Similarly to how we've always handled parameter types, we
now recursively expand tuples in result types and separately
determine a result convention for each result.
The most important code-generation change here is that
indirect results are now returned separately from each
other and from any direct results. It is generally far
better, when receiving an indirect result, to receive it
as an independent result; the caller is much more likely
to be able to directly receive the result in the address
they want to initialize, rather than having to receive it
in temporary memory and then copy parts of it into the
target.
The most important conceptual change here that clients and
producers of SIL must be aware of is the new distinction
between a SILFunctionType's *parameters* and its *argument
list*. The former is just the formal parameters, derived
purely from the parameter types of the original function;
indirect results are no longer in this list. The latter
includes the indirect result arguments; as always, all
the indirect results strictly precede the parameters.
Apply instructions and entry block arguments follow the
argument list, not the parameter list.
A relatively minor change is that there can now be multiple
direct results, each with its own result convention.
This is a minor change because I've chosen to leave
return instructions as taking a single operand and
apply instructions as producing a single result; when
the type describes multiple results, they are implicitly
bound up in a tuple. It might make sense to split these
up and allow e.g. return instructions to take a list
of operands; however, it's not clear what to do on the
caller side, and this would be a major change that can
be separated out from this already over-large patch.
Unsurprisingly, the most invasive changes here are in
SILGen; this requires substantial reworking of both call
emission and reabstraction. It also proved important
to switch several SILGen operations over to work with
RValue instead of ManagedValue, since otherwise they
would be forced to spuriously "implode" buffers.
This improves support for promoting to and generating
unchecked_ref_cast so we no longer need unchecked_ref_bit_cast, which
will just go away in the next commit.
Swift SVN r32597
_unsafeCastReference allows casting of any references types, regardless
of whether they are references to objects or class existentials. The
implementation is responsible for converting between representations.
_unsafeCastReference provides a dynamic check to ensure that the source
and dest are both actually references. If not, the implementation will
trap at runtime. Generally, the optimizer can prove that the source
and dest are references, and promote this cast to an
unchecked_ref_cast bitcast. There is no dynamic check that the
references types are compatible.
This differs from unsafeDownCast in two ways:
(1) The source and dest types are not statically typed
AnyObjects. Therefore, unsafeCastReference can be used when the
surrounding code dynamically handles both reference and nonreference
types.
(2) The source and dest also need not dynamically conform to AnyObject.
Either side of the cast may be a class existential. The primary
requirement is that the source and dest refer to the same reference
counted object.
Swift SVN r32588
This fixes Builtin.reinterpretCast for used in generic code.
Previously, casting from trivial to nontrivial dynamic types would
result in prematurely freeing the object. Now the result of the cast
will be retained if necessary and cleanup up independently from the
source of the cast.
Swift SVN r30310
This fixes a bug where reinterpret cast would cause an object to be
freed prematurely. In the common case of casting a known reference
type to another reference type, we still elide the extra retain/release.
And finally, this builtin should have identical semantics for concrete
types and unbounds generics.
Swift SVN r30217
This new method eliminates repeated code sequences that all create an
unchecked_trivial_bit_cast if the result type is trivial or
unchecked_ref_bit_cast otherwise.
NFC.
Swift SVN r29486
Currently they do nothing but allow stdlib code to use regular (Bool)
types. However, soon the wrappers for the _native variants will
provide point-of-use sanity checking.
These need to be fully generic to support class protocols and
single-payload enums (not just for optional). It also avoids a massive
amount of overloading for all the reference type variations
(AnyObject, Native, Unknown, Bridge) x 2 for optional versions of
each.
Because the wrapper is generic, type checking had to be deferred until
IRGen. Generating code for the wrapper itself will result in an
IRGen-time type error. They need to be transparent anyway for proper
diagnostics, but also must be internal.
Note that the similar external API type checks ok because it
forces conformance to AnyObject.
The sanity checks are disabled because our current facilities for
unsafe type casting are incomplete and unsound. SILCombine can
remove UnsafeMutablePointer and RawPointer casts by assuming layout
compatibility. IRGen will later discover layout incompatibility and
generate a trap.
I'll send out a proposal for improving the casting situation so we can
get the sanity checks back.
Swift SVN r28057
This reverts commit 64e9f11211a19fa603f5bc2d2bea171a9b07d3fa.
I think this is breaking ExistentialCollection test in the
Release + stdlib asserts build.
Swift SVN r27947
The wrappers for the _native variants provide point-of-use sanity checking.
They also allows stdlib code to use regular (Bool) types.
These need to be fully generic to support class protocols. It also
avoids a massive amount of overloading for all the reference type
variations (AnyObject, Native, Unknown, Bridge) x 2 for optional
versions of each.
Because the wrapper is generic, type checking had to be deferred until
IRGen. Generating code for the wrapper itself will result in an
IRGen-time type error. They need to be transparent anyway for proper
diagnostics, but also must be internal.
The external API passes type checks because it forces conformance to AnyObject.
Swift SVN r27930
Preparation to fix <rdar://problem/18151694> Add Builtin.checkUnique
to avoid lost Array copies.
