spirv-opt problems

[mihaly-sisak]

I try to ship optimized OpenGL code in my game EvoLife. Without this steps the shader compilation takes longer on first launch. My optimizing pipeline:

glslang --quiet -G -S <stage> -o <filename>.spv <filename>.glsl
spirv-opt -Oconfig=glsl_opt_config.cfg -o <filename>_opt.spv <filename>.spv
spirv-cross --version 430 --no-es --output <filename>_opt.<stage>.glsl <filename>_opt.spv

My problem is that I can not run spirv-opt with -O, I have to use -Oconfig with the file attached. My starting point was the -O list and I bisected which options cause issues.
glsl_opt_config.txt
Line 3 --merge-return: causes glsl shaders to behave differently than unoptimized versions
Line 4 --inline-entry-points-exhaustive: can not run without merge-return
Line 40 and 43 --merge-blocks: causes spirv-cross to abort on some shaders

Please let me know how can I help to resolve this problem. In the meantime maybe others will find this and can use the same workaround.

[cassiebeckley]

Thank you for reporting this issue. Would you be able to post an example of a shader that behaves differently with --merge-return?

[mihaly-sisak]

The input file is a 11 kLOC file that contains almost all of my glsl source code. Is it possible to provide an example without it being public?

[cassiebeckley]

It would be better if you were able to provide a minimal reproducible example of a SPIR-V shader which has this issue. You might be able to create one semi-automatically using spirv-reduce on <filename>.spv. In the "interestingness function", you'd want to run glslang -O and test for whether the behavior has changed.

It may also help if you can describe the change in the behavior of glsl shaders after running the merge-return pass.