[ConstantFold] Remove unnecessarily complicated evaluateFCmpRelation() (NFCI)

The only thing this actually handles is if the operands are the
same, in which case ueq is returned.

Given that nearly all FP constant expressions have already been
removed, I think it's safe to say that we aren't going to extend
this code in a way that makes use of the more general structure.

Author: nikic

llvm/lib/IR/ConstantFold.cpp

@@ -1112,70 +1112,6 @@ Constant *llvm::ConstantFoldBinaryInstruction(unsigned Opcode, Constant *C1,
   return nullptr;
 }
 
-/// This function determines if there is anything we can decide about the two
-/// constants provided. This doesn't need to handle simple things like
-/// ConstantFP comparisons, but should instead handle ConstantExprs.
-/// If we can determine that the two constants have a particular relation to
-/// each other, we should return the corresponding FCmpInst predicate,
-/// otherwise return FCmpInst::BAD_FCMP_PREDICATE. This is used below in
-/// ConstantFoldCompareInstruction.
-///
-/// To simplify this code we canonicalize the relation so that the first
-/// operand is always the most "complex" of the two.  We consider ConstantFP
-/// to be the simplest, and ConstantExprs to be the most complex.
-static FCmpInst::Predicate evaluateFCmpRelation(Constant *V1, Constant *V2) {
-  assert(V1->getType() == V2->getType() &&
-         "Cannot compare values of different types!");
-
-  // We do not know if a constant expression will evaluate to a number or NaN.
-  // Therefore, we can only say that the relation is unordered or equal.
-  if (V1 == V2) return FCmpInst::FCMP_UEQ;
-
-  if (!isa<ConstantExpr>(V1)) {
-    if (!isa<ConstantExpr>(V2)) {
-      // Simple case, use the standard constant folder.
-      ConstantInt *R = nullptr;
-      R = dyn_cast<ConstantInt>(
-                      ConstantExpr::getFCmp(FCmpInst::FCMP_OEQ, V1, V2));
-      if (R && !R->isZero())
-        return FCmpInst::FCMP_OEQ;
-      R = dyn_cast<ConstantInt>(
-                      ConstantExpr::getFCmp(FCmpInst::FCMP_OLT, V1, V2));
-      if (R && !R->isZero())
-        return FCmpInst::FCMP_OLT;
-      R = dyn_cast<ConstantInt>(
-                      ConstantExpr::getFCmp(FCmpInst::FCMP_OGT, V1, V2));
-      if (R && !R->isZero())
-        return FCmpInst::FCMP_OGT;
-
-      // Nothing more we can do
-      return FCmpInst::BAD_FCMP_PREDICATE;
-    }
-
-    // If the first operand is simple and second is ConstantExpr, swap operands.
-    FCmpInst::Predicate SwappedRelation = evaluateFCmpRelation(V2, V1);
-    if (SwappedRelation != FCmpInst::BAD_FCMP_PREDICATE)
-      return FCmpInst::getSwappedPredicate(SwappedRelation);
-  } else {
-    // Ok, the LHS is known to be a constantexpr.  The RHS can be any of a
-    // constantexpr or a simple constant.
-    ConstantExpr *CE1 = cast<ConstantExpr>(V1);
-    switch (CE1->getOpcode()) {
-    case Instruction::FPTrunc:
-    case Instruction::FPExt:
-    case Instruction::UIToFP:
-    case Instruction::SIToFP:
-      // We might be able to do something with these but we don't right now.
-      break;
-    default:
-      break;
-    }
-  }
-  // There are MANY other foldings that we could perform here.  They will
-  // probably be added on demand, as they seem needed.
-  return FCmpInst::BAD_FCMP_PREDICATE;
-}
-
 static ICmpInst::Predicate areGlobalsPotentiallyEqual(const GlobalValue *GV1,
                                                       const GlobalValue *GV2) {
   auto isGlobalUnsafeForEquality = [](const GlobalValue *GV) {
@@ -1511,79 +1447,14 @@ Constant *llvm::ConstantFoldCompareInstruction(CmpInst::Predicate Predicate,
     return ConstantVector::get(ResElts);
   }
 
