Mapped encoding conflicts across 102 RISC-V extensions: 27 fatal collisions, vendor extensions all fighting over custom-0
Built from the registry's conflict detector. Every edge is an encoding collision between two extensions.
The red cluster is: FATAL same opcode, different instruction.
The custom-space cluster (67 warnings) is everyone reaching for custom-0.
Interactive: extensilica.com/compatibility
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EDIT (June 11, 2026): brucehoult and XIVN1987 correctly identified that shared major opcodes (like every RVV instruction sitting at OP-V 0x57) were being reported as FATAL conflicts on the compatibility graph. That was a too-coarse classification on my end.
Fix is live: those edges now read as INFO ("shared major opcode; not a conflict by itself. A true conflict requires overlapping full decode mask/match patterns, including any fixed register/immediate field constraints"). Full mask/match resolution (funct6, vm, register/immediate carve-outs) is the next iteration.
See https://extensilica.com/compatibility for the updated graph; technical details in the comments below.
Posted Jun 11, 2026, 2:28 AM UTC