Bug 91056

Couldn't reproduce on a GF108 (nvc1), which means this is nv50-specific. I did see some small render fail with the GF108 (the black polygon you mention happens in the blob too), and it didn't go away with NV50_PROG_OPTIMIZE=0.

So... you need to isolate the pass that's making things worse. This can be tricky as sometimes one pass will affect another. Start with

NV50_PROG_OPTIMIZE=1

If that fails identically, then go into nv50_ir_peephole.cpp, and look at

bool
Program::optimizeSSA(int level)
{
   RUN_PASS(1, DeadCodeElim, buryAll);
   RUN_PASS(1, CopyPropagation, run);
   RUN_PASS(1, MergeSplits, run);
   RUN_PASS(2, GlobalCSE, run);
   RUN_PASS(1, LocalCSE, run);
   RUN_PASS(2, AlgebraicOpt, run);
   RUN_PASS(2, ModifierFolding, run); // before load propagation -> less checks
   RUN_PASS(1, ConstantFolding, foldAll);
   RUN_PASS(1, LoadPropagation, run);
   RUN_PASS(2, MemoryOpt, run);
   RUN_PASS(2, LocalCSE, run);
   RUN_PASS(0, DeadCodeElim, buryAll);

   return true;
}

Try to find the smallest set of 1's you have to change into 2's, until NV50_PROG_OPTIMIZE=1 works. [By the way, since you commented on bug 90887, I assume you have the relevant patch from that too.]

If NV50_PROG_OPTIMIZE=1 already works, try flipping some 2's into 1's until it no longer works.

The game shows the rendering issues with NV50_PROG_OPTIMIZE=1 as well.

I found that it's sufficient to change either
RUN_PASS(1, CopyPropagation, run);

or

RUN_PASS(1, LoadPropagation, run);

to '2' and the game renders properly with NV50_PROG_OPTIMIZE=1 (those black bars remained whatever I changed though).

(In reply to Béla Gyebrószki from comment #2)
> The game shows the rendering issues with NV50_PROG_OPTIMIZE=1 as well.
> 
> I found that it's sufficient to change either
> RUN_PASS(1, CopyPropagation, run);
> 
> or
> 
> RUN_PASS(1, LoadPropagation, run);
> 
> to '2' and the game renders properly with NV50_PROG_OPTIMIZE=1 (those black
> bars remained whatever I changed though).

Interesting that it's *either*. I guess some instruction claims that it can accept things (in the code) that it, in actuality, can't. I assume you don't see any INVALID_OPCODE messages in dmesg?

The simplest next step is to find a draw call (using qapitrace) that renders properly without the optimizations but improperly with. Once you've identified the call number, the simplest thing would be to then run 'glretrace -D $call' through valgrind-mmt both ways, which, via 'demmt', should allow you to easily see what shaders were used in that last call.

Created attachment 116707 [details] [review]
provisional fix

OK, so this patch appears to fix it. The shaders at the end of that opt trace have

00000028: b5000409 08000780     add rn f32 $r2 $r2 neg c0[$a1]
00000040: b500060d 08004780     add rn f32 $r3 $r3 neg c0[$a1+0x4]

etc in them. Which seems innocuous enough, but... something about it is bad. Perhaps the neg + indirect. Perhaps just indirect. Perhaps... who knows. Needs testing.

(In reply to Ilia Mirkin from comment #4)
> Created attachment 116707 [details] [review] [review]
> provisional fix
> 
> OK, so this patch appears to fix it. The shaders at the end of that opt
> trace have
> 
> 00000028: b5000409 08000780     add rn f32 $r2 $r2 neg c0[$a1]
> 00000040: b500060d 08004780     add rn f32 $r3 $r3 neg c0[$a1+0x4]
> 
> etc in them. Which seems innocuous enough, but... something about it is bad.
> Perhaps the neg + indirect. Perhaps just indirect. Perhaps... who knows.
> Needs testing.

uniform vec4 colors[4];
uniform int index;
void main() { gl_FragColor = -vec4(0.2, 0.2, 0.2, 0) - colors[index]; }

generates

00000000: 10002001 2400c780     ld $r0 b32 c0[0x40]
00000008: 100d8009 0be4cccf     mov b32 $r2 0xbe4ccccd
00000010: 00040005 c0000780     shl $a1 $r0 0x4
00000018: b5000401 08000780     add rn f32 $r0 $r2 neg c0[$a1]
00000020: b5000405 08004780     add rn f32 $r1 $r2 neg c0[$a1+0x4]
00000028: b5000409 08008780     add rn f32 $r2 $r2 neg c0[$a1+0x8]
00000030: 1400060d 2400c780     ld $r3 b32 c0[$a1+0xc]

Which works fine. There's something even more subtle going on :(

So we try to do:

  4: ld u32 $r2 c0[$a1+0x0] (8)
  5: sub f32 $r2 $r2 c0[$a0+0x0] (8)
  6: mad f32 $r2 a[0x18] $r2 c0[$a0+0x0] (8)
  7: ld u32 $r3 c0[$a1+0x4] (8)
  8: sub f32 $r3 $r3 c0[$a0+0x4] (8)
  9: mad f32 $r3 a[0x18] $r3 c0[$a0+0x4] (8)

but it comes out as

00000020: 18000009 2400c780     ld $r2 b32 c0[$a2]
00000028: b5000409 08000780     add rn f32 $r2 $r2 neg c0[$a1]
00000030: e1020c09 00200780     add f32 $r2 (mul a[0x18] $r2) c0[0x0]
00000038: 1800020d 2400c780     ld $r3 b32 c0[$a2+0x4]
00000040: b500060d 08004780     add rn f32 $r3 $r3 neg c0[$a1+0x4]
00000048: e1030c0d 00204780     add f32 $r3 (mul a[0x18] $r3) c0[0x4]

oops. Either we can't propagate into the mad, or there's an indirect bit somewhere in there.

commit d5f1253b0c4637ad996fd0da45095165006d61d3
Author: Ilia Mirkin <imirkin@alum.mit.edu>
Date:   Tue Jun 30 02:46:26 2015 -0400

    nv50/ir: fix emission of address reg in 3rd source
    
    Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91056
    Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
    Cc: "10.5 10.6" <mesa-stable@lists.freedesktop.org>