Understanding purpose of components in a half bridge driver circuit
There's another important reason to the presence of the diode antiparalled to the gate resistor. In a bridge configuration, when a transitor goes on the switching, the voltage acroos the other transitor has a increased dV/dt.
In a MOSFET, that's the case of your H-brigde, there's three intrinsic capacitances composing its body, like in the image below (that shows other stray components of the Mosfet body):

When the Vds voltage increases, all the three capacitances need to be charged, like in the schematic below:



simulate this circuit &ndash; Schematic created using CircuitLab
Where the red arrows are current flowing through the circuit (when Vds are increasing).
So, if this resistance of the discharge isn't low, the Cgs capacitange could had a peak of charge, creating a short-time short-circuit, named punch through.
More information at this app. note
http://www.irf.com/technical-info/appnotes/an-936.pdf