[clang] [Headers][X86] VectorExprEvaluator::VisitCallExpr / InterpretBuiltin - allow PALIGNR byte shift intrinsics to be used in constexpr (PR #162005)

[Simon Pilgrim via cfe-commits]

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@@ -11665,8 +11665,20 @@ static bool evalShuffleGeneric(
     if (SrcIdx < 0) {
       // Zero out this element
       QualType ElemTy = VT->getElementType();
-      ResultElements.push_back(
-          APValue(APFloat::getZero(Info.Ctx.getFloatTypeSemantics(ElemTy))));
+      if (ElemTy->isRealFloatingType()) {
+        ResultElements.push_back(
+            APValue(APFloat::getZero(Info.Ctx.getFloatTypeSemantics(ElemTy))));
+      } else if (ElemTy->isIntegerType()) {
+        unsigned BitWidth = Info.Ctx.getTypeSize(ElemTy);
+        bool IsUnsigned = ElemTy->isUnsignedIntegerType();
+        llvm::APSInt ZeroValue(BitWidth, IsUnsigned);
+        ZeroValue = 0;
+        ResultElements.push_back(APValue(ZeroValue));
----------------
RKSimon wrote:

`APValue Zero(Info.Ctx.MakeIntValue(0, ElemT));` ?

@tbaederr Would a general `Info.Ctx.MakeNullValue(ElemT))` helper make sense or is there something like that already?

https://github.com/llvm/llvm-project/pull/162005