PR42104: Support instantiations of lambdas that implicitly capture

packs.

Two changes:
 * Track odr-use via FunctionParmPackExprs to properly handle dependent
   odr-uses of packs in generic lambdas.
 * Do not instantiate implicit captures; instead, regenerate them by
   instantiating the body of the lambda. This is necessary to
   distinguish between cases where only one element of a pack is
   captured and cases where the entire pack is captured.

This reinstates r362358 (reverted in r362375) with a fix for an
uninitialized variable use in UpdateMarkingForLValueToRValue.

llvm-svn: 362531

1 files changed, 3 insertions, 8 deletions

diff --git a/clang/lib/Sema/SemaExprCXX.cpp b/clang/lib/Sema/SemaExprCXX.cpp
index ac050fa1ef5..5884cf906fd 100644
--- a/clang/lib/Sema/SemaExprCXX.cpp
+++ b/clang/lib/Sema/SemaExprCXX.cpp
@@ -7427,12 +7427,7 @@ static void CheckIfAnyEnclosingLambdasMustCaptureAnyPotentialCaptures(
   // All the potentially captureable variables in the current nested
   // lambda (within a generic outer lambda), must be captured by an
   // outer lambda that is enclosed within a non-dependent context.
-  const unsigned NumPotentialCaptures =
-      CurrentLSI->getNumPotentialVariableCaptures();
-  for (unsigned I = 0; I != NumPotentialCaptures; ++I) {
-    Expr *VarExpr = nullptr;
-    VarDecl *Var = nullptr;
-    CurrentLSI->getPotentialVariableCapture(I, Var, VarExpr);
+  CurrentLSI->visitPotentialCaptures([&] (VarDecl *Var, Expr *VarExpr) {
     // If the variable is clearly identified as non-odr-used and the full
     // expression is not instantiation dependent, only then do we not
     // need to check enclosing lambda's for speculative captures.
@@ -7446,7 +7441,7 @@ static void CheckIfAnyEnclosingLambdasMustCaptureAnyPotentialCaptures(
     // }
     if (CurrentLSI->isVariableExprMarkedAsNonODRUsed(VarExpr) &&
         !IsFullExprInstantiationDependent)
-      continue;
+      return;
 
     // If we have a capture-capable lambda for the variable, go ahead and
     // capture the variable in that lambda (and all its enclosing lambdas).
@@ -7478,7 +7473,7 @@ static void CheckIfAnyEnclosingLambdasMustCaptureAnyPotentialCaptures(
                           DeclRefType, nullptr);
       }
     }
-  }
+  });
 
   // Check if 'this' needs to be captured.
   if (CurrentLSI->hasPotentialThisCapture()) {