[Bug 101442] Piglit shaders@ssa@fs-if-def-else-break fails with sb but passes with R600_DEBUG=nosb

[Bug 101442] Piglit shaders@ssa@fs-if-def-else-break fails with sb but passes with R600_DEBUG=nosb

[bugzilla-daemon]

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https://bugs.freedesktop.org/show_bug.cgi?id=101442

            Bug ID: 101442
           Summary: Piglit shaders@ssa@fs-if-def-else-break fails with sb
                    but passes with R600_DEBUG=nosb
           Product: Mesa
           Version: git
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: Drivers/Gallium/r600
          Assignee: dri-devel@lists.freedesktop.org
          Reporter: gw.fossdev@gmail.com
        QA Contact: dri-devel@lists.freedesktop.org

The  piglit test 

  shaders@ssa@fs-if-def-else-break

fails with only with sb enabled but passes without it.

The relevant parts of the failing shader before and after optimization look
like this: 

===== SHADER #12 ====================================== PS/BARTS/EVERGREEN
=====
===== 90 dw ===== 9 gprs ===== 2 stack ==================================
[...]
0060  801f00fe 0100229c     6 MP   x: PRED_SETNE_INT     R8.x,  PV.x, 0
0018  0000000b 82800000 JUMP @22
0020  0000001f a00c0000 ALU 4 @62
 0062  000000f8 00200c90     7      x: MOV                R1.x,  0      <----
 0064  000004f9 20200c90            y: MOV                R1.y,  1.0    <----
 0066  000000f8 40200c90            z: MOV                R1.z,  0
 0068  800004f9 60200c90            w: MOV                R1.w,  1.0
0022  0000000d 83400001 ELSE @26 POP:1
0024  00000023 a80c0000 ALU_POP_AFTER 4 @70
 0070  000004f9 00200c90     8      x: MOV                R1.x,  1.0    <----
 0072  000000f8 20200c90            y: MOV                R1.y,  0      <----
 0074  000000f8 40200c90            z: MOV                R1.z,  0
 0076  800004f9 60200c90            w: MOV                R1.w,  1.0
0026  40000027 a4040000 ALU_PUSH_BEFORE 2 @78 KC0[CB0:0-15]
 0078  80000081 00801990     9      x: NOT_INT            R4.x,  KC0[1].x

 0080  801f00fe 0100229c    10 MP   x: PRED_SETNE_INT     R8.x,  PV.x, 0
0028  00000011 82800001 JUMP @34 POP:1
0030  00000011 82400000 LOOP_BREAK @34
0032  00000011 83800001 POP @34 POP:1
0034  00000002 81400000 LOOP_END @4
0036  00000029 a00c0000 ALU 4 @82
 0082  00000001 00000c90    11      x: MOV                R0.x,  R1.x
 0084  00000401 20000c90            y: MOV                R0.y,  R1.y
 0086  00000801 40000c90            z: MOV                R0.z,  R1.z
 0088  80000c01 60000c90            w: MOV                R0.w,  R1.w
0038  c0000000 95200688 EXPORT_DONE        PIXEL 0     R0.xyzw  EOP
===== SHADER_END
===============================================================



===== SHADER #12 OPT ================================== PS/BARTS/EVERGREEN
=====
===== 50 dw ===== 1 gprs ===== 2 stack
=========================================
[...]

 0040  801f0800 00002284     3 M    x: PRED_SETNE_INT     __.x,  R0.z, 0
0018  0000000d 82800001 JUMP @26 POP:1
0020  00000015 a0040000 ALU 2 @42
 0042  000000f9 00000c90     4      x: MOV                R0.x,  1.0   <-----
 0044  800000f8 20000c90            y: MOV                R0.y,  0     <-----
0022  0000000e 82400000 LOOP_BREAK @28
0024  0000000d 83800001 POP @26 POP:1
0026  00000017 a0040000 ALU 2 @46
 0046  000000f9 00000c90     5      x: MOV                R0.x,  1.0   <-----
 0048  800000f8 20000c90            y: MOV                R0.y,  0     <-----
0028  00000002 81400000 LOOP_END @4
0030  c0000000 95200a44 EXPORT_DONE        PIXEL 0     R0.0xy1  EOP
===== SHADER_END
===============================================================

In short after the optimization R0.xy get the same values assigned in both
decision paths. 

Best, 
Gert

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[Bug 101442] Piglit shaders@ssa@fs-if-def-else-break fails with sb but passes with R600_DEBUG=nosb

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https://bugs.freedesktop.org/show_bug.cgi?id=101442

--- Comment #1 from Gert Wollny <gw.fossdev@gmail.com> ---
Also shaders@ssa@fs-while-loop-rotate-value fails with sb enabled, but passes
with nosb.

