[EPIC]: Improve rasterization tests coverage

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## Legend

### 🏗️ - Requires backend/yaml work
### 👍 - Testable

## Vertex Shader

#### Semantics
- [x] SV_VertexID
- https://github.com/llvm/offload-test-suite/pull/1142
- [x] SV_Position
- Already covered by all graphics tests
- [ ] SV_ClipDistance[n]
- https://github.com/llvm/offload-test-suite/pull/1168
- [ ] SV_CullDistance[n]
- https://github.com/llvm/offload-test-suite/pull/1168
- [ ] SV_InstanceID - 🏗️
- [ ] SV_StartVertexLocation - 🏗️
- [ ] SV_StartInstanceLocation - 🏗️
- [ ] SV_RenderTargetArrayIndex - 🏗️
- [ ] SV_ViewportArrayIndex - 🏗️
- [ ] SV_ViewID - 🏗️

#### Functional
- [ ] Non-`Float32` vertex attribute formats (`Int32`, `UInt32`, `Float16`, `Int16`, `UInt16`) - 👍
- [ ] Normalized integer attribute formats (`UNorm8`, `SNorm8`, `UNorm16`, `SNorm16`) - 👍
- [x] Multiple varyings to PS — many simultaneous user semantics, mixed integer/float types
- https://github.com/llvm/offload-test-suite/pull/1255
- [ ] Struct-typed varyings between VS and PS - 👍
- [x] CBuffer read in VS (real `mul(MVP, position)` instead of pass-through)
- https://github.com/llvm/offload-test-suite/pull/1255
- [ ] Push constants in VS - 👍
- [x] `StructuredBuffer` read from VS
- https://github.com/llvm/offload-test-suite/pull/1255
- [x] `ByteAddressBuffer` read from VS
- https://github.com/llvm/offload-test-suite/pull/1255
- [ ] `RWStructuredBuffer` write from VS (different UAV path than PS-side write) - 👍
- [ ] `Texture2D.SampleLevel(...)` from VS (no derivatives in VS) - 👍
- [ ] `Texture2D.Load(...)` from VS - 👍
- [x] `SV_Position` with W ≠ 1 (verify perspective divide downstream)
- https://github.com/llvm/offload-test-suite/pull/1255
- [ ] Multiple vertex buffer slots (stream 0 + stream 1) - 🏗️
- [ ] Per-instance attributes (input rate `INSTANCE`) - 🏗️
- [ ] Indexed draws + `BaseVertex` - 🏗️
- [ ] Strip topologies + primitive restart - 🏗️

#### Niche / vendor behavior
- [ ] Provoking-vertex consistency (FIRST is the default on D3D12 / VK / MTL) with a `nointerpolation` integer varying - 👍
- [ ] Vertex at clip-plane boundary (x = ±w, y = ±w, z = 0 / w) - 👍
- [ ] Vertex with W close to 0 (numerical stability) - 👍
- [ ] `NaN` / `Inf` in `SV_Position` (must be clipped, no rasterized output) - 👍
- [ ] Subnormal positions (FTZ vs preserve at the rasterizer) - 👍
- [ ] Negative-area / degenerate triangles - 👍

## Pixel Shader

#### Semantics
- [x] `SV_Position` (input)
- Implicitly used by every graphics test; explicitly asserted at pixel center in `GraphicsSystemValues.test`
- [x] `SV_PrimitiveID`
- https://github.com/llvm/offload-test-suite/pull/1142
- [x] `SV_IsFrontFace`
- https://github.com/llvm/offload-test-suite/pull/1142
- [ ] `SV_ClipDistance[n]` (input) - 👍
- [ ] `SV_CullDistance[n]` (input) - 👍
- [ ] `SV_Depth` (output) - 👍
- [ ] `SV_DepthGreaterEqual` (output) - 👍
- [ ] `SV_DepthLessEqual` (output) - 👍
- [ ] `SV_Target1`..`SV_Target7` (MRT) - 🏗️
- [ ] `SV_StencilRef` (output) - 🏗️
- [ ] `SV_SampleIndex` (input) - 🏗️
- [ ] `SV_Coverage` (input) - 🏗️
- [ ] `SV_Coverage` (output) - 🏗️
- [ ] `SV_InnerCoverage` (input) - 🏗️
- [ ] `SV_Barycentrics` (input) - 🏗️
- [ ] `SV_RenderTargetArrayIndex` (input from VS/GS) - 🏗️
- [ ] `SV_ViewportArrayIndex` (input from VS/GS) - 🏗️

