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

1 files changed, 1 insertions, 0 deletions

diff --git a/docs/user-guide/a2-target-specific-features.md b/docs/user-guide/a2-target-specific-features.md
index 495148c49..7949a00db 100644
--- a/docs/user-guide/a2-target-specific-features.md
+++ b/docs/user-guide/a2-target-specific-features.md
@@ -11,6 +11,7 @@ In this chapter:
 1. [SPIR-V target specific](./a2-01-spirv-target-specific.md)
 2. [Metal target specific](./a2-02-metal-target-specific.md)
 3. [WGSL target specific](./a2-03-wgsl-target-specific.md)
+4. [GLSL target specific](./a2-04-glsl-target-specific.md)
 
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