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The mechanism behind initializing a union's tag is a bit complicated, depending on whether the union is initialized at runtime, forced comptime, or implicit comptime. `coerce_result_ptr` now does not force a block to be a runtime context; instead of adding runtime instructions directly, it forwards analysis to the respective functions for initializing optionals and error unions. `validateUnionInit` now has logic to still emit a runtime `set_union_tag` instruction even if the union pointer is comptime-known, for the case of a pointer that is not comptime mutable, such as a variable or the result of `@intToPtr`. `validateStructInit` looks for a completely different pattern now; it now handles the possibility of the corresponding AIR instruction for the `field_ptr` to be missing or the corresponding `store` to be missing. See the new comment added to the function for more details. An equivalent change should probably be made to `validateArrayInit`. `analyzeOptionalPayloadPtr` and `analyzeErrUnionPayloadPtr` functions now emit a `optional_payload_ptr_set` or `errunion_payload_ptr_set` instruction respectively if `initializing` is true and the pointer value is not comptime-mutable. `storePtr2` now tries the comptime pointer store before checking if the element type has one possible value because the comptime pointer store can have side effects of setting a union tag, setting an optional payload non-null, or setting an error union to be non-error. The LLVM backend `lowerParentPtr` function is improved to take into account the differences in how the LLVM values are lowered depending on the Zig type. It now handles unions correctly as well as additionally handling optionals and error unions. In the LLVM backend, the instructions `optional_payload_ptr_set` and `errunion_payload_ptr_set` check liveness analysis and only do the side effects in the case the result of the instruction is unused. A few wasm and C backend test cases regressed, but they are due to TODOs in lowering of constants, so this is progress.