#### Functional
- [x] `discard`
- `test/Graphics/discard.test` (#1119)
- [x] `ddx_fine`, `ddy_fine`, `fwidth`
- `test/Graphics/..`
- [ ] `clip()` intrinsic (companion to `discard`) - 👍
- [ ] `ddx` / `ddy` (default precision) - 👍
- [x] `ddx_coarse` / `ddy_coarse`
- https://github.com/llvm/offload-test-suite/pull/489
- [ ] `fwidth_coarse` / `fwidth_fine` - 👍
- [x] Interpolation modifier: `nointerpolation` (flat) - https://github.com/llvm/offload-test-suite/pull/1151
- [x] Interpolation modifier: `noperspective` - https://github.com/llvm/offload-test-suite/pull/1151
- [x] Interpolation modifier: `centroid` - https://github.com/llvm/offload-test-suite/pull/1151
- [x] Interpolation modifier: `linear` - https://github.com/llvm/offload-test-suite/pull/1151
- [ ] `EvaluateAttributeAtCentroid` - 👍
- [ ] `EvaluateAttributeSnapped` - 👍
- [ ] `EvaluateAttributeAtSample` - 🏗️
- [ ] Interpolation modifier: `sample` - 🏗️
- [ ] PS UAV write to `RWBuffer` - 👍
- [ ] PS UAV write to `RWByteAddressBuffer` - 👍
- [ ] PS UAV write to `RWTexture2D` - 👍
- [ ] PS reads `Texture2D` with all sample overloads (`Sample`, `SampleBias`, `SampleGrad`, `SampleLevel`, `SampleCmp`, `Gather`) - 👍

#### Niche / vendor behavior
- [ ] Helper-invocation suppression — discarded lane's writes blocked, but its derivatives still drive the quad's other lanes - 👍
- [ ] Quad message-passing (`QuadReadAcrossX/Y/Diagonal`) under partial coverage - 👍
- [x] `SV_Position.xy` exactly at pixel center `(x + 0.5, y + 0.5)`
- https://github.com/llvm/offload-test-suite/pull/1142
- [ ] Depth clamping outside `[MinDepth, MaxDepth]` (clipped vs clamped vs undefined) - 👍
- [ ] `SV_IsFrontFace` for zero-area / degenerate triangles - 👍
- [ ] `discard` + `SV_Depth` write interaction (depth must not be written) - 👍
- [ ] `clip()` with `NaN` / `Inf` operand - 👍
- [ ] Pixel coverage at exact triangle edge (top-left rule) - 👍
- [ ] Sample-frequency shading (PS runs per-sample, not per-pixel) - 🏗️

## Hull Shader

#### Semantics
- [x] `SV_TessFactor` (3 / 4 / 2 floats by domain)
- 2: https://github.com/llvm/offload-test-suite/pull/1285
- 3: https://github.com/llvm/offload-test-suite/pull/1224
- 4: https://github.com/llvm/offload-test-suite/pull/1254
- [x] `SV_InsideTessFactor` (1 / 2 / 0 floats by domain)
- 0: https://github.com/llvm/offload-test-suite/pull/1285
- 1: https://github.com/llvm/offload-test-suite/pull/1224
- 2: https://github.com/llvm/offload-test-suite/pull/1254
- [x] `SV_OutputControlPointID`
- https://github.com/llvm/offload-test-suite/pull/1224
- [ ] `SV_PrimitiveID` (HS input)
- https://github.com/llvm/offload-test-suite/pull/1304
- [ ] `HullSystemValues.test` — bundled test
- https://github.com/llvm/offload-test-suite/pull/1304

