I forgot about this part of the design when I was working on this. To ensure
that the whole design works as expected, I included a small end-to-end test
using an experimental design for simd that uses polymorphic builtins that test
this functionally.
NOTE: The experimental design is only intended to exercise the code functionally.
rdar://48248417
TLDR: This patch introduces a new kind of builtin, "a polymorphic builtin". One
calls it like any other builtin, e.x.:
```
Builtin.generic_add(x, y)
```
but it has a contract: it must be specialized to a concrete builtin by the time
we hit Lowered SIL. In this commit, I add support for the following generic
operations:
Type | Op
------------------------
FloatOrVector |FAdd
FloatOrVector |FDiv
FloatOrVector |FMul
FloatOrVector |FRem
FloatOrVector |FSub
IntegerOrVector|AShr
IntegerOrVector|Add
IntegerOrVector|And
IntegerOrVector|ExactSDiv
IntegerOrVector|ExactUDiv
IntegerOrVector|LShr
IntegerOrVector|Mul
IntegerOrVector|Or
IntegerOrVector|SDiv
IntegerOrVector|SRem
IntegerOrVector|Shl
IntegerOrVector|Sub
IntegerOrVector|UDiv
IntegerOrVector|Xor
Integer |URem
NOTE: I only implemented support for the builtins in SIL and in SILGen. I am
going to implement the optimizer parts of this in a separate series of commits.
DISCUSSION
----------
Today there are polymorphic like instructions in LLVM-IR. Yet, at the
swift and SIL level we represent these operations instead as Builtins whose
names are resolved by splatting the builtin into the name. For example, adding
two things in LLVM:
```
%2 = add i64 %0, %1
%2 = add <2 x i64> %0, %1
%2 = add <4 x i64> %0, %1
%2 = add <8 x i64> %0, %1
```
Each of the add operations are done by the same polymorphic instruction. In
constrast, we splat out these Builtins in swift today, i.e.:
```
let x, y: Builtin.Int32
Builtin.add_Int32(x, y)
let x, y: Builtin.Vec4xInt32
Builtin.add_Vec4xInt32(x, y)
...
```
In SIL, we translate these verbatim and then IRGen just lowers them to the
appropriate polymorphic instruction. Beyond being verbose, these prevent these
Builtins (which need static types) from being used in polymorphic contexts where
we can guarantee that eventually a static type will be provided.
In contrast, the polymorphic builtins introduced in this commit can be passed
any type, with the proviso that the expert user using this feature can guarantee
that before we reach Lowered SIL, the generic_add has been eliminated. This is
enforced by IRGen asserting if passed such a builtin and by the SILVerifier
checking that the underlying builtin is never called once the module is in
Lowered SIL.
In forthcoming commits, I am going to add two optimizations that give the stdlib
tool writer the tools needed to use this builtin:
1. I am going to add an optimization to constant propagation that changes a
"generic_*" op to the type of its argument if the argument is a type that is
valid for the builtin (i.e. integer or vector).
2. I am going to teach the SILCloner how to specialize these as it inlines. This
ensures that when we transparent inline, we specialize the builtin automatically
and can then form SSA at -Onone using predictable memory access operations.
The main implication around these polymorphic builtins are that if an author is
not able to specialize the builtin, they need to ensure that after constant
propagation, the generic builtin has been DCEed. The general rules are that the
-Onone optimizer will constant fold branches with constant integer operands. So
if one can use a bool of some sort to trigger the operation, one can be
guaranteed that the code will not codegen. I am considering putting in some sort
of diagnostic to ensure that the stdlib writer has a good experience (e.x. get
an error instead of crashing the compiler).
Returns `true` if `T.Type` is known to refer to a concrete type. The
implementation allows for the optimizer to specialize this at -O and
eliminate conditional code.
Includes `Swift._isConcrete<T>(T.Type) -> Bool` wrapper function.
A function may be eliminated as dead code after initial builtin lowering
occurs. When this happens, an entry in the profile symbol table for the
function is not guaranteed. Its coverage record should be dropped.
rdar://42564768
When we generate code that asks for complete metadata for a fully concrete specific type that
doesn't have trivial metadata access, like `(Int, String)` or `[String: [Any]]`,
generate a cache variable that points to a mangled name, and use a common accessor function
that turns that cache variable into a pointer to the instantiated metadata. This saves a bunch
of code size, and should have minimal runtime impact, since the demangling of any string only
has to happen once.
This mostly just works, though it exposed a couple of issues:
- Mangling a type ref including objc protocols didn't cause the objc protocol record to get
instantiated. Fixed as part of this patch.
- The runtime type demangler doesn't correctly handle retroactive conformances. If there are
multiple retroactive conformances in a process at runtime, then even though the mangled string
refers to a specific conformance, the runtime still just picks one without listening to the
mangler. This is left to fix later, rdar://problem/53828345.
There is some more follow-up work that we can do to further improve the gains:
- We could improve the runtime-provided entry points, adding versions that don't require size
to be cached, and which can handle arbitrary metadata requests. This would allow for mangled
names to also be used for incomplete metadata accesses and improve code size of some generic
type accessors. However, we'd only be able to take advantage of the new entry points in
OSes that ship a new runtime.
- We could choose to always symbolic reference all type references, which would generally reduce
the size of mangled strings, as well as make runtime demangling more efficient, since it wouldn't
need to hit the runtime caches. This would however require that we be able to handle symbolic
references across files in the MetadataReader in order to avoid regressing remote mirror
functionality.
To display a failure message in the debugger, create a function in the debug info which has the name of the failure message.
The debug location of the trap/cond_fail is then wrapped into this function and the function is declared as "inlined".
