Andrew Waterman's PhD thesis "Design of the RISC-V Instruction Set Architecture" ("Why Develop a New Instruction Set?") has a nice comparison of ISA encoding an

Andrew Waterman's PhD thesis "Design of the RISC-V Instruction Set Architecture" ("Why Develop a New Instruction Set?") has a nice comparison of ISA encoding and density of RISC-V, MIPS, SPARC, Alpha, ARMv7/8, Thumb, OpenRISC, and x86/x86-64. https://people.eecs.berkeley.edu/~krste/papers/EECS-2016-1.pdf https://people.eecs.berkeley.edu/~krste/papers/EECS-2016-1.p...