How much memory do you actually need for your variables? Both idata and pdata generate better optimized code and thereby reduce the number of temporaries which SDCC automatically stores in data. You probably have a lot of those temporaries now and that's why you run out of (data) memory. Moving some variables to idata or pdata might help.

And if you use the default small memory model all function parameters are also in data memory. Using --model-large might help.

Finally SDCC tries to overlay variables in data but is not very good at it. Using --stack-auto might help as that automatically overlays everything on stack.