Enzyme AD

Enzyme Automatic Differentiation Framework


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. On applicable LLVM versions (up to and including LLVM 15), you can specify that opt useees the old pass manager by adding the --enable-new-pm=0 flag. Alternatively, you can use the new pass manager, which uses the following syntax for opt:

opt input.ll -load-pass-plugin=/path/to/LLVMEnzyme-VERSION.so -passes=enzyme -o output.ll -S

If you are using CMake, Enzyme exports a special ClangEnzymeFlags target which will automatically add the correct flags. See here for an example.

I receive an __enzime_autodiff undefined symbol either at runtime or at compile time 

This error means that you have Enzyme calls which did not run the the Enzyme AD transformation. Please check that you have Enzyme run as part of the compilation which resulted in the error. In projects with multisource and/or complex building systems it’s possible to overlook one source file being compiled/linked without the appropriate Enzyme plugin pass. When using LLDEnzyme and LTO, make sure that all object file rules include the -flto argument and that the final linking step includes both -fuse-ld=lld and -flto. Obviously, such final linking step must also include the Enzyme plugin with something like -Wl,--load-pass-plugin=/path/to/LLDEnzyme-<VERSION>.so

Many errors occur, starting with Failed to load passes from '/path/to/LLDEnzyme-<VERSION>.so'. Request ignored. 

This means that the Enzyme plugin has not been loaded. There may be various reasons for this to happen, some common ones are

  • typo in the /path/to/ part
  • plugin (e.g. using LLDEnzyme plugin for Clang or LLVM or some other incorrect combination)
  • shared object not present because its compilation failed or had been deleted
  • the /path/to contains shells expansions not honored by the build system, for example Makefile may fail to expand ~ but does correctly expland $(HOME)


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