Caught a critical exception: jit_var_eval(): variable r3953 remains dirty after evaluation!

[gerwang]

I'm implementing a custom path integrator that additionally outputs an aov, which records the last ray direction in a light path that reaches emitters. This integrator works fine when using a perspective sensor but crashes when using a radiancemeter sensor. I provide the code and scene XML that reproduces the issue.

I start with the current master branch of mitsuba3 (37af1e54ad285d9bdb83006666035fbe075b3dc2) and add a new file src/integrators/my_path.cpp with the following content (full file at the bottom of my post):

...
        Ray3f ray           = Ray3f(ray_);
        Spectrum throughput = 1.f;
        Spectrum result     = 0.f;
        Float eta           = 1.f;
        UInt32 depth        = 0;
        Vector3f si_wi      = 0.f;
...
                // Accumulate, being careful with polarization (see spec_fma)
                result =
                    spec_fma(throughput,
                             dr::select(emitter_mask && prev_bsdf_pdf > 0.f,
                                        mis_bsdf, 0.f),
                             result);
                si_wi = dr::select(emitter_mask, si.wi, si_wi);
            }

            // Continue tracing the path at this point?
            Bool active_next =
                (depth + 1 < m_max_depth) && si.is_valid() && !emitter_mask;
...

        *aovs++ = si_wi.x();
        *aovs++ = si_wi.y();
        *aovs++ = si_wi.z();
        return { /* spec  = */ dr::select(valid_ray, result, 0.f),
                 /* valid = */ valid_ray };
    }
...

and add a line add_plugin(my_path my_path.cpp) to src/integrators/CMakeLists.txt.

I use a scene config file of a cornell box scene_test.xml:

...                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       <!-- Camera and Rendering Parameters -->

	<integrator type="my_path" id="integrator">
		<integer name="max_depth" value="8"/>
	</integrator>
    <!--<sensor type="perspective" id="sensor">-->
        <!--<string name="fov_axis" value="smaller"/>-->
        <!--<float name="near_clip" value="0.001000"/>-->
        <!--<float name="far_clip" value="100.000000"/>-->
        <!--<integer name="focus_distance" value="1000"/>-->
        <!--<float name="fov" value="39.307700"/>-->
        <!--<transform name="to_world">-->
            <!--<rotate x="1" angle="180.00000500895632"/>-->
            <!--<rotate z="1" angle="180.00000500895632"/>-->
            <!--<translate value="0.000000 0.000000 3.900000"/>-->
        <!--</transform>-->
        <!--<sampler type="independent">-->
            <!--<integer name="sample_count" value="$spp"/>-->
        <!--</sampler>-->
        <!--<film type="hdrfilm">-->
            <!--<integer name="width" value="$resx"/>-->
            <!--<integer name="height" value="$resy"/>-->
            <!--<rfilter type="gaussian"/>-->
            <!--<string name="pixel_format" value="rgb"/>-->
            <!--<string name="component_format" value="float32"/>-->
        <!--</film>-->
    <!--</sensor>-->
    <sensor type="radiancemeter" id="sensor">
        <film type="hdrfilm">
            <integer name="width" value="1"/>
            <integer name="height" value="1"/>
            <rfilter type="box" />
        </film>
        <sampler type="independent">
            <integer name="sample_count" value="1"/>
        </sampler>
    </sensor>                                                                                                                                                                                                                                                                 
...

If I comment the radiancemeter and use perspective instead in the XML, and run the command
mitsuba -m cuda_ad_rgb scene_test.xml, the program exits normally and I can get proper results like below:

But, if I keep the XML file intact and use the radiancemeter sensor instead, the program crashes with the following error:

Caught a critical exception: jit_var_eval(): variable r3953 remains dirty after evaluation!
jit_shutdown(): detected variable leaks:
 - variable r1664 is still being referenced! (ref=1, ref_se=0, type=pointer, size=1, stmt="<value>", dep=[0, 0, 0, 1663])
 - variable r978 is still being referenced! (ref=2, ref_se=0, type=float32, size=1, stmt="mov.$t0 $r0, $r1", dep=[945, 972, 0, 0])
[1]    56022 segmentation fault (core dumped)  mitsuba -m cuda_ad_rgb scene_test.xml 2>&1 > log.txt

I'm providing my_path.cpp and scene_test.xml my_path_and_scene_test.zip to facilitate reproducing the issue. Could you please help me figure out what causes this crash? My hypotheses is that radiancemeter differs from perspective by setting ray.has_differentials = false;, therefore causing si.wi non-differentiable.

Thank you!

[njroussel]

Hi @gerwang

si_wi should be a loop state variable in your my_path integrator. (It's surprising that this works at all with the perspective sensor.)