[Mesa-dev] [PATCH] intel/compiler: Reset default flag register in brw_find_live_channel()

[Matt Turner]

emit_uniformize() emits SHADER_OPCODE_FIND_LIVE_CHANNEL with its
flag_subreg set, so that the IR knows which flag is accessed. However
the flag is only used on Gen7 in Align1 mode, and it is used as an
explicit source and destination.

To avoid setting unnecessary bits in the instruction words, get the
information we need and reset the default flag register. This allows
round-tripping through the assembler/disassembler.
---
 src/intel/compiler/brw_eu_emit.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/src/intel/compiler/brw_eu_emit.c b/src/intel/compiler/brw_eu_emit.c
index 45e2552783b..e6f6d6419d2 100644
--- a/src/intel/compiler/brw_eu_emit.c
+++ b/src/intel/compiler/brw_eu_emit.c
@@ -3312,6 +3312,14 @@ brw_find_live_channel(struct brw_codegen *p, struct brw_reg dst,
 
    brw_push_insn_state(p);
 
+   /* The flag register is only used on Gen7 in align1 mode, so avoid setting
+    * unnecessary bits in the instruction words, get the information we need
+    * and reset the default flag register.
+    */
+   const struct brw_reg flag = brw_flag_reg(p->current->flag_subreg / 2,
+                                            p->current->flag_subreg % 2);
+   brw_set_default_flag_reg(p, 0, 0);
+
    if (brw_get_default_access_mode(p) == BRW_ALIGN_1) {
       brw_set_default_mask_control(p, BRW_MASK_DISABLE);
 
@@ -3345,9 +3353,6 @@ brw_find_live_channel(struct brw_codegen *p, struct brw_reg dst,
           */
          inst = brw_FBL(p, vec1(dst), exec_mask);
       } else {
-         const struct brw_reg flag = brw_flag_reg(p->current->flag_subreg / 2,
-                                                  p->current->flag_subreg % 2);
-
          brw_set_default_exec_size(p, BRW_EXECUTE_1);
          brw_MOV(p, retype(flag, BRW_REGISTER_TYPE_UD), brw_imm_ud(0));
 
-- 
2.19.2