#### Functional
- [x] Pass-through HS (factor 1, identity control points)
- https://github.com/llvm/offload-test-suite/pull/1254
- [x] `InputPatch` reading from VS output
- https://github.com/llvm/offload-test-suite/pull/1224
- [x] `OutputPatch` to DS
- https://github.com/llvm/offload-test-suite/pull/1224
- [ ] Patch-constant function reading CBuffer - 👍
- [ ] Per-edge varying tess factors - 👍
- [ ] Patch culling via `SV_TessFactor = 0` (entire patch discarded) - 👍
- [ ] Negative tess factor (must be treated as 0) - 👍
- [ ] `SV_TessFactor` clamping at `[maxtessfactor]` - 👍
- [ ] HS reads UAV / SRV - 👍

#### Niche / vendor behavior
- [ ] Tess factor `Inf` / `NaN` handling (spec says clamped to max) - 👍
- [ ] Patch with all coincident control points (degenerate) - 👍
- [ ] Tess factor `> 64` (spec says clamp; observe driver behavior) - 👍
- [ ] HS invocations seeing partial control-point arrays - 👍

## Domain Shader

#### Semantics
- [x] `SV_DomainLocation`
- float3 for bary: https://github.com/llvm/offload-test-suite/pull/1224
- float2 for uv: https://github.com/llvm/offload-test-suite/pull/1254
- [ ] `SV_PrimitiveID` (DS input)
- https://github.com/llvm/offload-test-suite/pull/1304
- [x] `SV_Position` (DS output to rasterizer)
- https://github.com/llvm/offload-test-suite/pull/1224
- [ ] `SV_ClipDistance` / `SV_CullDistance` (DS output) - 👍
- [ ] `DomainSystemValues.test` — bundled test
- https://github.com/llvm/offload-test-suite/pull/1304

#### Functional
- [x] Domain: `tri` (barycentric `SV_DomainLocation`)
- https://github.com/llvm/offload-test-suite/pull/1224
- [x] Domain: `quad` (UV `SV_DomainLocation`)
- https://github.com/llvm/offload-test-suite/pull/1284
- https://github.com/llvm/offload-test-suite/pull/1254
- [x] Domain: `isoline`
- https://github.com/llvm/offload-test-suite/pull/1285
- [x] Partitioning: `integer`
- https://github.com/llvm/offload-test-suite/pull/1224
- [ ] Partitioning: `fractional_even` - 👍
- [ ] Partitioning: `fractional_odd` - 👍
- [ ] Partitioning: `pow2` - 👍
- [x] Output topology: `triangle_cw`
- https://github.com/llvm/offload-test-suite/pull/1224
- [x] Output topology: `triangle_ccw`
- https://github.com/llvm/offload-test-suite/pull/1284
- [ ] Output topology: `line` - 👍
- [x] Output topology: `point`
- https://github.com/llvm/offload-test-suite/pull/1254
- [ ] Adaptive tessellation: varying per-edge factors, no T-junctions between adjacent patches - 👍
- [ ] DS displacement (sample heightmap, write modified `SV_Position`) - 👍
- [ ] DS reads CBuffer / SRV - 👍

#### Niche / vendor behavior
- [ ] `fractional_*` partitioning vertex-count is implementation-defined within bounds — assert with tolerance, not exact - 👍
- [ ] `SV_DomainLocation` precision near 0 / 1 boundaries - 👍
- [x] Isoline `outside.x` (density) vs `outside.y` (detail) — easy to invert
- https://github.com/llvm/offload-test-suite/pull/1285
- [ ] CW / CCW output topology must match the rasterizer's front-face convention (vendors sometimes invert one path) - 👍
- [ ] Sub-pixel tessellation precision (zoom in on a quad and verify smoothness) - 👍

## Geometry Shader

#### Semantics
- [ ] `SV_PrimitiveID` (GS input — auto-generated per input primitive)
- Also exercised by https://github.com/llvm/offload-test-suite/pull/1222
- [ ] `SV_GSInstanceID` (when `[instance(N)]` is used) - 👍
- [ ] `SV_RenderTargetArrayIndex` (GS output) - 🏗️
- [ ] `SV_ViewportArrayIndex` (GS output) - 🏗️
- [ ] `GeometrySystemValues.test` — bundled test - 👍

