Various rustc_codegen_ssa cleanups

[bjorn3]

No description provided.

[rustbot]

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[rustbot]

Some changes occurred in compiler/rustc_codegen_gcc

cc @antoyo, @GuillaumeGomez

[matthiaskrgr]

this could be an assert!()?

[bjorn3]

This is just moving some code around.

[bors]

☔ The latest upstream changes (presumably #126605) made this pull request unmergeable. Please resolve the merge conflicts.

[wesleywiser]

r? rust-lang/compiler

[compiler-errors]

r? compiler-errors @bors r+

[bors]

📌 Commit 84f45bb has been approved by compiler-errors

It is now in the queue for this repository.

[tgross35]

Any chance this could have failed the rollup with #127066 (comment)? That same error happened in another rollup too. Seems unlikely, but nothing else seems more likely

[bjorn3]

The failing test seems to be

// foo.rs

// This is kept because of `#[used]`:
#[used]
static FOO: u32 = 0;

// This is removable because it is unused:
#[allow(dead_code)]
static BAR: u32 = 0;

// This is kept because it is publicly reachable:
pub static BAZ: u32 = 0;

// This is kept because it is referenced by a public, reachable function:
static QUUX: u32 = 0;

pub fn quux() -> &'static u32 {
    &QUUX
}

// This is removable because it is referenced by a private, unused (dead) function:
static CORGE: u32 = 0;

#[allow(dead_code)]
fn corge() -> &'static u32 {
    &CORGE
}

Maybe #127052 is related given that this uses #[used]?