On 08/11/2016 11:54 AM, Thomas Helland wrote: > 2016-08-11 18:19 GMT+02:00 Ian Romanick <i...@freedesktop.org>: >> ping >> >> On 07/19/2016 10:37 PM, Ian Romanick wrote: >>> From: Ian Romanick <ian.d.roman...@intel.com> >>> >>> Some shaders include code that looks like: >>> >>> uniform int i; >>> uniform vec4 bones[...]; >>> >>> foo(bones[i * 3], bones[i * 3 + 1], bones[i * 3 + 2]); >>> >>> CSE would do some work on this: >>> >>> x = i * 3 >>> foo(bones[x], bones[x + 1], bones[x + 2]); >>> >>> The compiler may then add '<< 4 + base' to the index calculations. >>> This results in expressions like >>> >>> x = i * 3 >>> foo(bones[x << 4], bones[(x + 1) << 4], bones[(x + 2) << 4]); >>> > > This may just be me being dense, but why is the compiler adding the shift? > It seems like this would be "un-optimizing" and so it shouldn't be added?
The shift is to convert the array offset to a byte offset. A vec4 is 16 bytes. > This patch is also a good argument for adding a constant reassociation pass. > At least the (a * #b) << #c ---> a * (#b << #c) would be caught by that. > > I was confused whether the optimization was preserving signed-ness correctly > but after a couple rounds with myself I believe it is correct. > > The change looks good and is: > > Reviewed-by: Thomas Helland <thomashellan...@gmail.com> > > (Oh, and yes, I'm back to hobby mesa development after finally > securing a new job and a new apartment) Welcome back! >>> Just rearranging the math to produce (i * 48) + 16 saves an >>> instruction, and it allows CSE to do more work. >>> >>> x = i * 48; >>> foo(bones[x], bones[x + 16], bones[x + 32]); >>> >>> So, ~6 instructions becomes ~3. >>> >>> Some individual shader-db results look pretty bad. However, I have a >>> really, really hard time believing the change in estimated cycles in, >>> for example, 3dmmes-taiji/51.shader_test after looking that change in >>> the generated code. >>> >>> G45 >>> total instructions in shared programs: 4020840 -> 4010070 (-0.27%) >>> instructions in affected programs: 177460 -> 166690 (-6.07%) >>> helped: 894 >>> HURT: 0 >>> >>> total cycles in shared programs: 98829000 -> 98784990 (-0.04%) >>> cycles in affected programs: 3936648 -> 3892638 (-1.12%) >>> helped: 894 >>> HURT: 0 >>> >>> Ironlake >>> total instructions in shared programs: 6418887 -> 6408117 (-0.17%) >>> instructions in affected programs: 177460 -> 166690 (-6.07%) >>> helped: 894 >>> HURT: 0 >>> >>> total cycles in shared programs: 143504542 -> 143460532 (-0.03%) >>> cycles in affected programs: 3936648 -> 3892638 (-1.12%) >>> helped: 894 >>> HURT: 0 >>> >>> Sandy Bridge >>> total instructions in shared programs: 8357887 -> 8339251 (-0.22%) >>> instructions in affected programs: 432715 -> 414079 (-4.31%) >>> helped: 2795 >>> HURT: 0 >>> >>> total cycles in shared programs: 118284184 -> 118207412 (-0.06%) >>> cycles in affected programs: 6114626 -> 6037854 (-1.26%) >>> helped: 2478 >>> HURT: 317 >>> >>> Ivy Bridge >>> total instructions in shared programs: 7669390 -> 7653822 (-0.20%) >>> instructions in affected programs: 388234 -> 372666 (-4.01%) >>> helped: 2795 >>> HURT: 0 >>> >>> total cycles in shared programs: 68381982 -> 68263684 (-0.17%) >>> cycles in affected programs: 1972658 -> 1854360 (-6.00%) >>> helped: 2458 >>> HURT: 307 >>> >>> Haswell >>> total instructions in shared programs: 7082636 -> 7067068 (-0.22%) >>> instructions in affected programs: 388234 -> 372666 (-4.01%) >>> helped: 2795 >>> HURT: 0 >>> >>> total cycles in shared programs: 68282020 -> 68164158 (-0.17%) >>> cycles in affected programs: 1891820 -> 1773958 (-6.23%) >>> helped: 2459 >>> HURT: 261 >>> >>> Broadwell >>> total instructions in shared programs: 9002466 -> 8985875 (-0.18%) >>> instructions in affected programs: 658784 -> 642193 (-2.52%) >>> helped: 2795 >>> HURT: 5 >>> >>> total cycles in shared programs: 78503092 -> 78450404 (-0.07%) >>> cycles in affected programs: 2873304 -> 2820616 (-1.83%) >>> helped: 2275 >>> HURT: 415 >>> >>> Skylake >>> total instructions in shared programs: 9156978 -> 9140387 (-0.18%) >>> instructions in affected programs: 682625 -> 666034 (-2.43%) >>> helped: 2795 >>> HURT: 5 >>> >>> total cycles in shared programs: 75591392 -> 75550574 (-0.05%) >>> cycles in affected programs: 3192120 -> 3151302 (-1.28%) >>> helped: 2271 >>> HURT: 425 >>> >>> Signed-off-by: Ian Romanick <ian.d.roman...@intel.com> >>> --- >>> src/compiler/nir/nir_opt_algebraic.py | 11 +++++++++++ >>> 1 file changed, 11 insertions(+) >>> >>> diff --git a/src/compiler/nir/nir_opt_algebraic.py >>> b/src/compiler/nir/nir_opt_algebraic.py >>> index 0f0896b..37cb700 100644 >>> --- a/src/compiler/nir/nir_opt_algebraic.py >>> +++ b/src/compiler/nir/nir_opt_algebraic.py >>> @@ -119,6 +119,17 @@ optimizations = [ >>> (('~fadd@64', a, ('fmul', c , ('fadd', b, ('fneg', a)))), >>> ('flrp', a, b, c), '!options->lower_flrp64'), >>> (('ffma', a, b, c), ('fadd', ('fmul', a, b), c), 'options->lower_ffma'), >>> (('~fadd', ('fmul', a, b), c), ('ffma', a, b, c), 'options->fuse_ffma'), >>> + >>> + # (a * #b + #c) << #d >>> + # ((a * #b) << #d) + (#c << #d) >>> + # (a * (#b << #d)) + (#c << #d) >>> + (('ishl', ('iadd', ('imul', a, '#b'), '#c'), '#d'), >>> + ('iadd', ('imul', a, ('ishl', b, d)), ('ishl', c, d))), >>> + >>> + # (a * #b) << #c >>> + # a * (#b << #c) >>> + (('ishl', ('imul', a, '#b'), '#c'), ('imul', a, ('ishl', b, c))), >>> + >>> # Comparison simplifications >>> (('~inot', ('flt', a, b)), ('fge', a, b)), >>> (('~inot', ('fge', a, b)), ('flt', a, b)), >>> >> >> _______________________________________________ >> mesa-dev mailing list >> mesa-dev@lists.freedesktop.org >> https://lists.freedesktop.org/mailman/listinfo/mesa-dev > _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/mesa-dev