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swift-mirror/test/IRGen/weaklinked_import.swift
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Erik Eckstein 8c9a5ba1b6 Optimizer: rewrite the DeadObjectElimination pass 
DeadObjectElimination  eliminates dead `alloc_stack` and `alloc_ref` allocations.

**Stack allocations**

A stack allocation is dead if its stored values never escape and all loads can be forwarded directly to the stored values:

```
  %s = alloc_stack $Foo
  store %v to [init] %s : $*Foo
  %l = load [take] %s : $*Foo
  dealloc_stack %s : $*Foo
```
->
```
  // %l is replaced with %v
```

This also handles field-level stores and loads. Destroy instructions for field values whose containing object is destroyed replace the original aggregate destroy:

```
  %s = alloc_stack $Foo
  %fa = struct_element_addr %s : $*Foo, #Foo.x
  store %x to [init] %fa : $*Int
  destroy_addr %s : $*Foo
  dealloc_stack %s : $*Foo
```
->
```
  destroy_value %x : $Int
```

**Heap allocations**

A heap allocation is dead if it never escapes and its destructor has no observable side effects. Stored field values are destroyed in place of the object destructor:

```
  %obj = alloc_ref $Foo
  %addr = ref_element_addr %obj : $Foo, #Foo.x
  store %x to [init] %addr : $*Int
  destroy_value %obj : $Foo
```
->
```
  destroy_value %x : $Int
```

The pass replaces the old DeadObjectElimination and SILMem2Reg. It combines the advantages of both passes:

* The old DeadObjectElimination can only remove an `alloc_stack` or `alloc_ref` if there are no loads from such allocations.

* SILMem2Reg can handle loads, but can only remove `alloc_stack`s and not `alloc_ref`s.

The new pass can handle loads from both, `alloc_stack` and `alloc_ref`.
This means, for example, it can do array element propagation (an array buffer is an `alloc_ref) and, if there are no other uses of the array,
completely eliminate the array.

Also, the new pass has other improvements compared to the old passes. E.g. it can deal with objects where the individual fields are initialized with separate stores.

This change also adds the pass variant MandatoryDeadObjectElimination. It replaces the old PredictableDeadAllocationElimination pass.
2026-07-13 10:04:16 +02:00

