[llvm-branch-commits] [llvm] release/19.x: [PowerPC] Respect endianness when bitcasting to fp128 (#95931) (PR #105623)

[Trevor Gross via llvm-branch-commits]

tgross35 wrote:

(I'm not really involved with LLVM but I am doing a lot of f128 work and requested the backport)

This seems unlikely to be a regression. There have a handful of f128-related bugs on various ppc platforms so I suspect this is just something that hadn't been tested before now.

The problem this fixes is pretty fundamental, it means any sort of soft float operations are completely broken on some ppc targets. This is how I originally identified the issue, in https://github.com/rust-lang/compiler-builtins/pull/606#issuecomment-2105657287. Backporting isn't critical; at this time it probably only affects those of us that are experimenting with f128 support, there can't be many/any end users. I was just hoping for a fix soonish to get ppc f128 caught up to the other targets, since is one of the few popular 64-bit linux target to still have bugs (our more complete list: https://github.com/rust-lang/rust/blob/3f121b9461cce02a703a0e7e450568849dfaa074/library/std/build.rs#L123-L141)

https://github.com/llvm/llvm-project/pull/105623