Vec4ClampToZero and Vec2ClampToZero only ever fed Vec4Pack31To8 and
Vec2Pack31To16, for vi2uc and vi2us. The packs now clamp negative lanes
to zero themselves, which saves an op and a vector temp, and lets x64
clamp with PACKUSWB's saturation after an arithmetic shift.
While at it, RISC-V compiles Vec2Unpack16To31, Vec2Pack31To16 and
Vec4Pack32To8, and LoongArch Vec2Unpack16To31, Vec2Pack31To16 and the
non-LSX Vec4Pack32To8, all of which went to the IR interpreter.
LoongArch's Vec2Pack32To16 and Vec2Unpack16To32 now take their scalar
path with LSX too, instead of falling back.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
vi2uc, vi2c, vi2us, vi2s, vuc2i, vc2i, vus2i and vs2i lowered to IR ops
that x64 left to the IR interpreter. They're now SSE2: shifts into
place, then PACKSSDW/PACKUSWB for the packs and self-unpacks for the
unpacks. An output overlapping its input still goes the slow way.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