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[Bug 101442] Piglit shaders@ssa@fs-if-def-else-break fails with sb but passes with R600_DEBUG=nosb

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https://bugs.freedesktop.org/show_bug.cgi?id=101442

--- Comment #2 from Gert Wollny <gw.fossdev@gmail.com> ---
spec@glsl-1.10@execution@variable-indexing@
   vs-output-array-float-index-wr
   vs-output-array-vec3-index-wr
   vs-output-array-vec4-index-wr 

also fail with sb enabled but pass without it.

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[Bug 101442] Piglit shaders@ssa@fs-if-def-else-break fails with sb but passes with R600_DEBUG=nosb

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https://bugs.freedesktop.org/show_bug.cgi?id=101442

--- Comment #3 from romain.naour@gmail.com ---
Hello,

I'm using an HD6310 graphic card and when I'm running piglit with
mesa-17.3-rc5, I have the same error.

What's the status of this bug ?

Best regards,
Romain Naour

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[Bug 101442] Piglit shaders@ssa@fs-if-def-else-break fails with sb but passes with R600_DEBUG=nosb

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https://bugs.freedesktop.org/show_bug.cgi?id=101442

--- Comment #4 from Gert Wollny <gw.fossdev@gmail.com> ---
After reviewing the byte code of fs-if-def-else-break  I found that the problem
is a bit different: 

In the original code BREAK is called in the loop when (KC0[0].x != 0) just like
implemented in the glsl code: 

0002  LOOP_START_DX10 @36
0004   ALU_PUSH_BEFORE 2 @48 KC0[CB0:0-15]
 0048      2      x: MOV                R2.x,  1
 0050      3 MP   x: PRED_SETNE_INT     R6.x,  KC0[0].x, 0
0006   JUMP @10                       << JUMP is called if condition fails 
0008   ALU 2 @52
 0052      4      x: MOV                R2.x,  [0x00000002 2.8026e-45].x
 0054  00000002 
0010   ELSE @16 POP:1
0012   LOOP_BREAK @34
0014   POP @16 POP:1

however, in the optimized code the assignment and its branch is optimized away,
and BREAK is called when (KC0[0].x == 0), i.e. exactly the opposite of the 

 0002 LOOP_START_DX10 @30
0004   PUSH @6
0006   ALU 1 @38 KC0[CB0:0-15]
 0038       2 M    x: PRED_SETNE_INT     __.x,  KC0[0].x, 0
0008   JUMP @14 POP:1          << JUMP is called if condition fails 
0010   LOOP_BREAK @28
0012   POP @14 POP:1

i.e. the optimizer removed the if branch, keeps the else branch but acts as if
it were the if branch, hence the failure.

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[Bug 101442] Piglit shaders@ssa@fs-if-def-else-break fails with sb but passes with R600_DEBUG=nosb

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https://bugs.freedesktop.org/show_bug.cgi?id=101442

--- Comment #5 from Gert Wollny <gw.fossdev@gmail.com> ---
With a bit more digging I found out that the sb optimizer simply drops the ELSE
if no ALU instructions are found in the else branch, i.e. 

   while(cond1)
      if (cond2) {
          a = b + c; 
      } else {
          break; 
      }
   }

becomes 

   while(cond1)
      if (cond2) {
         a = b + c; 
         break; 
   }
}

after the first sb/dce_cleanup pass, and this is obviously wrong. With the
break in the if path this is not a problem. I'll attach two piglits that
illustrate the behaviour.

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[Bug 101442] Piglit shaders@ssa@fs-if-def-else-break fails with sb but passes with R600_DEBUG=nosb

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https://bugs.freedesktop.org/show_bug.cgi?id=101442

--- Comment #6 from Gert Wollny <gw.fossdev@gmail.com> ---
Created attachment 136995
  --> https://bugs.freedesktop.org/attachment.cgi?id=136995&action=edit
Test that fails with r600/sb

Other then in the fs-if-def-else-break piglit here the if path doesn't get
completely optimized away.

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[Bug 101442] Piglit shaders@ssa@fs-if-def-else-break fails with sb but passes with R600_DEBUG=nosb

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https://bugs.freedesktop.org/show_bug.cgi?id=101442

--- Comment #7 from Gert Wollny <gw.fossdev@gmail.com> ---
Created attachment 136996
  --> https://bugs.freedesktop.org/attachment.cgi?id=136996&action=edit
Test that doesn't fail

Here the break is in the if path and other then ELSE the JUMP instruction
doesn't get optimized away. Since the ELSE clause contains an ALU clause it
also doesn't get optimized away.

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[Bug 101442] Piglit shaders@ssa@fs-if-def-else-break fails with sb but passes with R600_DEBUG=nosb

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https://bugs.freedesktop.org/show_bug.cgi?id=101442

Emil Velikov <emil.l.velikov@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|NEW                         |RESOLVED

--- Comment #8 from Emil Velikov <emil.l.velikov@gmail.com> ---
Should be resolved with

commit 8d633f067b8a3d74e3f39faea0773a229d4b93b3
Author: Dave Airlie <airlied@redhat.com>
Date:   Tue Jan 30 16:38:51 2018 +1000

    r600/sb: insert the else clause when we might depart from a loop

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