[clang][bytecode] Implement HLSLVectorTruncation casts (#108499)

1 files changed, 25 insertions, 0 deletions

diff --git a/clang/lib/AST/ByteCode/Compiler.cpp b/clang/lib/AST/ByteCode/Compiler.cpp
index 265350e..5247b8c 100644
--- a/clang/lib/AST/ByteCode/Compiler.cpp
+++ b/clang/lib/AST/ByteCode/Compiler.cpp
@@ -644,6 +644,31 @@ bool Compiler<Emitter>::VisitCastExpr(const CastExpr *CE) {
     return true;
   }
 
+  case CK_HLSLVectorTruncation: {
+    assert(SubExpr->getType()->isVectorType());
+    if (std::optional<PrimType> ResultT = classify(CE)) {
+      assert(!DiscardResult);
+      // Result must be either a float or integer. Take the first element.
+      if (!this->visit(SubExpr))
+        return false;
+      return this->emitArrayElemPop(*ResultT, 0, CE);
+    }
+    // Otherwise, this truncates from one vector type to another.
+    assert(CE->getType()->isVectorType());
+
+    if (!Initializing) {
+      unsigned LocalIndex = allocateTemporary(CE);
+      if (!this->emitGetPtrLocal(LocalIndex, CE))
+        return false;
+    }
+    unsigned ToSize = CE->getType()->getAs<VectorType>()->getNumElements();
+    assert(SubExpr->getType()->getAs<VectorType>()->getNumElements() > ToSize);
+    if (!this->visit(SubExpr))
+      return false;
+    return this->emitCopyArray(classifyVectorElementType(CE->getType()), 0, 0,
+                               ToSize, CE);
+  };
+
   case CK_ToVoid:
     return discard(SubExpr);