https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56118
--- Comment #4 from Marc Glisse <glisse at gcc dot gnu.org> --- #include <x86intrin.h> __m128d f(){ __m128d r; r[0]=1; r[1]=2; return r; } Currently, SLP vectorizes it with -fvect-cost-model=unlimited, but not by default because: Vector inside of basic block cost: 1 Vector prologue cost: 1 Vector epilogue cost: 0 Scalar cost of basic block: 2 r.c:4:9: note: not vectorized: vectorization is not profitable. And if r is initialized to {3,4} as in the initial testcase, we don't vectorize either: r.c:3:17: note: not vectorized: no vectype for stmt: # .MEM_2 = VDEF <.MEM_1(D)> rD.15637 = { 3.0e+0, 4.0e+0 }; scalar_type: __m128dD.4386 r.c:3:17: note: not vectorized: not enough data-refs in basic block.