Sub MAJ_F1()
Dim F1 As Worksheet, F2 As Worksheet, P As Range, t1, t2, d As Object, i&
Set F1 = Sheets("Feuil1"): Set F2 = Sheets("Feuil2") 'noms à adapter
Set P = Intersect(F1.[A:B], F1.UsedRange.EntireRow)
t1 = P 'matrice, plus rapide
t2 = Intersect(F2.[A:B], F2.UsedRange.EntireRow)
Set d = CreateObject("Scripting.Dictionary")
d.CompareMode = vbTextCompare 'la casse est ignorée
For i = 1 To UBound(t2)
If t2(i, 2) <> "" Then If Not d.exists(t2(i, 2)) Then d(t2(i, 2)) = t2(i, 1)
Next
For i = 1 To UBound(t1)
If d.exists(t1(i, 1)) Then t1(i, 2) = d(t1(i, 1))
Next
P = t1
End Sub