[IVDescriptor] Explicitly check for isMinMaxRecurrenceKind in getReductionOpChain. NFC (#132025)

There are other types of recurrences with an icmp/fcmp opcode, AnyOf and
FindLastIV, so don't rely on the opcode to detect them.
This makes adding support for AnyOf in #131830 easier.

Note that these currently fail the ExpectedUses/isCorrectOpcode checks
anyway, so there shouldn't be any functional change.

Author: lukel97

llvm/lib/Analysis/IVDescriptors.cpp

@@ -1167,6 +1167,7 @@ SmallVector<Instruction *, 4>
 RecurrenceDescriptor::getReductionOpChain(PHINode *Phi, Loop *L) const {
   SmallVector<Instruction *, 4> ReductionOperations;
   unsigned RedOp = getOpcode();
+  const bool IsMinMax = isMinMaxRecurrenceKind(Kind);
 
   // Search down from the Phi to the LoopExitInstr, looking for instructions
   // with a single user of the correct type for the reduction.
@@ -1184,15 +1185,15 @@ RecurrenceDescriptor::getReductionOpChain(PHINode *Phi, Loop *L) const {
   // more expensive than out-of-loop reductions, and need to be costed more
   // carefully.
   unsigned ExpectedUses = 1;
-  if (RedOp == Instruction::ICmp || RedOp == Instruction::FCmp)
+  if (IsMinMax)
     ExpectedUses = 2;
 
   auto getNextInstruction = [&](Instruction *Cur) -> Instruction * {
     for (auto *User : Cur->users()) {
       Instruction *UI = cast<Instruction>(User);
       if (isa<PHINode>(UI))
         continue;
-      if (RedOp == Instruction::ICmp || RedOp == Instruction::FCmp) {
+      if (IsMinMax) {
         // We are expecting a icmp/select pair, which we go to the next select
         // instruction if we can. We already know that Cur has 2 uses.
         if (isa<SelectInst>(UI))
@@ -1204,7 +1205,7 @@ RecurrenceDescriptor::getReductionOpChain(PHINode *Phi, Loop *L) const {
     return nullptr;
   };
   auto isCorrectOpcode = [&](Instruction *Cur) {
-    if (RedOp == Instruction::ICmp || RedOp == Instruction::FCmp) {
+    if (IsMinMax) {
       Value *LHS, *RHS;
       return SelectPatternResult::isMinOrMax(
           matchSelectPattern(Cur, LHS, RHS).Flavor);