nir: Teach nir_opt_algebraic about adding and subtracting the same thing

This optimizes a + b - b to just a. Modest shader-db results (BDW):

  total instructions in shared programs: 7842452 -> 7841862 (-0.01%)
  instructions in affected programs:     61938 -> 61348 (-0.95%)
  total loops in shared programs:        2131 -> 2131 (0.00%)
  helped:                                263
  HURT:                                  0
  GAINED:                                0
  LOST:                                  0

but the optimization turns

  gl_VertexID - gl_BaseVertexARB

into just a reference to SYSTEM_VALUE_VERTEX_ID_ZERO_BASE, which the
i965 hardware supports natively. That means we can avoid using the
internal vertex buffer for gl_BaseVertexARB in this case.

Reviewed-by: Eduardo Lima Mitev <elima@igalia.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>

diff --git a/src/glsl/nir/nir_opt_algebraic.py b/src/glsl/nir/nir_opt_algebraic.py
index cb715c0b2c1a6e8c279228349c04aadb13c8336f..1fdad3d78a6a6bf8c1a16a659b4627e8eb9a9e0f 100644 (file)
--- a/src/glsl/nir/nir_opt_algebraic.py
+++ b/src/glsl/nir/nir_opt_algebraic.py
@@ -62,6 +62,10 @@ optimizations = [
    (('iadd', ('imul', a, b), ('imul', a, c)), ('imul', a, ('iadd', b, c))),
    (('fadd', ('fneg', a), a), 0.0),
    (('iadd', ('ineg', a), a), 0),
+   (('iadd', ('ineg', a), ('iadd', a, b)), b),
+   (('iadd', a, ('iadd', ('ineg', a), b)), b),
+   (('fadd', ('fneg', a), ('fadd', a, b)), b),
+   (('fadd', a, ('fadd', ('fneg', a), b)), b),
    (('fmul', a, 0.0), 0.0),
    (('imul', a, 0), 0),
    (('umul_unorm_4x8', a, 0), 0),