ac/llvm: implement load_pixel_coord

Reviewed-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/31864>

src/amd/llvm/ac_nir_to_llvm.c

@@ -2879,6 +2879,14 @@ emit_load_frag_coord(struct ac_nir_context *ctx)
    return ac_to_integer(&ctx->ac, ac_build_gather_values(&ctx->ac, values, 4));
 }
 
+static LLVMValueRef
+emit_load_pixel_coord(struct ac_nir_context *ctx)
+{
+   LLVMValueRef value = ac_get_arg(&ctx->ac, ctx->args->pos_fixed_pt);
+
+   return LLVMBuildBitCast(ctx->ac.builder, value, ctx->ac.v2i16, "");
+}
+
 static bool visit_intrinsic(struct ac_nir_context *ctx, nir_intrinsic_instr *instr)
 {
    LLVMValueRef result = NULL;
@@ -3023,6 +3031,9 @@ static bool visit_intrinsic(struct ac_nir_context *ctx, nir_intrinsic_instr *ins
    case nir_intrinsic_load_frag_coord:
       result = emit_load_frag_coord(ctx);
       break;
+   case nir_intrinsic_load_pixel_coord:
+      result = emit_load_pixel_coord(ctx);
+      break;
    case nir_intrinsic_load_frag_shading_rate:
       result = emit_load_frag_shading_rate(ctx);
       break;