ValueTracking: Identify implied fp classes by general fcmp

llvm/include/llvm/Analysis/ValueTracking.h

@@ -235,6 +235,40 @@ std::pair<Value *, FPClassTest> fcmpToClassTest(CmpInst::Predicate Pred,
                                                 const APFloat *ConstRHS,
                                                 bool LookThroughSrc = true);
 
+/// Compute the possible floating-point classes that \p LHS could be based on
+/// fcmp \Pred \p LHS, \p RHS.
+///
+/// Returns { TestedValue, ClassesIfTrue, ClassesIfFalse }
+///
+/// If the compare returns an exact class test, ClassesIfTrue == ~ClassesIfFalse
+///
+/// This is a less exact version of fcmpToClassTest (e.g. fcmpToClassTest will
+/// only succeed for a test of x > 0 implies positive, but not x > 1).
+///
+/// If \p LookThroughSrc is true, consider the input value when computing the
+/// mask. This may look through sign bit operations.
+///
+/// If \p LookThroughSrc is false, ignore the source value (i.e. the first pair
+/// element will always be LHS.
+///
+std::tuple<Value *, FPClassTest, FPClassTest>
+fcmpImpliesClass(CmpInst::Predicate Pred, const Function &F, Value *LHS,
+                 Value *RHS, bool LookThroughSrc = true);
+std::tuple<Value *, FPClassTest, FPClassTest>
+fcmpImpliesClass(CmpInst::Predicate Pred, const Function &F, Value *LHS,
+                 FPClassTest RHS, bool LookThroughSrc = true);
+std::tuple<Value *, FPClassTest, FPClassTest>
+fcmpImpliesClass(CmpInst::Predicate Pred, const Function &F, Value *LHS,
+                 const APFloat &RHS, bool LookThroughSrc = true);
+
+#if 0
+inline std::tuple<Value *, FPClassTest, FPClassTest>
+fcmpImpliesClass(CmpInst::Predicate Pred, const Function &F, Value *LHS,
+                 const APFloat &RHS, bool LookThroughSrc = true) {
+  return fcmpImpliesClass(Pred, F, LHS, RHS.classify(), LookThroughSrc);
+}
+#endif
+
 struct KnownFPClass {
   /// Floating-point classes the value could be one of.
   FPClassTest KnownFPClasses = fcAllFlags;