Fix IR layout of 3-element vectors in cbuffers for -fvk-use-dx-layout (#7282)

* Better handling for 16-byte boundary of d3d cbuffer

Fixes #6921

D3D cbuffers have slightly different packing rules that allow packing
vectors into a 16-byte slot at element alignments, except when
a field would cross a 16-byte boundary. In that case, we need to
realign the field to the next 16-byte boundary.

In particular, this impacts vec3s, which are not a power of two in
size and thus require slightly different alignment logic, compared to
std430 and std140. (Example: a float and float3 should fit together in
that order in a single slot.)

Adds test cases.

Adds documentation page for GLSL target

0 files changed, 0 insertions, 0 deletions