it should be the case for both debug and release builds.

Do you think that clippy should provide warnings for this kind of code?

I just ran into this issue and spent quite a while getting very confused. It's very surprising that code using AVX2 intrinsics compiles and then behaves nonsensically without the correct target feature attribute.

Auto merge of #55073 - alexcrichton:demote-simd, r=<try>

rustc: Fix (again) simd vectors by-val in ABI

Rollup merge of rust-lang#55073 - alexcrichton:demote-simd, r=nagisa

This test case still produces the incorrect result with -C opt-level=3 (or Cargo’s --release), in both 1.31.1 and 1.33.0-nightly (e40548b 2018-12-21).

Playground link.

I guess this is because #55073 was reverted as #55281? This should maybe be reopened then.

Yes, the fix was reverted. I don't think it's necessary to reopen this one, as the general issue is already tracked at #50154. This is just one more manifestation of the same problem.

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Release builds using AVX code produce incorrect output #54583

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Release builds using AVX code produce incorrect output #54583

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nicokoch commented on Sep 26, 2018

hanna-kruppe commented on Sep 26, 2018

vladglv commented on Sep 26, 2018

theotherphil commented on Oct 3, 2018

andersk commented on Dec 22, 2018

nikic commented on Dec 22, 2018

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