Assign APValues by swapping from a temporary. Removes a bunch of unnecessary
copy-construction, which Daniel Dunbar reports as giving a 0.75% speedup on
403.gcc/combine.c. The performance differences on my constexpr torture tests
are below the noise floor.
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@152455 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/AST/ExprConstant.cpp b/lib/AST/ExprConstant.cpp
index 5f9b050..97c906c 100644
--- a/lib/AST/ExprConstant.cpp
+++ b/lib/AST/ExprConstant.cpp
@@ -1518,7 +1518,7 @@
// This object might be initialized later.
return false;
- const APValue *O = &Obj;
+ APValue *O = &Obj;
// Walk the designator's path to find the subobject.
for (unsigned I = 0, N = Sub.Entries.size(); I != N; ++I) {
if (ObjType->isArrayType()) {
@@ -1616,7 +1616,13 @@
}
}
- Obj = APValue(*O);
+ // This may look super-stupid, but it serves an important purpose: if we just
+ // swapped Obj and *O, we'd create an object which had itself as a subobject.
+ // To avoid the leak, we ensure that Tmp ends up owning the original complete
+ // object, which is destroyed by Tmp's destructor.
+ APValue Tmp;
+ O->swap(Tmp);
+ Obj.swap(Tmp);
return true;
}