In this PR, preFixUp function in SILCloner is added which can be
overidden by implementations so that the SIL is cleaned for `commonFixup` processing.
For begin_apply inlining, blocks split due to end_apply and abort_apply
are fixed when no yields are found.
Fixes a couple of compiler warnings that occur frequently when building the compiler:
- Copy the nullability annotation definitions from `Visibility.h` to `BridgedSwiftObject.h` and wrap all code that contains nullability annotations in `SWIFT_BEGIN_NULLABILITY_ANNOTATIONS` and `SWIFT_END_NULLABILITY_ANNOTATIONS` (supressing the warning `type nullability specifier '_Nullable' is a Clang extension [-Wnullability-extension]`)
- Suppress warnings about using `$` (mangling prefix) as an identifier using pragmas (supressing the warning `'$' in identifier [-Wdollar-in-identifier-extension]`)
- Change the macro condition of `SWIFT_NODISCARD` from `__cplusplus >= 201402l` (which checked for >= C++14) to `__cplusplus > 201402l`. This appears to have been a copy-paste error from `LLVM_NODISCARD` (supressing the warning `use of the 'nodiscard' attribute is a C++17 extension [-Wc++17-extensions]`)
This mainly simplifies the utility, but also improves optimization as
a side effect.
Update OSSA RAUW after replacing BorrowedAddress with AddressOwnership.
InteriorPointer is no longer needed. This simplifies the fixup
context. Eventually the fixup context will be very lightweight. This
is just the first step.
Given a computed ValueLifetimeBoundary, visit all the points at which
the lifetime needs to be terminated, e.g. via and end_borrow or
destroy_value.
Especially useful for creating a borrow scope over guaranteed uses.
This completely decouples the DeadBlocks analysis from the liveness
analysis.
It will allow phasing out the complex and bug-prone
ValueLifetimeAnalysis::Frontier API.
Previously, the addArgumentToBranch only allowed one to add a single
additional argument to a branch. It then verified the argument count.
That is a problem if multiple arguments have to be added to arrive at
the correct argument count.
Specifically, that was a problem when running Mem2Reg on a lexical
alloc_stack, where three new phi arguments are added.
Here, the function name is changed to addArgumentsToBranch (plural
arguments) and the function accepts a SmallVector<SILValue> rather than
a single SILValue, allowing one to add all the arguments that are
necessary in order to verify that the resulting number of arguments is
correct.
To print the module, use the new llvm flag -sil-print-canonical-module
which parallels the existing flag -sil-view-canonical-cfg. When that
flag is passed, the new pass ModulePrinter is added to the diagnostic
pass pipeline after mandatory diagnostics have run. The new pass just
prints the module to stdout.
Handle SSA update (phi creation) when extending an owned lifetime over
a borrowed lifetime.
This is a layer of logic above BorrowedValue but below
OwnershipLifetimeExtender and other higher-level utilities.
In OSSA RLE for loops, in certain cases SSAUpdater will not create a new
SILPhiArgument to be used as the forwarding value. Based on dominator info
it may return the newly copied available value as the forwarding value.
This newly copied available value in the dominating predecessor
will have destroy values at leaking blocks.
Rename makeNewValueAvailable to makeValueAvailable and handle users so that only
additional required destroy_values are inserted.
ARC operations don't have an effect on immortal objects, like the empty array singleton or statically allocated arrays.
Therefore we can freely remove and retain/release instructions on such objects, even if there is no paired balanced ARC operation.
This optimization can only be done with a minimum deployment target of Swift 5.1, because in that version we added immortal ref count bits.
The optimization is implemented in libswift. Additionally, the remaining logic of simplifying strong_retain and strong_release is also ported to libswift.
rdar://81482156
* unify FunctionPassContext and InstructionPassContext
* add a modification API: PassContext.setOperand
* automatic invalidation notifications when the SIL is modified
Ownership rauw uses a shared ownership fixup context to maintain state.
When ownership rauw fails, due to some invalid condition, we leave
behind stale data in this shared ownership fixup context.
This stale context can indvertantly affect the next rauw on addresses.
In addition to setting the ownership fixup context to nullptr, we
should also clear it so that it's internal data structures are
cleared.
