[NFC] Method for evaluation of FCmpInst for constant operands

[sepavloff]

Summary

New method FCmpInst::compare is added, which evaluates the given
compare predicate for constant operands. Interface is made similar to
ICmpInst::compare.

[nikic]

LG

llvm/lib/IR/ConstantFold.cpp

1804–1805

It's pretty weird that this function accepts the predicate as unsigned short. Would be great to switch it to CmpInst::Predicate (separately).

[sepavloff]

Thanks!

[sepavloff]

llvm/lib/IR/ConstantFold.cpp

1804–1805

The patch is here: D116379.

llvm/include/llvm/IR/Instructions.h

void swapOperands() {
     setPredicate(getSwappedPredicate());
     Op<0>().swap(Op<1>());
   }
 
   /// Returns the sequence of all FCmp predicates.
   ///
   static auto predicates() { return FCmpPredicates(); }
 
+  /// Return result of `LHS Pred RHS` comparison.
+  static bool compare(const APFloat &LHS, const APFloat &RHS,
+                      FCmpInst::Predicate Pred);
+
   /// Methods for support type inquiry through isa, cast, and dyn_cast:
   static bool classof(const Instruction *I) {
     return I->getOpcode() == Instruction::FCmp;
   }
   static bool classof(const Value *V) {
     return isa<Instruction>(V) && classof(cast<Instruction>(V));
   }
 };

llvm/lib/IR/ConstantFold.cpp

Constant *llvm::ConstantFoldCompareInstruction(unsigned short pred,
   if (isa<ConstantInt>(C1) && isa<ConstantInt>(C2)) {
     const APInt &V1 = cast<ConstantInt>(C1)->getValue();
     const APInt &V2 = cast<ConstantInt>(C2)->getValue();
     return ConstantInt::get(
         ResultTy, ICmpInst::compare(V1, V2, (ICmpInst::Predicate)pred));
   } else if (isa<ConstantFP>(C1) && isa<ConstantFP>(C2)) {
     const APFloat &C1V = cast<ConstantFP>(C1)->getValueAPF();
     const APFloat &C2V = cast<ConstantFP>(C2)->getValueAPF();
-    APFloat::cmpResult R = C1V.compare(C2V);
-    switch (pred) {
-    default: llvm_unreachable("Invalid FCmp Predicate");
-    case FCmpInst::FCMP_FALSE: return Constant::getNullValue(ResultTy);
-    case FCmpInst::FCMP_TRUE:  return Constant::getAllOnesValue(ResultTy);
-    case FCmpInst::FCMP_UNO:
-      return ConstantInt::get(ResultTy, R==APFloat::cmpUnordered);
-    case FCmpInst::FCMP_ORD:
-      return ConstantInt::get(ResultTy, R!=APFloat::cmpUnordered);
-    case FCmpInst::FCMP_UEQ:
-      return ConstantInt::get(ResultTy, R==APFloat::cmpUnordered ||
-                                        R==APFloat::cmpEqual);
-    case FCmpInst::FCMP_OEQ:
-      return ConstantInt::get(ResultTy, R==APFloat::cmpEqual);
-    case FCmpInst::FCMP_UNE:
-      return ConstantInt::get(ResultTy, R!=APFloat::cmpEqual);
-    case FCmpInst::FCMP_ONE:
-      return ConstantInt::get(ResultTy, R==APFloat::cmpLessThan ||
-                                        R==APFloat::cmpGreaterThan);
-    case FCmpInst::FCMP_ULT:
-      return ConstantInt::get(ResultTy, R==APFloat::cmpUnordered ||
-                                        R==APFloat::cmpLessThan);
-    case FCmpInst::FCMP_OLT:
-      return ConstantInt::get(ResultTy, R==APFloat::cmpLessThan);
-    case FCmpInst::FCMP_UGT:
-      return ConstantInt::get(ResultTy, R==APFloat::cmpUnordered ||
-                                        R==APFloat::cmpGreaterThan);
-    case FCmpInst::FCMP_OGT:
-      return ConstantInt::get(ResultTy, R==APFloat::cmpGreaterThan);
-    case FCmpInst::FCMP_ULE:
-      return ConstantInt::get(ResultTy, R!=APFloat::cmpGreaterThan);
-    case FCmpInst::FCMP_OLE:
-      return ConstantInt::get(ResultTy, R==APFloat::cmpLessThan ||
-                                        R==APFloat::cmpEqual);
-    case FCmpInst::FCMP_UGE:
-      return ConstantInt::get(ResultTy, R!=APFloat::cmpLessThan);
-    case FCmpInst::FCMP_OGE:
-      return ConstantInt::get(ResultTy, R==APFloat::cmpGreaterThan ||
-                                        R==APFloat::cmpEqual);
-    }
+    CmpInst::Predicate Predicate = CmpInst::Predicate(pred);
+    return ConstantInt::get(ResultTy, FCmpInst::compare(C1V, C2V, Predicate));
   } else if (auto *C1VTy = dyn_cast<VectorType>(C1->getType())) {
 
