Mesa (master): i965: Implement b2f and b2i using negation.

[Francisco Jerez]

Module: Mesa
Branch: master
Commit: 3ee2daf23dc91b8dfc017b5c89c10ab1376ba4df
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=3ee2daf23dc91b8dfc017b5c89c10ab1376ba4df

Author: Francisco Jerez <currojerez at riseup.net>
Date:   Fri Jul 10 19:18:39 2015 +0300

i965: Implement b2f and b2i using negation.

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: 6349082 -> 6346693 (-0.04%)
instructions in affected programs:     40948 -> 38559 (-5.83%)
helped:                                123
HURT:                                  1
GAINED:                                1
LOST:                                  0

Reviewed-by: Matt Turner <mattst88 at gmail.com>

---

 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 10903a1..1987032 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
@@ -968,10 +968,8 @@ 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 67f2b5c..8a352d3 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));