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