[cfe-commits] r105919 - /cfe/trunk/lib/AST/RecordLayoutBuilder.cpp

[Anders Carlsson]

Author: andersca
Date: Sun Jun 13 12:49:16 2010
New Revision: 105919

URL: http://llvm.org/viewvc/llvm-project?rev=105919&view=rev
Log:
Implement part of the EmptySubobjectMap optimization described in PR6998. We still need to do this for bases.

Modified:
    cfe/trunk/lib/AST/RecordLayoutBuilder.cpp

Modified: cfe/trunk/lib/AST/RecordLayoutBuilder.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/AST/RecordLayoutBuilder.cpp?rev=105919&r1=105918&r2=105919&view=diff
==============================================================================
--- cfe/trunk/lib/AST/RecordLayoutBuilder.cpp (original)
+++ cfe/trunk/lib/AST/RecordLayoutBuilder.cpp Sun Jun 13 12:49:16 2010
@@ -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();
     }