[all-commits] [llvm/llvm-project] bf8d03: [Inliner] Add some additional tests for progagatin...

[goldsteinn via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: bf8d03921d3cb599eebcd77e1c0f7d7dd59d42d5
      https://github.com/llvm/llvm-project/commit/bf8d03921d3cb599eebcd77e1c0f7d7dd59d42d5
  Author: Noah Goldstein <goldstein.w.n at gmail.com>
  Date:   2023-09-28 (Thu, 28 Sep 2023)

  Changed paths:
    A llvm/test/Transforms/Inline/access-attributes-prop.ll
    A llvm/test/Transforms/Inline/ret_attr_align_and_noundef.ll

  Log Message:
  -----------
  [Inliner] Add some additional tests for progagating attributes before inlining; NFC


  Commit: 2f3b7d33f421b723728262a6978041d93f1f8c5c
      https://github.com/llvm/llvm-project/commit/2f3b7d33f421b723728262a6978041d93f1f8c5c
  Author: Noah Goldstein <goldstein.w.n at gmail.com>
  Date:   2023-09-28 (Thu, 28 Sep 2023)

  Changed paths:
    M llvm/lib/Transforms/Utils/InlineFunction.cpp
    M llvm/test/Transforms/Inline/ret_attr_align_and_noundef.ll

  Log Message:
  -----------
  [Inliner] Fix bug when propagating poison generating return attributes

Poison generating return attributes can't be propagated the same as
others, as they can change the behavior of other uses and/or create UB
where it otherwise wouldn't have occurred.

For example:
```
define nonnull ptr @foo() {
    %p = call ptr @bar()
    call void @use(ptr %p)
    ret ptr %p
}
```

If we inline `@foo` and propagate `nonnull` to `@bar`, it could change
the behavior of `@use` as instead of taking `null`, `@use` will
now be passed `poison`.

This can be even worth in a case like:
```
define nonnull ptr @foo() {
    %p = call noundef ptr @bar()
    ret ptr %p
}
```

Where propagating `nonnull` to `@bar` will cause UB on `null` return
of `@bar` (`noundef` + `poison`) where it previously wouldn't
have occurred.

To fix this, we only propagate poison generating return attributes if
either 1) The only use of the callsite to propagate too is return and
the callsite to propagate too doesn't have `noundef`. Or 2) the
callsite to be be inlined has `noundef`.

The former case ensures no new UB or `poison` values will be
added. The latter is UB anyways if the value is `poison` so we can go
ahead without worrying about behavior changes.


Compare: https://github.com/llvm/llvm-project/compare/3e9c36303ca7...2f3b7d33f421