[clang] [llvm] Add length HLSL function to DirectX Backend (PR #101256)

[Farzon Lotfi via llvm-commits]

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@@ -63,5 +63,6 @@ let TargetPrefix = "spv" in {
   def int_spv_frac : DefaultAttrsIntrinsic<[LLVMMatchType<0>], [llvm_anyfloat_ty]>;
   def int_spv_lerp : Intrinsic<[LLVMMatchType<0>], [llvm_anyfloat_ty, LLVMMatchType<0>,LLVMMatchType<0>], 
     [IntrNoMem, IntrWillReturn] >;
+  def int_spv_length : DefaultAttrsIntrinsic<[LLVMVectorElementType<0>], [llvm_anyfloat_ty]>;
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farzonl wrote:

He has to define this because of `CGM.getHLSLRuntime().getLengthIntrinsic()`. the alternative would be to just emit `int_dx_length` in `CGBuiltin.cpp` until there is a spirv implementation. then swap in `getLengthIntrinsic`

https://github.com/llvm/llvm-project/pull/101256