nir: Add algebraic optimizations for exponential/logarithmic functions.

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: 6025505 -> 6018717 (-0.11%)
i965 instructions in affected programs:     261295 -> 254507 (-2.60%)
helped:                                     1295
HURT:                                       3

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Jason Ekstrand <jason.ekstrand@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 40722de1ea5b28bcf13ec454073723647cedf046..42846e1202b0b7453f10b0123d6424a25f95d9ce 100644 (file)
--- a/src/glsl/nir/nir_opt_algebraic.py
+++ b/src/glsl/nir/nir_opt_algebraic.py
@@ -96,6 +96,16 @@ optimizations = [
    (('ishr', a, 0), a),
    (('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))),