Unoptimized/Debug builds with dead code elimination disabled?

[jakubtomsu]

Currently the sokol-shdc compiler aggressively eliminates dead code, which is a bit annoying when iterating on shaders. That's because it also removes all of the uniform and texture slots from the generated headers.

I looked into the source but unfortunately couldn't find a way to disable it in the backend. Maybe there is a way to somehow still generate the binding slots correctly even if they compile out..?

[floooh]

That's a surprisingly tricky topic because the removal can happen in different stages (starting at the initial GLSL to SPIRV compilation, but even as late as in the actual sokol application - for instance GL driver GLSL compilers are free to remove unused bindings as well).

In the past there was also a situation where unused vertex attributes were dropped by the SPIRVTools optimizer passes, but that had been fixed in this commit:

16492a0

The optionally generated reflection-info functions (only in the C code generation so far) are also a (somewhat awkward) way to deal with the problem, but that's not a great solution for iterating and experimenting.

Long story short, I haven't found a good solution for this. Unfortunately it's not as easy as disabling all optimizations. Unrelated to that I have thought about a command line option to disable the SPIRVTools optimizer passes completely (here:

sokol-tools/src/shdc/spirv.cc

Lines 119 to 164 in 6362c8f

	static void spirv_optimize(slang_t::type_t slang, std::vector<uint32_t>& spirv) {
	if (slang == slang_t::WGSL) {
	return;
	}
	spv_target_env target_env;
	target_env = SPV_ENV_UNIVERSAL_1_2;
	spvtools::Optimizer optimizer(target_env);
	optimizer.SetMessageConsumer(
	[](spv_message_level_t level, const char *source, const spv_position_t &position, const char *message) {
	// FIXME
	});
	optimizer.RegisterPass(spvtools::CreateDeadBranchElimPass());
	/*
	optimizer.RegisterPass(spvtools::CreateMergeReturnPass());
	optimizer.RegisterPass(spvtools::CreateInlineExhaustivePass());
	*/
	optimizer.RegisterPass(spvtools::CreateEliminateDeadFunctionsPass());
	optimizer.RegisterPass(spvtools::CreateScalarReplacementPass());
	optimizer.RegisterPass(spvtools::CreateLocalAccessChainConvertPass());
	optimizer.RegisterPass(spvtools::CreateLocalSingleBlockLoadStoreElimPass());
	optimizer.RegisterPass(spvtools::CreateLocalSingleStoreElimPass());
	optimizer.RegisterPass(spvtools::CreateSimplificationPass());
	optimizer.RegisterPass(spvtools::CreateAggressiveDCEPass(true)); // NOTE: call the "preserveInterface" version of CreateAggressiveDCEPass()
	optimizer.RegisterPass(spvtools::CreateVectorDCEPass());
	optimizer.RegisterPass(spvtools::CreateDeadInsertElimPass());
	optimizer.RegisterPass(spvtools::CreateAggressiveDCEPass(true));
	optimizer.RegisterPass(spvtools::CreateDeadBranchElimPass());
	// NOTE: it's the BlockMergePass which moves the init statement of a for-loop
	// out of the for-statement, which makes it invalid for WebGL
	// optimizer.RegisterPass(spvtools::CreateBlockMergePass());
	// NOTE: this is the pass which may create invalid WebGL code
	// optimizer.RegisterPass(spvtools::CreateLocalMultiStoreElimPass());
	optimizer.RegisterPass(spvtools::CreateIfConversionPass());
	optimizer.RegisterPass(spvtools::CreateSimplificationPass());
	optimizer.RegisterPass(spvtools::CreateAggressiveDCEPass(true));
	optimizer.RegisterPass(spvtools::CreateVectorDCEPass());
	optimizer.RegisterPass(spvtools::CreateDeadInsertElimPass());
	optimizer.RegisterPass(spvtools::CreateRedundancyEliminationPass());
	optimizer.RegisterPass(spvtools::CreateAggressiveDCEPass(true));
	optimizer.RegisterPass(spvtools::CreateCFGCleanupPass());
	spvtools::OptimizerOptions spvOptOptions;
	spvOptOptions.set_run_validator(false); // The validator may run as a separate step later on
	optimizer.Run(spirv.data(), spirv.size(), &spirv, spvOptOptions);
	}

), but that alone definitely won't solve the issue that unused binding declarations are removed.