Bug 90347

Summary: [NVE0+] Failure to insert texbar under some circumstances (causing bad colors in Terasology)
Product: Mesa Reporter: Ilia Mirkin <imirkin>
Component: Drivers/DRI/nouveauAssignee: Nouveau Project <nouveau>
Status: RESOLVED FIXED QA Contact: Nouveau Project <nouveau>
Severity: normal    
Priority: medium    
Version: git   
Hardware: Other   
OS: All   
Whiteboard:
i915 platform: i915 features:
Attachments: terasology.tgsi

Description Ilia Mirkin 2015-05-06 18:38:07 UTC
Created attachment 115602 [details]
terasology.tgsi

The problem is that the attached shader compiles to:

...
 34: mov u32 $r0 $r3 (8)
 35: mov u32 $r1 $r5 (8)
 36: tex 2D $r0 $s0 f32 $r0t $r0d (8)
 37: join mov u32 $r7 $r1 (8)
BB:3 (4 instructions) - idom = BB:0, df = { BB:4 }
 -> BB:4 (forward)
 38: mov u32 $r0 $r3 (8)
 39: mov u32 $r1 $r5 (8)
 40: tex 2D $r1 $s0 f32 $r0t $r0d (8)
 41: join mov u32 $r7 $r1 (8)
...

And there is no texbar before the mov happens. This causes funky rendering in Terasology.

Somehow things get merged during RA s.t. the findFirstUses logic decides that the tex itself is a use (it isn't!) and so it never picks up on the actual use in that BB (since there's a check to make sure that we only pick the earliest use in a BB). This much shorter shader reproduces a similar issue as well:

FRAG
DCL IN[0], COLOR, COLOR
DCL OUT[0], COLOR
DCL OUT[1], COLOR[1]
DCL SAMP[0]
DCL SAMP[1]
DCL TEMP[0..4], LOCAL
IMM[0] FLT32 {    0.0010,     1.0000,     0.0000,     2.5000}
  5: MOV TEMP[0].xy, IN[0].xyxx
  7: FSLT TEMP[2].x, IMM[0].yyyy, IN[0].xxxx
 10: UIF TEMP[2].xxxx :0
 30:   TEX TEMP[1], TEMP[0], SAMP[0], 2D
 32: ELSE :0
 34:   TEX TEMP[1], TEMP[0], SAMP[1], 2D
 36: ENDIF
 47: UIF TEMP[2].xxxx :0
 50:   MUL TEMP[1], TEMP[1], IMM[0].xyyy
 54: ENDIF
 84: MOV TEMP[0].xyz, TEMP[1].xyzx
 93: MOV TEMP[1].xyz, TEMP[0].wwww
 94: MOV OUT[0], TEMP[0]
 95: MOV OUT[1], TEMP[1]
 97: END
Comment 1 Ilia Mirkin 2015-06-15 18:46:11 UTC
Should be fixed by

commit a2af42c1d2dc91f4c31e25ff9fff15a89a9b6ead
Author: Ilia Mirkin <imirkin@alum.mit.edu>
Date:   Fri Jun 12 16:09:05 2015 +0200

    nvc0/ir: fix collection of first uses for texture barrier insertion
    
    One of the places we have to insert texbars is in situations where the
    result of the tex gets overwritten by a different instruction (e.g. in a
    conditional statement). However in some situations it can actually
    appear as though the original tex itself is an overwriting instruction.
    This can naturally never really happen, so just ignore the tex
    instruction when it comes up.
    
    Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=90347
    Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
    Cc: "10.5 10.6" <mesa-stable@lists.freedesktop.org>

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