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

[Chris B via cfe-commits]

================
@@ -18901,6 +18901,150 @@ case Builtin::BI__builtin_hlsl_elementwise_isinf: {
         CGM.getHLSLRuntime().getRadiansIntrinsic(), ArrayRef<Value *>{Op0},
         nullptr, "hlsl.radians");
   }
+  // This should only be called when targeting DXIL
+  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 HLSLOutArgExpr *OutArg1 = dyn_cast<HLSLOutArgExpr>(E->getArg(1));
+    const HLSLOutArgExpr *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().getArch() == llvm::Triple::dxil) {
+
+      llvm::StructType *retType = llvm::StructType::get(Int32Ty, Int32Ty);
+
+      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);
+      }
+
+      CallInst *CI =
+          Builder.CreateIntrinsic(retType, Intrinsic::dx_splitdouble, {Op0},
+                                  nullptr, "hlsl.splitdouble");
+
+      Value *arg0 = Builder.CreateExtractValue(CI, 0);
+      Value *arg1 = Builder.CreateExtractValue(CI, 1);
+
+      Builder.CreateStore(arg0, Op1TmpLValue.getAddress());
+      auto *s = Builder.CreateStore(arg1, Op2TmpLValue.getAddress());
+
+      EmitWritebacks(*this, Args);
+      return s;
+    }
+
----------------
llvm-beanz wrote:

nit: I'd add something like:

```
assert(!CGM.getTarget().getTriple().isDXIL() && "For non-DXIL targets we generate the instructions");

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