Doing a diff between structs and struct records generated code, I noticed that an extra copy is done in methods using copy and update.

Repro steps

• Create a struct type
• Create a struct record
• implement the same method that copy and update the type
• compare IL both

[<Struct>]
type Structure = 
    val Line: int
    val OriginalLine: int
    val StartOfLineAbsoluteOffset: int
    new(l,ol,s) = { Line =l; OriginalLine = ol; StartOfLineAbsoluteOffset = s }
    member x.NextLine =
        Structure(x.Line+1, x.OriginalLine+1,x.StartOfLineAbsoluteOffset)
[<Struct>]
type Rec = {
    Line: int
    OriginalLine: int
    StartOfLineAbsoluteOffset: int
} with
    member x.NextLine =
        { x with Line = x.Line + 1; OriginalLine = x.OriginalLine+1}

Expected behavior

IL should be the same

Actual behavior

There is a few extra instructions for struct records:

  .maxstack  5
  .locals init (valuetype Program/Rec V_0)
  IL_0000:  ldarg.0
  IL_0001:  ldobj      Program/Rec
  IL_0006:  stloc.0

the rest is exactly similar.

Known workarounds

Use struct types.

Related information

Is this needed ? The Structure.NextLine seems ok without it.

These lines seems generated by a call to mkAddrGet function (TastOps.fs) for byref value types.