[Bug target/92658] New: x86 lacks vector extend / truncate

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92658

            Bug ID: 92658
           Summary: x86 lacks vector extend / truncate
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rguenth at gcc dot gnu.org
  Target Milestone: ---

After

2019-11-14  Richard Sandiford  <richard.sandif...@arm.com>

        * tree-cfg.c (verify_gimple_assign_unary): Handle conversions
        between vector types.
        * tree-vect-stmts.c (vectorizable_conversion): Extend the
        non-widening and non-narrowing path to handle standard
        conversion codes, if the target supports them.
        * expr.c (convert_move): Try using the extend and truncate optabs
        for vectors.
        * optabs-tree.c (supportable_convert_operation): Likewise.
        * config/aarch64/iterators.md (Vnarroqw): New iterator.
        * config/aarch64/aarch64-simd.md (<optab><Vnarrowq><mode>2)
        (trunc<mode><Vnarrowq>2): New patterns.

it would now be possible to BB vectorize the following but the x86 backend
lacks appropriate patterns for the vector mode variants (here V8HI -> V8QI
narrowing).

typedef unsigned char v16qi __attribute__((vector_size(16)));
typedef unsigned short v8hi __attribute__((vector_size(16)));

void bar (v8hi *dst, v16qi * __restrict src)
{
  unsigned short tem[8];
  tem[0] = (*src)[0];
  tem[1] = (*src)[1];
  tem[2] = (*src)[2];
  tem[3] = (*src)[3];
  tem[4] = (*src)[4];
  tem[5] = (*src)[5];
  tem[6] = (*src)[6];
  tem[7] = (*src)[7];
  dst[0] = *(v8hi *)tem;
}
void foo (v8hi *dst, v16qi src)
{
  unsigned short tem[8];
  tem[0] = src[0];
  tem[1] = src[1];
  tem[2] = src[2];
  tem[3] = src[3];
  tem[4] = src[4];
  tem[5] = src[5];
  tem[6] = src[6];
  tem[7] = src[7];
  dst[0] = *(v8hi *)tem;
}