[Mesa-dev] [PATCH 18/21] i965/fs: Allow specifying arbitrary execution sizes up to 32 to FIND_LIVE_CHANNEL.

[Francisco Jerez]

Due to a Gen7-specific hardware bug native 32-wide instructions get
the lower 16 bits of the execution mask applied incorrectly to both
halves of the instruction, so the MOV trick we currently use wouldn't
work.  Instead emit multiple 16-wide MOV instructions in 32-wide mode
in order to cover the whole execution mask.
---
 src/mesa/drivers/dri/i965/brw_eu_emit.c | 25 +++++++++++++++++--------
 1 file changed, 17 insertions(+), 8 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_eu_emit.c b/src/mesa/drivers/dri/i965/brw_eu_emit.c
index af7caed..d36877c 100644
--- a/src/mesa/drivers/dri/i965/brw_eu_emit.c
+++ b/src/mesa/drivers/dri/i965/brw_eu_emit.c
@@ -3330,6 +3330,7 @@ void
 brw_find_live_channel(struct brw_codegen *p, struct brw_reg dst)
 {
    const struct brw_device_info *devinfo = p->devinfo;
+   const unsigned exec_size = 1 << brw_inst_exec_size(devinfo, p->current);
    brw_inst *inst;
 
    assert(devinfo->gen >= 7);
@@ -3359,15 +3360,23 @@ brw_find_live_channel(struct brw_codegen *p, struct brw_reg dst)
 
          brw_MOV(p, flag, brw_imm_ud(0));
 
-         /* Run a 16-wide instruction returning zero with execution masking
-          * and a conditional modifier enabled in order to get the current
-          * execution mask in f1.0.
+         /* Run enough instructions returning zero with execution masking and
+          * a conditional modifier enabled in order to get the full execution
+          * mask in f1.0.  We could use a single 32-wide move here if it
+          * weren't because of the hardware bug that causes channel enables to
+          * be applied incorrectly to the second half of 32-wide instructions
+          * on Gen7.
           */
-         inst = brw_MOV(p, brw_null_reg(), brw_imm_ud(0));
-         brw_inst_set_exec_size(devinfo, inst, BRW_EXECUTE_16);
-         brw_inst_set_mask_control(devinfo, inst, BRW_MASK_ENABLE);
-         brw_inst_set_cond_modifier(devinfo, inst, BRW_CONDITIONAL_Z);
-         brw_inst_set_flag_reg_nr(devinfo, inst, 1);
+         const unsigned lower_size = MIN2(16, exec_size);
+         for (unsigned i = 0; i < exec_size / lower_size; i++) {
+            inst = brw_MOV(p, retype(brw_null_reg(), BRW_REGISTER_TYPE_UW),
+                           brw_imm_uw(0));
+            brw_inst_set_mask_control(devinfo, inst, BRW_MASK_ENABLE);
+            brw_inst_set_group(devinfo, inst, lower_size * i);
+            brw_inst_set_cond_modifier(devinfo, inst, BRW_CONDITIONAL_Z);
+            brw_inst_set_flag_reg_nr(devinfo, inst, 1);
+            brw_inst_set_exec_size(devinfo, inst, cvt(lower_size) - 1);
+         }
 
          brw_FBL(p, vec1(dst), flag);
       }
-- 
2.7.3