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
computed property" errors when SILGen could determine that there was
an inout writeback alias, and have the code instead perform CSE of the
writebacks directly.
This means that we produce more efficient code, that a lot of things
now "just work" the way users would expect, and that the still erroneous
cases now get diagnosed with the "inout arguments are not allowed to
alias each other" error, which people have a hope of understanding.
There is still more to do here in terms of detecting identical cases,
but that was true of the previous diagnostic as well.
Swift SVN r20658
We want to generally treat blocks as heap objects until proven stack-able by escape analysis, like we do generally with other heap entities. The only place we should be exposed to stack blocks is when they're passed as arguments, so handle this by copy_block'ing any block arguments we get in the function prolog. Optimization can eliminate them when analysis shows the block doesn't escape or is already on the heap.
Swift SVN r16096
If all of the bindings in a pattern column are 'let' bindings, don't box the binding. If there is any 'var' in the column, conservatively fall back to binding a box. Factor out the logic for producing an initialization for a variable into an new emitInitializationForVarDecl method that SILGenPattern can use. Add a 'copyInto' method to RValue that can bind a copy of an rvalue to an Initialization.
This doesn't use Chris's new +0 ManagedValue optimization yet, so we end up with an extra copy_value when the value is bound that might still be avoidable.
Swift SVN r12903
as ::copy, but doesn't have the assertion that the copied-from
value has a cleanup associated with it. Various bits of silgen
are trafficing in SILValue's when they are known to be live, and
this allows us to use the centralized "copy" instead of rolling
it ourselves inline.
Swift SVN r11929
making LValue ManagedValues, and switch SILGenLValue to use
this form of managed value consistently for lvalues, instead of
using unmanaged values in some cases. NFC.
Swift SVN r11878
with qualifiers on it, we have two distinct types:
- LValueType(T) aka @lvalue T, which is used for mutable values on the LHS of an
assignment in the typechecker.
- InOutType(T) aka @inout T, which is used for @inout arguments, and the implicit
@inout self argument of mutable methods on value types. This type is also used
at the SIL level for address types.
While I detangled a number of cases that were checking for LValueType (without checking
qualifiers) and only meant @inout or @lvalue, there is more to be done here. Notably,
getRValueType() still strips @inout, which is totally and unbearably wrong.
Swift SVN r11727
emit the cleanup for the initializing expression when the expression was
complete, instead of at the end of the let decl scope (releasing things
too early).
This fixes rdar://15689514, thanks to DaveA for the great testcase.
Swift SVN r11516
of having to lower to an RValue.
This is valuable because we can often emit an expression to a
desired abstraction level more efficiently than just emitting
it to minimal abstraction and then generalizing.
Swift SVN r10455
If a struct has [unowned] fields and an implicit elementwise constructor, then the constructor receives a strong reference argument corresponding to the unowned field, and we have to introduce that conversion as part of the construction.
Swift SVN r8207
Tuple exploding happens during RValue construction, so changed the constructor and addElement() method to take the location parameter. The imploding happens on RValue::forwardAsSingleValue and RValue::getAsSingleValue(). Make sure the right SIL locations are passed to all of these
Also, added some missing locations in pattern matching code.
Swift SVN r7916
