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Add EXPERIMENTAL_FEATURE(SymbolLinkageMarkers, true)
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‎docs/ReferenceGuides/UnderscoredAttributes.md

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@@ -832,6 +832,12 @@ Fully bypasses access control, allowing access to private declarations
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in the imported module. The imported module needs to be compiled with
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`-Xfrontend -enable-private-imports` for this to work.
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## `@_section("section_name")`
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Places a global variable or a top-level function into a section of the object
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file with the given name. It's the equivalent of clang's
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`__attribute__((section))`.
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## `@_semantics("uniquely.recognized.id")`
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Allows the optimizer to make use of some key invariants in performance critical
@@ -994,6 +1000,12 @@ for more details.
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This `async` function uses the pre-SE-0338 semantics of unsafely inheriting the caller's executor. This is an underscored feature because the right way of inheriting an executor is to pass in the required executor and switch to it. Unfortunately, there are functions in the standard library which need to inherit their caller's executor but cannot change their ABI because they were not defined as `@_alwaysEmitIntoClient` in the initial release.
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## `@_used`
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Marks a global variable or a top-level function as "used externally" even if it
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does not have visible users in the compilation unit. It's the equivalent of
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clang's `__attribute__((used))`.
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## `@_weakLinked`
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Allows a declaration to be weakly-referenced, i.e., any references emitted by

‎include/swift/AST/DiagnosticsSema.def

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@@ -1702,6 +1702,9 @@ ERROR(cdecl_empty_name,none,
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ERROR(cdecl_throws,none,
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"raising errors from @_cdecl functions is not supported", ())
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// @_used and @_section
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ERROR(section_linkage_markers_disabled,none,
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"attribute requires '-enable-experimental-feature SymbolLinkageMarkers'", ())
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ERROR(used_not_at_top_level,none,
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"@_used can only be applied to global functions and variables", ())
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ERROR(section_not_at_top_level,none,

‎include/swift/Basic/Features.def

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@@ -122,6 +122,9 @@ EXPERIMENTAL_FEATURE(FlowSensitiveConcurrencyCaptures, false)
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EXPERIMENTAL_FEATURE(CodeItemMacros, true)
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EXPERIMENTAL_FEATURE(TupleConformances, false)
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// Whether to enable @_used and @_section attributes
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EXPERIMENTAL_FEATURE(SymbolLinkageMarkers, true)
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// FIXME: MoveOnlyClasses is not intended to be in production,
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// but our tests currently rely on it, and we want to run those
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// tests in non-asserts builds too.

‎lib/AST/ASTPrinter.cpp

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@@ -3211,6 +3211,10 @@ static bool usesFeatureTupleConformances(Decl *decl) {
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return false;
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}
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static bool usesFeatureSymbolLinkageMarkers(Decl *decl) {
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return false;
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}
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static bool usesFeatureLayoutPrespecialization(Decl *decl) {
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auto &attrs = decl->getAttrs();
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return std::any_of(attrs.begin(), attrs.end(), [](auto *attr) {

‎lib/Sema/TypeCheckAttr.cpp

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@@ -2071,12 +2071,22 @@ void AttributeChecker::visitExposeAttr(ExposeAttr *attr) {
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}
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void AttributeChecker::visitUsedAttr(UsedAttr *attr) {
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if (!Ctx.LangOpts.hasFeature(Feature::SymbolLinkageMarkers)) {
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diagnoseAndRemoveAttr(attr, diag::section_linkage_markers_disabled);
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return;
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}
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// Only top-level func/var decls are currently supported.
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if (D->getDeclContext()->isTypeContext())
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diagnose(attr->getLocation(), diag::used_not_at_top_level);
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}
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void AttributeChecker::visitSectionAttr(SectionAttr *attr) {
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if (!Ctx.LangOpts.hasFeature(Feature::SymbolLinkageMarkers)) {
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diagnoseAndRemoveAttr(attr, diag::section_linkage_markers_disabled);
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return;
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}
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// Only top-level func/var decls are currently supported.
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if (D->getDeclContext()->isTypeContext())
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diagnose(attr->getLocation(), diag::section_not_at_top_level);

