Hello. I have the following apitrace that seems to indicate a uniform variable being erroneously optimized out:
http://ataxia.io7m.com/2017/04/23/r2.trace Note the (rather large) shader sources at frame 1, call 8383 (glShaderSource). Trimming the sources to the relevant parts gives the following (abbreviated) code: --8<-- struct R2_light_ambient_t { /// The light color. The components are assumed to be in the range `[0, 1]`. vec3 color; /// The light intensity. float intensity; /// The occlusion map. sampler2D occlusion; }; vec3 R2_lightAmbientTerm ( const R2_light_ambient_t light, const vec2 uv) { float occ = texture (light.occlusion, uv).x; return light.color * (light.intensity * occ); } uniform R2_light_ambient_t R2_light_ambient; R2_light_output_t R2_deferredLightMain( const R2_reconstructed_surface_t surface) { vec3 diffuse = R2_lightAmbientTerm (R2_light_ambient, surface.uv); vec3 specular = vec3 (0.0); return R2_light_output_t (diffuse, specular); } layout(location = 0) out vec4 R2_out_image; void R2_lightShaderWrite( const R2_reconstructed_surface_t surface, const R2_light_output_t o) { R2_out_image = vec4 (surface.albedo * (o.diffuse + o.specular), 1.0); } uniform R2_viewport_t R2_light_viewport; uniform R2_gbuffer_input_t R2_light_gbuffer; uniform float R2_light_depth_coefficient; uniform R2_view_rays_t R2_light_view_rays; in float R2_light_volume_positive_eye_z; void main (void) { // Rendering of light volumes is expected to occur with depth // writes disabled. However, it's necessary to calculate the // correct logarithmic depth value for each fragment of the light // volume in order to get correct depth testing with respect to the // contents of the G-Buffer. float depth_log = R2_logDepthEncodePartial( R2_light_volume_positive_eye_z, R2_light_depth_coefficient); // Reconstruct the surface R2_reconstructed_surface_t surface = R2_deferredSurfaceReconstruct( R2_light_gbuffer, R2_light_viewport, R2_light_view_rays, R2_light_depth_coefficient, gl_FragCoord.xy); // Evaluate light R2_light_output_t o = R2_deferredLightMain(surface); R2_lightShaderWrite(surface, o); gl_FragDepth = depth_log; } --8<-- However, in the trace at call 8404, the linked program only returns four uniforms and R2_light_ambient isn't one of them. For some reason, the compiler appears to be optimizing it out. The uniform R2_light_ambient is referenced from R2_deferredLightMain and is involved in a computation, the result of which is returned from R2_deferredLightMain. The result is then passed to R2_lightShaderWrite where it is involved in an addition, the result of which is written to the output variable R2_out_image. I'm having a hard time coming up with a reason that the compiler could optimize out R2_light_ambient. Can anyone shed any light on this? Relevant system info: Linux copperhead 4.10.11-1-ARCH #1 SMP PREEMPT Tue Apr 18 08:39:42 CEST 2017 x86_64 GNU/Linux OpenGL vendor string: Intel Open Source Technology Center OpenGL renderer string: Mesa DRI Intel(R) Sandybridge Mobile OpenGL core profile version string: 3.3 (Core Profile) Mesa 17.0.4 OpenGL core profile shading language version string: 3.30 OpenGL core profile context flags: (none) OpenGL core profile profile mask: core profile OpenGL core profile extensions: OpenGL version string: 3.0 Mesa 17.0.4 OpenGL shading language version string: 1.30 OpenGL context flags: (none) OpenGL extensions: OpenGL ES profile version string: OpenGL ES 3.0 Mesa 17.0.4 OpenGL ES profile shading language version string: OpenGL ES GLSL ES 3.00 I'm using a 3.3 context and don't seem to get any compilation errors or warnings. M
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