Enum rustc_middle::mir::syntax::TerminatorKind
source · [−]pub enum TerminatorKind<'tcx> {
Show 15 variants
Goto {
target: BasicBlock,
},
SwitchInt {
discr: Operand<'tcx>,
switch_ty: Ty<'tcx>,
targets: SwitchTargets,
},
Resume,
Abort,
Return,
Unreachable,
Drop {
place: Place<'tcx>,
target: BasicBlock,
unwind: Option<BasicBlock>,
},
DropAndReplace {
place: Place<'tcx>,
value: Operand<'tcx>,
target: BasicBlock,
unwind: Option<BasicBlock>,
},
Call {
func: Operand<'tcx>,
args: Vec<Operand<'tcx>>,
destination: Place<'tcx>,
target: Option<BasicBlock>,
cleanup: Option<BasicBlock>,
from_hir_call: bool,
fn_span: Span,
},
Assert {
cond: Operand<'tcx>,
expected: bool,
msg: AssertMessage<'tcx>,
target: BasicBlock,
cleanup: Option<BasicBlock>,
},
Yield {
value: Operand<'tcx>,
resume: BasicBlock,
resume_arg: Place<'tcx>,
drop: Option<BasicBlock>,
},
GeneratorDrop,
FalseEdge {
real_target: BasicBlock,
imaginary_target: BasicBlock,
},
FalseUnwind {
real_target: BasicBlock,
unwind: Option<BasicBlock>,
},
InlineAsm {
template: &'tcx [InlineAsmTemplatePiece],
operands: Vec<InlineAsmOperand<'tcx>>,
options: InlineAsmOptions,
line_spans: &'tcx [Span],
destination: Option<BasicBlock>,
cleanup: Option<BasicBlock>,
},
}
Expand description
The various kinds of terminators, representing ways of exiting from a basic block.
A note on unwinding: Panics may occur during the execution of some terminators. Depending on the
-C panic
flag, this may either cause the program to abort or the call stack to unwind. Such
terminators have a cleanup: Option<BasicBlock>
field on them. If stack unwinding occurs, then
once the current function is reached, execution continues at the given basic block, if any. If
cleanup
is None
then no cleanup is performed, and the stack continues unwinding. This is
equivalent to the execution of a Resume
terminator.
The basic block pointed to by a cleanup
field must have its cleanup
flag set. cleanup
basic blocks have a couple restrictions:
- All
cleanup
fields in them must beNone
. Return
terminators are not allowed in them.Abort
andUnwind
terminators are.- All other basic blocks (in the current body) that are reachable from
cleanup
basic blocks must also becleanup
. This is a part of the type system and checked statically, so it is still an error to have such an edge in the CFG even if it’s known that it won’t be taken at runtime.
Variants
Goto
Fields
target: BasicBlock
Block has one successor; we continue execution there.
SwitchInt
Fields
discr: Operand<'tcx>
The discriminant value being tested.
switch_ty: Ty<'tcx>
The type of value being tested.
This is always the same as the type of discr
.
FIXME: remove this redundant information. Currently, it is relied on by pretty-printing.
targets: SwitchTargets
Switches based on the computed value.
First, evaluates the discr
operand. The type of the operand must be a signed or unsigned
integer, char, or bool, and must match the given type. Then, if the list of switch targets
contains the computed value, continues execution at the associated basic block. Otherwise,
continues execution at the “otherwise” basic block.
Target values may not appear more than once.
Resume
Indicates that the landing pad is finished and that the process should continue unwinding.
Like a return, this marks the end of this invocation of the function.
Only permitted in cleanup blocks. Resume
is not permitted with -C unwind=abort
after
deaggregation runs.
Abort
Indicates that the landing pad is finished and that the process should abort.
Used to prevent unwinding for foreign items or with -C unwind=abort
. Only permitted in
cleanup blocks.
Return
Returns from the function.
Like function calls, the exact semantics of returns in Rust are unclear. Returning very
likely at least assigns the value currently in the return place (_0
) to the place
specified in the associated Call
terminator in the calling function, as if assigned via
dest = move _0
. It might additionally do other things, like have side-effects in the
aliasing model.
