OpenCL: comp mode optimization

Disable compatibility mode if intensity is a multiple of worksize. In that case enabled compaibility mode will only slow down the miner.

xmrstak/backend/amd/amd_gpu/gpu.cpp

@@ -411,13 +411,16 @@ size_t InitOpenCLGpu(cl_context opencl_ctx, GpuContext* ctx, const char* source_
 				strided_index = 0;
 		}
 
+		// if intensity is a multiple of worksize than comp mode is not needed
+		int needCompMode = ctx->compMode && ctx->rawIntensity % ctx->workSize != 0 ? 1 : 0;
+
 		std::string options;
 		options += " -DITERATIONS=" + std::to_string(hashIterations);
 		options += " -DMASK=" + std::to_string(threadMemMask) + "U";
 		options += " -DWORKSIZE=" + std::to_string(ctx->workSize) + "U";
 		options += " -DSTRIDED_INDEX=" + std::to_string(strided_index);
 		options += " -DMEM_CHUNK_EXPONENT=" + std::to_string(mem_chunk_exp) + "U";
-		options += " -DCOMP_MODE=" + std::to_string(ctx->compMode ? 1u : 0u);
+		options += " -DCOMP_MODE=" + std::to_string(needCompMode);
 		options += " -DMEMORY=" + std::to_string(hashMemSize) + "LLU";
 		options += " -DALGO=" + std::to_string(miner_algo[ii]);
 		options += " -DCN_UNROLL=" + std::to_string(ctx->unroll);