Currently uniform buffers have more restrictive layout constraints than storage buffers.
13.4.1 Alignment and Size says that for uniform buffers, array strides must be a multiple of 16, and structs must be aligned to 16 bytes or greater.

These constraints come from:

• Vulkan when unextended is similar to GLSL std140. See "Standard Buffer Layout" from https://docs.vulkan.org/spec/latest/chapters/interfaces.html#interfaces-resources-layout
• D3D "Legacy" constant buffer layout: https://github.com/microsoft/DirectXShaderCompiler/wiki/Buffer-Packing#legacy-constant-buffer-basics-excluding-min-precision-or-16-bit-types

This is a legacy hardware requirement that is not needed on more modern hardware.

It would be nice to eliminate those special round-up-to-16 alignment requirements for uniform buffers: use the same rules in uniform buffer as for storage buffer.

• Metal supports this
• Vulkan has VK_KHR_uniform_buffer_standard_layout is this feature, and is always supported in Vulkan 1.2 or later.
• DXC offers -no-legacy-cbuf-layout: https://github.com/microsoft/DirectXShaderCompiler/wiki/Buffer-Packing#non-legacy-packing--no-legacy-cbuf-layout

See also scalar block layout which goes even further, in that the alignment requirement for a vector is lowered to the alignment requirement of its component type. See #4040