We report on a pressure (P)-induced evolution of magnetism and superconductivity (SC) in a helical magnet CeRhIn5 with an incommensurate wave vector Q(i) = (1/2, 1/2, 0.297) through the In-115 nuclear quadrupole resonance (NQR) measurements under P. Systematic measurements of the In-115-NQR spectrum reveal that the commensurate antiferromagnetism (AFM) with Q(c) = (1/2, 1/2, 1/2) is realized above P-m similar to 1.7 GPa. An important finding is that the size of SC gap and T-c increase as the magnitude of the AFM moment decreases in the P region, where SC uniformly coexists with the commensurate AFM. This result provides evidence of strong coupling between the commensurate AFM order parameter (OP) and SC OP.