[PATCH] D20349: Fix a clang bug in lambda capture of 'this'

Taewook Oh via cfe-commits cfe-commits at lists.llvm.org
Tue May 17 21:23:04 PDT 2016

twoh created this revision.
twoh added reviewers: faisalv, rsmith.
twoh added a subscriber: cfe-commits.

(This is a fix for Bug 27797 https://llvm.org/bugs/show_bug.cgi?id=27797).

Currently when RebuildLambdaScopeInfo() function in lib/Sema/SemaDecl.cpp observes lambda capturing 'this', it calls Sema::getCurrentThisType() to get the type of 'this'. However, clang (revision 269789) crashes with an assertion failure inside Sema::getCurrentThisType() if template instantiation creates nested lambdas. Inside, Sema::getCurrentThisType(), there is an assertion saying that getCurLambda() never returns nullptr, but nest lambdas created by template instantiation makes getCurLambda() returns nullptr. 

Actually, even without the assertion failure, calling Sema::getCurrentThisType() from RebuildLambdaScopeInfo() seems wrong. When there are nested lambdas, what is required from Sema::getCurrentThisType() is a type of 'this' for nesting lambda, while what is supposed to be returned from Sema::getCurrentThisType() is a type of 'this' for nested lambda.

This patch addresses this issue and makes RebuildLambdaScopeInfo() compute the correct 'this' type. 



Index: lib/Sema/SemaDecl.cpp
--- lib/Sema/SemaDecl.cpp
+++ lib/Sema/SemaDecl.cpp
@@ -11109,8 +11109,16 @@
           CaptureType, /*Expr*/ nullptr);
     } else if (C.capturesThis()) {
+      QualType ThisTy = CallOperator->getThisType(S.Context);
+      QualType BaseTy = ThisTy->getPointeeType();
+      if (C.getCaptureKind() == LCK_StarThis &&
+          CallOperator->isConst() &&
+          !BaseTy.isConstQualified()) {
+        BaseTy.addConst();
+        ThisTy = S.Context.getPointerType(BaseTy);
+      }
       LSI->addThisCapture(/*Nested*/ false, C.getLocation(),
-                              S.getCurrentThisType(), /*Expr*/ nullptr,
+                              ThisTy, /*Expr*/ nullptr,
                               C.getCaptureKind() == LCK_StarThis);
     } else {
       LSI->addVLATypeCapture(C.getLocation(), I->getType());

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