63ca8483d0
This introduces `!captures` metadata on stores, which looks like this:
```
store ptr %x, ptr %y, !captures !{!"address", !"read_provenance"}
```
The semantics are the same as replacing the store with a call like this:
```
call void @llvm.store(ptr captures(address, read_provenance) %x, ptr %y)
```
This metadata is intended for annotation by frontends -- it's not
something we can feasibly infer at this point, as it would require
analyzing uses of the pointer stored in memory.
The motivating use case for this is Rust's `println!()` machinery, which
involves storing a reference to the value inside a structure. This means
that printing code (including conditional debugging code), can inhibit
optimizations because the pointer escapes. With the new metadata we can
annotate this as a read-only capture, which has less impact on
optimizations.
This directory contains testcases that the verifier is supposed to detect as malformed LLVM code. Testcases for situations that the verifier incorrectly identifies as malformed should go in the test/Assembler directory.