Avoid needlessly copying a block to the heap when a block literal

initializes a local auto variable or is assigned to a local auto
variable that is declared in the scope that introduced the block
literal.

rdar://problem/13289333

https://reviews.llvm.org/D58514

llvm-svn: 355012

1 files changed, 19 insertions, 0 deletions

diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index e91115aec5b..266120dfdc7 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -12443,6 +12443,25 @@ ExprResult Sema::CreateBuiltinBinOp(SourceLocation OpLoc,
     if (!ResultTy.isNull()) {
       DiagnoseSelfAssignment(*this, LHS.get(), RHS.get(), OpLoc, true);
       DiagnoseSelfMove(LHS.get(), RHS.get(), OpLoc);
+
+      // Avoid copying a block to the heap if the block is assigned to a local
+      // auto variable that is declared in the same scope as the block. This
+      // optimization is unsafe if the local variable is declared in an outer
+      // scope. For example:
+      //
+      // BlockTy b;
+      // {
+      //   b = ^{...};
+      // }
+      // // It is unsafe to invoke the block here if it wasn't copied to the
+      // // heap.
+      // b();
+
+      if (auto *BE = dyn_cast<BlockExpr>(RHS.get()->IgnoreParens()))
+        if (auto *DRE = dyn_cast<DeclRefExpr>(LHS.get()->IgnoreParens()))
+          if (auto *VD = dyn_cast<VarDecl>(DRE->getDecl()))
+            if (VD->hasLocalStorage() && getCurScope()->isDeclScope(VD))
+              BE->getBlockDecl()->setCanAvoidCopyToHeap();
     }
     RecordModifiableNonNullParam(*this, LHS.get());
     break;