Fix spurious Wunused-lambda-capture warning

Summary:
Clang emits unused-lambda-capture warning for captures in generic lambdas even though they are actually used.

Fixes PR31815.

Reviewers: malcolm.parsons, aaron.ballman, rsmith

Reviewed By: malcolm.parsons

Subscribers: ahatanak, cfe-commits

Differential Revision: https://reviews.llvm.org/D33526

llvm-svn: 305315

1 files changed, 11 insertions, 5 deletions

diff --git a/clang/lib/Sema/SemaLambda.cpp b/clang/lib/Sema/SemaLambda.cpp
index a6239283b47..d6b70610d46 100644
--- a/clang/lib/Sema/SemaLambda.cpp
+++ b/clang/lib/Sema/SemaLambda.cpp
@@ -1492,6 +1492,7 @@ ExprResult Sema::BuildLambdaExpr(SourceLocation StartLoc, SourceLocation EndLoc,
   bool ExplicitResultType;
   CleanupInfo LambdaCleanup;
   bool ContainsUnexpandedParameterPack;
+  bool IsGenericLambda;
   {
     CallOperator = LSI->CallOperator;
     Class = LSI->Lambda;
@@ -1500,7 +1501,8 @@ ExprResult Sema::BuildLambdaExpr(SourceLocation StartLoc, SourceLocation EndLoc,
     ExplicitResultType = !LSI->HasImplicitReturnType;
     LambdaCleanup = LSI->Cleanup;
     ContainsUnexpandedParameterPack = LSI->ContainsUnexpandedParameterPack;
-    
+    IsGenericLambda = Class->isGenericLambda();
+
     CallOperator->setLexicalDeclContext(Class);
     Decl *TemplateOrNonTemplateCallOperatorDecl = 
         CallOperator->getDescribedFunctionTemplate()  
@@ -1520,8 +1522,13 @@ ExprResult Sema::BuildLambdaExpr(SourceLocation StartLoc, SourceLocation EndLoc,
       bool IsImplicit = I >= LSI->NumExplicitCaptures;
 
       // Warn about unused explicit captures.
-      if (!CurContext->isDependentContext() && !IsImplicit && !From.isODRUsed())
-        DiagnoseUnusedLambdaCapture(From);
+      if (!CurContext->isDependentContext() && !IsImplicit && !From.isODRUsed()) {
+        // Initialized captures that are non-ODR used may not be eliminated.
+        bool NonODRUsedInitCapture =
+            IsGenericLambda && From.isNonODRUsed() && From.getInitExpr();
+        if (!NonODRUsedInitCapture)
+          DiagnoseUnusedLambdaCapture(From);
+      }
 
       // Handle 'this' capture.
       if (From.isThisCapture()) {
@@ -1568,8 +1575,7 @@ ExprResult Sema::BuildLambdaExpr(SourceLocation StartLoc, SourceLocation EndLoc,
     //   same parameter and return types as the closure type's function call
     //   operator.
     // FIXME: Fix generic lambda to block conversions.
-    if (getLangOpts().Blocks && getLangOpts().ObjC1 && 
-                                              !Class->isGenericLambda())
+    if (getLangOpts().Blocks && getLangOpts().ObjC1 && !IsGenericLambda)
       addBlockPointerConversion(*this, IntroducerRange, Class, CallOperator);
     
     // Finalize the lambda class.