[CodeGenObjCXX] Don't rematerialize default arguments of function

parameters in the body of a block.

This fixes a bug where clang would materialize the default argument
inside the body of a block instead of passing the value via the block
descriptor.

For example, in the code below, foo1 would always print 42 regardless
of the value of argument "a" passed to foo1.

void foo1(const int a = 42 ) {
  auto block = ^{
    printf("%d\n", a);
  };
  block();
}

rdar://problem/24449235

llvm-svn: 268314

1 files changed, 5 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CGBlocks.cpp b/clang/lib/CodeGen/CGBlocks.cpp
index ea164aad915..88786bc9fcf 100644
--- a/clang/lib/CodeGen/CGBlocks.cpp
+++ b/clang/lib/CodeGen/CGBlocks.cpp
@@ -262,6 +262,11 @@ static bool isSafeForCXXConstantCapture(QualType type) {
 static llvm::Constant *tryCaptureAsConstant(CodeGenModule &CGM,
                                             CodeGenFunction *CGF,
                                             const VarDecl *var) {
+  // Don't rematerialize default arguments of function parameters.
+  if (auto *PD = dyn_cast<ParmVarDecl>(var))
+    if (PD->hasDefaultArg())
+      return nullptr;
+
   QualType type = var->getType();
 
   // We can only do this if the variable is const.