[IndVars] Use getSigned() in FP transform

This transform is working on signed integer, so this is the
logically correct API.

Split off from llvm#80309.

Author: nikic

llvm/lib/Transforms/Scalar/IndVarSimplify.cpp

@@ -357,19 +357,19 @@ bool IndVarSimplify::handleFloatingPointIV(Loop *L, PHINode *PN) {
   // Insert new integer induction variable.
   PHINode *NewPHI =
       PHINode::Create(Int32Ty, 2, PN->getName() + ".int", PN->getIterator());
-  NewPHI->addIncoming(ConstantInt::get(Int32Ty, InitValue),
+  NewPHI->addIncoming(ConstantInt::getSigned(Int32Ty, InitValue),
                       PN->getIncomingBlock(IncomingEdge));
   NewPHI->setDebugLoc(PN->getDebugLoc());
 
-  Instruction *NewAdd =
-      BinaryOperator::CreateAdd(NewPHI, ConstantInt::get(Int32Ty, IncValue),
-                                Incr->getName() + ".int", Incr->getIterator());
+  Instruction *NewAdd = BinaryOperator::CreateAdd(
+      NewPHI, ConstantInt::getSigned(Int32Ty, IncValue),
+      Incr->getName() + ".int", Incr->getIterator());
   NewAdd->setDebugLoc(Incr->getDebugLoc());
   NewPHI->addIncoming(NewAdd, PN->getIncomingBlock(BackEdge));
 
-  ICmpInst *NewCompare =
-      new ICmpInst(TheBr->getIterator(), NewPred, NewAdd,
-                   ConstantInt::get(Int32Ty, ExitValue), Compare->getName());
+  ICmpInst *NewCompare = new ICmpInst(
+      TheBr->getIterator(), NewPred, NewAdd,
+      ConstantInt::getSigned(Int32Ty, ExitValue), Compare->getName());
   NewCompare->setDebugLoc(Compare->getDebugLoc());
 
   // In the following deletions, PN may become dead and may be deleted.