diff options
Diffstat (limited to 'tvix/eval/src/opcode.rs')
| -rw-r--r-- | tvix/eval/src/opcode.rs | 277 |
1 files changed, 192 insertions, 85 deletions
diff --git a/tvix/eval/src/opcode.rs b/tvix/eval/src/opcode.rs index f89c1c12e7fd..ddf1304b3aea 100644 --- a/tvix/eval/src/opcode.rs +++ b/tvix/eval/src/opcode.rs @@ -52,8 +52,7 @@ 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. +/// Op represents all instructions in the Tvix abstract machine. /// /// In documentation comments, stack positions are referred to by /// indices written in `{}` as such, where required: @@ -70,187 +69,182 @@ pub struct Count(pub usize); /// /// 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 { +#[repr(u8)] +#[derive(Debug, PartialEq, Eq)] +pub enum Op { /// Push a constant onto the stack. - OpConstant(ConstantIdx), + Constant, - // Unary operators - /// Discard a value from the stack. - OpPop, + /// Discard the value on top of the stack. + Pop, /// Invert the boolean at the top of the stack. - OpInvert, + Invert, - // Binary operators /// Invert the sign of the number at the top of the stack. - OpNegate, + Negate, /// Sum up the two numbers at the top of the stack. - OpAdd, + Add, /// Subtract the number at {1} from the number at {2}. - OpSub, + Sub, /// Multiply the two numbers at the top of the stack. - OpMul, + Mul, /// Divide the two numbers at the top of the stack. - OpDiv, + Div, - // Comparison operators /// Check the two values at the top of the stack for Nix-equality. - OpEqual, + Equal, /// Check whether the value at {2} is less than {1}. - OpLess, + Less, /// Check whether the value at {2} is less than or equal to {1}. - OpLessOrEq, + LessOrEq, /// Check whether the value at {2} is greater than {1}. - OpMore, + More, /// Check whether the value at {2} is greater than or equal to {1}. - OpMoreOrEq, + MoreOrEq, - // Logical operators & generic jumps /// Jump forward in the bytecode specified by the number of /// instructions in its usize operand. - OpJump(JumpOffset), + Jump, /// 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), + JumpIfTrue, /// 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), + JumpIfFalse, /// 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), + JumpIfCatchable, /// 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), + JumpIfNotFound, /// 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), + JumpIfNoFinaliseRequest, + + /// Construct an attribute set from the given number of key-value pairs on + /// the top of the stack. The operand gives 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. + Attrs, - // 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, + AttrsUpdate, /// Select the attribute with the name at {1} from the set at {2}. - OpAttrsSelect, + AttrsSelect, /// 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, + AttrsTrySelect, /// Check for the presence of the attribute with the name at {1} in the set /// at {2}. - OpHasAttr, + HasAttr, /// 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, + ValidateClosedFormals, - // `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), + PushWith, /// Pop the last runtime `with`-stack element. - OpPopWith, + PopWith, /// Dynamically resolve an identifier with the name at {1} from the runtime /// `with`-stack. - OpResolveWith, + ResolveWith, // Lists /// Construct a list from the given number of values at the top of the /// stack. - OpList(Count), + List, /// Concatenate the lists at {2} and {1}. - OpConcat, + Concat, // Strings /// Interpolate the given number of string fragments into a single string. - OpInterpolate(Count), + Interpolate, /// Force the Value on the stack and coerce it to a string - OpCoerceToString(crate::CoercionKind), + CoerceToString, // Paths /// Attempt to resolve the Value on the stack using the configured [`NixSearchPath`][] /// /// [`NixSearchPath`]: crate::nix_search_path::NixSearchPath - OpFindFile, + FindFile, /// Attempt to resolve a path literal relative to the home dir - OpResolveHomePath, + ResolveHomePath, // Type assertion operators /// Assert that the value at {1} is a boolean, and fail with a runtime error /// otherwise. - OpAssertBool, - OpAssertAttrs, + AssertBool, + AssertAttrs, /// Access local identifiers with statically