//! This module implements the instruction set running on the abstract
//! machine implemented by tvix.
use std::ops::{AddAssign, Sub};
/// Index of a constant in the current code chunk.
#[repr(transparent)]
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub struct ConstantIdx(pub usize);
/// Index of an instruction in the current code chunk.
#[repr(transparent)]
#[derive(Clone, Copy, Debug)]
pub struct CodeIdx(pub usize);
impl AddAssign<usize> for CodeIdx {
fn add_assign(&mut self, rhs: usize) {
*self = CodeIdx(self.0 + rhs)
}
}
impl Sub<usize> for CodeIdx {
type Output = Self;
fn sub(self, rhs: usize) -> Self::Output {
CodeIdx(self.0 - rhs)
}
}
/// Index of a value in the runtime stack. This is an offset
/// *relative to* the VM value stack_base of the CallFrame
/// containing the opcode which contains this StackIdx.
#[repr(transparent)]
#[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd)]
pub struct StackIdx(pub usize);
/// Index of an upvalue within a closure's bound-variable upvalue
/// list. This is an absolute index into the Upvalues of the
/// CallFrame containing the opcode which contains this UpvalueIdx.
#[repr(transparent)]
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub struct UpvalueIdx(pub usize);
/// Offset by which an instruction pointer should change in a jump.
#[repr(transparent)]
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub struct JumpOffset(pub usize);
/// Provided count for an instruction (could represent e.g. a number
/// of elements).
#[repr(transparent)]
#[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.
///
/// In documentation comments, stack positions are referred to by
/// indices written in `{}` as such, where required:
///
/// ```notrust
/// --- top of the stack
/// /
/// v
/// [ ... | 3 | 2 | 1 | 0 ]
/// ^
/// /
/// 2 values deep ---
/// ```
///
/// Unless otherwise specified, operations leave their result at the
/// top of the stack.
#[warn(variant_size_differences)]
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum OpCode {
/// Push a constant onto the stack.
OpConstant(ConstantIdx),
// Unary operators
/// Discard a value from the stack.
OpPop,
/// Invert the boolean at the top of the stack.
OpInvert,
// Binary operators
/// Invert the sign of the number at the top of the stack.
OpNegate,
/// Sum up the two numbers at the top of the stack.
OpAdd,
/// Subtract the number at {1} from the number at {2}.
OpSub,
/// Multiply the two numbers at the top of the stack.
OpMul,
/// Divide the two numbers at the top of the stack.
OpDiv,
// Comparison operators
/// Check the two values at the top of the stack for Nix-equality.
OpEqual,
/// Check whether the value at {2} is less than {1}.
OpLess,
/// Check whether the value at {2} is less than or equal to {1}.
OpLessOrEq,
/// Check whether the value at {2} is greater than {1}.
OpMore,
/// Check whether the value at {2} is greater than or equal to {1}.
OpMoreOrEq,
// Logical operators & generic jumps
/// Jump forward in the bytecode specified by the number of
/// instructions in its usize operand.
OpJump(JumpOffset),
/// Jump forward in the bytecode specified by the number of
/// instructions in its usize operand, *if* the value at the top
/// of the stack is `true`.
OpJumpIfTrue(JumpOffset),
/// Jump forward in the bytecode specified by the number of
/// instructions in its usize operand, *if* the value at the top
/// of the stack is `false`.
OpJumpIfFalse(JumpOffset),
/// Pop one stack item and jump forward in the bytecode
/// specified by the number of instructions in its usize
/// operand, *if* the value at the top of the stack is a
/// Value::Catchable.
OpJumpIfCatchable(JumpOffset),
/// Jump forward in the bytecode specified by the number of
/// instructions in its usize operand, *if* the value at the top
/// of the stack is the internal value representing a missing
/// attribute set key.
OpJumpIfNotFound(JumpOffset),
/// Jump forward in the bytecode specified by the number of
/// instructions in its usize operand, *if* the value at the top
/// of the stack is *not* the internal value requesting a
/// stack value finalisation.
