Emit optimization remarks to the final binary, not the console

[tschuett]

Since #90833 rustc prints remarks with -Cremark to the console.

LLVM can include the remarks into the executable. Then you can read the remarks and analyze them.

https://llvm.org/docs/Remarks.html

I never managed to thread the flags through rustc.

[matthiaskrgr]

RUSTFLAGS="-C llvm-args=--pass-remarks=.* -Cdebuginfo=2" cargo build --release

does that work for you?

[tschuett]

It still pollutes my console.

[tschuett]

RUSTFLAGS="-C llvm-args=--pass-remarks-output=filename -Cdebuginfo=2" cargo build --release

This fails because rustc does not know about: pass-remarks-output

[Kobzol]

With #113040, remarks can now be outputted into a directory, in the same (YAML) format as clang outputs them.

[yugr]

There seems to be something fishy about -C remark. This code

$ cat test.rs
#[no_mangle]
pub fn foo(v: &[i32], n: usize) -> i32 {
    let mut ans = 0;
    for i in 0..n {
        ans += v[i];
    }
    ans
}

is clearly vectorized:

$ rustc --crate-type=rlib -O -C target-cpu=native test.rs
$ objdump -d libtest.rlib
...
  50:   c5 fd fe 04 87          vpaddd (%rdi,%rax,4),%ymm0,%ymm0
  55:   c5 f5 fe 4c 87 20       vpaddd 0x20(%rdi,%rax,4),%ymm1,%ymm1
  5b:   c5 ed fe 54 87 40       vpaddd 0x40(%rdi,%rax,4),%ymm2,%ymm2
  61:   c5 e5 fe 5c 87 60       vpaddd 0x60(%rdi,%rax,4),%ymm3,%ymm3
  67:   48 83 c0 20             add    $0x20,%rax
  6b:   48 39 c1                cmp    %rax,%rcx
  6e:   75 e0                   jne    50 <foo+0x50>
...

and -C llvm-args=--pass-remarks=.* tells me that (and nothing else):

$ rustc --crate-type=rlib -O -C target-cpu=native -C debuginfo=1 -C llvm-args=--pass-remarks=.* test.rs
remark: /rustc/17067e9ac6d7ecb70e50f92c1944e545188d2359/library/core/src/iter/range.rs:764:12: vectorized loop (vectorization width: 8, interleaved count: 4)

On the other hand -C remark=all tells me a lot of other things but nothing about vectorization:

$ rustc --crate-type=rlib -O -C target-cpu=native -C debuginfo=1 -C remark=all test.rs  |& wc -l
$ rustc --crate-type=rlib -O -C target-cpu=native -C debuginfo=1 -C remark=all test.rs  |& grep -i vector

Moreover trying to ask about Loop Vectorizer also fails:

$ rustc  --crate-type=rlib -O -C target-cpu=native -C debuginfo=1 -C remark=loop-vectorize test.rs  | wc -l
0

I'm on

yugr@cfarm13:~/src/rust/llvm-tool/tests$ rustc --version
rustc 1.87.0 (17067e9ac 2025-05-09)