iter_mut codegen

https://godbolt.org/z/v7fq5q7q8
following code:

pub fn example(x: &mut [f32; 1024]) {
    for x in x.iter_mut() {
        *x *= 4.0;
    }
}

when compiled with codegen_gcc gives following assembly:

example::example:
        test    rdi, rdi
        je      .L6
        movss   xmm1, DWORD PTR .LC0[rip]
        lea     rax, 4092[rdi]
        jmp     .L9
.L19:
        add     rdi, 4
        je      .L6
.L9:
        movss   xmm0, DWORD PTR [rdi]
        mulss   xmm0, xmm1
        movss   DWORD PTR [rdi], xmm0
        cmp     rdi, rax
        jne     .L19
.L6:
        ret
.LC0:
        .long   1082130432

compared to llvm codegen, it seems (at least to me, but i'm definietly not an asm expert) that:

• llvm version is vectorised, gcc not
• while llvm version has 1 label and conditional jump (which is not suprisings for simple loop), gcc version seems unnecessary convoluted, with 3 labels and 4 jump instructions
• gcc version starts with something that looks like a null check , which is strange given that &mut cannot be null

i'm not sure if this is really a problem, but i figured out it is worth asking :)

Anyway, thank you for working on this project, it is really exciting development :)

Start with the linked Godbolt example and reproduce the Rust iter_mut function using codegen_gcc, then compare its assembly with the LLVM output. Investigate whether the null check, extra labels, jumps, and lack of vectorisation are expected; done means explaining the differences or correcting the generated code.