On 2012-06-28 07:05, Jakub Jelinek wrote: > Unfortunately the addition of the builtin_mul_widen_* hooks on i?86 seems > to pessimize the generated code for gcc.dg/vect/pr51581-3.c > testcase (at least with -O3 -mavx) compared to when the hooks aren't > present, because i?86 has more natural support for widen mult lo/hi > compoared to widen mult even/odd, but I assume that on powerpc it is the > other way around. So, how should I find out if both VEC_WIDEN_MULT_*_EXPR > and builtin_mul_widen_* are possible for the particular vectype which one > will be cheaper?
I would assume that if the builtin exists, then it is cheaper. I disagree about "x86 has more natural support for hi/lo". The basic sse2 multiplication is even. One shift per input is needed to generate odd. On the other hand, one interleave per input is required for both hi/lo. So 4 setup insns for hi/lo, and 2 setup insns for even/odd. And on top of all that, XOP includes multiply odd at least for signed V4SI. I'll have a look at the test case you mention while I re-look at the patches... r~
