[llvm-branch-commits] [llvm] [HLSLSemanticSignatures] Implement the optimal packing of elements (PR #218064)

[Deric C. via llvm-branch-commits]

================
@@ -105,6 +105,42 @@ static uint8_t getStartColumn(uint8_t ColumnMask) {
   return countr_zero(ColumnMask);
 }
 
+// Returns a lower value for groups that must be packed earlier.
+static unsigned
+getOptimizedPackingPriority(const SemanticSignatureElement &Element,
+                            Triple::EnvironmentType ShaderStage, IOType IOTy) {
+  const SemanticInterpretation Interpretation =
+      getInterpretationKind(Element.SemanticKind, ShaderStage, IOTy);
+  assert((Interpretation != SemanticInterpretation::Invalid &&
+          Interpretation != SemanticInterpretation::Target) &&
+         "unexpected semantic interpretation for optimized packing");
+
+  if (Element.Cols == MaxSignatureCols &&
+      (Interpretation == SemanticInterpretation::Arbitrary ||
+       Interpretation == SemanticInterpretation::SV))
+    return 0;
----------------
Icohedron wrote:

[SUGGESTION] Create an enum to name each of these constants?
```cpp
// Groups are packed in increasing order.
enum PackingGroup : unsigned {
 FourColumn,
 IndexedTessFactor,
 Arbitrary,
 SystemValue,
 ClipCull,
 SystemGenerated,
 NotAllocated,
};
```

https://github.com/llvm/llvm-project/pull/218064