[Bug 110507] [Regression] [Bissected] SDL_CreateRenderer() hits assert in shader compiler when SIMD32 is enabled

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=110507

            Bug ID: 110507
           Summary: [Regression] [Bissected] SDL_CreateRenderer() hits
                    assert in shader compiler when SIMD32 is enabled
           Product: Mesa
           Version: git
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: Drivers/DRI/i965
          Assignee: intel-3d-bugs at lists.freedesktop.org
          Reporter: itoral at igalia.com
        QA Contact: intel-3d-bugs at lists.freedesktop.org

Created attachment 144082
  --> https://bugs.freedesktop.org/attachment.cgi?id=144082&action=edit
Minimal SDL2 program that reproduces the problem

I filed this for i965, but the issue is in the shader compiler, so it also
affects the Vulkan driver and, presumably, Iris.

The problem only happens when INTEL_DEBUG=do32 is used, in which case SDL2
generates a shader that hits the following assertion:

../src/intel/compiler/brw_fs.cpp:1745: void fs_visitor::assign_urb_setup():
Assertion `inst->src[i].offset < REG_SIZE / 2' failed.

I bisected the regression to this commit:

commit c0504569eac5e5c305e9f0c240e248aca9d8891f (HEAD -> master)
Author: Rafael Antognolli <rafael.antognolli at intel.com>
Date:   Fri Oct 19 15:44:15 2018 -0700

    intel/fs: Move the scalar-region conversion to the generator.

    Move the scalar-region conversion from the IR to the generator, so it
    doesn't affect the Gen11 path. We need the non-scalar regioning
    for a later lowering pass that we are adding.

    v2: Better commit message (Matt)

    Reviewed-by: Matt Turner <mattst88 at gmail.com>

I am attaching a minimal SDL2 sample program that reproduces the problem.

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