Bug 90580

Summary: [HSW bisected] integer multiplication bug
Product: Mesa Reporter: Tapani Pälli <lemody>
Component: Drivers/DRI/i965Assignee: Matt Turner <mattst88>
Status: RESOLVED FIXED QA Contact: Intel 3D Bugs Mailing List <intel-3d-bugs>
Severity: normal    
Priority: medium    
Version: git   
Hardware: Other   
OS: All   
Whiteboard:
i915 platform: i915 features:
Attachments: test

Description Tapani Pälli 2015-05-22 07:35:43 UTC 
Shader doing integer multiplication fails like this:

--- 8< ---
shader_runner: brw_ir_fs.h:195: fs_reg half(fs_reg, unsigned int): Assertion `!"Cannot take half of this register type"' failed.
Aborted (core dumped)


Bisected to:

commit 4ec09c77471e39e6ff81c99f1edde2e1713a7f24
Author: Matt Turner <mattst88@gmail.com>
Date:   Tue May 12 15:51:44 2015 -0700

    i965/fs: Support integer multiplication in SIMD16 on Haswell.
    
    Ivybridge (and presumably Baytrail) have a bug that prevents this from
    working.
    
    Reviewed-by: Jason Ekstrand <jason.ekstrand@intel.com>
Comment 1 Tapani Pälli 2015-05-22 07:36:32 UTC 
Created attachment 115967 [details]
test

piglit shader_test case to hit the bug
Comment 2 Tapani Pälli 2015-05-22 07:38:42 UTC 
Following conformance test hits this issue:

ES3-CTS.shaders.loops.for_constant_iterations.unconditional_break_fragment
Comment 3 Tapani Pälli 2015-05-22 07:47:23 UTC 
Oops, the test I posted actually fails like this:

---8< ---
shader_runner: brw_fs_generator.cpp:106: brw_reg brw_reg_from_fs_reg(fs_reg*): Assertion `reg->type == reg->fixed_hw_reg.type' failed.
Aborted (core dumped)
---8< ---

with some changes it failed like in comment #1, I can try to get them back.
Comment 4 Tapani Pälli 2015-05-22 07:58:23 UTC 
(In reply to Tapani Pälli from comment #3)
> with some changes it failed like in comment #1, I can try to get them back.

nope, that only happens when bisecting between commits which I believe fix this thing, so the relevant error is what comes with the current master:

shader_runner: brw_fs_generator.cpp:106: brw_reg brw_reg_from_fs_reg(fs_reg*): Assertion `reg->type == reg->fixed_hw_reg.type' failed.
Aborted (core dumped)
Comment 5 Matt Turner 2015-05-22 17:35:29 UTC 
Oh wow, we end up propagating the conditional_mod to an integer multiply that we'll have to lower:

> {  1}    2: mul.le.f0.0(8) null:D, vgrf0:D, vgrf0:D 

which then doesn't work. Thanks for the report. I'll see what I can do.
Comment 6 Matt Turner 2015-05-27 18:20:11 UTC 
Patch on the list:

> i965/fs: Fix lowering of integer multiplication with cmod.
Comment 7 Matt Turner 2015-05-28 21:37:03 UTC 
Fixed with

commit 0596134410a0decc2f6bba77bfedb82d308aabbe
Author: Matt Turner <mattst88@gmail.com>
Date:   Wed May 27 10:44:45 2015 -0700

    i965/fs: Fix lowering of integer multiplication with cmod.

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