[Mesa-dev] [PATCH 3/3] i965/vec4: Always use the predicated MOV path for FIND_LIVE_CHANNEL

[Jason Ekstrand]

The old method of looking at ce0 assumed that the enabled channels are
tightly packed.  There is no documentation that guarantees this, however,
so it's a bit dangerous to assume it.  In any case, the predicated MOV
implementation was only 2 instructions so it's not that bad to just use
that all the time and we know for 100% sure it's correct.

Signed-off-by: Jason Ekstrand <jason at jlekstrand.net>
---
 src/mesa/drivers/dri/i965/brw_eu_emit.c | 32 +++++++++++---------------------
 1 file changed, 11 insertions(+), 21 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_eu_emit.c b/src/mesa/drivers/dri/i965/brw_eu_emit.c
index 04fca74..836d555 100644
--- a/src/mesa/drivers/dri/i965/brw_eu_emit.c
+++ b/src/mesa/drivers/dri/i965/brw_eu_emit.c
@@ -3437,28 +3437,18 @@ brw_find_live_channel(struct brw_codegen *p, struct brw_reg dst,
    } else {
       brw_set_default_mask_control(p, BRW_MASK_DISABLE);
 
-      if (devinfo->gen >= 8) {
-         /* In SIMD4x2 mode the first active channel index is just the
-          * negation of the first bit of the mask register.
-          */
-         inst = brw_AND(p, brw_writemask(dst, WRITEMASK_X),
-                        negate(retype(brw_mask_reg(0), BRW_REGISTER_TYPE_UD)),
-                        brw_imm_ud(1));
-
-      } else {
-         /* Overwrite the destination without and with execution masking to
-          * find out which of the channels is active.
-          */
-         brw_push_insn_state(p);
-         brw_set_default_exec_size(p, BRW_EXECUTE_4);
-         brw_MOV(p, brw_writemask(vec4(dst), WRITEMASK_X),
-                 brw_imm_ud(1));
+      /* Overwrite the destination without and with execution masking to
+       * find out which of the channels is active.
+       */
+      brw_push_insn_state(p);
+      brw_set_default_exec_size(p, BRW_EXECUTE_4);
+      brw_MOV(p, brw_writemask(vec4(dst), WRITEMASK_X),
+              brw_imm_ud(1));
 
-         inst = brw_MOV(p, brw_writemask(vec4(dst), WRITEMASK_X),
-                        brw_imm_ud(0));
-         brw_pop_insn_state(p);
-         brw_inst_set_mask_control(devinfo, inst, BRW_MASK_ENABLE);
-      }
+      inst = brw_MOV(p, brw_writemask(vec4(dst), WRITEMASK_X),
+                     brw_imm_ud(0));
+      brw_pop_insn_state(p);
+      brw_inst_set_mask_control(devinfo, inst, BRW_MASK_ENABLE);
    }
 
    brw_pop_insn_state(p);
-- 
2.5.0.400.gff86faf