Two different vertex programs that compute the same position give
bit-identical depth on the GPU, which a depth pre-pass followed by an
equal-or-greater redraw relies on. Without Invariant, a Vulkan driver may
compile the same position arithmetic differently in each shader (for
example contracting into an FMA in only one), so the redraw fails the
depth test.
Decorate the gl_PerVertex Position member and the mesh shader's Position
output Invariant, and check both in a new recompiler test.
AI-assisted: yes
fma-rc
Gjon Gojcevic