[Mesa-dev] [PATCH 3/3] i965/fs: Use MOV.nz instead of AND.nz to generate flag on SNB+

[Ian Romanick]

From: Ian Romanick <ian.d.romanick at intel.com>

On SNB+, the Boolean result is always 0 or ~0, so MOV.nz produces the
same effect as AND.nz.  However, later cmod propagation passes can
handle the MOV.nz, but they cannot handle the AND.nz due to src1 being
1.

Shader-db results:

Ivy Bridge (0x0166):
total instructions in shared programs: 6324484 -> 6322033 (-0.04%)
instructions in affected programs:     644645 -> 642194 (-0.38%)
helped:                                2667
HURT:                                  216
GAINED:                                0
LOST:                                  0

Haswell (0x0426):
total instructions in shared programs: 5951948 -> 5949497 (-0.04%)
instructions in affected programs:     588543 -> 586092 (-0.42%)
helped:                                2667
HURT:                                  216
GAINED:                                0
LOST:                                  0

Broadwell (0x162E):
total instructions in shared programs: 7040870 -> 7038378 (-0.04%)
instructions in affected programs:     591031 -> 588539 (-0.42%)
helped:                                2678
HURT:                                  216
GAINED:                                0
LOST:                                  0

No change on other platforms.

Signed-off-by: Ian Romanick <ian.d.romanick at intel.com>
---
 src/mesa/drivers/dri/i965/brw_fs_visitor.cpp | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
index 2f74716..5bacb68 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
@@ -2584,7 +2584,14 @@ fs_visitor::emit_bool_to_cond_code(ir_rvalue *ir)
    if (!expr || expr->operation == ir_binop_ubo_load) {
       ir->accept(this);
 
-      fs_inst *inst = emit(AND(reg_null_d, this->result, fs_reg(1)));
+      fs_inst *inst;
+
+      if (brw->gen <= 5) {
+         inst = emit(AND(reg_null_d, this->result, fs_reg(1)));
+      } else {
+         inst = emit(MOV(reg_null_d, this->result));
+      }
+
       inst->conditional_mod = BRW_CONDITIONAL_NZ;
       return;
    }
@@ -2604,7 +2611,11 @@ fs_visitor::emit_bool_to_cond_code(ir_rvalue *ir)
 
    switch (expr->operation) {
    case ir_unop_logic_not:
-      inst = emit(AND(reg_null_d, op[0], fs_reg(1)));
+      if (brw->gen <= 5) {
+         inst = emit(AND(reg_null_d, op[0], fs_reg(1)));
+      } else {
+         inst = emit(MOV(reg_null_d, op[0]));
+      }
       inst->conditional_mod = BRW_CONDITIONAL_Z;
       break;
 
-- 
2.1.0