[ValueTracking] Avoid FP cast constant expressions

Use the constant folding API instead.

Author: nikic

llvm/lib/Analysis/ValueTracking.cpp

@@ -7880,22 +7880,22 @@ static Value *lookThroughCast(CmpInst *CmpI, Value *V1, Value *V2,
     }
     break;
   case Instruction::FPTrunc:
-    CastedTo = ConstantExpr::getFPExtend(C, SrcTy, true);
+    CastedTo = ConstantFoldCastOperand(Instruction::FPExt, C, SrcTy, DL);
     break;
   case Instruction::FPExt:
-    CastedTo = ConstantExpr::getFPTrunc(C, SrcTy, true);
+    CastedTo = ConstantFoldCastOperand(Instruction::FPTrunc, C, SrcTy, DL);
     break;
   case Instruction::FPToUI:
-    CastedTo = ConstantExpr::getUIToFP(C, SrcTy, true);
+    CastedTo = ConstantFoldCastOperand(Instruction::UIToFP, C, SrcTy, DL);
     break;
   case Instruction::FPToSI:
-    CastedTo = ConstantExpr::getSIToFP(C, SrcTy, true);
+    CastedTo = ConstantFoldCastOperand(Instruction::SIToFP, C, SrcTy, DL);
     break;
   case Instruction::UIToFP:
-    CastedTo = ConstantExpr::getFPToUI(C, SrcTy, true);
+    CastedTo = ConstantFoldCastOperand(Instruction::FPToUI, C, SrcTy, DL);
     break;
   case Instruction::SIToFP:
-    CastedTo = ConstantExpr::getFPToSI(C, SrcTy, true);
+    CastedTo = ConstantFoldCastOperand(Instruction::FPToSI, C, SrcTy, DL);
     break;
   default:
     break;