Cycles: Use native saturate function for CUDA

This more a workaround for CUDA optimizer which can't optimize clamp(x, 0, 1)
into a single instruction and uses 4 instructions instead.

Original patch by @lockal with own modification:

  Don't make changes outside of the kernel. They don't make any difference
  anyway and term saturate() has a bit different meaning outside of kernel.

This gives around 2% of speedup in Barcelona file, but in more complex shader
setups with lots of math nodes with clamping speedup could be much nicer.

Subscribers: dingto

Projects: #cycles

Differential Revision: https://developer.blender.org/D1224

1 files changed, 2 insertions, 2 deletions

diff --git a/intern/cycles/kernel/kernel_globals.h b/intern/cycles/kernel/kernel_globals.h
index 0a9753baca2..be2c879adb9 100644
--- a/intern/cycles/kernel/kernel_globals.h
+++ b/intern/cycles/kernel/kernel_globals.h
@@ -94,7 +94,7 @@ typedef struct KernelGlobals {
 
 ccl_device float lookup_table_read(KernelGlobals *kg, float x, int offset, int size)
 {
-	x = clamp(x, 0.0f, 1.0f)*(size-1);
+	x = saturate(x)*(size-1);
 
 	int index = min(float_to_int(x), size-1);
 	int nindex = min(index+1, size-1);
@@ -110,7 +110,7 @@ ccl_device float lookup_table_read(KernelGlobals *kg, float x, int offset, int s
 
 ccl_device float lookup_table_read_2D(KernelGlobals *kg, float x, float y, int offset, int xsize, int ysize)
 {
-	y = clamp(y, 0.0f, 1.0f)*(ysize-1);
+	y = saturate(y)*(ysize-1);
 
 	int index = min(float_to_int(y), ysize-1);
 	int nindex = min(index+1, ysize-1);