[Serialization] Serialize hasCReferences to keep linkage

hasCReferences is used to determine that the function is externally
available. If a function has @_cdecl and not used from anywhere in Swift
side code, it will be emitted due to its hasCReferences. But if the
attribute is not restored from sib, it won't be emitted even if it's
used externally. So we need to serialize the attribute.

Author: kateinoigakukun

lib/Serialization/DeserializeSIL.cpp

@@ -511,14 +511,14 @@ SILDeserializer::readSILFunctionChecked(DeclID FID, SILFunction *existingFn,
   GenericSignatureID genericSigID;
   unsigned rawLinkage, isTransparent, isSerialized, isThunk,
       isWithoutactuallyEscapingThunk, specialPurpose, inlineStrategy,
-      optimizationMode, subclassScope, effect, numSpecAttrs,
+      optimizationMode, subclassScope, hasCReferences, effect, numSpecAttrs,
       hasQualifiedOwnership, isWeakImported, LIST_VER_TUPLE_PIECES(available),
       isDynamic, isExactSelfClass;
   ArrayRef<uint64_t> SemanticsIDs;
   SILFunctionLayout::readRecord(
       scratch, rawLinkage, isTransparent, isSerialized, isThunk,
       isWithoutactuallyEscapingThunk, specialPurpose, inlineStrategy,
-      optimizationMode, subclassScope, effect, numSpecAttrs,
+      optimizationMode, subclassScope, hasCReferences, effect, numSpecAttrs,
       hasQualifiedOwnership, isWeakImported, LIST_VER_TUPLE_PIECES(available),
       isDynamic, isExactSelfClass, funcTyID, replacedFunctionID, genericSigID,
       clangNodeOwnerID, SemanticsIDs);
@@ -639,6 +639,7 @@ SILDeserializer::readSILFunctionChecked(DeclID FID, SILFunction *existingFn,
     fn->setOptimizationMode(OptimizationMode(optimizationMode));
     fn->setAlwaysWeakImported(isWeakImported);
     fn->setClassSubclassScope(SubclassScope(subclassScope));
+    fn->setHasCReferences(bool(hasCReferences));
 
     llvm::VersionTuple available;
     DECODE_VER_TUPLE(available);
@@ -2824,14 +2825,14 @@ bool SILDeserializer::hasSILFunction(StringRef Name,
   GenericSignatureID genericSigID;
   unsigned rawLinkage, isTransparent, isSerialized, isThunk,
       isWithoutactuallyEscapingThunk, isGlobal, inlineStrategy,
-      optimizationMode, subclassScope, effect, numSpecAttrs,
+      optimizationMode, subclassScope, hasCReferences, effect, numSpecAttrs,
       hasQualifiedOwnership, isWeakImported, LIST_VER_TUPLE_PIECES(available),
       isDynamic, isExactSelfClass;
   ArrayRef<uint64_t> SemanticsIDs;
   SILFunctionLayout::readRecord(
       scratch, rawLinkage, isTransparent, isSerialized, isThunk,
       isWithoutactuallyEscapingThunk, isGlobal, inlineStrategy,
-      optimizationMode, subclassScope, effect, numSpecAttrs,
+      optimizationMode, subclassScope, hasCReferences, effect, numSpecAttrs,
       hasQualifiedOwnership, isWeakImported, LIST_VER_TUPLE_PIECES(available),
       isDynamic, isExactSelfClass, funcTyID, replacedFunctionID, genericSigID,
       clangOwnerID, SemanticsIDs);

lib/Serialization/ModuleFormat.h

@@ -55,7 +55,7 @@ const uint16_t SWIFTMODULE_VERSION_MAJOR = 0;
 /// describe what change you made. The content of this comment isn't important;
 /// it just ensures a conflict if two people change the module format.
 /// Don't worry about adhering to the 80-column limit for this line.
-const uint16_t SWIFTMODULE_VERSION_MINOR = 575; // GlobalInitOnceFunction SILFunction purpose
+const uint16_t SWIFTMODULE_VERSION_MINOR = 576; // hasCReferences
 
 /// A standard hash seed used for all string hashes in a serialized module.
 ///

lib/Serialization/SILFormat.h

@@ -281,6 +281,7 @@ namespace sil_block {
                      BCFixed<2>,  // inlineStrategy
                      BCFixed<2>,  // optimizationMode
                      BCFixed<2>,  // classSubclassScope
+                     BCFixed<1>,  // hasCReferences
                      BCFixed<3>,  // side effect info.
                      BCVBR<8>,    // number of specialize attributes
                      BCFixed<1>,  // has qualified ownership

lib/Serialization/SerializeSIL.cpp

@@ -433,9 +433,9 @@ void SILSerializer::writeSILFunction(const SILFunction &F, bool DeclOnly) {
       Out, ScratchRecord, abbrCode, toStableSILLinkage(Linkage),
       (unsigned)F.isTransparent(), (unsigned)F.isSerialized(),
       (unsigned)F.isThunk(), (unsigned)F.isWithoutActuallyEscapingThunk(),
-      (unsigned)F.getSpecialPurpose(),
-      (unsigned)F.getInlineStrategy(), (unsigned)F.getOptimizationMode(),
-      (unsigned)F.getClassSubclassScope(), (unsigned)F.getEffectsKind(),
+      (unsigned)F.getSpecialPurpose(), (unsigned)F.getInlineStrategy(),
+      (unsigned)F.getOptimizationMode(), (unsigned)F.getClassSubclassScope(),
+      (unsigned)F.hasCReferences(), (unsigned)F.getEffectsKind(),
       (unsigned)numSpecAttrs, (unsigned)F.hasOwnership(),
       F.isAlwaysWeakImported(), LIST_VER_TUPLE_PIECES(available),
       (unsigned)F.isDynamicallyReplaceable(), (unsigned)F.isExactSelfClass(),

test/Serialization/cdecl_attr.swift

@@ -0,0 +1,12 @@
+// RUN: %empty-directory(%t)
+// Ensure .swift -> .ll
+// RUN: %target-swift-frontend -emit-ir %s | %FileCheck %s
+
+// Ensure .swift -> .sib -> .ll
+// RUN: %target-swift-frontend -emit-sib %s -o %t/cdecl_attr.sib
+// RUN: %target-swift-frontend -emit-ir %t/cdecl_attr.sib | %FileCheck %s
+
+// CHECK: define hidden {{.*}} @foo
+
+@_cdecl("foo")
+func foo() {}