[llvm] [KnownFPClass] Refine fdiv and fdiv_self class propagation + some minor fixes for propagateXorSign (PR #215014)

[Max Graey via llvm-commits]

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@@ -1294,8 +1294,7 @@ define nofpclass(inf) half @ret_noinf__nzero_or_nan__fdiv__not_inf_or_nan(half n
 define nofpclass(inf) half @ret_noinf__not_inf_or_nan__fdiv__nzero_or_nan(half nofpclass(nan) %not.nan, half nofpclass(inf sub norm pzero) %nzero.or.nan) {
 ; CHECK-LABEL: define nofpclass(inf) half @ret_noinf__not_inf_or_nan__fdiv__nzero_or_nan(
 ; CHECK-SAME: half nofpclass(nan) [[NOT_NAN:%.*]], half nofpclass(inf pzero sub norm) [[NZERO_OR_NAN:%.*]]) {
-; CHECK-NEXT:    [[DIV:%.*]] = fdiv half [[NOT_NAN]], [[NZERO_OR_NAN]]
-; CHECK-NEXT:    ret half [[DIV]]
+; CHECK-NEXT:    ret half +qnan
 ;
   %div = fdiv half %not.nan, %nzero.or.nan
   ret half %div
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MaxGraey wrote:

It;s valid. See proof: https://alive2.llvm.org/ce/z/ZreKar

https://github.com/llvm/llvm-project/pull/215014