In the basic case, simply do the string substitution.
For one case with many instances, capture the Itanium-
mangled filename and assert its reuse instead.

We raised our LLVM minimum to 15, so these tests seem pointless.

The test fails on Windows with the diff

    -  = help: to create the module `unknown`, create file "unknown.rs" or "unknown/mod.rs"
    +  = help: to create the module `unknown`, create file "unknown.rs" or "unknown\mod.rs"

There is no need to run this test on Windows, so ignore it.

Only a single example is given

Only one example is given

Co-authored-by: Ralf Jung <post@ralfj.de>

…imulacrum

Implement `Option::take_if`

Tracking issue: rust-lang#98934
ACP: rust-lang/libs-team#70 [accepted]

…Simulacrum

Add regression test for `echo 'mod unknown;' | rustc -`

Closes rust-lang#65601

The bug is fixed since long ago, probably by rust-lang#69838 (see rust-lang#65601 (comment) for more details).
Add a regression test so we can close the issue.

… r=Mark-Simulacrum

Nest tests/codegen/sanitizer*.rs tests in sanitizer dir

The sanitizer tests are the largest and most meticulously tested set of tests in tests/codegen. That's good! They all clearly belong to a subject and thus could go in a directory, but are not, instead being placed simply in tests/codegen. That's bad! Fix this by placing them in their own directory and renaming them to be less repetitive after that move.

A few tests are brittle, and embed their filename in the test's checks. This is acceptable for the ones where it is used only two times, but one test embeds the test's mangled filename in the test *over 50 times*! This may have been one of the things discouraging anyone from moving it, and thus from moving the set. Fortunately, I have some knowledge of Itanium mangling (involuntarily), regex, and the FileCheck syntax. With a capturing variable, FileCheck allows us to now move this test around again without diffing it on ~50 lines, while still guaranteeing that the mangled substring is the same each time.

This also clarifies why the substring is repeated a zillion times, instead of being cryptic. They don't call it mangling because the result is pretty and easy to understand, but now it is slightly easier! Yay descriptive variables!

…nest, r=Mark-Simulacrum

Nest other codegen test topics

This PR is like rust-lang#114229 in that it mostly pushes codegen tests around, shoving them into their own directories, but because all of the changes are very simple cleanups I pulled them into a separate PR. The other PR might involve actually evaluating the correctness of the test after changes, but here it is mostly a matter of taste. The only "functional" change is deleting a few tests that... hinge on a version of LLVM that we don't support (as of rust-lang#114148 anyways).

I considered a few different ways to group other topics but I feel the question of whether `tests/codegen/{vec,array,slice}` should exist is more subtle than these choices, as it might be better to group such related tests by other topics like bounds check elision, thus I avoided making it.

string.rs: remove "Basic usage" text

Only a single example is given

str.rs: remove "Basic usage" text

Only one example is given

…r=cjgillot

Add a new `compare_bytes` intrinsic instead of calling `memcmp` directly

As discussed in rust-lang#113435, this lets the backends be the place that can have the "don't call the function if n == 0" logic, if it's needed for the target.  (I didn't actually *add* those checks, though, since as I understood it we didn't actually need them on known targets?)

Doing this also let me make it `const` (unstable), which I don't think `extern "C" fn memcmp` can be.

cc `@RalfJung` `@Amanieu`

…art, r=petrochenkov

Style fix and refactor on resolve diagnostics

- coding style
- refactor api of `span_look_ahead`