>> So emit a v4qi->v8qi gimple conversion >> then a regular widen_lo/hi using the existing backend patterns/optabs? > >I was thinking of using a v8qi->v8hi convert on each operand followed >by a normal v8hi subtraction. That's what we'd generate if the target >didn't define the widening patterns.
Is there a reason that conversion is preferred? If we use a widening subtract then we don't need to rely on RTL fusing later.
