[Mesa-dev] [PATCH 09/23] glsl: Distribute multiply over b2f

[Ian Romanick]

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

Convert cases like (x * bool(b)) to 'mix(0, x, b)'.

Note: This may hurt the code generated for GPUs that represent Boolean
values using floating point.  shader-db doesn't play well with i915, so
I haven't been able to check it.

On at least BDW shaders/warsow/85.shader_test is hurt by about 10%, so
that may be worth investigating.

v2: Use swizzle_if_required on opeands.  Fixes
arb_texture_buffer_object-formats in debug builds.  Without this,
ir_validate fails on that test.

Shader-db results:

GM45 (0x2A42):
total instructions in shared programs: 3548093 -> 3545804 (-0.06%)
instructions in affected programs:     213889 -> 211600 (-1.07%)
helped:                                543
HURT:                                  2

Iron Lake (0x0046):
total instructions in shared programs: 4978454 -> 4975982 (-0.05%)
instructions in affected programs:     226063 -> 223591 (-1.09%)
helped:                                597
HURT:                                  5

Sandy Bridge (0x0116):
total instructions in shared programs: 6806814 -> 6803487 (-0.05%)
instructions in affected programs:     447885 -> 444558 (-0.74%)
helped:                                1612
HURT:                                  36

Sandy Bridge (0x0116) NIR:
total instructions in shared programs: 6813527 -> 6811992 (-0.02%)
instructions in affected programs:     329020 -> 327485 (-0.47%)
helped:                                1002
HURT:                                  196

Ivy Bridge (0x0166):
total instructions in shared programs: 6283080 -> 6279862 (-0.05%)
instructions in affected programs:     421859 -> 418641 (-0.76%)
helped:                                1592
HURT:                                  36

Ivy Bridge (0x0166) NIR:
total instructions in shared programs: 6319944 -> 6317148 (-0.04%)
instructions in affected programs:     303221 -> 300425 (-0.92%)
helped:                                998
HURT:                                  176
GAINED:                                4

Haswell (0x0426):
total instructions in shared programs: 5766971 -> 5764623 (-0.04%)
instructions in affected programs:     382796 -> 380448 (-0.61%)
helped:                                1559
HURT:                                  63

Haswell (0x0426) NIR:
total instructions in shared programs: 5793258 -> 5792647 (-0.01%)
instructions in affected programs:     276929 -> 276318 (-0.22%)
helped:                                837
HURT:                                  343
GAINED:                                4

Broadwell (0x162E):
total instructions in shared programs: 6813995 -> 6811377 (-0.04%)
instructions in affected programs:     469734 -> 467116 (-0.56%)
helped:                                1772
HURT:                                  78
LOST:                                  1

Broadwell (0x162E) NIR:
total instructions in shared programs: 7009761 -> 7009142 (-0.01%)
instructions in affected programs:     298433 -> 297814 (-0.21%)
helped:                                866
HURT:                                  373

Signed-off-by: Ian Romanick <ian.d.romanick at intel.com>
---
 src/glsl/opt_algebraic.cpp | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/src/glsl/opt_algebraic.cpp b/src/glsl/opt_algebraic.cpp
index 69c03ea..837b080 100644
--- a/src/glsl/opt_algebraic.cpp
+++ b/src/glsl/opt_algebraic.cpp
@@ -560,6 +560,28 @@ ir_algebraic_visitor::handle_expression(ir_expression *ir)
             }
          }
       }
+
+      /* If one of the multiplicands is an ir_unop_b2f, we can convert the
+       * multiply to a simple csel.
+       *
+       *     x * b2f(condition) => mix( 0,  x, condition)
+       */
+      for (unsigned i = 0; i < 2; i++) {
+         if (op_expr[i] == NULL)
+            continue;
+
+         if (op_expr[i]->operation != ir_unop_b2f)
+            continue;
+
+         /* swizzle_if_required is necessary on both operands.  The b2f could
+          * be a scalar (common) with the other a vector, or the b2f could be
+          * a vector with the other a scalar (as in piglit's
+          * arb_texture_buffer_object-formats test).
+          */
+         return csel(swizzle_if_required(ir, op_expr[i]->operands[0]),
+                     swizzle_if_required(ir, ir->operands[i ^ 1]),
+                     ir_constant::zero(ir, ir->type));
+      }
       break;
 
    case ir_binop_div:
-- 
2.1.0