[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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@@ -2735,6 +2735,160 @@ static bool interp__builtin_ia32_pmul(InterpState &S, CodePtr OpPC,
   return true;
 }
 
+static bool interp_builtin_horizontal_int_binop(
+    InterpState &S, CodePtr OpPC, const CallExpr *Call,
+    llvm::function_ref<APInt(const APSInt &, const APSInt &)> Fn) {
+  assert(Call->getNumArgs() == 2);
+
+  assert(Call->getArg(0)->getType()->isVectorType() &&
+         Call->getArg(1)->getType()->isVectorType());
+  const auto *VT = Call->getArg(0)->getType()->castAs<VectorType>();
+  assert(VT->getElementType()->isIntegralOrEnumerationType());
+  PrimType ElemT = *S.getContext().classify(VT->getElementType());
+  bool DestUnsigned = Call->getType()->isUnsignedIntegerOrEnumerationType();
+
+  const Pointer &RHS = S.Stk.pop<Pointer>();
+  const Pointer &LHS = S.Stk.pop<Pointer>();
+  const Pointer &Dst = S.Stk.peek<Pointer>();
+
+  unsigned SourceLen = VT->getNumElements();
+  assert(SourceLen % 2 == 0 &&
+         Call->getArg(1)->getType()->castAs<VectorType>()->getNumElements() ==
+             SourceLen);
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RKSimon wrote:

don't waste your time with asserts like this - the defs in BuiltsX86.td mean that the types should be correct, else Sema will catch it.

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