In case the debugger stops at the trap instruction, it displays the inline function, which looks like the failure message.
For example:
* thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0)
frame #0: 0x0000000100000cbf a.out`testit3(_:) [inlined] Unexpectedly found nil while unwrapping an Optional value at test.swift:14:11 [opt]
11
12 @inline(never)
13 func testit(_ a: Int?) -> Int {
-> 14 return a!
15 }
16
This change is currently not enabled by default, but can be enabled with the option "-Xllvm -enable-trap-debug-info".
Enabling this feature needs some changes in lldb. When the lldb part is done, this option can be removed and the feature enabled by default.
To display a failure message in the debugger, create a function in the debug info which has the name of the failure message.
The debug location of the trap/cond_fail is then wrapped into this function and the function is declared as "inlined".
In case the debugger stops at the trap instruction, it displays the inline function, which looks like the failure message.
For example:
* thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0)
frame #0: 0x0000000100000cbf a.out`testit3(_:) [inlined] Unexpectedly found nil while unwrapping an Optional value at test.swift:14:11 [opt]
11
12 @inline(never)
13 func testit(_ a: Int?) -> Int {
-> 14 return a!
15 }
16
This change is currently not enabled by default, but can be enabled with the option "-Xllvm -enable-trap-debug-info".
Enabling this feature needs some changes in lldb. When the lldb part is done, this option can be removed and the feature enabled by default.
String -> Builtin.RawPointer that given a string constructed from a
literal, returns the address of the string literal in the global string
table of the compiled binary as a pointer.
* Remove apparently obsolete builtin functions.
- Remove s_to_u_checked_conversion and u_to_s_checked_conversion functions from builtin AST parsing, SIL/IR generation and from SIL optimisations.
* Remove apparently obsolete builtin functions - unit tests.
- Remove unit tests for SIL transformations relating to s_to_u_checked_conversion and u_to_s_checked_conversion builtin functions.
* Remove apparently obsolete builtin functions.
- Remove s_to_u_checked_conversion and u_to_s_checked_conversion functions from builtin AST parsing, SIL/IR generation and from SIL optimisations.
* Remove apparently obsolete builtin functions - unit tests.
- Remove unit tests for SIL transformations relating to s_to_u_checked_conversion and u_to_s_checked_conversion builtin functions.
SIL optimizations may rewrite profiling intrinsics in a way that IRGen
can't lower (r://39146527). Don't claim that a coverage mapping has a
guaranteed associated symbol table entry when this happens.
I have not added a test, as this is a defensive workaround until we can
land add a SIL verifier check that prevents profiling intrinsics from
being rewritten.
rdar://40133800
The SIL optimizer may rewrite the name argument to profiling intrinsics
in a way that makes them impossible to lower.
Avoid lowering ill-formed intrinsics until the issue is addressed
(r://39146527).
rdar://38926982
This corrects a prior change to ignore profiling intrinsics imported
from swift modules. The argument Explosion passed to visitBuiltinInst
neds to be cleared before it's destroyed.
PR #14729 made more calls to llvm.trap() non-mergeable. This follow-up
adds asserts to IRBuilder which make it harder to accidentally introduce
mergeable calls to llvm.trap() in the future.
The newly-added assertions exposed an issue in GenBuiltin while
compiling parts of the stdlib. This PR fixes the issue.
Suggested by Adrian Prantl!
rdar://32772768
Having such a builtin makes it easier for the optimizer to reason about what is actually happening.
I plan to add later some optimizations which can optimize pieces of code dominated by such a check.
Replace `NameOfType foo = dyn_cast<NameOfType>(bar)` with DRY version `auto foo = dyn_cast<NameOfType>(bar)`.
The DRY auto version is by far the dominant form already used in the repo, so this PR merely brings the exceptional cases (redundant repetition form) in line with the dominant form (auto form).
See the [C++ Core Guidelines](https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#es11-use-auto-to-avoid-redundant-repetition-of-type-names) for a general discussion on why to use `auto` to avoid redundant repetition of type names.
Introduce a new runtime entry point,
`swift_objc_swift3ImplicitObjCEntrypoint`, which is called from any
Objective-C method that was generated due to `@objc` inference rules
that were removed by SE-0160. Aside from being a central place where
users can set a breakpoint to catch when this occurs, this operation
provides logging capabilities that can be enabled by setting the
environment variable SWIFT_DEBUG_IMPLICIT_OBJC_ENTRYPOINT:
SWIFT_DEBUG_IMPLICIT_OBJC_ENTRYPOINT=0 (default): do not log
SWIFT_DEBUG_IMPLICIT_OBJC_ENTRYPOINT=1: log failed messages
SWIFT_DEBUG_IMPLICIT_OBJC_ENTRYPOINT=2: log failed messages with
backtrace
SWIFT_DEBUG_IMPLICIT_OBJC_ENTRYPOINT=3: log failed messages with
backtrace and abort the process.
The log messages look something like:
***Swift runtime: entrypoint -[t.MyClass foo] generated by
implicit @objc inference is deprecated and will be removed in
Swift 4
...and IRGen it into a call to __tsan_write1 in compiler-rt. This is
preparatory work for a later patch that will add an experimental
option to treat Swift inout accesses as TSan writes.
While invoking the instrprof_increment intrinsic, we used to pass the
profile name variable by using a GEP instruction to get to the string
constant. That prevented llvm from uniquing the names. Use a constexpr
GEP to fix the issue.
SubstitutionList is going to be a more compact representation of
a SubstitutionMap, suitable for inline allocation inside another
object.
For now, it's just a typedef for ArrayRef<Substitution>.