known positions. - OpGetLocal(StackIdx), + GetLocal, /// Close scopes while leaving their expression value around. - OpCloseScope(Count), // number of locals to pop + CloseScope, /// Return an error indicating that an `assert` failed - OpAssertFail, + AssertFail, // Lambdas & closures /// Call the value at {1} in a new VM callframe - OpCall, + Call, /// Retrieve the upvalue at the given index from the closure or thunk /// currently under evaluation. - OpGetUpvalue(UpvalueIdx), + GetUpvalue, /// Construct a closure which has upvalues but no self-references - OpClosure(ConstantIdx), + Closure, /// Construct a closure which has self-references (direct or via upvalues) - OpThunkClosure(ConstantIdx), + ThunkClosure, /// Construct a suspended thunk, used to delay a computation for laziness. - OpThunkSuspended(ConstantIdx), + ThunkSuspended, /// Force the value at {1} until it is a `Thunk::Evaluated`. - OpForce, + Force, /// 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), + Finalise, /// Final instruction emitted in a chunk. Does not have an /// inherent effect, but can simplify VM logic as a marker in some @@ -258,27 +252,140 @@ pub enum OpCode { /// /// 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, + Return, + + /// Sentinel value to signal invalid bytecode. This MUST always be the last + /// value in the enum. Do not move it! + Invalid, +} + +const _ASSERT_SMALL_OP: () = assert!(std::mem::size_of::<Op>() == 1); + +impl From<u8> for Op { + fn from(num: u8) -> Self { + if num >= Self::Invalid as u8 { + return Self::Invalid; + } + + // SAFETY: As long as `Invalid` remains the last variant of the enum, + // and as long as variant values are not specified manually, this + // conversion is safe. + unsafe { std::mem::transmute(num) } + } +} + +pub enum OpArg { + None, + Uvarint, + Fixed, + Custom, +} + +impl Op { + pub fn arg_type(&self) -> OpArg { + match self { + Op::Constant + | Op::Attrs + | Op::PushWith + | Op::List + | Op::Interpolate + | Op::GetLocal + | Op::CloseScope + | Op::GetUpvalue + | Op::Finalise => OpArg::Uvarint, + + Op::Jump + | Op::JumpIfTrue + | Op::JumpIfFalse + | Op::JumpIfCatchable + | Op::JumpIfNotFound + | Op::JumpIfNoFinaliseRequest => OpArg::Fixed, + + Op::CoerceToString | Op::Closure | Op::ThunkClosure | Op::ThunkSuspended => { + OpArg::Custom + } + _ => OpArg::None, + } + } +} + +/// Position is used to represent where to capture an upvalue from. +#[derive(Clone, Copy)] +pub struct Position(pub u64); + +impl Position { + pub fn stack_index(idx: StackIdx) -> Self { + Position((idx.0 as u64) << 2) + } + + pub fn deferred_local(idx: StackIdx) -> Self { + Position(((idx.0 as u64) << 2) | 1) + } + + pub fn upvalue_index(idx: UpvalueIdx) -> Self { + Position(((idx.0 as u64) << 2) | 2) + } + + pub fn runtime_stack_index(&self) -> Option<StackIdx> { + if (self.0 & 0b11) == 0 { + return Some(StackIdx((self.0 >> 2) as usize)); + } + + None + } + + pub fn runtime_deferred_local(&self) -> Option<StackIdx> { + if (self.0 & 0b11) == 1 { + return Some(StackIdx((self.0 >> 2) as usize)); + } + + None + } + + pub fn runtime_upvalue_index(&self) -> Option<UpvalueIdx> { + if (self.0 & 0b11) == 2 { + return Some(UpvalueIdx((self.0 >> 2) as usize)); + } + + None + } +} + +#[cfg(test)] +mod position_tests { + use super::Position; // he-he + use super::{StackIdx, UpvalueIdx}; + + #[test] + fn test_stack_index_position() { + let idx = StackIdx(42); + let pos = Position::stack_index(idx); + let result = pos.runtime_stack_index(); + + assert_eq!(result, Some(idx)); + assert_eq!(pos.runtime_deferred_local(), None); + assert_eq!(pos.runtime_upvalue_index(), None); + } + + #[test] + fn test_deferred_local_position() { + let idx = StackIdx(42); + let pos = Position::deferred_local(idx); + let result = pos.runtime_deferred_local(); + + assert_eq!(result, Some(idx)); + assert_eq!(pos.runtime_stack_index(), None); + assert_eq!(pos.runtime_upvalue_index(), None); + } + + #[test] + fn test_upvalue_index_position() { + let idx = UpvalueIdx(42); + let pos = Position::upvalue_index(idx); + let result = pos.runtime_upvalue_index(); + + assert_eq!(result, Some(idx)); + assert_eq!(pos.runtime_stack_index(), None); + assert_eq!(pos.runtime_deferred_local(), None); + } } |