‎test/IRGen/section.swift

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@@ -1,10 +1,10 @@
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// RUN: %target-swift-frontend -primary-file %s -emit-sil | %FileCheck %s --check-prefix=SIL --check-prefix=SIL-TOPLEVEL
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// RUN: %target-swift-frontend -primary-file %s -emit-ir | %FileCheck %s --check-prefix=IR --check-prefix=IR-TOPLEVEL
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// RUN: %target-swift-frontend -primary-file %s -emit-sil -parse-as-library | %FileCheck %s --check-prefix=SIL --check-prefix=SIL-LIBRARY
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// RUN: %target-swift-frontend -primary-file %s -emit-ir -parse-as-library | %FileCheck %s --check-prefix=IR --check-prefix=IR-LIBRARY
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// RUN: %target-swift-frontend -enable-experimental-feature SymbolLinkageMarkers -primary-file %s -emit-sil | %FileCheck %s --check-prefix=SIL --check-prefix=SIL-TOPLEVEL
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// RUN: %target-swift-frontend -enable-experimental-feature SymbolLinkageMarkers -primary-file %s -emit-ir | %FileCheck %s --check-prefix=IR --check-prefix=IR-TOPLEVEL
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// RUN: %target-swift-frontend -enable-experimental-feature SymbolLinkageMarkers -primary-file %s -emit-sil -parse-as-library | %FileCheck %s --check-prefix=SIL --check-prefix=SIL-LIBRARY
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// RUN: %target-swift-frontend -enable-experimental-feature SymbolLinkageMarkers -primary-file %s -emit-ir -parse-as-library | %FileCheck %s --check-prefix=IR --check-prefix=IR-LIBRARY
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// RUN: %target-swift-frontend -primary-file %s -S | %FileCheck %s --check-prefix=ASM --check-prefix ASM-%target-os
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// RUN: %target-swift-frontend -primary-file %s -S -parse-as-library | %FileCheck %s --check-prefix=ASM --check-prefix ASM-%target-os
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// RUN: %target-swift-frontend -enable-experimental-feature SymbolLinkageMarkers -primary-file %s -S | %FileCheck %s --check-prefix=ASM --check-prefix ASM-%target-os
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// RUN: %target-swift-frontend -enable-experimental-feature SymbolLinkageMarkers -primary-file %s -S -parse-as-library | %FileCheck %s --check-prefix=ASM --check-prefix ASM-%target-os
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// REQUIRES: swift_in_compiler
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‎test/IRGen/used.swift

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@@ -1,11 +1,11 @@
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// RUN: %target-swift-frontend -primary-file %s -emit-sil | %FileCheck %s --check-prefix=SIL
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// RUN: %target-swift-frontend -primary-file %s -O -emit-sil | %FileCheck %s --check-prefix=SIL
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// RUN: %target-swift-frontend -primary-file %s -emit-ir | %FileCheck %s --check-prefix=IR
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// RUN: %target-swift-frontend -primary-file %s -O -emit-ir | %FileCheck %s --check-prefix=IR
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// RUN: %target-swift-frontend -primary-file %s -emit-sil -parse-as-library | %FileCheck %s --check-prefix=SIL
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// RUN: %target-swift-frontend -primary-file %s -O -emit-sil -parse-as-library | %FileCheck %s --check-prefix=SIL
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// RUN: %target-swift-frontend -primary-file %s -emit-ir -parse-as-library | %FileCheck %s --check-prefix=IR
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// RUN: %target-swift-frontend -primary-file %s -O -emit-ir -parse-as-library | %FileCheck %s --check-prefix=IR
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// RUN: %target-swift-frontend -enable-experimental-feature SymbolLinkageMarkers -primary-file %s -emit-sil | %FileCheck %s --check-prefix=SIL
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// RUN: %target-swift-frontend -enable-experimental-feature SymbolLinkageMarkers -primary-file %s -O -emit-sil | %FileCheck %s --check-prefix=SIL
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// RUN: %target-swift-frontend -enable-experimental-feature SymbolLinkageMarkers -primary-file %s -emit-ir | %FileCheck %s --check-prefix=IR
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// RUN: %target-swift-frontend -enable-experimental-feature SymbolLinkageMarkers -primary-file %s -O -emit-ir | %FileCheck %s --check-prefix=IR
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// RUN: %target-swift-frontend -enable-experimental-feature SymbolLinkageMarkers -primary-file %s -emit-sil -parse-as-library | %FileCheck %s --check-prefix=SIL
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// RUN: %target-swift-frontend -enable-experimental-feature SymbolLinkageMarkers -primary-file %s -O -emit-sil -parse-as-library | %FileCheck %s --check-prefix=SIL
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// RUN: %target-swift-frontend -enable-experimental-feature SymbolLinkageMarkers -primary-file %s -emit-ir -parse-as-library | %FileCheck %s --check-prefix=IR
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// RUN: %target-swift-frontend -enable-experimental-feature SymbolLinkageMarkers -primary-file %s -O -emit-ir -parse-as-library | %FileCheck %s --check-prefix=IR
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// REQUIRES: swift_in_compiler
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