#### Functional
- [x] Pass-through GS (1 in, 1 out, same topology — verifies pipeline plumbing)
- https://github.com/llvm/offload-test-suite/pull/1221
- [x] Point-to-quad expansion (point sprite — input point, 4 vertices out as triangle strip)
- https://github.com/llvm/offload-test-suite/pull/1203
- [ ] Line-to-triangle ribbons (line in, two triangles out) - 👍
- [x] Triangle subdivision (1 input → 4 output triangles)
- https://github.com/llvm/offload-test-suite/pull/1223
- [ ] Topology change: triangle in → line out (wireframe) - 👍
- [x] Selective output: `if (cond) stream.Append(v);` — some primitives produce 0 outputs
- https://github.com/llvm/offload-test-suite/pull/1222
- [ ] `[instance(N)]` GS instancing — N invocations per input primitive - 👍
- [ ] Adjacency input `triangleadj` (6 vertices: 3 triangle + 3 neighbors), use neighbor data for silhouette detection - 👍
- [ ] `[maxvertexcount(1024)]` — spec minimum upper bound; verify large outputs - 👍
- [ ] GS UAV write (each invocation writes a unique slot) - 👍
- [ ] GS reads CBuffer / SRV - 👍
- [x] `RestartStrip()` mid-output
- https://github.com/llvm/offload-test-suite/pull/1223

#### Niche / vendor behavior
- [x] Empty stream — `[maxvertexcount(N)]` declared, 0 emitted, primitive vanishes
- https://github.com/llvm/offload-test-suite/pull/1222
- [ ] Provoking vertex of GS-emitted primitives (implementation-defined, assert consistency) - 👍
- [ ] Exceeding `[maxvertexcount]` (undefined per spec, observe behavior) - 👍
- [ ] GS-emitted primitive interaction with `SV_RenderTargetArrayIndex` — different primitives to different RT slices - 🏗️

## Cross-cutting / Pipeline

#### Topologies
- [x] Triangle list
- All current graphics tests
- [ ] Triangle strip - 🏗️
- [ ] Line list - 👍
- [ ] Line strip - 🏗️
- [x] Point list
- https://github.com/llvm/offload-test-suite/pull/1203
- [ ] Triangle list with adjacency - 🏗️
- [ ] Line list with adjacency - 🏗️
- [ ] Patch lists (3, 4, 16, 32 control points) - 👍
- [ ] Primitive restart with strip topologies - 🏗️

#### Pipeline state
- [ ] Multiple render targets (`NumRenderTargets > 1`) - 🏗️
- [ ] Depth-only rendering (no color attachment) - 🏗️
- [ ] Stencil read / write - 🏗️
- [ ] Configurable blend state - 🏗️
- [ ] Conservative rasterization - 🏗️
- [ ] Variable-rate shading - 🏗️
- [ ] MSAA pipeline state (`SampleCount > 1`) - 🏗️

#### Multi-stage pipelines
- [x] VS → HS → DS → PS (no GS)
- https://github.com/llvm/offload-test-suite/pull/1224
- [x] VS → GS → PS (no tessellation)
- https://github.com/llvm/offload-test-suite/pull/1203
- [x] VS → HS → DS → GS → PS (full pipeline)
- https://github.com/llvm/offload-test-suite/pull/1254
- [ ] Resource visibility flags per stage (`D3D12_SHADER_VISIBILITY_*`) - 👍
- [ ] CBuffer accessed from multiple stages (deduplication, single binding) - 👍
- [ ] Push constants accessed from multiple stages - 👍
- [ ] Stage-interface signature compatibility (mismatched semantics between adjacent stages must error) - 👍

#### Cross-backend determinism
- [ ] Same shader produces byte-exact PNG across DX / VK / MTL on simple geometry - 👍
- [ ] Document `DiffRMS` / `Intervals` tolerance per goldenimage test - 👍
- [ ] WARP vs hardware GPU drift profile per test (existing tests already absorb it; document explicitly) - 👍

Start by reviewing the existing graphics tests, including test/Graphics/discard.test and GraphicsSystemValues.test, then choose one unchecked item marked 👍 in this epic. Compare the selected coverage with nearby tests and add the corresponding rasterization test; done means the test passes and the checklist item can be linked to the change.

Written by the indexing model from the issue text.