Is the lack of replies a sign that I missed to explain something in my email?
Cheers, Paulo Matos > -----Original Message----- > From: gcc-ow...@gcc.gnu.org [mailto:gcc-ow...@gcc.gnu.org] On Behalf Of Paulo > Matos > Sent: 29 November 2012 17:04 > To: gcc@gcc.gnu.org > Subject: Failure to vectorize widen mult through intermediate steps > > Hello, > > I have been looking at a piece of code that fails to vectorize because > GCC4.7.0 is unable in suportable_widening_operation to provide proper > conversions for a WIDEN_MULT_EXPR. vectype_in is V8HI and vectype_out is > V2DI. The problem seems to be that GCC code at the end of this functions > blocks the search for intermediate conversions. If GCC would look for them it > would find: > vec_widen_smult_lo_v8hi with v4si output > vec_widen_smult_lo_v4si with v2di output > however, since this search doesn't occur, vectorization fails. > > How can I instruct GCC that it should take this steps to enable vectorization > between these vectypes? > I thought about defining vec_widen_smult_lo_v8hi with v2di output but can't > because of the constraints on the pattern ("Multiply the high/low elements of > the two vectors, and put the N/2 products of size 2*S in the output vector > (operand 0)."). > > The hook TARGET_VECTORIZE_BUILTIN_CONVERSION sounds like it could be what I > want but I added some test code and in my simple example this function is > never called. > > Any suggestions on how to work this out in the backend? > > Cheers, > > Paulo Matos >
