[clang] [X86] Add MMX/SSE/AVX PHADD/SUB & HADDPS/D intrinsics to be used in constexpr (PR #156822)

[Simon Pilgrim via cfe-commits]

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@@ -579,6 +594,8 @@ let Features = "avx", Attributes = [NoThrow, Const, Constexpr, RequiredVectorWid
 let Features = "avx2", Attributes = [NoThrow, Const, RequiredVectorWidth<256>] in {
   def mpsadbw256 : X86Builtin<"_Vector<32, char>(_Vector<32, char>, _Vector<32, char>, _Constant char)">;
   def palignr256 : X86Builtin<"_Vector<32, char>(_Vector<32, char>, _Vector<32, char>, _Constant int)">;
+  def pmaddubsw256 : X86Builtin<"_Vector<16, short>(_Vector<32, char>, _Vector<32, char>)">;
+  def pmaddwd256 : X86Builtin<"_Vector<8, int>(_Vector<16, short>, _Vector<16, short>)">;
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RKSimon wrote:

these needs removing as they're defined as constexpr someplace else

https://github.com/llvm/llvm-project/pull/156822