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OpPhi
A shader instruction that picks a value depending on which code path was taken to reach it.
In SSA form (the structured way compilers and SPIR-V represent code), a variable can't be reassigned, so when two branches produce different values that merge, OpPhi selects the right one based on which branch actually ran. It's the mechanism that lets branchy logic resolve to a single value at a join point. Essentially it's an if/else result expressed as one instruction.
See also
- OpKillThe GPU shader instruction that throws away the current pixel so it's never drawn.
- OpEmitVertex / OpEndPrimitiveThe GPU shader instructions that output a vertex and finish a shape inside a geometry shader.
- off-by-oneA bug where a count or index is wrong by exactly one — stopping one step too early or late.