Implement part of the EmptySubobjectMap optimization described in PR6998. We still need to do this for bases.
llvm-svn: 105919
diff --git a/clang/lib/AST/RecordLayoutBuilder.cpp b/clang/lib/AST/RecordLayoutBuilder.cpp
index 7c0c808..6b8d7cf 100644
--- a/clang/lib/AST/RecordLayoutBuilder.cpp
+++ b/clang/lib/AST/RecordLayoutBuilder.cpp
@@ -415,7 +415,14 @@
void EmptySubobjectMap::UpdateEmptyFieldSubobjects(const CXXRecordDecl *RD,
const CXXRecordDecl *Class,
uint64_t Offset) {
-
+ // We know that the only empty subobjects that can conflict with empty
+ // field subobjects are subobjects empty bases that can be placed at offset
+ // zero. Because of this, we only need to keep track of empty field
+ // subobjects with offsets less than the size of the largest empty
+ // subobject for our class.
+ if (Offset >= SizeOfLargestEmptySubobject)
+ return;
+
AddSubobjectAtOffset(RD, Offset);
const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
@@ -480,6 +487,14 @@
uint64_t ElementOffset = Offset;
for (uint64_t I = 0; I != NumElements; ++I) {
+ // We know that the only empty subobjects that can conflict with empty
+ // field subobjects are subobjects empty bases that can be placed at
+ // offset zero. Because of this, we only need to keep track of empty field
+ // subobjects with offsets less than the size of the largest empty
+ // subobject for our class.
+ if (ElementOffset >= SizeOfLargestEmptySubobject)
+ return;
+
UpdateEmptyFieldSubobjects(RD, RD, ElementOffset);
ElementOffset += Layout.getSize();
}