Vulkan input attachment from previous subpass - vulkan

Question

I am trying to use the color attachment created in subpass 0 as an input attachment in subpass 1. However there is an issue that i cant get past.
My problem currently is the following, i try to clear attachment 0 at the beginning of the pass using VK_ATTACHMENT_LOAD_OP_CLEAR however gives the error.
Cannot clear attachment 0 with invalid first layout VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL.
Which seems weird to me, attachment 0 does not get layout VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL untill subpass 1 where it is a input attachment, while the clear should have already happened when the layout was still VK_IMAGE_LAYOUT_COLOR_ATTACHMENT_OPTIMAL (AFAIK).
I have now tried to just continue running after the validation error, and attachment 0 does get cleared, which makes me even more unsure. I can apparently just ignore the validation error, but something weird might be going on that could cause problems later on so I am not confidant enough to just ignore it.
Here is the minimal code that will give the error:
VkAttachmentDescription attachments[1] {};
attachments[0].format = VK_FORMAT_R16G16B16A16_SFLOAT;
attachments[0].samples = VK_SAMPLE_COUNT_1_BIT;
attachments[0].loadOp = VK_ATTACHMENT_LOAD_OP_CLEAR;
attachments[0].storeOp = VK_ATTACHMENT_STORE_OP_STORE;
attachments[0].stencilLoadOp = VK_ATTACHMENT_LOAD_OP_DONT_CARE;
attachments[0].stencilStoreOp = VK_ATTACHMENT_STORE_OP_DONT_CARE;
attachments[0].initialLayout = VK_IMAGE_LAYOUT_COLOR_ATTACHMENT_OPTIMAL;
attachments[0].finalLayout = VK_IMAGE_LAYOUT_COLOR_ATTACHMENT_OPTIMAL;
VkAttachmentReference pass_0_ColorAttachments[1];
pass_0_ColorAttachments[0].attachment = 0;
pass_0_ColorAttachments[0].layout = VK_IMAGE_LAYOUT_COLOR_ATTACHMENT_OPTIMAL;
VkAttachmentReference pass_1_InputAttachments[1];
pass_1_InputAttachments[0].attachment = 0;
pass_1_InputAttachments[0].layout = VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL;
VkSubpassDescription subpasses[2] {};
subpasses[0].colorAttachmentCount = 1;
subpasses[0].pColorAttachments = pass_0_ColorAttachments;
subpasses[0].pipelineBindPoint = VK_PIPELINE_BIND_POINT_GRAPHICS;
subpasses[1].inputAttachmentCount = 1;
subpasses[1].pInputAttachments = pass_1_InputAttachments;
subpasses[1].pipelineBindPoint = VK_PIPELINE_BIND_POINT_GRAPHICS;
VkSubpassDependency subpassDependancies[1] {};
subpassDependancies[0].srcSubpass = 0;
subpassDependancies[0].dstSubpass = 1;
subpassDependancies[0].srcStageMask = VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT;
subpassDependancies[0].dstStageMask = VK_PIPELINE_STAGE_FRAGMENT_SHADER_BIT;
subpassDependancies[0].srcAccessMask = VK_ACCESS_COLOR_ATTACHMENT_WRITE_BIT;
subpassDependancies[0].dstAccessMask = VK_ACCESS_INPUT_ATTACHMENT_READ_BIT;
subpassDependancies[0].dependencyFlags = VK_DEPENDENCY_BY_REGION_BIT;
VkRenderPassCreateInfo renderpassCreateInfo {};
renderpassCreateInfo.sType = VK_STRUCTURE_TYPE_RENDER_PASS_CREATE_INFO;
renderpassCreateInfo.attachmentCount = 1;
renderpassCreateInfo.pAttachments = attachments;
renderpassCreateInfo.subpassCount = 2;
renderpassCreateInfo.pSubpasses = subpasses;
renderpassCreateInfo.dependencyCount = 1;
renderpassCreateInfo.pDependencies = subpassDependancies;
VkRenderPass renderPass;
vkCreateRenderPass(device, &renderpassCreateInfo, nullptr, &renderPass);
The next part is only relevant if it is impossible to specify VK_ATTACHMENT_LOAD_OP_CLEAR for an attachment used as color attachment first and in a later subpass as input attachment (i see no reason why this would be impossible, unless vulkan does the load operation each subpass). So this is kind of a separate problem.
I could, instead of using VK_ATTACHMENT_LOAD_OP_CLEAR, manually clear the attachment using vkCmdClearAttachments and use VK_ATTACHMENT_LOAD_OP_DONT_CARE for the load operation of the attachment.
I have a crash error on calling vkCmdClearAttachments
I started the command buffer recording and the renderpass, and in the first subpass I call:
VkClearAttachment clearAtts[] = {{VK_IMAGE_ASPECT_COLOR_BIT, 1, {0,0,0,0}}};
VkClearRect rect = {{{0,0}, {1,1}}, 0, 1};
vkCmdClearAttachments(vkCommandBuffer, 1, clearAtts, 1, &rect);
{1,1} as the extent to show this is not the problem

Answer 1

You're having the same problem as was discovered here. It's a bug in the validation layer in 1.0.17. It would appear that the current Github head has a fix, but that fix is not in the 1.0.21 release.
But you still need to fix the stuff below ;)
subpassDependancies[0].dstAccessMask = VK_ACCESS_COLOR_ATTACHMENT_WRITE_BIT | VK_ACCESS_COLOR_ATTACHMENT_READ_BIT;
You are not going to read the image as a color attachment. You're going to read it as an input attachment. From the fragment shader. So that would mean VK_ACCESS_INPUT_ATTACHMENT_READ_BIT.
If that fixes the error, then I'd guess the validation layer got confused by your oddball dependency access mask. It therefore couldn't establish a valid dependency chain between subpasses 0 and 1, and thus thought that subpass 1 was first.
Also, your srcStageMask and dstStageMask bits are way over-specified. Every graphics stage is not going to write to the image, and every graphics stage is not going to access it after. You only wrote to the image as a color attachment, and you're only going to read from it in the fragment shader.
So your srcStageMask ought to just be VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT, and your dstStageMask ought to be VK_PIPELINE_STAGE_FRAGMENT_SHADER_BIT.