[Mesa-dev] [PATCH 09/10] nir: Add algebraic optimizations for exponential/logarithmic functions.

[Kenneth Graunke]

Most of these exist in the GLSL IR algebraic pass already.  However,
SSA allows us to find more instances of the patterns.

total NIR instructions in shared programs: 2015593 -> 2011430 (-0.21%)
NIR instructions in affected programs:     124189 -> 120026 (-3.35%)
helped:                                    604

total i965 instructions in shared programs: 6025508 -> 6018718 (-0.11%)
i965 instructions in affected programs:     261070 -> 254280 (-2.60%)
helped:                                     1295
HURT:                                       2 (by 1 instruction each)
GAINED:                                     6

Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
---
 src/glsl/nir/nir_opt_algebraic.py | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/src/glsl/nir/nir_opt_algebraic.py b/src/glsl/nir/nir_opt_algebraic.py
index dec250b..a5b5715 100644
--- a/src/glsl/nir/nir_opt_algebraic.py
+++ b/src/glsl/nir/nir_opt_algebraic.py
@@ -99,6 +99,16 @@ optimizations = [
    (('ishr', a, 0), 0),
    (('ushr', 0, a), 0),
    (('ushr', a, 0), 0),
+   # Exponential/logarithmic identities
+   (('fexp2', ('flog2', a)), a), # 2^lg2(a) = a
+   (('fexp',  ('flog',  a)), a), # e^ln(a)  = a
+   (('flog2', ('fexp2', a)), a), # lg2(2^a) = a
+   (('flog',  ('fexp',  a)), a), # ln(e^a)  = a
+   (('fexp2', ('fmul', ('flog2', a), b)), ('fpow', a, b)), # 2^(lg2(a)*b) = a^b
+   (('fexp',  ('fmul', ('flog', a), b)),  ('fpow', a, b)), # e^(ln(a)*b) = a^b
+   (('fpow', a, 1.0), a),
+   (('fpow', a, 2.0), ('fmul', a, a)),
+   (('fpow', 2.0, a), ('fexp2', a)),
 
 # This one may not be exact
    (('feq', ('fadd', a, b), 0.0), ('feq', a, ('fneg', b))),
-- 
2.2.2