diff options
| author | Ian Romanick <[email protected]> | 2020-03-03 10:21:18 -0800 |
|---|---|---|
| committer | Marge Bot <[email protected]> | 2020-03-18 20:36:29 +0000 |
| commit | 5b07f542e5a4ab698becbc238ff2ccc4720418bf (patch) | |
| tree | 589863ba9c02698061b4e98eb10845c20df1a321 | |
| parent | 617a69107ee58e23ace06093bc49fa2c86b7dd4b (diff) | |
soft-fp64: Optimize __fmin64 and __fmax64 by using different evaluation order [v2]
v2: Go to extra effort to avoid flow control inserted to implement
short-circuit evaluation rules.
Results on the 308 shaders extracted from the fp64 portion of the OpenGL
CTS:
Tiger Lake and Ice Lake had similar results. (Tiger Lake shown)
total instructions in shared programs: 797779 -> 796849 (-0.12%)
instructions in affected programs: 3499 -> 2569 (-26.58%)
helped: 21
HURT: 0
helped stats (abs) min: 8 max: 112 x̄: 44.29 x̃: 44
helped stats (rel) min: 16.09% max: 33.15% x̄: 25.72% x̃: 24.62%
95% mean confidence interval for instructions value: -55.94 -32.63
95% mean confidence interval for instructions %-change: -28.14% -23.30%
Instructions are helped.
total cycles in shared programs: 6601355 -> 6588351 (-0.20%)
cycles in affected programs: 25376 -> 12372 (-51.25%)
helped: 21
HURT: 0
helped stats (abs) min: 156 max: 1410 x̄: 619.24 x̃: 526
helped stats (rel) min: 42.39% max: 53.98% x̄: 50.12% x̃: 50.75%
95% mean confidence interval for cycles value: -776.58 -461.89
95% mean confidence interval for cycles %-change: -51.57% -48.67%
Cycles are helped.
Reviewed-by: Jason Ekstrand <[email protected]> [v1]
Reviewed-by: Matt Turner <[email protected]> [v1]
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4142>
| -rw-r--r-- | src/compiler/glsl/float64.glsl | 24 |
1 files changed, 16 insertions, 8 deletions
diff --git a/src/compiler/glsl/float64.glsl b/src/compiler/glsl/float64.glsl index 67e0e657c55..3cc8aa7fa4b 100644 --- a/src/compiler/glsl/float64.glsl +++ b/src/compiler/glsl/float64.glsl @@ -1784,21 +1784,29 @@ __fround64(uint64_t __a) uint64_t __fmin64(uint64_t a, uint64_t b) { - if (__is_nan(a)) return b; - if (__is_nan(b)) return a; + /* This weird layout matters. Doing the "obvious" thing results in extra + * flow control being inserted to implement the short-circuit evaluation + * rules. Flow control is bad! + */ + bool b_nan = __is_nan(b); + bool a_lt_b = __flt64_nonnan(a, b); + bool a_nan = __is_nan(a); - if (__flt64_nonnan(a, b)) return a; - return b; + return (b_nan || a_lt_b) && !a_nan ? a : b; } uint64_t __fmax64(uint64_t a, uint64_t b) { - if (__is_nan(a)) return b; - if (__is_nan(b)) return a; + /* This weird layout matters. Doing the "obvious" thing results in extra + * flow control being inserted to implement the short-circuit evaluation + * rules. Flow control is bad! + */ + bool b_nan = __is_nan(b); + bool a_lt_b = __flt64_nonnan(a, b); + bool a_nan = __is_nan(a); - if (__flt64_nonnan(a, b)) return b; - return a; + return (b_nan || a_lt_b) && !a_nan ? b : a; } uint64_t |