FAQ

Enzyme builds successfully but won’t run tests ¶

Double check that Enzyme’s build can find lit, LLVM’s testing framework. This can be done by explicitly passing lit as an argument to CMake as described here .

Enzyme is Crashing ¶

LLVM’s plugin infrastructure is broken in many versions. Empirically LLVM 8 and up will often incorrectly disallow memory from being passed between LLVM and a plugin. If you see one of these errors and want to use the same version of LLVM try passing the flag enzyme_preopt=0 described here . The flag disables preprocessing optimizations that Enzyme runs and tends to reduce these errors. If this doesn’t work, check the following.

Illegal TypeAnalysis on LLVM 10+ ¶

There is a known bug in an existing LLVM optimization pass (SROA) that will incorrectly generate type information from a memcpy. This bug has been fixed in LLVM 13

opt can’t find -enzyme option ¶

When you use opt command like below: opt input.ll -load=/path/to/LLVMEnzyme-VERSION.so -enzyme -o output.ll -S opt reports a error:opt: unknown pass name 'enzyme'

May be because you are using LLVM 13 or a higher version, which has switched to the new pass manager pipeline and we haven’t yet turned that on within enzyme. For now you can just tell llvm to use the old pass manager by adding the --enable-new-pm=0 flag to opt or -flegacy-pass-manager to clang.

UNREACHABLE executed (GVN error) ¶

Until June 2020, LLVM’s exisitng GVN pass had a bug handling invariant.load’s that would cause it to crash. These tend to be generated a lot by Enzyme for better optimization. This was reported here and resolved in master. Options for resolving include updating to later verison of LLVM with the fix, or disabling creation of invariant.load’s.

Other ¶

If you have an issue not resolved here, please make an issue on Github and consider making a pull request to this FAQ!