     // Fast path for splatted constants.
     if (Constant *C1Splat = C1->getSplatValue())
       if (Constant *C2Splat = C2->getSplatValue())
         return ConstantVector::getSplat(
             C1VTy->getElementCount(),
             ConstantExpr::getCompare(pred, C1Splat, C2Splat));

llvm/lib/IR/Instructions.cpp

case ICmpInst::Predicate::ICMP_SLT:
     return LHS.slt(RHS);
   case ICmpInst::Predicate::ICMP_SLE:
     return LHS.sle(RHS);
   default:
     llvm_unreachable("Unexpected non-integer predicate.");
   };
 }
 
+bool FCmpInst::compare(const APFloat &LHS, const APFloat &RHS,
+                       FCmpInst::Predicate Pred) {
+  APFloat::cmpResult R = LHS.compare(RHS);
+  switch (Pred) {
+  default:
+    llvm_unreachable("Invalid FCmp Predicate");
+  case FCmpInst::FCMP_FALSE:
+    return false;
+  case FCmpInst::FCMP_TRUE:
+    return true;
+  case FCmpInst::FCMP_UNO:
+    return R == APFloat::cmpUnordered;
+  case FCmpInst::FCMP_ORD:
+    return R != APFloat::cmpUnordered;
+  case FCmpInst::FCMP_UEQ:
+    return R == APFloat::cmpUnordered || R == APFloat::cmpEqual;
+  case FCmpInst::FCMP_OEQ:
+    return R == APFloat::cmpEqual;
+  case FCmpInst::FCMP_UNE:
+    return R != APFloat::cmpEqual;
+  case FCmpInst::FCMP_ONE:
+    return R == APFloat::cmpLessThan || R == APFloat::cmpGreaterThan;
+  case FCmpInst::FCMP_ULT:
+    return R == APFloat::cmpUnordered || R == APFloat::cmpLessThan;
+  case FCmpInst::FCMP_OLT:
+    return R == APFloat::cmpLessThan;
+  case FCmpInst::FCMP_UGT:
+    return R == APFloat::cmpUnordered || R == APFloat::cmpGreaterThan;
+  case FCmpInst::FCMP_OGT:
+    return R == APFloat::cmpGreaterThan;
+  case FCmpInst::FCMP_ULE:
+    return R != APFloat::cmpGreaterThan;
+  case FCmpInst::FCMP_OLE:
+    return R == APFloat::cmpLessThan || R == APFloat::cmpEqual;
+  case FCmpInst::FCMP_UGE:
+    return R != APFloat::cmpLessThan;
+  case FCmpInst::FCMP_OGE:
+    return R == APFloat::cmpGreaterThan || R == APFloat::cmpEqual;
+  }
+}
+
 CmpInst::Predicate CmpInst::getFlippedSignednessPredicate(Predicate pred) {
   assert(CmpInst::isRelational(pred) &&
          "Call only with non-equality predicates!");
 
   if (isSigned(pred))
     return getUnsignedPredicate(pred);
   if (isUnsigned(pred))
     return getSignedPredicate(pred);