[IRGen][DebugInfo] split method declaration and definition.

Author: dianqk

lib/IRGen/IRGenDebugInfo.cpp

@@ -2468,6 +2468,18 @@ IRGenDebugInfoImpl::emitFunction(const SILDebugScope *DS, llvm::Function *Fn,
       /*IsLocalToUnit=*/Fn ? Fn->hasInternalLinkage() : true,
       /*IsDefinition=*/true, /*IsOptimized=*/Opts.shouldOptimize());
 
+  // When the function is a method, we only want a DW_AT_declaration there,
+  // because LLVM LTO can't unify type definitions when a child DIE is a full
+  // subprogram definition.
+  if (Rep == SILFunctionTypeRepresentation::Method) {
+    llvm::DISubprogram::DISPFlags SPFlags = llvm::DISubprogram::toSPFlags(
+        /*IsLocalToUnit=*/Fn ? Fn->hasInternalLinkage() : true,
+        /*IsDefinition=*/false, /*IsOptimized=*/Opts.shouldOptimize());
+    Decl = DBuilder.createMethod(Scope, Name, LinkageName, File, Line, DIFnTy,
+                                 0, 0, nullptr, Flags, SPFlags,
+                                 TemplateParameters, Error);
+  }
+
   // Construct the DISubprogram.
   llvm::DISubprogram *SP = DBuilder.createFunction(
       Scope, Name, LinkageName, File, Line, DIFnTy, ScopeLine, Flags, SPFlags,

test/DebugInfo/method.swift

@@ -0,0 +1,27 @@
+// RUN: %target-swift-frontend -primary-file %s -emit-ir -gdwarf-types -o - | %FileCheck %s
+
+// Verify that we added a declaration for a method.
+public struct Foo {
+    static func static_method() {}
+    func method() {}
+}
+
+public class Bar {
+    static func static_method() {}
+    func method() {}
+}
+
+func a_function() {}
+
+// CHECK: distinct !DISubprogram(name: "static_method",
+// CHECK-SAME: declaration:
+// CHECK: distinct !DISubprogram(name: "method",
+// CHECK-SAME: declaration:
+// CHECK: distinct !DISubprogram(name: "static_method",
+// CHECK-SAME: declaration:
+// CHECK: distinct !DISubprogram(name: "method",
+// CHECK-SAME: declaration:
+
+// CHECK: distinct !DISubprogram(name: "a_function",
+// CHECK-NOT: declaration:
+// CHECK-SAME: )