diff options
Diffstat (limited to 'tvix/eval/src/opcode.rs')
| -rw-r--r-- | tvix/eval/src/opcode.rs | 17 |
1 files changed, 12 insertions, 5 deletions
diff --git a/tvix/eval/src/opcode.rs b/tvix/eval/src/opcode.rs index 70ef1a3b53..ee1684d7cf 100644 --- a/tvix/eval/src/opcode.rs +++ b/tvix/eval/src/opcode.rs @@ -48,6 +48,8 @@ pub struct JumpOffset(pub usize); #[derive(Clone, Copy, Debug, PartialEq, Eq)] pub struct Count(pub usize); +/// All variants of this enum carry a bounded amount of data to +/// ensure that no heap allocations are needed for an Opcode. #[warn(variant_size_differences)] #[derive(Clone, Copy, Debug, PartialEq, Eq)] pub enum OpCode { @@ -146,12 +148,17 @@ pub enum OpCode { /// given stack index after the scope is fully bound. OpFinalise(StackIdx), - // The closure and thunk creation instructions have a variable - // number of arguments to the instruction, which is represented - // here by making their data part of the opcodes. + // [`OpClosure`] and [`OpThunk`] have a variable number of + // arguments to the instruction, which is represented here by + // making their data part of the opcodes. Each of these two + // opcodes has a `ConstantIdx`, which must reference a + // `Value::Blueprint(Lambda)`. The `upvalue_count` field in + // that `Lambda` indicates the number of arguments it takes, and + // the `OpClosure` or `OpThunk` must be followed by exactly this + // number of `Data*` opcodes. The VM skips over these by + // advancing the instruction pointer. // - // The VM skips over these by advancing the instruction pointer - // according to the count. + // It is illegal for a `Data*` opcode to appear anywhere else. DataLocalIdx(StackIdx), DataDeferredLocal(StackIdx), DataUpvalueIdx(UpvalueIdx), |