This adds the following new builtins:
isUnique : <T> (inout T[?]) -> Int1
isUniqueOrPinned : <T> (inout T[?]) -> Int1
These builtins take an inout object reference and return a
boolean. Passing the reference inout forces the optimizer to preserve
a retain distinct from what’s required to maintain lifetime for any of
the reference's source-level copies, because the called function is
allowed to replace the reference, thereby releasing the referent.
Before this change, the API entry points for uniqueness checking
already took an inout reference. However, after full inlining, it was
possible for two source-level variables that reference the same object
to appear to be the same variable from the optimizer's perspective
because an address to the variable was longer taken at the point of
checking uniqueness. Consequently the optimizer could remove
"redundant" copies which were actually needed to implement
copy-on-write semantics. With a builtin, the variable whose reference
is being checked for uniqueness appears mutable at the level of an
individual SIL instruction.
The kind of reference count checking that Builtin.isUnique performs
depends on the argument type:
- Native object types are directly checked by reading the
strong reference count:
(Builtin.NativeObject, known native class reference)
- Objective-C object types require an additional check that the
dynamic object type uses native swift reference counting:
(Builtin.UnknownObject, unknown class reference, class existential)
- Bridged object types allow the dymanic object type check to be
bypassed based on the pointer encoding:
(Builtin.BridgeObject)
Any of the above types may also be wrapped in an optional. If the
static argument type is optional, then a null check is also performed.
Thus, isUnique only returns true for non-null, native swift object
references with a strong reference count of one.
isUniqueOrPinned has the same semantics as isUnique except that it
also returns true if the object is marked pinned regardless of the
reference count. This allows for simultaneous non-structural
modification of multiple subobjects.
In some cases, the standard library can dynamically determine that it
has a native reference even though the static type is a bridge or
unknown object. Unsafe variants of the builtin are available to allow
the additional pointer bit mask and dynamic class lookup to be
bypassed in these cases:
isUnique_native : <T> (inout T[?]) -> Int1
isUniqueOrPinned_native : <T> (inout T[?]) -> Int1
These builtins perform an implicit cast to NativeObject before
checking uniqueness. There’s no way at SIL level to cast the address
of a reference, so we need to encapsulate this operation as part of
the builtin.
Swift SVN r27887
the call instead of during the formal evaluation of the argument.
This is the last major chunk of the semantic changes proposed
in the accessors document. It has two purposes, both related
to the fact that it shortens the duration of the formal access.
First, the change isolates later evaluations (as long as they
precede the call) from the formal access, preventing them from
spuriously seeing unspecified behavior. For example::
foo(&array[0], bar(array))
Here the value passed to bar is a proper copy of 'array',
and if bar() decides to stash it aside, any modifications
to 'array[0]' made by foo() will not spontaneously appear
in the copy. (In contrast, if something caused a copy of
'array' during foo()'s execution, that copy would violate
our formal access rules and would therefore be allowed to
have an arbitrary value at index 0.)
Second, when a mutating access uses a pinning addressor, the
change limits the amount of arbitrary code that falls between
the pin and unpin. For example::
array[0] += countNodes(subtree)
Previously, we would begin the access to array[0] before the
call to countNodes(). To eliminate the pin and unpin, the
optimizer would have needed to prove that countNodes didn't
access the same array. With this change, the call is evaluated
first, and the access instead begins immediately before the call
to +=. Since that operator is easily inlined, it becomes
straightforward to eliminate the pin/unpin.
A number of other changes got bundled up with this in ways that
are hard to tease apart. In particular:
- RValueSource is now ArgumentSource and can now store LValues.
- It is now illegal to use emitRValue to emit an l-value.
- Call argument emission is now smart enough to emit tuple
shuffles itself, applying abstraction patterns in reverse
through the shuffle. It also evaluates varargs elements
directly into the array.
- AllowPlusZero has been split in two. AllowImmediatePlusZero
is useful when you are going to immediately consume the value;
this is good enough to avoid copies/retains when reading a 'var'.
AllowGuaranteedPlusZero is useful when you need a stronger
guarantee, e.g. when arbitrary code might intervene between
evaluation and use; it's still good enough to avoid copies
from a 'let'. The upshot is that we're now a lot smarter
about generally avoiding retains on lets, but we've also
gotten properly paranoid about calling non-mutating methods
on vars.
(Note that you can't necessarily avoid a copy when passing
something in a var to an @in_guaranteed parameter! You
first have to prove that nothing can assign to the var during
the call. That should be easy as long as the var hasn't
escaped, but that does need to be proven first, so we can't
do it in SILGen.)
Swift SVN r24709
use a thin function type.
We still need thin-function-to-RawPointer conversions
for generic code, but that's fixable with some sort of
partial_apply_thin_recoverable instruction.
Swift SVN r24364
NFC for now, but I've also added the infrastructure to allow
"early emission", i.e. emission directly from the original
RValueSource, which can be useful either as an optimization
(e.g. for Builtin.initialize) or a requirement for particularly
hacky SIL intrinsics should we need them (and I'm thinking of
needing one).
Swift SVN r23953
