brw/lower_regioning: Allow integer conversions in SEL

The Bspec says that SEL sources and destination can be any mix of *B,
*W, and *D. We should allow those. Specifically, without this change,
this instruction

    sel.sat.l(8) v548:UD, v899:D, 255d

gets unnecessarily split into two instructions.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/38978>

src/intel/compiler/brw/brw_lower_regioning.cpp

@@ -452,8 +452,16 @@ namespace {
       switch (inst->opcode) {
       case BRW_OPCODE_MOV:
          return false;
-      case BRW_OPCODE_SEL:
-         return inst->dst.type != get_exec_type(inst);
+      case BRW_OPCODE_SEL: {
+         const brw_reg_type exec_type = get_exec_type(inst);
+
+         if (inst->dst.type == exec_type)
+            return false;
+
+         /* SEL can mix integer sizes and signed/unsigned. */
+         return !brw_type_is_int(inst->dst.type) ||
+                !brw_type_is_int(exec_type);
+      }
       default:
          /* FIXME: We assume the opcodes not explicitly mentioned before just
           * work fine with arbitrary conversions, unless they need to be

src/intel/compiler/brw/meson.build

@@ -163,6 +163,7 @@ if with_tests
         'test_helpers.cpp',
         'test_helpers.h',
         'test_insert_load_reg.cpp',
+        'test_lower_regioning.cpp',
         'test_lower_scoreboard.cpp',
         'test_opt_algebraic.cpp',
         'test_opt_cmod_propagation.cpp',

src/intel/compiler/brw/test_lower_regioning.cpp

@@ -0,0 +1,24 @@
+/*
+ * Copyright © 2025 Intel Corporation
+ * SPDX-License-Identifier: MIT
+ */
+
+#include "test_helpers.h"
+#include "brw_builder.h"
+
+class lower_regioning_test : public brw_shader_pass_test {
+};
+
+TEST_F(lower_regioning_test, sel_ud_d_d)
+{
+   brw_builder bld = make_shader();
+
+   brw_reg dest = vgrf(bld, BRW_TYPE_UD);
+   brw_reg src0 = vgrf(bld, BRW_TYPE_D);
+   brw_reg src1 = vgrf(bld, BRW_TYPE_D);
+
+   bld.SEL(dest, src0, src1)
+      ->saturate = true;
+
+   EXPECT_NO_PROGRESS(brw_lower_regioning, bld);
+}