[clang] [clang][bytecode][HLSL] Complete the HLSL aggregate splat and elementwise cast implementations, and enable the new constant interpreter on all HLSL tests with static asserts (PR #189126)

[Timm Baeder via cfe-commits]

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@@ -991,20 +931,14 @@ bool Compiler<Emitter>::VisitCastExpr(const CastExpr *E) {
     if (!this->emitSetLocal(PT_Ptr, SrcOffset, E))
       return false;
 
-    unsigned NumElems = std::min(SrcNumElems, DestNumElems);
-    for (unsigned I = 0; I != NumElems; ++I) {
-      if (!this->emitGetLocal(PT_Ptr, SrcOffset, E))
-        return false;
-      if (!this->emitArrayElemPop(SrcElemT, I, E))
-        return false;
-      if (SrcElemT != DestElemT) {
-        if (!this->emitPrimCast(SrcElemT, DestElemT, DestElemType, E))
-          return false;
-      }
-      if (!this->emitInitElem(DestElemT, I, E))
-        return false;
-    }
-    return true;
+    // Only flatten as many source elements as the destination requires.
+    unsigned MaxElems = countHLSLFlatElements(DestType);
+
+    SmallVector<HLSLFlatElement, 16> Elements;
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tbaederr wrote:

Does a `.reserve(MaxElems)` make sense here?

https://github.com/llvm/llvm-project/pull/189126