Add `vk::offset` to specify member offsets for push constants (#6797)

* Add struct member offset qualifier for SPIRV

* Implement for GLSL target and add tests

* clean up

* fix formatting

* fix typo

* renamed GLSLStructOffset to VkStructOffset and added emit-spirv-via-glsl test case

2 files changed, 76 insertions, 0 deletions

diff --git a/tests/diagnostics/vk-offset.slang b/tests/diagnostics/vk-offset.slang
new file mode 100644
index 000000000..5dbd821c6
--- /dev/null
+++ b/tests/diagnostics/vk-offset.slang
@@ -0,0 +1,34 @@
+//DIAGNOSTIC_TEST:SIMPLE(filecheck=CHECK): -target spirv -emit-spirv-directly -entry vertexMain -stage vertex
+
+// CHECK: error 31002: attribute 'vk_offset' is not valid here
+// CHECK-NEXT: [vk::offset(16)]] struct S1
+// CHECK: error 31002: attribute 'vk_offset' is not valid here
+// CHECK-NEXT: [vk::offset(8)]] VertexOutput output;
+
+[[vk::offset(16)]] struct S1
+{
+    [[vk::offset(32)]]
+    float2 a;
+
+    float3 b;
+
+    [[vk::offset(16)]]
+    float4 c;
+  }
+
+[[vk::push_constant]]
+S1 pc;
+
+struct VertexOutput
+{
+    float3 position : SV_Position;
+}
+
+[shader("vertex")]
+VertexOutput vertexMain()
+{
+    [[vk::offset(8)]] VertexOutput output;
+    output.position = float3(pc.a.x, pc.b.y, pc.c.z);
+    return output;
+}
+
diff --git a/tests/spirv/vk-offset.slang b/tests/spirv/vk-offset.slang
new file mode 100644
index 000000000..64cec1b55
--- /dev/null
+++ b/tests/spirv/vk-offset.slang
@@ -0,0 +1,42 @@
+//TEST:SIMPLE(filecheck=CHECK_SPV): -target spirv -emit-spirv-directly -entry vertexMain -stage vertex
+//TEST:SIMPLE(filecheck=CHECK_SPV): -target spirv -emit-spirv-via-glsl -entry vertexMain -stage vertex
+//TEST:SIMPLE(filecheck=CHECK_GLSL): -target glsl -entry vertexMain -stage vertex
+
+struct S1
+{
+    [[vk::offset(32)]]
+    float2 a;
+
+    float3 b;
+
+    [[vk::offset(16)]]
+    float4 c;
+  }
+
+[[vk::push_constant]]
+S1 pc;
+
+struct VertexOutput
+{
+    float3 position : SV_Position;
+}
+
+// CHECK_SPV: OpDecorate [[STRUCT:%[a-zA-Z0-9_]+]] Block
+// CHECK_SPV-NEXT: OpMemberDecorate [[STRUCT]] 0 Offset 32
+// CHECK_SPV-NEXT: OpMemberDecorate [[STRUCT]] 1 Offset 48
+// CHECK_SPV-NEXT: OpMemberDecorate [[STRUCT]] 2 Offset 16
+
+// CHECK_GLSL: layout(std430) uniform
+// CHECK_GLSL-NEXT: {
+// CHECK_GLSL-NEXT: layout(offset = 32) vec2 a
+// CHECK_GLSL-NEXT: vec3 b
+// CHECK_GLSL-NEXT: layout(offset = 16) vec4 c
+
+[shader("vertex")]
+VertexOutput vertexMain()
+{
+    VertexOutput output;
+    output.position = float3(pc.a.x, pc.b.y, pc.c.z);
+    return output;
+}
+