Bug 47201

Summary:	Absolute modifier does not work with 3-source TGSI instructions
Product:	Mesa	Reporter:	Vic Lee <llyzs>
Component:	Drivers/Gallium/r600	Assignee:	Default DRI bug account <dri-devel>
Status:	RESOLVED FIXED	QA Contact:
Severity:	normal
Priority:	medium
Version:	8.0
Hardware:	Other
OS:	Linux (All)
Whiteboard:
i915 platform:		i915 features:
Attachments:	test program to reproduce the bug r600g patch to fix dropped abs() modifier on op3 alu operations.

Description Vic Lee 2012-03-11 05:40:45 UTC

Recently I found a TGSI fragment shader does not render correctly with r600 driver and I further identified the issue down to instructions in this form:

CMP TEMP[0].yz, -|TEMP[1].xxxx|, TEMP[2].xxxx, CONST[0].xyxw

If I covert all those instructions to the equivalents:

ABS TEMP[5], TEMP[1].xxxx
CMP TEMP[0].yz, -TEMP[5], TEMP[2].xxxx, CONST[0].xyxw

It then works fine. However, the original instructions work just fine with nouveau and swrast driver, so it should be a r600 bug. Any clue on this issue?

Comment 1 Vic Lee 2012-03-11 06:24:37 UTC

The issue might be related to r600_bytecode_alu_build() in r600_asm.c. In the codes below:

    if (alu->is_op3) {
        // in this code branch it does not use absolute modifier at all.
    } else {
    ...

Looks like whenever is_op3 is true (which is the case of CMP), absolute modifier is just ignored.

Comment 2 Vic Lee 2012-03-11 06:47:32 UTC

OK I found the reference info in r600 instruction document and this is a hardware limitation. So this probably has to be solved in higher level rather than in driver.

Sorry for the noise.

Comment 3 Tom Stellard 2012-03-11 18:07:27 UTC

The is a bug in the r600 driver.  The shader compiler should be lowering this to the hardware equivalent of this sequence:

ABS TEMP[5], TEMP[1].xxxx
CMP TEMP[0].yz, -TEMP[5], TEMP[2].xxxx, CONST[0].xyxw

Is there a piglit test or application that is hitting this bug?

Comment 4 Vic Lee 2012-03-12 06:33:54 UTC

Thanks for concerning this bug. It will be great if this can be fixed at driver level. I created a smallest possible test program which will be able to test the shader I am having problem with.

Please see the file header for test info.

Comment 5 Vic Lee 2012-03-12 06:34:57 UTC

Created attachment 58317 [details]
test program to reproduce the bug

Comment 6 xbx 2015-01-28 20:10:49 UTC

Created attachment 112920 [details] [review]
r600g patch to fix dropped abs() modifier on op3 alu operations.

Comment 7 xbx 2015-01-28 20:11:23 UTC

I stumbled upon this bug while testing and debugging a game using the st/nine.

And I made a tentative fix that works for me. 
(caveat: I know nothing about mesa/gallium/graphic cards, but hey..)

Here is the proposed patch:

https://github.com/xxxbxxx/Mesa-3D/commit/0722d721f8e5ec496bf8ce4591a3b8a5bf87745d

or attached.

Comment 8 Gert Wollny 2018-03-06 18:29:30 UTC

This was fixed with ad84689f737edefe.

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