Is it possible to use LLVM instructions for vector operations not implemented in the standard library?

lalinsky · May 31, 2026, 7:41am

Here is an example of dynamic shuffle that Zig does not support, but LLVM does:

src/streamvbyte.zig

main


      
          
          // Backend detection - only use LLVM intrinsics with LLVM backend
          const use_llvm_intrinsics = switch (builtin.zig_backend) {
              .stage2_llvm => true,
              else => false,
          };
          const use_inline_asm = true;
          
          // StreamVByte shuffle implementation with multi-tier fallback
          // Uses pshufb/vpshufb behavior: high bit set in mask -> output 0
          fn shuffle(x: Vu8x16, m: Vu8x16) Vu8x16 {
              if (use_llvm_intrinsics and has_ssse3) {
                  // Use LLVM intrinsic - compiles to single pshufb/vpshufb
                  const builtin_fn = struct {
                      extern fn @"llvm.x86.ssse3.pshuf.b.128"(Vu8x16, Vu8x16) Vu8x16;
                  }.@"llvm.x86.ssse3.pshuf.b.128";
                  return builtin_fn(x, m);
              } else if (use_inline_asm and has_ssse3) {
                  // Use inline assembly fallback
                  var result = x;
                  asm ("pshufb %[mask], %[result]"