r600/sb: Fix loop optimization related hangs on eg

r600/sb: Fix loop optimization related hangs on eg

Make sure unused ops and their references are removed, prior to entering
the GCM (global code motion) pass, to stop GCM from breaking the loop
logic and thus hanging the GPU.

Turns out, that sb has problems with loops and node optimizations
regarding associative folding:

- the global code motion (gcm) pass moves ops up a loop level/basic block
until they've fulfilled their total usage count
- if there are ops folded into others, the usage count won't be
fulfilled and thus the op moved way up to the top
- within GCM the op would be visited and their deps would be moved
alongside it, to fulfill the src constaints
- in a loop, an unused op is moved out of the loop and GCM would move
the src value ops up as well
- now here arises the problem: if the loop counter is one of the src
values it would get moved up as well, the loop break condition would
never get hit and the shader turn into an endless loop, resulting in the
GPU hanging and being reset

A reduced (albeit nonsense) piglit example would be:

[require]
GLSL >= 1.20

[fragment shader]

uniform int SIZE;
uniform vec4 lights[512];

void main()
{
    float x = 0;
    for(int i = 0; i < SIZE; i++)
        x += lights[2*i+1].x;
}

[test]
uniform int SIZE 1
draw rect -1 -1 2 2

Which gets optimized to:

===== SHADER #12 OPT ================================== PS/BARTS/EVERGREEN =====
===== 42 dw ===== 1 gprs ===== 2 stack =========================================
ALU 3 @24
     1      y: MOV                R0.y,  0
            t: MULLO_UINT         R0.w,  [0x00000002 2.8026e-45].x, R0.z

LOOP_START_DX10 @22
PUSH @6
ALU 1 @30 KC0[CB0:0-15]
     2 M    x: PRED_SETGE_INT     __.x,  R0.z, KC0[0].x
JUMP @14 POP:1
LOOP_BREAK @20
POP @14 POP:1
ALU 2 @32
     3      x: ADD_INT            R0.x,  R0.w, [0x00000002 2.8026e-45].x

TEX 1 @36
               VFETCH             R0.x___, R0.x,   RID:0   MFC:16 UCF:0 FMT[..]
ALU 1 @40
     4      y: ADD                R0.y,  R0.y, R0.x
LOOP_END @4
EXPORT_DONE        PIXEL 0     R0.____  EOP
===== SHADER_END ===============================================================

Notice R0.z being the loop counter/break condition relevant register
and being never incremented at all. Also some of the loop content
has been moved out of it, to fulfill the requirements for the one unused
op.

With a debug build of mesa this would produce an error like
error at : PRED_SETGE_INT     __, __, EM.2,    R1.x.2||FP@R0.z, C0.x
  : operand value R1.x.2||FP@R0.z was not previously written to its gpr
and the compilation would fail due to this. On a release build it gets
passed to the GPU.

When using this patch, the loop remains intact:

===== SHADER #12 OPT ================================== PS/BARTS/EVERGREEN =====
===== 48 dw ===== 1 gprs ===== 2 stack =========================================
ALU 2 @24
     1      y: MOV                R0.y,  0
            z: MOV                R0.z,  0
LOOP_START_DX10 @22
PUSH @6
ALU 1 @28 KC0[CB0:0-15]
     2 M    x: PRED_SETGE_INT     __.x,  R0.z, KC0[0].x
JUMP @14 POP:1
LOOP_BREAK @20
POP @14 POP:1
ALU 4 @30
     3      t: MULLO_UINT         T0.x,  [0x00000002 2.8026e-45].x, R0.z

     4      x: ADD_INT            R0.x,  T0.x, [0x00000002 2.8026e-45].x

TEX 1 @40
               VFETCH             R0.x___, R0.x,   RID:0   MFC:16 UCF:0 FMT[..]
ALU 2 @44
     5      y: ADD                R0.y,  R0.y, R0.x
            z: ADD_INT            R0.z,  R0.z, 1
LOOP_END @4
EXPORT_DONE        PIXEL 0     R0.____  EOP
===== SHADER_END ===============================================================

Piglit: ./piglit summary console -d results/*_gpu_noglx
        name: unpatched_gpu_noglx patched_gpu_noglx
        ----  ------------------- -----------------
        pass:               18016             18021
        fail:                 748               743
        crash:                  7                 7
        skip:                1124              1124
        timeout:                0                 0
        warn:                  13                13
        incomplete:             0                 0
        dmesg-warn:             0                 0
        dmesg-fail:             0                 0
        changes:                0                 5
        fixes:                  0                 5
        regressions:            0                 0
        total:              19908             19908

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=94900
Tested-by: Heiko Przybyl <lil_tux@web.de>
Tested-on: Barts PRO HD6850
Signed-off-by: Heiko Przybyl <lil_tux@web.de>
Signed-off-by: Marek Olšák <marek.olsak@amd.com>