-  if (C1->getType()->isFloatingPointTy() &&
-      // Only call evaluateFCmpRelation if we have a constant expr to avoid
-      // infinite recursive loop
-      (isa<ConstantExpr>(C1) || isa<ConstantExpr>(C2))) {
-    int Result = -1;  // -1 = unknown, 0 = known false, 1 = known true.
-    switch (evaluateFCmpRelation(C1, C2)) {
-    default: llvm_unreachable("Unknown relation!");
-    case FCmpInst::FCMP_UNO:
-    case FCmpInst::FCMP_ORD:
-    case FCmpInst::FCMP_UNE:
-    case FCmpInst::FCMP_ULT:
-    case FCmpInst::FCMP_UGT:
-    case FCmpInst::FCMP_ULE:
-    case FCmpInst::FCMP_UGE:
-    case FCmpInst::FCMP_TRUE:
-    case FCmpInst::FCMP_FALSE:
-    case FCmpInst::BAD_FCMP_PREDICATE:
-      break; // Couldn't determine anything about these constants.
-    case FCmpInst::FCMP_OEQ: // We know that C1 == C2
-      Result =
-          (Predicate == FCmpInst::FCMP_UEQ || Predicate == FCmpInst::FCMP_OEQ ||
-           Predicate == FCmpInst::FCMP_ULE || Predicate == FCmpInst::FCMP_OLE ||
-           Predicate == FCmpInst::FCMP_UGE || Predicate == FCmpInst::FCMP_OGE);
-      break;
-    case FCmpInst::FCMP_OLT: // We know that C1 < C2
-      Result =
-          (Predicate == FCmpInst::FCMP_UNE || Predicate == FCmpInst::FCMP_ONE ||
-           Predicate == FCmpInst::FCMP_ULT || Predicate == FCmpInst::FCMP_OLT ||
-           Predicate == FCmpInst::FCMP_ULE || Predicate == FCmpInst::FCMP_OLE);
-      break;
-    case FCmpInst::FCMP_OGT: // We know that C1 > C2
-      Result =
-          (Predicate == FCmpInst::FCMP_UNE || Predicate == FCmpInst::FCMP_ONE ||
-           Predicate == FCmpInst::FCMP_UGT || Predicate == FCmpInst::FCMP_OGT ||
-           Predicate == FCmpInst::FCMP_UGE || Predicate == FCmpInst::FCMP_OGE);
-      break;
-    case FCmpInst::FCMP_OLE: // We know that C1 <= C2
-      // We can only partially decide this relation.
-      if (Predicate == FCmpInst::FCMP_UGT || Predicate == FCmpInst::FCMP_OGT)
-        Result = 0;
-      else if (Predicate == FCmpInst::FCMP_ULT ||
-               Predicate == FCmpInst::FCMP_OLT)
-        Result = 1;
-      break;
-    case FCmpInst::FCMP_OGE: // We known that C1 >= C2
-      // We can only partially decide this relation.
-      if (Predicate == FCmpInst::FCMP_ULT || Predicate == FCmpInst::FCMP_OLT)
-        Result = 0;
-      else if (Predicate == FCmpInst::FCMP_UGT ||
-               Predicate == FCmpInst::FCMP_OGT)
-        Result = 1;
-      break;
-    case FCmpInst::FCMP_ONE: // We know that C1 != C2
-      // We can only partially decide this relation.
-      if (Predicate == FCmpInst::FCMP_OEQ || Predicate == FCmpInst::FCMP_UEQ)
-        Result = 0;
-      else if (Predicate == FCmpInst::FCMP_ONE ||
-               Predicate == FCmpInst::FCMP_UNE)
-        Result = 1;
-      break;
-    case FCmpInst::FCMP_UEQ: // We know that C1 == C2 || isUnordered(C1, C2).
-      // We can only partially decide this relation.
+  if (C1->getType()->isFPOrFPVectorTy()) {
+    if (C1 == C2) {
+      // We know that C1 == C2 || isUnordered(C1, C2).
       if (Predicate == FCmpInst::FCMP_ONE)
-        Result = 0;
+        return ConstantInt::getFalse(ResultTy);
       else if (Predicate == FCmpInst::FCMP_UEQ)
-        Result = 1;
-      break;
+        return ConstantInt::getTrue(ResultTy);
     }
-
-    // If we evaluated the result, return it now.
-    if (Result != -1)
-      return ConstantInt::get(ResultTy, Result);
-
   } else {
     // Evaluate the relation between the two constants, per the predicate.
     int Result = -1;  // -1 = unknown, 0 = known false, 1 = known true.