[clang] [llvm] [HLSL] Implement dot2add intrinsic (PR #131237)

[Sumit Agarwal via llvm-commits]

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@@ -4894,7 +4894,7 @@ def HLSLDotProduct : LangBuiltin<"HLSL_LANG"> {
 def HLSLDot2Add : LangBuiltin<"HLSL_LANG"> {
   let Spellings = ["__builtin_hlsl_dot2add"];
   let Attributes = [NoThrow, Const, CustomTypeChecking];
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sumitsays wrote:

`clang.exe` is not able to compile `clang/test/CodeGenHLSL/builtins/dot2add.hlsl` even after passing the flag `-fnative-half-type` saying 

`error: passing 'vector<_Float16, 2>' (vector of 2 '_Float16' values) to parameter of incompatible type '__attribute__((__vector_size__(2 * sizeof(half)))) half' (vector of 2 'half' values)`.

https://github.com/llvm/llvm-project/pull/131237