[llvm] [ConstantFPRange] Implement `ConstantFPRange::makeAllowedFCmpRegion` (PR #110082)

[Matt Arsenault via llvm-commits]

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@@ -103,11 +103,115 @@ ConstantFPRange ConstantFPRange::getNaNOnly(const fltSemantics &Sem,
                          MayBeSNaN);
 }
 
+ConstantFPRange ConstantFPRange::getNonNaN(const fltSemantics &Sem) {
+  return ConstantFPRange(APFloat::getInf(Sem, /*Negative=*/true),
+                         APFloat::getInf(Sem, /*Negative=*/false),
+                         /*MayBeQNaN=*/false, /*MayBeSNaN=*/false);
+}
+
+/// Return [-inf, V) or [-inf, V]
+static ConstantFPRange makeLessThan(APFloat V, FCmpInst::Predicate Pred) {
+  const fltSemantics &Sem = V.getSemantics();
+  if (!(Pred & FCmpInst::FCMP_OEQ)) {
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arsenm wrote:

All of these !(Pred & ) checks aren't intuitive. I assume this is an isLessThan. Can you move that into a named help function 

https://github.com/llvm/llvm-project/pull/110082