ac: add per output is_16bit flag to ac_shader_abi

Outputs are always f32 except for FS that may use unpacked f16.
Store this information here to make it available to later processing.

Reviewed-by: Mihai Preda <mhpreda@gmail.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17361>

src/amd/llvm/ac_nir_to_llvm.c

@@ -5377,8 +5377,9 @@ void ac_handle_shader_output_decl(struct ac_llvm_context *ctx, struct ac_shader_
    LLVMTypeRef type = is_16bit ? ctx->f16 : ctx->f32;
    for (unsigned i = 0; i < attrib_count; ++i) {
       for (unsigned chan = 0; chan < 4; chan++) {
-         abi->outputs[ac_llvm_reg_index_soa(output_loc + i, chan)] =
-            ac_build_alloca_undef(ctx, type, "");
+         int idx = ac_llvm_reg_index_soa(output_loc + i, chan);
+         abi->outputs[idx] = ac_build_alloca_undef(ctx, type, "");
+         abi->is_16bit[idx] = is_16bit;
       }
    }
 }

src/amd/llvm/ac_shader_abi.h

@@ -38,7 +38,9 @@
  * radv to share a compiler backend.
  */
 struct ac_shader_abi {
+   /* Each entry is a pointer to a f32 or a f16 value (only possible for FS) */
    LLVMValueRef outputs[AC_LLVM_MAX_OUTPUTS * 4];
+   bool is_16bit[AC_LLVM_MAX_OUTPUTS * 4];
 
    /* These input registers sometimes need to be fixed up. */
    LLVMValueRef vertex_id;