Enzyme compilation failure with eigen matrix

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#2,654 opened on Jan 12, 2026 0 comments 0 reactions 0 assignees View on GitHub

Dominant language: LLVM
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Description

Environment:
- OS:
- Compiler: clang++ -std=c++17
- Enzyme commit: 8cf040b1

I’m seeing a compile-time failure (log attached in error.txt) when differentiating an Eigen-based function with Enzyme. The failure happens only for one intermediate matrix (M2) when calling M2.sum(). All other similar sum() calls on other intermediates compile and run correctly.

Minimal reproducible example

```cpp
#include
#include
#include

using Matrix = Eigen::Matrix;
void enzyme_func_matrix(Matrix* mats, double& sol){

Matrix M0, M1, M2, M3, M4;

M0= mats[0] * mats[1];
M1 = M0 + mats[1];
M2 = mats[2] + M1;
M3 = M2 - M1;
M4 = M1 * M2;

// This fails
sol = M2.sum();
// All of these below work
// sol = M0.sum();
// sol = M1.sum();
// sol = M3.sum();
// sol = M4.sum();

}

int main() {
std::vector>> inputs
{
{{0.1, 0.2}, {0.3, 0.4}},
{{0.1, 0.2}, {0.3, 0.4}},
{{0.1, 0.2}, {0.3, 0.4}}
};

size_t input_size = inputs.size();
size_t matrix_size = inputs[0].size();

std::vector>> results(input_size,
std::vector>(matrix_size, std::vector(matrix_size, 0.0)));

std::vector mats(input_size), dmats(input_size);
for (size_t mat_idx = 0; mat_idx < input_size; mat_idx++){
dmats[mat_idx].resize(matrix_size, matrix_size);
dmats[mat_idx].setZero();
for (size_t i = 0; i < matrix_size; i++){
for (size_t j = 0; j < matrix_size; j++){
mats[mat_idx](i, j) = inputs[mat_idx][i][j];
}
}
}

double y, lambda;
y = 0.0, lambda = 1.0;

__enzyme_autodiff((void*)enzyme_func_matrix,
enzyme_dup, mats.data(), dmats.data(),
enzyme_dup, &y, &lambda);

for (size_t mat_idx = 0; mat_idx < input_size; mat_idx++){
for (size_t i = 0; i < matrix_size; i++){
for (size_t j = 0; j < matrix_size; j++){
results[mat_idx][i][j] = dmats[mat_idx](i, j);
std::cout << "results[" << mat_idx << "][" << i << "][" << j << "] = "<< results[mat_idx][i][j] << std::endl;
}
}
}

}
```

compilation_error.txt

```text

In file included from ./example.cpp:3:
In file included from ../../build/debug/include/Eigen/Dense:1:
In file included from ../../build/debug/include/Eigen/Core:276:
../../build/debug/include/Eigen/src/Core/Product.h:109:50: error: Enzyme: Cannot deduce type of load %0 = load ptr, ptr %m_rhs, align 8, !dbg !9787 vd:{[-1,0]:Float@double, [-1,8]:Float@double} start:0 size: 8 dt:Unknown

%m_rhs = getelementptr inbounds %"class.Eigen::Product", ptr %this, i32 0, i32 1, !dbg !9787: {[-1]:Pointer, [-1,0,0]:Float@double, [-1,0,8]:Float@double, [-1,1,0]:Float@double, [-1,1,8]:Float@double, [-1,2,0]:Float@double, [-1,2,8]:Float@double, [-1,3,0]:Float@double, [-1,3,8]:Float@double, [-1,4,0]:Float@double, [-1,4,8]:Float@double, [-1,5,0]:Float@double, [-1,5,8]:Float@double, [-1,6,0]:Float@double, [-1,6,8]:Float@double, [-1,7,0]:Float@double, [-1,7,8]:Float@double}, intvals: {}
%0 = load ptr, ptr %m_rhs, align 8, !dbg !9787: {[-1,0]:Float@double, [-1,8]:Float@double}, intvals: {}
ptr %this: {[-1]:Pointer, [-1,0]:Pointer, [-1,8,0]:Float@double, [-1,8,8]:Float@double, [-1,9,0]:Float@double, [-1,9,8]:Float@double, [-1,10,0]:Float@double, [-1,10,8]:Float@double, [-1,11,0]:Float@double, [-1,11,8]:Float@double, [-1,12,0]:Float@double, [-1,12,8]:Float@double, [-1,13,0]:Float@double, [-1,13,8]:Float@double, [-1,14,0]:Float@double, [-1,14,8]:Float@double, [-1,15,0]:Float@double, [-1,15,8]:Float@double}, intvals: {}

const RhsNestedCleaned& rhs() const { return m_rhs; }
^
../../build/debug/include/Eigen/src/Core/Product.h:109:50: error: Enzyme: Cannot deduce type of load %0 = load ptr, ptr %m_rhs, align 8, !dbg !9787 vd:{[-1,0]:Float@double, [-1,8]:Float@double} start:0 size: 8 dt:Unknown

../../build/debug/include/Eigen/src/Core/Product.h:109:50: error: Enzyme: Cannot deduce type of load %0 = load ptr, ptr %m_rhs, align 8, !dbg !9787 vd:{[-1,0]:Float@double, [-1,8]:Float@double} start:0 size: 8 dt:Unknown

fatal error: too many errors emitted, stopping now [-ferror-limit=]
```

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Enzyme compilation failure with eigen matrix

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