[llvm] [VPlan] First step towards VPlan cost modeling. (PR #92555)

[Florian Hahn via llvm-commits]

fhahn wrote:

> unreduced input, running through `opt -O3` should reproduce the crash: [a.ll.txt](https://github.com/user-attachments/files/15875049/a.ll.txt)
> 
> this was from building chromium ([instructions](https://www.chromium.org/developers/how-tos/get-the-code/)), specifically on mac x64, although I think I saw this on Linux x64 as well. `is_debug = false` is the important gn argument to set.
> 
> I'm also fine with recommitting this change with fixes and seeing if anything else breaks, or I can test a change for you by building a couple of configurations

Thanks, building now. The recommit plus the necessary fixes is available here: https://github.com/fhahn/llvm-project/tree/recommit-vplan-cost-cm-in-ctx. I'm currently building chrome for macOS x64, which surfaced another issue (which is already fixed on the branch).

I've not been able to fully build chrome for ARM64 macOS, due to some issue with building the rust-toolchain: it only has the ARM64 rust stdlib, but tries to use/build the x64 one. Not sure if you by any chance know how that could be fixed.

My args.gn is 

```
is_debug = false
clang_base_path = "/Users/florianhahn/projects/llvm-project/builds/release-with-assertions/stage1"
clang_use_chrome_plugins = false
target_cpu = "arm64"
```



https://github.com/llvm/llvm-project/pull/92555