OpJumpIfNoFinaliseRequest(JumpOffset),
// Attribute sets
/// Construct an attribute set from the given number of key-value pairs on the top of the stack
///
/// Note that this takes the count of *pairs*, not the number of *stack values* - the actual
/// number of values popped off the stack will be twice the argument to this op
OpAttrs(Count),
/// Merge the attribute set at {2} into the attribute set at {1},
/// and leave the new set at the top of the stack.
OpAttrsUpdate,
/// Select the attribute with the name at {1} from the set at {2}.
OpAttrsSelect,
/// Select the attribute with the name at {1} from the set at {2}, but leave
/// a `Value::AttrNotFound` in the stack instead of failing if it is
/// missing.
OpAttrsTrySelect,
/// Check for the presence of the attribute with the name at {1} in the set
/// at {2}.
OpHasAttr,
/// Throw an error if the attribute set at the top of the stack has any attributes
/// other than those listed in the formals of the current lambda
///
/// Panics if the current frame is not a lambda with formals
OpValidateClosedFormals,
// `with`-handling
/// Push a value onto the runtime `with`-stack to enable dynamic identifier
/// resolution. The absolute stack index of the value is supplied as a usize
/// operand.
OpPushWith(StackIdx),
/// Pop the last runtime `with`-stack element.
OpPopWith,
/// Dynamically resolve an identifier with the name at {1} from the runtime
/// `with`-stack.
OpResolveWith,
// Lists
/// Construct a list from the given number of values at the top of the
/// stack.
OpList(Count),
/// Concatenate the lists at {2} and {1}.
OpConcat,
// Strings
/// Interpolate the given number of string fragments into a single string.
OpInterpolate(Count),
/// Force the Value on the stack and coerce it to a string, always using
/// `CoercionKind::Weak`.
OpCoerceToString,
// Paths
/// Attempt to resolve the Value on the stack using the configured [`NixSearchPath`][]
///
/// [`NixSearchPath`]: crate::nix_search_path::NixSearchPath
OpFindFile,
/// Attempt to resolve a path literal relative to the home dir
OpResolveHomePath,
// Type assertion operators
/// Assert that the value at {1} is a boolean, and fail with a runtime error
/// otherwise.
OpAssertBool,
OpAssertAttrs,
/// Access local identifiers with statically known positions.
OpGetLocal(StackIdx),
/// Close scopes while leaving their expression value around.
OpCloseScope(Count), // number of locals to pop
/// Return an error indicating that an `assert` failed
OpAssertFail,
// Lambdas & closures
/// Call the value at {1} in a new VM callframe
OpCall,
/// Retrieve the upvalue at the given index from the closure or thunk
/// currently under evaluation.
OpGetUpvalue(UpvalueIdx),
/// Construct a closure which has upvalues but no self-references
OpClosure(ConstantIdx),
/// Construct a closure which has self-references (direct or via upvalues)
OpThunkClosure(ConstantIdx),
/// Construct a suspended thunk, used to delay a computation for laziness.
OpThunkSuspended(ConstantIdx),
/// Force the value at {1} until it is a `Thunk::Evaluated`.
OpForce,
/// Finalise initialisation of the upvalues of the value in the given stack
/// index (which must be a Value::Thunk) after the scope is fully bound.
OpFinalise(StackIdx),
/// Final instruction emitted in a chunk. Does not have an
/// inherent effect, but can simplify VM logic as a marker in some
/// cases.
///
/// Can be thought of as "returning" the value to the parent
/// frame, hence the name.
OpReturn,
// [`OpClosure`], [`OpThunkSuspended`], and [`OpThunkClosure`] 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 opcode must be followed by exactly this number
// of `Data*` opcodes. The VM skips over these by advancing the
// instruction pointer.
//
// It is illegal for a `Data*` opcode to appear anywhere else.
/// Populate a static upvalue by copying from the stack immediately.
DataStackIdx(StackIdx),
/// Populate a static upvalue of a thunk by copying it the stack, but do
/// when the thunk is finalised (by OpFinalise) rather than immediately.
DataDeferredLocal(StackIdx),
/// Populate a static upvalue by copying it from the upvalues of an
/// enclosing scope.
DataUpvalueIdx(UpvalueIdx),
/// Populate dynamic upvalues by saving a copy of the with-stack.
DataCaptureWith,
}
