20380, "bradcray", "Make LLVM support library more explicit/configurable in chplenv/chplconfig settings", "2022-08-03T22:41:24Z"
[branched off from Should util/quickstart/setchplenv.bash use system LLVM when available? · Issue #20273 · chapel-lang/chapel · GitHub]
Now that we're relying on the LLVM support library within the compiler, even when CHPL_LLVM=none, we're relying on LLVM to build the compiler, which seems potentially confusing / inconsistent. This issue proposes introducing a CHPL_LLVM_SUPPORT environment variable that would only support system and bundled as options such that the involvement of LLVM would be more explicit and a user could query / choose where that LLVM support was coming from.
Related, today my understanding is that, today, when CHPL_LLVM=none, CHPL_LLVM_SUPPORT will effectively default to bundled even if there is a reasonable system implementation of LLVM available to use. It would be nice to have this variable default to system in such cases to avoid needing to build the bundled LLVM. This could be split off into its own issue if it's too hard to get working along with the support for adding the variable and explicitly choosing between the options (but I put it here, optimsitically).
I'm marking this as "high priority" because it feels to me like it would be a shame to have 1.28 introduce the reliance on the LLVM support libraries without this support.