[clang] [llvm] Adding splitdouble HLSL function (PR #109331)

[Justin Bogner via cfe-commits]

================
@@ -18901,6 +18901,159 @@ case Builtin::BI__builtin_hlsl_elementwise_isinf: {
         CGM.getHLSLRuntime().getRadiansIntrinsic(), ArrayRef<Value *>{Op0},
         nullptr, "hlsl.radians");
   }
+  case Builtin::BI__builtin_hlsl_splitdouble: {
+
+    assert((E->getArg(0)->getType()->hasFloatingRepresentation() &&
+            E->getArg(1)->getType()->hasUnsignedIntegerRepresentation() &&
+            E->getArg(2)->getType()->hasUnsignedIntegerRepresentation()) &&
+           "asuint operands types mismatch");
+    Value *Op0 = EmitScalarExpr(E->getArg(0));
+    const auto *OutArg1 = dyn_cast<HLSLOutArgExpr>(E->getArg(1));
+    const auto *OutArg2 = dyn_cast<HLSLOutArgExpr>(E->getArg(2));
+
+    CallArgList Args;
+    auto [Op1BaseLValue, Op1TmpLValue] =
+        EmitHLSLOutArgExpr(OutArg1, Args, OutArg1->getType());
+    auto [Op2BaseLValue, Op2TmpLValue] =
+        EmitHLSLOutArgExpr(OutArg2, Args, OutArg2->getType());
+
+    if (CGM.getTarget().getTriple().isDXIL()) {
+
+      llvm::StructType *RetType = nullptr;
+
+      if (Op0->getType()->isVectorTy()) {
+        auto *Op0VecTy = E->getArg(0)->getType()->getAs<VectorType>();
+
+        llvm::VectorType *i32VecTy = llvm::VectorType::get(
+            Int32Ty, ElementCount::getFixed(Op0VecTy->getNumElements()));
+        RetType = llvm::StructType::get(i32VecTy, i32VecTy);
+      } else {
+        RetType = llvm::StructType::get(Int32Ty, Int32Ty);
+      }
----------------
bogner wrote:

This can be simplified by making it work out the element type instead of the struct type. Something like the following:

```c++
      llvm::Type *RetElementTy = Int32Ty;
      if (auto *Op0VecTy = E->getArg(0)->getType()->getAs<VectorType>())
        RetElementTy = llvm::VectorType::get(
            Int32Ty, ElementCount::getFixed(Op0VecTy->getNumElements()));
      auto *RetTy = llvm::StructType::get(RetElementTy, RetElementTy);
```

https://github.com/llvm/llvm-project/pull/109331