OSSA rauw cleans up end of scope markers before rauw'ing.
This can lead to inadvertant deleting of end_lifetime, later
resulting in an ownership verifier error indicating a leak.
This PR stops treating end_lifetime scope ending like end_borrow/end_access.
SROA and Mem2Reg now can leverage DIExpression -- op_fragment, more
specifically -- to generate correct debug info for optimized SIL. Some
important highlights:
- The new swift::salvageDebugInfo, similar to llvm::salvageDebugInfo,
tries to restore / transfer debug info from a deleted instruction.
Currently I only implemented this for store instruction whose
destination is an alloc_stack value.
- Since we now have source-variable-specific SIL location inside a
`debug_value` instruction (and its friends), this patch teaches
SILCloner and SILInliner to remap the debug scope there in addition
to debug scope of the instruction.
- DCE now does not remove `debug_value` instruction whose associating
with a function argument SSA value that is not used elsewhere. Since
that SSA value will not disappear so we should keep the debug info.
This rewrites functionality that was mostly disabled but is now ready
to be enabled.
Allow lifetime canonicalization of owned values and function arguments
as a simple stand-alone utility. This is now being called from within
SILCombine, so we should only do the kind of canonicalization that
makes sense in that context.
Canonicalizing other borrow scopes should *not* be invoked as a
single-value cleanup because it affects other lifetimes outside the
borrow scope boundary. It is a somewhat complicated process that
hoists and sinks forwarding instructions and can generate surrounding
compensation code. The copy propagation pass knows how to post-process
the related lifetimes in just the right order. So borrow scope
rewriting should only be done in the copy propagation pass.
Similarly, only do simple canonicalization of owned values and
function arguments at -Onone.
The feature to canoncalize borrow scopes is now ready to be
enabled (-canonical-ossa-rewrite-borrows), but flipping the switch
should be a separate commit. So most of the functionality that was
affected is not exposed by this PR.
Changes:
Split canonicalization of owned lifetimes vs. borrowed lifetimes into
separate utilities. The owned lifetime utility is now back to being
the simple utility that I originally envisioned. So not much happened
to it other than removing complexity.
We now have a separate entry point for finding the starting point for
rewriting borrow scopes:
CanonicalizeBorrowScope::getCanonicalBorrowedDef.
We now have a utility that defines forwarding instructions that we can
treat consistently as part of a guaranteed lifetime,
CanonicalizeBorrowScope::isRewritableOSSAForward.
We now have a utility that defines the uses of a borrowed value that
are considered part of its lifetime,
CanonicalizeBorrowScope::visitBorrowScopeUses. This single utility is
used to implement three different parts of the alogrithm:
1. Find any uses of the borrowed value that need to be propagated
outside the borrow scope
2. RewriteInnerBorrowUses for SILFunction arguments and borrow scopes
with no outer uses.
3. RewriteOuterBorrowUses for borrow scopes with outer uses. Handling
these involves creating new copies outside the borrow scope and
hoisting forwarding instructions.
The end result is that a lot of borrow scopes can be eliminated and
owned values can be forwarded to destructures, reducing copies and
destroys.
If we stop generating borrow scopes for all interior pointers, then
we'll need to design a comparable optimization that works on
"implicit" borrow scopes:
%ownedDef = ...
%element struct_extract %ownedDef
%copy = copy_value %element
apply(@guaranteed %element)
apply(@owned %copy)
destroy %ownedDef
Should be:
%ownedDef = ...
%borrowedElement = destructure_struct @guaranteed %ownedDef
apply(@guaranteed %borrowedElement)
%ownedElement = destructure_struct %ownedDef
apply(@owned %copy)
TLDR: The reason why I am doing this is that often times people confuse assembly
vision remarks for normal opt remarks. I want to accentuate that this is
actually trying to do something different than a traditional opt remark. To that
end I renamed things in the compiler and added a true attribute
`@_assemblyVision` to trigger the compiler to emit these remarks to help
everyone remember what this is in their ontology. I explain below the
difference.
