diff options
| author | Kenneth Graunke <[email protected]> | 2016-04-06 22:34:39 -0700 |
|---|---|---|
| committer | Kenneth Graunke <[email protected]> | 2016-04-11 18:43:55 -0700 |
| commit | 5886cd79a0ed10b887840f6afb980a5a6a47e26e (patch) | |
| tree | 6c994bb93e9255240ab9c766f54084ad9514319e /src/compiler | |
| parent | 1c7ba7f15646367006d615180e89d5ea34a3d5f6 (diff) | |
nir: Do basic constant reassociation.
Many shaders contain expression trees of the form:
const_1 * (value * const_2)
Reorganizing these to
(const_1 * const_2) * value
will allow constant folding to combine the constants. Sometimes, these
constants are 2 and 0.5, so we can remove a multiply altogether. Other
times, it can create more immediate constants, which can actually hurt.
Finding a good balance here is tricky. While much more could be done,
this simple patch seems to have a lot of positive benefit while having
a low downside.
shader-db results on Broadwell:
total instructions in shared programs: 8963768 -> 8961369 (-0.03%)
instructions in affected programs: 438318 -> 435919 (-0.55%)
helped: 1502
HURT: 245
total cycles in shared programs: 71527354 -> 71421516 (-0.15%)
cycles in affected programs: 11541788 -> 11435950 (-0.92%)
helped: 3445
HURT: 1224
Signed-off-by: Kenneth Graunke <[email protected]>
Reviewed-by: Eduardo Lima Mitev <[email protected]>
Reviewed-by: Jason Ekstrand <[email protected]>
Reviewed-by: Matt Turner <[email protected]>
Diffstat (limited to 'src/compiler')
| -rw-r--r-- | src/compiler/nir/nir_opt_algebraic.py | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/src/compiler/nir/nir_opt_algebraic.py b/src/compiler/nir/nir_opt_algebraic.py index e72b4a791cb..420d9d9330e 100644 --- a/src/compiler/nir/nir_opt_algebraic.py +++ b/src/compiler/nir/nir_opt_algebraic.py @@ -274,6 +274,14 @@ optimizations = [ (('fmul', ('fneg', a), b), ('fneg', ('fmul', a, b))), (('imul', ('ineg', a), b), ('ineg', ('imul', a, b))), + # Reassociate constants in add/mul chains so they can be folded together. + # For now, we only handle cases where the constants are separated by + # a single non-constant. We could do better eventually. + (('~fmul', '#a', ('fmul', b, '#c')), ('fmul', ('fmul', a, c), b)), + (('imul', '#a', ('imul', b, '#c')), ('imul', ('imul', a, c), b)), + (('~fadd', '#a', ('fadd', b, '#c')), ('fadd', ('fadd', a, c), b)), + (('iadd', '#a', ('iadd', b, '#c')), ('iadd', ('iadd', a, c), b)), + # Misc. lowering (('fmod', a, b), ('fsub', a, ('fmul', b, ('ffloor', ('fdiv', a, b)))), 'options->lower_fmod'), (('uadd_carry', a, b), ('b2i', ('ult', ('iadd', a, b), a)), 'options->lower_uadd_carry'), |