If the body is a generator body, this has slightly different semantics; it instead causes a
GeneratorState::Returned(_0)
to be created (as if by an Aggregate
rvalue) and assigned
to the return place.
Unreachable
Indicates a terminator that can never be reached.
Executing this terminator is UB.
Drop
The behavior of this statement differs significantly before and after drop elaboration.
After drop elaboration, Drop
executes the drop glue for the specified place, after which
it continues execution/unwinds at the given basic blocks. It is possible that executing drop
glue is special - this would be part of Rust’s memory model. (FIXME: due we have an
issue tracking if drop glue has any interesting semantics in addition to those of a function
call?)
Drop
before drop elaboration is a conditional execution of the drop glue. Specifically, the
Drop
will be executed if…
Needs clarification: End of that sentence. This in effect should document the exact behavior of drop elaboration. The following sounds vaguely right, but I’m not quite sure:
The drop glue is executed if, among all statements executed within this
Body
, an assignment to the place or one of its “parents” occurred more recently than a move out of it. This does not consider indirect assignments.
DropAndReplace
Drops the place and assigns a new value to it.
This first performs the exact same operation as the pre drop-elaboration Drop
terminator;
it then additionally assigns the value
to the place
as if by an assignment statement.
This assignment occurs both in the unwind and the regular code paths. The semantics are best
explained by the elaboration:
BB0 {
DropAndReplace(P <- V, goto BB1, unwind BB2)
}
becomes
BB0 {
Drop(P, goto BB1, unwind BB2)
}
BB1 {
// P is now uninitialized
P <- V
}
BB2 {
// P is now uninitialized -- its dtor panicked
P <- V
}
Disallowed after drop elaboration.
Call
Fields
func: Operand<'tcx>
The function that’s being called.
args: Vec<Operand<'tcx>>
Arguments the function is called with. These are owned by the callee, which is free to modify them. This allows the memory occupied by “by-value” arguments to be reused across function calls without duplicating the contents.
destination: Place<'tcx>
Where the returned value will be written
target: Option<BasicBlock>
Where to go after this call returns. If none, the call necessarily diverges.
cleanup: Option<BasicBlock>
Cleanups to be done if the call unwinds.
from_hir_call: bool
true
if this is from a call in HIR rather than from an overloaded
operator. True for overloaded function call.
fn_span: Span
This Span
is the span of the function, without the dot and receiver
(e.g. foo(a, b)
in x.foo(a, b)
Roughly speaking, evaluates the func
operand and the arguments, and starts execution of
the referred to function. The operand types must match the argument types of the function.
The return place type must match the return type. The type of the func
operand must be
callable, meaning either a function pointer, a function type, or a closure type.
Needs clarification: The exact semantics of this. Current backends rely on move
operands not aliasing the return place. It is unclear how this is justified in MIR, see
#71117.
Assert
Fields
cond: Operand<'tcx>
expected: bool
msg: AssertMessage<'tcx>
target: BasicBlock
cleanup: Option<BasicBlock>
Evaluates the operand, which must have type bool
. If it is not equal to expected
,
initiates a panic. Initiating a panic corresponds to a Call
terminator with some
unspecified constant as the function to call, all the operands stored in the AssertMessage
as parameters, and None
for the destination. Keep in mind that the cleanup
path is not
necessarily executed even in the case of a panic, for example in -C panic=abort
. If the
assertion does not fail, execution continues at the specified basic block.
Yield
Fields
value: Operand<'tcx>
The value to return.
resume: BasicBlock
Where to resume to.
resume_arg: Place<'tcx>
The place to store the resume argument in.
drop: Option<BasicBlock>
Cleanup to be done if the generator is dropped at this suspend point.
Marks a suspend point.
Like Return
terminators in generator bodies, this computes value
and then a
GeneratorState::Yielded(value)
as if by Aggregate
rvalue. That value is then assigned to
the return place of the function calling this one, and execution continues in the calling
function. When next invoked with the same first argument, execution of this function
continues at the resume
basic block, with the second argument written to the resume_arg
place. If the generator is dropped before then, the drop
basic block is invoked.