----
Normal opt remarks work by the optimizer telling you if it succeeded or failed
to perform an optimization. Another way of putting this is that opt remarks is
trying to give back feedback to the user from an expert system about why it did
or not do something. There is inherently an act of interpretation in the
optimizer about whether or not to report an 'action' that it perpetrated to the
user.
Assembly Vision Remarks is instead trying to be an expert tool that acts like an
xray. Instead of telling the user about what the optimizer did, it is instead a
simple visitor that visits the IR and emits SourceLocations for where specific
hazards ending up in the program. In this sense it is just telling the user
where certain instructions ended up and using heuristics to relate this to
information at the IR level. To a get a sense of this difference, consider the
following Swift Code:
```
public class Klass {
func doSomething() {}
}
var global: Klass = Klass()
@inline(__always)
func bar() -> Klass { global }
@_assemblyVision
@inline(never)
func foo() {
bar().doSomething()
}
```
In this case, we will emit the following remarks:
```
test.swift:16:5: remark: begin exclusive access to value of type 'Klass'
bar().doSomething()
^
test.swift:7:5: note: of 'global'
var global: Klass = Klass()
^
test.swift:16:9: remark: end exclusive access to value of type 'Klass'
bar().doSomething()
^
test.swift:7:5: note: of 'global'
var global: Klass = Klass()
^
test.swift:16:11: remark: retain of type 'Klass'
bar().doSomething()
^
test.swift:7:5: note: of 'global'
var global: Klass = Klass()
^
test.swift:16:23: remark: release of type 'Klass'
bar().doSomething()
^
test.swift:7:5: note: of 'global'
var global: Klass = Klass()
^
```
Notice how the begin/end exclusive access are marked as actually being before
the retain, release of global. That seems weird since exclusive access to memory
seems like something that should not escape an exclusivity scope... but in fact
this corresponds directly to what we eventually see in the SIL:
```
// test.sil
sil hidden [noinline] [_semantics "optremark"] @$ss3fooyyF : $@convention(thin) () -> () {
bb0:
%0 = global_addr @$ss6globals5KlassCvp : $*Klass
%1 = begin_access [read] [dynamic] [no_nested_conflict] %0 : $*Klass
%2 = load %1 : $*Klass
end_access %1 : $*Klass
%4 = class_method %2 : $Klass, #Klass.doSomething : (Klass) -> () -> (), $@convention(method) (@guaranteed Klass) -> ()
strong_retain %2 : $Klass
%6 = apply %4(%2) : $@convention(method) (@guaranteed Klass) -> ()
strong_release %2 : $Klass
%8 = tuple ()
return %8 : $()
} // end sil function '$ss3fooyyF'
```
and assembly,
```
// test.S
_$ss3fooyyF:
pushq %rbp
movq %rsp, %rbp
pushq %r13
pushq %rbx
subq $32, %rsp
leaq _$ss6globals5KlassCvp(%rip), %rdi
leaq -40(%rbp), %rsi
xorl %edx, %edx
xorl %ecx, %ecx
callq _swift_beginAccess
movq _$ss6globals5KlassCvp(%rip), %r13
movq (%r13), %rax
movq 80(%rax), %rbx
movq %r13, %rdi
callq _swift_retain
callq *%rbx
movq %r13, %rdi
callq _swift_release
addq $32, %rsp
popq %rbx
popq %r13
popq %rbp
retq
```
so as one can see what we are trying to do is inform the user of hazards in the
code without trying to reason about it, automated a task that users often have
to perform by hand: inspection of assembly to determine where runtime calls and
other hazards ended up.
Instruction passes are basically visit functions in SILCombine for a specific instruction type.
With the macro SWIFT_INSTRUCTION_PASS such a pass can be declared in Passes.def.
SILCombine then calls the run function of the pass in libswift.
StackList is a very efficient data structure for worklist type things.
This is a port of the C++ utility with the same name.
Compared to Array, it does not require any memory allocations.
With the macro SWIFT_FUNCTION_PASS a new libswift function pass can be defined in Passes.def.
The SWIFT_FUNCTION_PASS_WITH_LEGACY is similar, but it allows to keep an original C++ “legacy” implementation of the pass, which is used if the compiler is not built with libswift.
