The Consilium takes a brief look at the relationship between two sacraments:
35. The eucharist should also be proposed to the faithful “as a remedy that frees us from our daily faults and preserves us from mortal sins.” [Council of Trent, sess. 13, Decr. de Eucharistia cap. 2: Denz-Schon 1638; see also sess. 22, Decr. de Missa cap. 1 and 2: Denz-Schon 1740 and 1743.] They should also receive an explanation of how to make use of the penitential parts of the Mass.
Apart from the explicitly penitential parts of the Mass, the Tridentine quote suggests that there is a preventative dimension to the Eucharist.
“Those wishing to receive communion should be reminded of the precept ‘let them examine themselves’ (1 Cor 1:28). Ecclesiastical custom shows that this examination is necessary so that none who are conscious of having committed mortal sin, no matter how contrite they believe themselves to be, should approach the holy eucharist without first making a sacramental confession.” [Council of Trent, sess. 13, Decr. de Eucharistia cap. 7: Denz-Schon 1740 and 1743.] “In a case of necessity, however, and when no confessor is available, a person should first make an act of perfect contrition.” [Codex Iuris Canonici (Rome, 1918) can. 859.]
Church teaching on being in a state of sin and what to do about it.
The faithful are to be constantly encouraged in the practice of receiving the sacrament of penance outside Mass, especially at the scheduled hours, so that the administration of the sacrament may be unhurried and genuinely useful and that people will not be impeded from active participation in the Mass. Daily or frequent communicants should be instructed to go to confession regularly, depending on their individual needs.
I don’t know how widespread the practice of hearing confessions during Mass used to be, but this paragraph seems eminently sensible. One might also suggest that the time immediately before Mass isn’t the best time to schedule the sacrament, either. At our parish, I often see penitents still in the confession line at ten minutes before Mass.