[Mesa-dev] [PATCH 1/2] i965: Implement b2f and b2i using negation.

[Francisco Jerez]

Booleans are represented as 0/-1 on modern hardware which means we can
just negate them to convert them into a numeric type.  Negation has
the benefit that it can be implemented using a source modifier which
can easily be propagated into some other instruction.  shader-db
results on HSW:

 total instructions in shared programs: 5264246 -> 5264211 (-0.00%)
 instructions in affected programs:     1464 -> 1429 (-2.39%)
 helped:                                15
 HURT:                                  1

No piglit regressions.
---
 src/mesa/drivers/dri/i965/brw_fs_nir.cpp       | 4 +---
 src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp | 7 +------
 2 files changed, 2 insertions(+), 9 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_fs_nir.cpp b/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
index 4690d00..64ff24c 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
@@ -969,10 +969,8 @@ fs_visitor::nir_emit_alu(const fs_builder &bld, nir_alu_instr *instr)
       break;
 
    case nir_op_b2i:
-      bld.AND(result, op[0], fs_reg(1));
-      break;
    case nir_op_b2f:
-      bld.AND(retype(result, BRW_REGISTER_TYPE_UD), op[0], fs_reg(0x3f800000u));
+      bld.MOV(result, negate(op[0]));
       break;
 
    case nir_op_f2b:
diff --git a/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp b/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
index c9c2661..fd94a70 100644
--- a/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
@@ -1733,16 +1733,11 @@ vec4_visitor::visit(ir_expression *ir)
       emit(MOV(result_dst, op[0]));
       break;
    case ir_unop_b2i:
-      emit(AND(result_dst, op[0], src_reg(1)));
-      break;
    case ir_unop_b2f:
       if (devinfo->gen <= 5) {
          resolve_bool_comparison(ir->operands[0], &op[0]);
       }
-      op[0].type = BRW_REGISTER_TYPE_D;
-      result_dst.type = BRW_REGISTER_TYPE_D;
-      emit(AND(result_dst, op[0], src_reg(0x3f800000u)));
-      result_dst.type = BRW_REGISTER_TYPE_F;
+      emit(MOV(result_dst, negate(op[0])));
       break;
    case ir_unop_f2b:
       emit(CMP(result_dst, op[0], src_reg(0.0f), BRW_CONDITIONAL_NZ));
-- 
2.4.3