Add tracing to validate_operand

[Stypox]

This PR adds a tracing call to keep track of how much time is spent in validate_operand and const_validate_operand. Let me know if more fine-grained tracing is needed (e.g. adding tracing to validate_operand_internal too, which is just called from those two functions).

I also fixed the rustdoc of validate_operand and const_validate_operand since it was referencing an older name for the val parameter which was renamed in cbdcbf0.

Here is some tracing output when Miri is run on src/tools/miri/tests/pass/hello.rs, visualizable in ui.perfetto.dev: trace-1750932222218210.json

Note: obtaining tracing output depends on rust-lang/miri#4406, but this PR is standalone and can be merged without waiting for rust-lang/miri#4406.

r? @RalfJung

[RalfJung]

Note: this PR is not ready yet as it requires rust-lang/miri#4406 to disable the changes in the Miri code when "tracing" is disabled.

What happens if this gets merged without that PR? By default, all tracing is still disabled in Miri, right?

[Stypox]

What happens if this gets merged without that PR? By default, all tracing is still disabled in Miri, right?

Yes, this can be merged without issues even before rust-lang/miri#4406

[RalfJung]

Yes, this can be merged without issues even before rust-lang/miri#4406

Okay, then please make the PR & description ready for that. :)

[Stypox]

@rustbot ready

[rustbot]

Some changes occurred to the CTFE / Miri interpreter

cc @rust-lang/miri

Some changes occurred to the CTFE machinery

cc @RalfJung, @oli-obk, @lcnr

[RalfJung]

@bors r+ rollup

[bors]

📌 Commit 89a636f has been approved by RalfJung

It is now in the queue for this repository.