Not permitted in bodies that are not generator bodies, or after generator lowering.
Needs clarification: What about the evaluation order of the resume_arg
and value
?
GeneratorDrop
Indicates the end of dropping a generator.
Semantically just a return
(from the generators drop glue). Only permitted in the same situations
as yield
.
Needs clarification: Is that even correct? The generator drop code is always confusing to me, because it’s not even really in the current body.
Needs clarification: Are there type system constraints on these terminators? Should
there be a “block type” like cleanup
blocks for them?
FalseEdge
Fields
real_target: BasicBlock
The target normal control flow will take.
imaginary_target: BasicBlock
A block control flow could conceptually jump to, but won’t in practice.
A block where control flow only ever takes one real path, but borrowck needs to be more conservative.
At runtime this is semantically just a goto.
Disallowed after drop elaboration.
FalseUnwind
Fields
real_target: BasicBlock
The target normal control flow will take.
unwind: Option<BasicBlock>
The imaginary cleanup block link. This particular path will never be taken
in practice, but in order to avoid fragility we want to always
consider it in borrowck. We don’t want to accept programs which
pass borrowck only when panic=abort
or some assertions are disabled
due to release vs. debug mode builds. This needs to be an Option
because
of the remove_noop_landing_pads
and abort_unwinding_calls
passes.
A terminator for blocks that only take one path in reality, but where we reserve the right to unwind in borrowck, even if it won’t happen in practice. This can arise in infinite loops with no function calls for example.
At runtime this is semantically just a goto.
Disallowed after drop elaboration.
InlineAsm
Fields
template: &'tcx [InlineAsmTemplatePiece]
The template for the inline assembly, with placeholders.
operands: Vec<InlineAsmOperand<'tcx>>
The operands for the inline assembly, as Operand
s or Place
s.
options: InlineAsmOptions
Miscellaneous options for the inline assembly.
line_spans: &'tcx [Span]
Source spans for each line of the inline assembly code. These are used to map assembler errors back to the line in the source code.
destination: Option<BasicBlock>
Destination block after the inline assembly returns, unless it is diverging (InlineAsmOptions::NORETURN).
cleanup: Option<BasicBlock>
Cleanup to be done if the inline assembly unwinds. This is present if and only if InlineAsmOptions::MAY_UNWIND is set.
Block ends with an inline assembly block. This is a terminator since inline assembly is allowed to diverge.
Implementations
sourceimpl<'tcx> TerminatorKind<'tcx>
impl<'tcx> TerminatorKind<'tcx>
pub fn if_(
tcx: TyCtxt<'tcx>,
cond: Operand<'tcx>,
t: BasicBlock,
f: BasicBlock
) -> TerminatorKind<'tcx>
pub fn successors(&self) -> Successors<'_>
pub fn successors_mut(&mut self) -> SuccessorsMut<'_>
pub fn unwind(&self) -> Option<&Option<BasicBlock>>
pub fn unwind_mut(&mut self) -> Option<&mut Option<BasicBlock>>
pub fn as_switch(&self) -> Option<(&Operand<'tcx>, Ty<'tcx>, &SwitchTargets)>
pub fn as_goto(&self) -> Option<BasicBlock>
sourceimpl<'tcx> TerminatorKind<'tcx>
impl<'tcx> TerminatorKind<'tcx>
sourcepub fn fmt_head<W: Write>(&self, fmt: &mut W) -> Result
pub fn fmt_head<W: Write>(&self, fmt: &mut W) -> Result
Writes the “head” part of the terminator; that is, its name and the data it uses to pick the successor basic block, if any. The only information not included is the list of possible successors, which may be rendered differently between the text and the graphviz format.
sourcepub fn fmt_successor_labels(&self) -> Vec<Cow<'static, str>>
pub fn fmt_successor_labels(&self) -> Vec<Cow<'static, str>>
Returns the list of labels for the edges to the successor basic blocks.
