[VPlan] Preserve IR flags when widening casts

We have `nneg` for both `sext` and `uitofp`.

Fixes llvm#114856

Closes llvm#115373

Author: goldsteinn

llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp

@@ -1484,6 +1484,8 @@ void VPWidenCastRecipe::execute(VPTransformState &State) {
   Value *Cast = Builder.CreateCast(Instruction::CastOps(Opcode), A, DestTy);
   State.set(this, Cast);
   State.addMetadata(Cast, cast_or_null<Instruction>(getUnderlyingValue()));
+  if (auto *CastOp = dyn_cast<Instruction>(Cast))
+    setFlags(CastOp);
 }
 
 InstructionCost VPWidenCastRecipe::computeCost(ElementCount VF,

llvm/test/Transforms/LoopVectorize/uitofp-preserve-nneg.ll

@@ -13,7 +13,7 @@ define void @uitofp_preserve_nneg(ptr %result, i32 %size, float %y) {
 ; CHECK-NEXT:    [[INDEX1:%.*]] = phi i32 [ 0, [[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], [[VECTOR_BODY]] ]
 ; CHECK-NEXT:    [[VEC_IND:%.*]] = phi <4 x i32> [ <i32 0, i32 1, i32 2, i32 3>, [[VECTOR_PH]] ], [ [[VEC_IND_NEXT:%.*]], [[VECTOR_BODY]] ]
 ; CHECK-NEXT:    [[TMP1:%.*]] = add i32 [[INDEX1]], 0
-; CHECK-NEXT:    [[TMP0:%.*]] = uitofp <4 x i32> [[VEC_IND]] to <4 x float>
+; CHECK-NEXT:    [[TMP0:%.*]] = uitofp nneg <4 x i32> [[VEC_IND]] to <4 x float>
 ; CHECK-NEXT:    [[TMP3:%.*]] = fmul <4 x float> [[TMP0]], [[BROADCAST_SPLAT3]]
 ; CHECK-NEXT:    [[INDEX:%.*]] = zext nneg i32 [[TMP1]] to i64
 ; CHECK-NEXT:    [[TMP2:%.*]] = getelementptr inbounds float, ptr [[RESULT:%.*]], i64 [[INDEX]]