[PATCH] Allow nested lambdas in NSDMIs (i.e default initializers)

[Faisal Vali]

faisalv added you to the CC list for the revision "Allow nested lambdas in NSDMIs (i.e default initializers)".

Hi doug.gregor, rsmith, eli.friedman,

This patch fixes an infinite recursion issue when computing the linkage-visibility of nested lambdas in NSDMIs.
Allows compilation of this:
template<class T>
  struct L {
      T t{};
      T t2 = ([](int a) { return [](int b) { return b; };})(t)(t);    
  };
  L<int> l; 
}

Doug had glanced at this change in Chicago as part of my larger generic lambda patch - he thought it would be better addressed and reviewed as a separate patch (since the bug occurs with non-generic lambdas too).  

Thanks!

http://llvm-reviews.chandlerc.com/D1783

Files:
  lib/AST/Decl.cpp
  test/CodeGenCXX/lambda-expressions-nested-linkage.cpp
  test/SemaCXX/lambda-expressions.cpp

Index: lib/AST/Decl.cpp
===================================================================
--- lib/AST/Decl.cpp
+++ lib/AST/Decl.cpp
@@ -1092,6 +1092,19 @@
                      LV.isVisibilityExplicit());
 }
 
+static inline const CXXRecordDecl*
+getOutermostEnclosingLambda(const CXXRecordDecl *Record) {
+  const CXXRecordDecl *Ret = Record;
+  while (Record && Record->isLambda()) {
+    Ret = Record;
+    if (!Record->getParent()) break;
+    // Get the Containing Class of this Lambda Class
+    Record = dyn_cast_or_null<CXXRecordDecl>(
+      Record->getParent()->getParent());
+  }
+  return Ret;
+}
+
 static LinkageInfo computeLVForDecl(const NamedDecl *D,
                                     LVComputationKind computation) {
   // Objective-C: treat all Objective-C declarations as having external
@@ -1122,9 +1135,24 @@
           return LinkageInfo::internal();
         }
 
-        // This lambda has its linkage/visibility determined by its owner.
-        return getLVForClosure(D->getDeclContext()->getRedeclContext(),
-                               Record->getLambdaContextDecl(), computation);
+        // This lambda has its linkage/visibility determined:
+        //  - either by the outermost lambda if that lambda has no mangling 
+        //    number. 
+        //  - or by the parent of the outer most lambda
+        // This prevents infinite recursion in settings such as nested lambdas 
+        // used in NSDMI's, for e.g. 
+        //  struct L {
+        //    int t{};
+        //    int t2 = ([](int a) { return [](int b) { return b; };})(t)(t);    
+        //  };
+        const CXXRecordDecl *OuterMostLambda = 
+            getOutermostEnclosingLambda(Record);
+        if (!OuterMostLambda->getLambdaManglingNumber())
+          return LinkageInfo::internal();
+        
+        return getLVForClosure(
+                  OuterMostLambda->getDeclContext()->getRedeclContext(),
+                  OuterMostLambda->getLambdaContextDecl(), computation);
       }
       
       break;
Index: test/CodeGenCXX/lambda-expressions-nested-linkage.cpp
===================================================================
--- test/CodeGenCXX/lambda-expressions-nested-linkage.cpp
+++ test/CodeGenCXX/lambda-expressions-nested-linkage.cpp
@@ -0,0 +1,50 @@
+// RUN: %clang_cc1 -triple x86_64-apple-darwin10.0.0 -fblocks -emit-llvm -o - %s -fexceptions -std=c++11 | FileCheck %s
+
+// CHECK-LABEL: define void @_ZN19non_inline_function3fooEv()
+// CHECK-LABEL: define internal void @"_ZZN19non_inline_function3fooEvENK3$_0clEi"(%class.anon
+// CHECK-LABEL: define internal signext i8 @"_ZZZN19non_inline_function3fooEvENK3$_0clEiENKUlcE_clEc"(%class.anon
+namespace non_inline_function {
+void foo() {
+  auto L = [](int a) {
+    return [](char b) {
+     return b;
+    };
+  };
+  L(3)('a');
+}
+}
+
+namespace non_template {
+  struct L {
+    int t = ([](int a) { return [](int b) { return b; };})(2)(3);    
+  };
+  L l; 
+}
+
+namespace lambdas_in_NSDMIs_template_class {
+template<class T>
+struct L {
+    T t2 = ([](int a) { return [](int b) { return b; };})(T{})(T{});    
+};
+L<int> l;
+}
+
+// CHECK-LABEL: define linkonce_odr i32 @_ZN15inline_function3fooEv
+// CHECK: define linkonce_odr void @_ZZN15inline_function3fooEvENKUliE_clEi
+// CHECK: define linkonce_odr signext i8 @_ZZZN15inline_function3fooEvENKUliE_clEiENKUlcE_clEc
+namespace inline_function {
+inline int foo() {
+  auto L = [](int a) {
+    return [](char b) {
+     return b;
+    };
+  };
+  L(3)('a');
+}
+int use = foo();
+}
+// CHECK: define linkonce_odr void @_ZNK32lambdas_in_NSDMIs_template_class1LIiEUliE_clEi(%class.anon
+// CHECK: define linkonce_odr i32 @_ZZNK32lambdas_in_NSDMIs_template_class1LIiEUliE_clEiENKUliE_clEi(%class.anon
+
+// CHECK: define linkonce_odr void @_ZNK12non_template1L1tMUliE_clEi(%class.anon
+// CHECK: define linkonce_odr i32 @_ZZNK12non_template1L1tMUliE_clEiENKUliE_clEi(%class.anon
Index: test/SemaCXX/lambda-expressions.cpp
===================================================================
--- test/SemaCXX/lambda-expressions.cpp
+++ test/SemaCXX/lambda-expressions.cpp
@@ -265,3 +265,21 @@
 #endif
   }
 }
+
+
+namespace lambdas_in_NSDMIs {
+  template<class T>
+  struct L {
+      T t{};
+      T t2 = ([](int a) { return [](int b) { return b; };})(t)(t);    
+  };
+  L<int> l; 
+  
+  namespace non_template {
+    struct L {
+      int t = 0;
+      int t2 = ([](int a) { return [](int b) { return b; };})(t)(t);    
+    };
+    L l; 
+  }
+}
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