From: Ian Romanick <ian.d.roman...@intel.com>
An expression like
x = !condition ? a : b;
will get rewritten as
x = condition ? b : a;
This has two immediate advantages. First, it saves a (very small)
amount of memory. Second, and more importantly, it means that
transformations that look at the condition of an ir_triop_csel don't
have to handle cases where the root of the condition's expression tree
is an ir_unop_logic_not.
For example, commit 467077b adds an optimization to the i965 FS backend
for expressions like
x = gl_FrontFacing ? 1.0 : 0.0;
However, that optimization is oblivious to a preceeding logical-not, so
it fails to optimize an expression like
x = !gl_FrontFacing ? 0.0 : 1.0;
even though they are functionally identical.
The one place in shader-db that uses !gl_FrontFacing still doesn't hit
the optimization from 467077b because it uses integer values.
Shader-db results:
GM45 (0x2A42):
total instructions in shared programs: 3544133 -> 3544141 (0.00%)
instructions in affected programs: 1410 -> 1418 (0.57%)
HURT: 8
Iron Lake (0x0046):
total instructions in shared programs: 4973849 -> 4973858 (0.00%)
instructions in affected programs: 1606 -> 1615 (0.56%)
HURT: 9
Sandy Bridge (0x0116):
total instructions in shared programs: 6799682 -> 6799644 (-0.00%)
instructions in affected programs: 5926 -> 5888 (-0.64%)
helped: 22
HURT: 6
Sandy Bridge (0x0116) NIR:
total instructions in shared programs: 6787227 -> 6787141 (-0.00%)
instructions in affected programs: 9016 -> 8930 (-0.95%)
helped: 42
Ivy Bridge (0x0166):
total instructions in shared programs: 6273868 -> 6273830 (-0.00%)
instructions in affected programs: 5491 -> 5453 (-0.69%)
helped: 22
HURT: 6
Ivy Bridge (0x0166) NIR:
total instructions in shared programs: 6298635 -> 6298549 (-0.00%)
instructions in affected programs: 8199 -> 8113 (-1.05%)
helped: 42
Haswell (0x0426):
total instructions in shared programs: 5760189 -> 5760151 (-0.00%)
instructions in affected programs: 5030 -> 4992 (-0.76%)
helped: 22
HURT: 6
Haswell (0x0426) NIR:
total instructions in shared programs: 5767160 -> 5767074 (-0.00%)
instructions in affected programs: 7450 -> 7364 (-1.15%)
helped: 42
Broadwell (0x162E):
total instructions in shared programs: 6808224 -> 6808186 (-0.00%)
instructions in affected programs: 4978 -> 4940 (-0.76%)
helped: 22
HURT: 6
Broadwell (0x162E) NIR:
total instructions in shared programs: 6986297 -> 6986211 (-0.00%)
instructions in affected programs: 7410 -> 7324 (-1.16%)
helped: 42
Signed-off-by: Ian Romanick <ian.d.roman...@intel.com>
---
src/glsl/opt_algebraic.cpp | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/src/glsl/opt_algebraic.cpp b/src/glsl/opt_algebraic.cpp
index af22bed..f8bbb2a 100644
--- a/src/glsl/opt_algebraic.cpp
+++ b/src/glsl/opt_algebraic.cpp
@@ -1156,6 +1156,17 @@ ir_algebraic_visitor::handle_expression(ir_expression
*ir)
if (is_vec_one(op_const[1]) && is_vec_zero(op_const[2]))
return logic_not(ir->operands[0]);
}
+
+ /* Optimize an expression like 'mix(a, b, !condition)' to 'mix(b, a,
+ * condition)'.
+ */
+ if (op_expr[0] && op_expr[0]->operation == ir_unop_logic_not) {
+ ir->operands[0] = op_expr[0]->operands[0];
+
+ ir_rvalue *const tmp = ir->operands[1];
+ ir->operands[1] = ir->operands[2];
+ ir->operands[2] = tmp;
+ }
break;
default:
--
2.1.0
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