Till now there was no way in SIL to explicitly express a dependency of an instruction on any opened archetypes used by it. This was a cause of many errors and correctness issues. In many cases the code was moved around without taking into account these dependencies, which resulted in breaking the invariant that any uses of an opened archetype should be dominated by the definition of this archetype.
This patch does the following:
- Map opened archetypes to the instructions defining them, i.e. to open_existential instructions.
- Introduce a helper class SILOpenedArchetypesTracker for creating and maintaining such mappings.
- Introduce a helper class SILOpenedArchetypesState for providing a read-only API for looking up available opened archetypes.
- Each SIL instruction which uses an opened archetype as a type gets an additional opened archetype operand representing a dependency of the instruction on this archetype. These opened archetypes operands are an in-memory representation. They are not serialized. Instead, they are re-constructed when reading binary or textual SIL files.
- SILVerifier was extended to conduct more thorough checks related to the usage of opened archetypes.
It is a hint to the optimizer that the code, where this builtin is called, is on the fast path.
Specifically, the inliner takes it into account and increases the assumed benefit for code where the builtin is located.
Compared to the fastPath/slowPath builtins, this builtin can be placed into plain linear code and doesn't need to be used in conditions.
Compared to the @inline(__always) attribute, this builtin has also an effect on the caller function. Let's assume
foo() calls bar() contains onFastPath
and both foo and bar are small functions. Then if bar gets inlined into foo, the builtin also increases the chances that foo gets inlined.
This would not be the case if @inline(__always) is used just for bar.
When we emit calls to existential methods silgen produces a sequence of the
three instructions below:
open_existential_addr %0 : $*Pingable to $*@opened("1E467EB8-...") Pingable
witness_method $@opened("1E467EB8-...") Pingable, #Pingable.ping!1
apply %3<@opened("1E467EB8-...") Pingable>(%2)
This commit adds a new CSE-like pass that finds sequences of calls to protocol
methods and reuses the first two instructions open_existential_addr and
witness_method. The optimization finds arguments that must not alias and may not
escape and combines all of the existential method calls to use the same method
lookup. The optimization handles control flow by finding the top dominating
open_existential instruction, and uses that instruction.
related to rdar://22704464.
As there are no instructions left which produce multiple result values, this is a NFC regarding the generated SIL and generated code.
Although this commit is large, most changes are straightforward adoptions to the changes in the ValueBase and SILValue classes.
(libraries now)
It has been generally agreed that we need to do this reorg, and now
seems like the perfect time. Some major pass reorganization is in the
works.
This does not have to be the final word on the matter. The consensus
among those working on the code is that it's much better than what we
had and a better starting point for future bike shedding.
Note that the previous organization was designed to allow separate
analysis and optimization libraries. It turns out this is an
artificial distinction and not an important goal.
