Reciprocal assimilation

When both sounds (the assimilating and the assimilated one) under go changes.

Historically this has occurred in words like:

Soldier, picture or fissure.

where the reconstructable earlier pronunciation /‘soυldjər/, /‘pıktu:r/, /‘fısju:r/ has become /‘səυldзə/,/‘pıkt∫ə/, /fı∫ə/

In current colloquial English, similar assimilation occurs in phrases such as "What d’you want" /wt∫əwnt/ or
Could you?  /‘kυdZu:/.