Work around LLVM's reltable lookup optimization #1214
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Clang 14.0.0+ introduce a relative lookup table optimization that produces code that subtracts two pointers from different allocation regions, which is something that `crucible-llvm` is ill equipped to reason about. For lack of a viable alternative, we work around this issue by "undoing" this optimization before translating the code to Crucible. For the full details, see the new `Note [Undoing LLVM's relative table lookup conversion pass]` in `Lang.Crucible.LLVM.Globals`. Fixes #1174.
kquick
approved these changes
Jun 10, 2024
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There's a lot of very specific pattern recognition in buildLoadRelConstInitMap, which is good because it limits the functionality to a very specific case and prevents capturing unrelated scenarios, but for the same reasons this is also very brittle and I feel like we haven't seen the last of this. Nonetheless, I agree that this seems like the best way I can think of to handle this LLVM shortcut.
langston-barrett
approved these changes
Jun 11, 2024
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Clang 14.0.0+ introduce a relative lookup table optimization that produces code that subtracts two pointers from different allocation regions, which is something that
crucible-llvmis ill equipped to reason about. For lack of a viable alternative, we work around this issue by "undoing" this optimization before translating the code to Crucible. For the full details, see the newNote [Undoing LLVM's relative table lookup conversion pass]inLang.Crucible.LLVM.Globals.Fixes #1174.