diff options
| -rw-r--r-- | tvix/eval/src/opcode.rs | 17 | ||||
| -rw-r--r-- | tvix/eval/src/value/function.rs | 10 | ||||
| -rw-r--r-- | tvix/eval/src/value/mod.rs | 5 |
3 files changed, 27 insertions, 5 deletions
diff --git a/tvix/eval/src/opcode.rs b/tvix/eval/src/opcode.rs index 70ef1a3b5324..ee1684d7cf0f 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), diff --git a/tvix/eval/src/value/function.rs b/tvix/eval/src/value/function.rs index 6287cf76b81d..0923e1b1cba9 100644 --- a/tvix/eval/src/value/function.rs +++ b/tvix/eval/src/value/function.rs @@ -9,10 +9,20 @@ use crate::{ upvalues::{UpvalueCarrier, Upvalues}, }; +/// The opcodes for a thunk or closure, plus the number of +/// non-executable opcodes which are allowed after an OpClosure or +/// OpThunk referencing it. At runtime `Lambda` is usually wrapped +/// in `Rc` to avoid copying the `Chunk` it holds (which can be +/// quite large). #[derive(Debug, PartialEq)] pub struct Lambda { // name: Option<NixString>, pub(crate) chunk: Chunk, + + /// Number of upvalues which the code in this Lambda closes + /// over, and which need to be initialised at + /// runtime. Information about the variables is emitted using + /// data-carrying opcodes (see [`OpCode::DataLocalIdx`]). pub(crate) upvalue_count: usize, } diff --git a/tvix/eval/src/value/mod.rs b/tvix/eval/src/value/mod.rs index 93e194e37940..a1216452fbb5 100644 --- a/tvix/eval/src/value/mod.rs +++ b/tvix/eval/src/value/mod.rs @@ -43,8 +43,13 @@ pub enum Value { // Internal values that, while they technically exist at runtime, // are never returned to or created directly by users. Thunk(Thunk), + + // See [`compiler::compile_select_or()`] for explanation AttrNotFound, + + // this can only occur in Chunk::Constants and nowhere else Blueprint(Rc<Lambda>), + DeferredUpvalue(StackIdx), UnresolvedPath(PathBuf), } |