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// RUN: %empty-directory(%t)
// RUN: %target-swift-frontend -emit-module -emit-module-path %t/weaklinked_import_helper.swiftmodule -parse-as-library %S/Inputs/weaklinked_import_helper.swift -enable-library-evolution
//
// RUN: %target-swift-frontend -primary-file %s -I %t -emit-ir | %FileCheck %s
// UNSUPPORTED: OS=windows-msvc
@_weakLinked import weaklinked_import_helper
// CHECK-DAG: @"$s24weaklinked_import_helper12ConcreteTypeVAA13OtherProtocolAAWP" = extern_weak global ptr
// CHECK-DAG: @"$s24weaklinked_import_helper12ConcreteTypeVMn" = extern_weak global %swift.type_descriptor
// CHECK-DAG: @"$s24weaklinked_import_helper17ProtocolWithAssocMp" = extern_weak global %swift.protocol
// CHECK-DAG: @"$s24weaklinked_import_helper17ProtocolWithAssocP1TAC_AA05OtherD0Tn" = extern_weak global %swift.protocol_requirement
// CHECK-DAG: @"$s1T24weaklinked_import_helper17ProtocolWithAssocPTl" = extern_weak global %swift.protocol_requirement
// CHECK-DAG: @"$s24weaklinked_import_helper17ProtocolWithAssocP1fyyFTq" = extern_weak global %swift.method_descriptor
// CHECK-DAG: declare extern_weak {{.+}} @"$s24weaklinked_import_helper17ProtocolWithAssocPAAE1fyyF"
struct ConformsToProtocolWithAssoc: ProtocolWithAssoc {}
func testTopLevel() {
// CHECK-DAG: declare extern_weak {{.+}} @"$s24weaklinked_import_helper2fnyyF"()
fn()
// CHECK-DAG: declare extern_weak {{.+}} @"$s24weaklinked_import_helper12globalStoredSivg"
// CHECK-DAG: declare extern_weak {{.+}} @"$s24weaklinked_import_helper12globalStoredSivs"
// CHECK-DAG: declare extern_weak {{.+}} @"$s24weaklinked_import_helper12globalStoredSivM"
let x = globalStored
globalStored = x
globalStored += 1
// CHECK-DAG: declare extern_weak {{.+}} @"$s24weaklinked_import_helper14globalComputedSivg"
// CHECK-DAG: declare extern_weak {{.+}} @"$s24weaklinked_import_helper14globalComputedSivs"
// CHECK-DAG: declare extern_weak {{.+}} @"$s24weaklinked_import_helper14globalComputedSivM"
let y = globalComputed
globalComputed = y
globalComputed += 1
}
func testStruct() {
// CHECK-DAG: declare extern_weak {{.+}} @"$s24weaklinked_import_helper1SVMa"
_ = MemoryLayout<S>.size
// CHECK-DAG: declare extern_weak {{.+}} @"$s24weaklinked_import_helper1SVACycfC"
var s = S()
// CHECK-DAG: declare extern_weak {{.+}} @"$s24weaklinked_import_helper1SV2fnyyF"
s.fn()
// CHECK-DAG: declare extern_weak {{.+}} @"$s24weaklinked_import_helper1SV10storedPropSivg"
// CHECK-DAG: declare extern_weak {{.+}} @"$s24weaklinked_import_helper1SV10storedPropSivs"
// CHECK-DAG: declare extern_weak {{.+}} @"$s24weaklinked_import_helper1SV10storedPropSivM"
let x = s.storedProp
s.storedProp = x
s.storedProp += 1
// CHECK-DAG: declare extern_weak {{.+}} @"$s24weaklinked_import_helper1SV12computedPropSivg"
// CHECK-DAG: declare extern_weak {{.+}} @"$s24weaklinked_import_helper1SV12computedPropSivs"
// CHECK-DAG: declare extern_weak {{.+}} @"$s24weaklinked_import_helper1SV12computedPropSivM"
let y = s.computedProp
s.computedProp = y
s.computedProp += 1
// CHECK-DAG: declare extern_weak {{.+}} @"$s24weaklinked_import_helper1SVyS2icig"
// CHECK-DAG: declare extern_weak {{.+}} @"$s24weaklinked_import_helper1SVyS2icis"
// CHECK-DAG: declare extern_weak {{.+}} @"$s24weaklinked_import_helper1SVyS2iciM"
let z = s[0]
s[0] = z
s[0] += 1
}
func testEnum() {
// CHECK-DAG: declare extern_weak {{.+}} @"$s24weaklinked_import_helper1EOMa"
var x1 = MemoryLayout<E>.size
// CHECK-DAG: @"$s24weaklinked_import_helper1EO5basicyA2CmFWC" = extern_weak constant i32