Trait Implementations
sourceimpl<'tcx> Clone for TerminatorKind<'tcx>
impl<'tcx> Clone for TerminatorKind<'tcx>
sourcefn clone(&self) -> TerminatorKind<'tcx>
fn clone(&self) -> TerminatorKind<'tcx>
1.0.0 · sourcefn clone_from(&mut self, source: &Self)
fn clone_from(&mut self, source: &Self)
source
. Read moresourceimpl<'tcx> Debug for TerminatorKind<'tcx>
impl<'tcx> Debug for TerminatorKind<'tcx>
sourceimpl<'tcx, __D: TyDecoder<I = TyCtxt<'tcx>>> Decodable<__D> for TerminatorKind<'tcx>
impl<'tcx, __D: TyDecoder<I = TyCtxt<'tcx>>> Decodable<__D> for TerminatorKind<'tcx>
sourceimpl<'tcx, __E: TyEncoder<I = TyCtxt<'tcx>>> Encodable<__E> for TerminatorKind<'tcx>
impl<'tcx, __E: TyEncoder<I = TyCtxt<'tcx>>> Encodable<__E> for TerminatorKind<'tcx>
sourceimpl<'tcx> Hash for TerminatorKind<'tcx>
impl<'tcx> Hash for TerminatorKind<'tcx>
sourceimpl<'tcx, '__ctx> HashStable<StableHashingContext<'__ctx>> for TerminatorKind<'tcx>
impl<'tcx, '__ctx> HashStable<StableHashingContext<'__ctx>> for TerminatorKind<'tcx>
fn hash_stable(
&self,
__hcx: &mut StableHashingContext<'__ctx>,
__hasher: &mut StableHasher
)
sourceimpl<'tcx> PartialEq<TerminatorKind<'tcx>> for TerminatorKind<'tcx>
impl<'tcx> PartialEq<TerminatorKind<'tcx>> for TerminatorKind<'tcx>
sourcefn eq(&self, other: &TerminatorKind<'tcx>) -> bool
fn eq(&self, other: &TerminatorKind<'tcx>) -> bool
sourceimpl<'tcx> TypeFoldable<'tcx> for TerminatorKind<'tcx>
impl<'tcx> TypeFoldable<'tcx> for TerminatorKind<'tcx>
sourcefn try_fold_with<__F: FallibleTypeFolder<'tcx>>(
self,
__folder: &mut __F
) -> Result<Self, __F::Error>
fn try_fold_with<__F: FallibleTypeFolder<'tcx>>(
self,
__folder: &mut __F
) -> Result<Self, __F::Error>
sourcefn fold_with<F: TypeFolder<'tcx>>(self, folder: &mut F) -> Self
fn fold_with<F: TypeFolder<'tcx>>(self, folder: &mut F) -> Self
try_fold_with
for use with infallible
folders. Do not override this method, to ensure coherence with
try_fold_with
. Read moresourceimpl<'tcx> TypeVisitable<'tcx> for TerminatorKind<'tcx>
impl<'tcx> TypeVisitable<'tcx> for TerminatorKind<'tcx>
sourcefn visit_with<__V: TypeVisitor<'tcx>>(
&self,
__visitor: &mut __V
) -> ControlFlow<__V::BreakTy>
fn visit_with<__V: TypeVisitor<'tcx>>(
&self,
__visitor: &mut __V
) -> ControlFlow<__V::BreakTy>
sourcefn has_vars_bound_at_or_above(&self, binder: DebruijnIndex) -> bool
fn has_vars_bound_at_or_above(&self, binder: DebruijnIndex) -> bool
true
if self
has any late-bound regions that are either
bound by binder
or bound by some binder outside of binder
.
