Use vmulq_n_u32(..., 0x01010101) to distribute alphas.
This seems to make alphas() faster and Load[24]Alphas() no slower.
The change is particularly noticeable on xfermodes that call alphas()
twice (on src and dst), with a 10-12% speedup.
Xfermode_Difference_aa 29ms -> 28.4ms 0.98x
Xfermode_DstATop_aa 27.2ms -> 26.7ms 0.98x
Xfermode_Xor_aa 27.2ms -> 26.5ms 0.98x
Xfermode_DstOver 23.6ms -> 22.9ms 0.97x
Xfermode_DstOver_aa 27.8ms -> 26.8ms 0.96x
Xfermode_DstOut 22.6ms -> 21.7ms 0.96x
Xfermode_Multiply_aa 30ms -> 28.5ms 0.95x
Xfermode_DstOut_aa 26.1ms -> 24.8ms 0.95x
Xfermode_DstIn_aa 25.4ms -> 24.1ms 0.95x
Xfermode_DstATop 28.7ms -> 26ms 0.9x
Xfermode_Multiply 35.5ms -> 31.3ms 0.88x
Xfermode_Difference 31.8ms -> 27.7ms 0.87x
Xfermode_Xor 30.1ms -> 26.1ms 0.87x
BUG=skia:
Review URL: https://codereview.chromium.org/1203513002
1 file changed