https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106794
--- Comment #2 from David Binderman <dcb314 at hotmail dot com> --- Reduced code seems to be: template <class T> struct Vector3 { Vector3(); Vector3(T, T, T); T length() const; T x, y, z; }; template <class T> Vector3<T>::Vector3(T _x, T _y, T _z) : x(_x), y(_y), z(_z) {} Vector3<float> cross(Vector3<float> a, Vector3<float> b) { return Vector3<float>(a.y * b.z - a.z * b.y, a.z * b.x - a.x * b.z, a.x * b.y - a.y * b.x); } template <class T> T Vector3<T>::length() const { return z; } int generateNormals_i; float generateNormals_p2_0, generateNormals_p0_0; struct SphereMesh { void generateNormals(); float vertices; }; void SphereMesh::generateNormals() { Vector3<float> *faceNormals = new Vector3<float>; for (int j; j; j++) { float *p0 = &vertices + 3, *p1 = &vertices + j * 3, *p2 = &vertices + 3, *p3 = &vertices + generateNormals_i + j * 3; Vector3<float> v0(p1[0] - generateNormals_p0_0, p1[1] - 1, p1[2] - 2), v1(0, 1, 2); if (v0.length()) v1 = Vector3<float>(p3[0] - generateNormals_p2_0, p3[1] - p2[1], p3[2] - p2[2]); else v1 = Vector3<float>(generateNormals_p0_0 - p3[0], p0[1] - p3[1], p0[2] - p3[2]); Vector3<float> faceNormal = cross(v0, v1); faceNormals[j] = faceNormal; } } Flags -c -O3 -ffast-math -march=bdver2 required.