[llvm] [InstCombine] Fold redundant FP clamp selects; relax min-max-pattern bailout in visitFCmp (PR #173452)

[Yingwei Zheng via llvm-commits]

================
@@ -8679,6 +8679,40 @@ static Instruction *foldFCmpWithFloorAndCeil(FCmpInst &I,
   return nullptr;
 }
 
+/// Returns true if a select that implements a min/max is redundant and
+/// select result can be replaced with its non-constant operand, e.g.,
+///   select ( (si/ui-to-fp A) <= C ), C, (si/ui-to-fp A)
+/// where C is the FP constant equal to the minimum integer value
+/// representable by A.
+static bool isMinMaxCmpSelectEliminable(SelectPatternFlavor Flavor, Value *A,
+                                        Value *B) {
+  Constant *C = dyn_cast<Constant>(B);
+  if (isa<Constant>(A) || !C)
+    return false;
+
+  if (C->getType()->isVectorTy())
+    C = C->getSplatValue();
+  auto *CFP = dyn_cast_or_null<ConstantFP>(C);
+  if (!CFP)
+    return false;
----------------
dtcxzyw wrote:

```suggestion
  ConstantFP *CFP;
  if (!match(B, m_APFloat(CFP)))
    return false;
```

https://github.com/llvm/llvm-project/pull/173452