On Mon, Jun 27, 2016 at 4:44 AM, Rob Clark <robdcl...@gmail.com> wrote: > On Mon, Jun 27, 2016 at 7:13 AM, Alan Swanson <rei...@improbability.net> > wrote: >> On 2016-06-25 13:37, Rob Clark wrote: >>> >>> Some games are sloppy.. perhaps because it is defined behavior for DX or >>> perhaps because nv blob driver defaults things to zero. >>> >>> So add driconf param to force uninitialized variables to default to zero. >>> >>> This issue was observed with rust, from steam store. But has surfaced >>> elsewhere in the past. >>> >>> Signed-off-by: Rob Clark <robcl...@freedesktop.org> >>> --- >>> Note that I left out the drirc bit, since not entirely sure how to >>> identify this game. (I don't actually have the game, just working off >>> of an apitrace) >>> >>> Possibly worth mentioning that for the shaders using uninitialized vars >>> having zero-initializers lets constant-propagation get rid of a whole >>> lot of instructions. One shader I saw dropped to less than half of >>> it's original instruction count. >> >> >> If the default for uninitialised variables is undefined, then with the >> reported shader optimisations why bother with the (DRI) option when >> zeroing could still essentially be classed as undefined? >> >> Cuts the patch down to just the src/compiler/glsl/ast_to_hir.cpp change. > > I did suggest that on #dri-devel, but Jason had a theoretical example > where it would hurt.. iirc something like: > > float maybe_undef; > for (int i = 0; i < some_uniform_at_least_one; i++) > maybe_undef = ... > > also, he didn't want to hide shader bugs that app should fix. > > It would be interesting to rush shaderdb w/ glsl_zero_init=true and > see what happens, but I didn't get around to that yet.
Here's what I get on i965. It's not a clear win. total instructions in shared programs: 5249030 -> 5249002 (-0.00%) instructions in affected programs: 28936 -> 28908 (-0.10%) helped: 66 HURT: 132 total cycles in shared programs: 57966694 -> 57956306 (-0.02%) cycles in affected programs: 1136118 -> 1125730 (-0.91%) helped: 78 HURT: 106 _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/mesa-dev