If binder
is ty::INNERMOST
, this indicates whether
there are any late-bound regions that appear free. Read moresourcefn has_vars_bound_above(&self, binder: DebruijnIndex) -> bool
fn has_vars_bound_above(&self, binder: DebruijnIndex) -> bool
true
if this self
has any regions that escape binder
(and
hence are not bound by it). Read morefn has_escaping_bound_vars(&self) -> bool
fn has_type_flags(&self, flags: TypeFlags) -> bool
fn has_projections(&self) -> bool
fn has_opaque_types(&self) -> bool
fn references_error(&self) -> bool
fn error_reported(&self) -> Option<ErrorGuaranteed>
fn has_param_types_or_consts(&self) -> bool
fn has_infer_regions(&self) -> bool
fn has_infer_types(&self) -> bool
fn has_infer_types_or_consts(&self) -> bool
fn needs_infer(&self) -> bool
fn has_placeholders(&self) -> bool
fn needs_subst(&self) -> bool
sourcefn has_free_regions(&self) -> bool
fn has_free_regions(&self) -> bool
fn has_erased_regions(&self) -> bool
sourcefn has_erasable_regions(&self) -> bool
fn has_erasable_regions(&self) -> bool
sourcefn is_global(&self) -> bool
fn is_global(&self) -> bool
sourcefn has_late_bound_regions(&self) -> bool
fn has_late_bound_regions(&self) -> bool
sourcefn still_further_specializable(&self) -> bool
fn still_further_specializable(&self) -> bool
impl
specialization. Read moreimpl<'tcx> StructuralPartialEq for TerminatorKind<'tcx>
Auto Trait Implementations
impl<'tcx> !RefUnwindSafe for TerminatorKind<'tcx>
impl<'tcx> !Send for TerminatorKind<'tcx>
impl<'tcx> !Sync for TerminatorKind<'tcx>
impl<'tcx> Unpin for TerminatorKind<'tcx>
impl<'tcx> !UnwindSafe for TerminatorKind<'tcx>
Blanket Implementations
sourceimpl<T> BorrowMut<T> for Twhere
T: ?Sized,
impl<T> BorrowMut<T> for Twhere
T: ?Sized,
const: unstable · sourcefn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
sourceimpl<Ctxt, T> DepNodeParams<Ctxt> for Twhere
Ctxt: DepContext,
T: for<'a> HashStable<StableHashingContext<'a>> + Debug,
impl<Ctxt, T> DepNodeParams<Ctxt> for Twhere
Ctxt: DepContext,
T: for<'a> HashStable<StableHashingContext<'a>> + Debug,
default fn fingerprint_style() -> FingerprintStyle
sourcedefault fn to_fingerprint(&self, tcx: Ctxt) -> Fingerprint
default fn to_fingerprint(&self, tcx: Ctxt) -> Fingerprint
default fn to_debug_str(&self, Ctxt) -> String
sourcedefault fn recover(Ctxt, &DepNode<<Ctxt as DepContext>::DepKind>) -> Option<T>
default fn recover(Ctxt, &DepNode<<Ctxt as DepContext>::DepKind>) -> Option<T>
DepNode
,
something which is needed when forcing DepNode
s during red-green
evaluation. The query system will only call this method if
fingerprint_style()
is not FingerprintStyle::Opaque
.
It is always valid to return None
here, in which case incremental
compilation will treat the query as having changed instead of forcing it. Read moresourceimpl<T, R> InternIteratorElement<T, R> for T
impl<T, R> InternIteratorElement<T, R> for T
type Output = R
fn intern_with<I, F>(iter: I, f: F) -> <T as InternIteratorElement<T, R>>::Outputwhere
I: Iterator<Item = T>,
F: FnOnce(&[T]) -> R,
sourceimpl<T> MaybeResult<T> for T
impl<T> MaybeResult<T> for T
sourceimpl<CTX, T> Value<CTX> for Twhere
CTX: DepContext,
impl<CTX, T> Value<CTX> for Twhere
CTX: DepContext,
default fn from_cycle_error(tcx: CTX) -> T
impl<'a, T> Captures<'a> for Twhere
T: ?Sized,
Layout
Note: Most layout information is completely unstable and may even differ between compilations. The only exception is types with certain repr(...)
attributes. Please see the Rust Reference’s “Type Layout” chapter for details on type layout guarantees.
Size: 96 bytes
Size for each variant:
Goto
: 12 bytesSwitchInt
: 88 bytesResume
: 0 bytesAbort
: 0 bytesReturn
: 0 bytesUnreachable
: 0 bytesDrop
: 32 bytesDropAndReplace
: 56 bytesCall
: 96 bytesAssert
: 96 bytesYield
: 56 bytesGeneratorDrop
: 0 bytesFalseEdge
: 16 bytesFalseUnwind
: 16 bytesInlineAsm
: 80 bytes