Intel AVX has variable vector lengths of 128bit and 256bit. There are 128bit INT and 256bit FP vector arithmetic operations as well as asymmetric vector conversion operations:
256bit vector (V4DF/V4DI) <-> 256bit vector (D4SI/V4SF) 256bit vector (V8SI) <-> 256bit vecor (V8SF) The current vectorizer only supports different vector size based on scalar type. But it doesn't support asymmetric vector conversion nor different vector size based on operation. The current AVX branch limits vector size to 128bit for vectorizer: /* ??? No autovectorization into MMX or 3DNOW until we can reliably place emms and femms instructions. FIXME: AVX has 32byte floating point vector operations and 16byte integer vector operations. But vectorizer doesn't support different sizes for integer and floating point vectors. We limit vector size to 16byte. */ #define UNITS_PER_SIMD_WORD(MODE) \ (TARGET_AVX ? (((MODE) == DFmode || (MODE) == SFmode) ? 16 : 16) \ : (TARGET_SSE ? 16 : UNITS_PER_WORD)) -- Summary: Vectorizer doesn't support INT<->FP conversions with different size Product: gcc Version: 4.4.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: tree-optimization AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: hjl dot tools at gmail dot com http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36844