var x2 = E.basic
// CHECK-DAG: @"$s24weaklinked_import_helper1EO5assocyACSicACmFWC" = extern_weak constant i32
var x3 = E.assoc(0)
}
func testClass() {
// CHECK-DAG: declare extern_weak {{.+}} @"$s24weaklinked_import_helper1CCMa"
// CHECK-DAG: declare extern_weak {{.+}} @"$s24weaklinked_import_helper1CCACycfC"
let c = C()
// CHECK-DAG: declare extern_weak {{.+}} @"$s24weaklinked_import_helper1CC2fnyyFTj"
c.fn()
// CHECK-DAG: declare extern_weak swiftcc {{.+}} @"$s24weaklinked_import_helper1CC10storedPropSivgTj"
// CHECK-DAG: declare extern_weak swiftcc {{.+}} @"$s24weaklinked_import_helper1CC10storedPropSivsTj"
// CHECK-DAG: declare extern_weak swiftcc {{.+}} @"$s24weaklinked_import_helper1CC10storedPropSivMTj"
let x = c.storedProp
c.storedProp = x
c.storedProp += 1
// CHECK-DAG: declare extern_weak swiftcc {{.+}} @"$s24weaklinked_import_helper1CC12computedPropSivgTj"
// CHECK-DAG: declare extern_weak swiftcc {{.+}} @"$s24weaklinked_import_helper1CC12computedPropSivsTj"
// CHECK-DAG: declare extern_weak swiftcc {{.+}} @"$s24weaklinked_import_helper1CC12computedPropSivMTj"
let y = c.computedProp
c.computedProp = y
c.computedProp += 1
// CHECK-DAG: declare extern_weak swiftcc {{.+}} @"$s24weaklinked_import_helper1CCyS2icigTj"
// CHECK-DAG: declare extern_weak swiftcc {{.+}} @"$s24weaklinked_import_helper1CCyS2icisTj"
// CHECK-DAG: declare extern_weak swiftcc {{.+}} @"$s24weaklinked_import_helper1CCyS2iciMTj"
let z = c[0]
c[0] = z
c[0] += 1
}
// CHECK-DAG: @"$s24weaklinked_import_helper1CCMn" = extern_weak global %swift.type_descriptor
// CHECK-DAG: @"$s24weaklinked_import_helper1CCACycfCTq" = extern_weak global %swift.method_descriptor
// CHECK-DAG: declare extern_weak swiftcc {{.+}} @"$s24weaklinked_import_helper1CCACycfc"
// CHECK-DAG: declare extern_weak swiftcc {{.+}} @"$s24weaklinked_import_helper1CCfd"
class Sub: C {}
func testProtocolExistential(_ p: P) {
var mutP = p
// CHECK-DAG: declare extern_weak {{.+}} @"$s24weaklinked_import_helper1PP2fnyyFTj"
p.fn()
// CHECK-DAG: declare extern_weak swiftcc {{.+}} @"$s24weaklinked_import_helper1PP4propSivgTj"
// CHECK-DAG: declare extern_weak swiftcc {{.+}} @"$s24weaklinked_import_helper1PP4propSivsTj"
// CHECK-DAG: declare extern_weak swiftcc {{.+}} @"$s24weaklinked_import_helper1PP4propSivMTj"
let x = p.prop
mutP.prop = x
mutP.prop += 1
// CHECK-DAG: declare extern_weak swiftcc {{.+}} @"$s24weaklinked_import_helper1PPyS2icigTj"
// CHECK-DAG: declare extern_weak swiftcc {{.+}} @"$s24weaklinked_import_helper1PPyS2icisTj"
// CHECK-DAG: declare extern_weak swiftcc {{.+}} @"$s24weaklinked_import_helper1PPyS2iciMTj"
let z = p[0]
mutP[0] = z
mutP[0] += 1
}
func testProtocolGeneric<Impl: P>(_ type: Impl.Type) {
// CHECK-DAG: declare extern_weak {{.+}} @"$s24weaklinked_import_helper1PPxycfCTj"
var mutP = type.init()
mutP.fn()
let x = mutP.prop
mutP.prop = x
mutP.prop += 1
let z = mutP[0]
mutP[0] = z
mutP[0] += 1
}
// CHECK-DAG: @"$s24weaklinked_import_helper5BasePMp" = extern_weak global %swift.protocol
protocol RefinesP: BaseP {}
// CHECK-DAG: @"$s24weaklinked_import_helper1SVAA5BasePAAWP" = extern_weak global ptr
// CHECK-DAG: @"$s24weaklinked_import_helper1SVMn" = extern_weak global %swift.type_descriptor
extension S: RefinesP {}
func testInlining() {
// CHECK-DAG: define linkonce_odr hidden {{.+}} @"$s24weaklinked_import_helper22alwaysEmitIntoClientFnyyF"()
// CHECK-DAG: declare extern_weak {{.+}} @"$s24weaklinked_import_helper18usableFromInlineFnyyF"
alwaysEmitIntoClientFn()
}
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