[PATCH] D121750: Add a cmake flag to turn `llvm_unreachable()` into builtin_trap() when assertions are disabled

[Duncan P. N. Exon Smith via Phabricator via llvm-commits]

dexonsmith accepted this revision.
dexonsmith added a comment.
This revision is now accepted and ready to land.

It feels to me like this is worth documenting in llvm/docs/CMake.rst, maybe next to `LLVM_ABI_BREAKING_CHECKS` since they both seem assertion related, so that it's more easily discovered.

Otherwise, LGTM, with more wording suggestion inline.



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Comment at: llvm/CMakeLists.txt:468
 option(LLVM_ENABLE_DUMP "Enable dump functions even when assertions are disabled" OFF)
+option(LLVM_UNREACHABLE_OPTIMIZE "Whether llvm_unreachable() should be considered undefined behavior (default) or instead trap when assertions are disabled" ON)
 
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I wonder if the wording should be tied to the word "optimize". Also, note that trapping is a legit implementation of undefined behaviour; so another interpretation is that `llvm_unreachable()` is being treated as UB either way.

E.g.:

> A "reached" llvm_unreachable() is undefined behaviour; ON optimizes the unreachable control flow (default), while OFF triggers a guaranteed trap

WDYT?
(I'm okay with landing the wording as you had it if you prefer it; can always update it later)


Repository:
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https://reviews.llvm.org/D121750