From eb8bd2d9b3776ead6c185394806264522e29f6c4 Mon Sep 17 00:00:00 2001 From: Ben Langmuir Date: Fri, 10 Apr 2015 22:25:42 +0000 Subject: [PATCH] Workaround a performance issue with modules + PCH More fallout from r228234; when looking up an identifier in a PCH that imports the Cocoa module on Darwin, it was taking 2 to 5 seconds because we were hammering the MapVector::erase() function, which is O(n). For now, just clear() the contained SmallVector to get back to 0.25 - 0.5 seconds. This is probably not the long-term fix, because without modules or without PCH the performance is more like 0.02 seconds. llvm-svn: 234655 --- clang/lib/Serialization/ASTReader.cpp | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp index 034b8a4..d26ed222 100644 --- a/clang/lib/Serialization/ASTReader.cpp +++ b/clang/lib/Serialization/ASTReader.cpp @@ -8668,7 +8668,10 @@ void ASTReader::pushExternalDeclIntoScope(NamedDecl *D, DeclarationName Name) { if (It != PendingFakeLookupResults.end()) { for (auto *ND : PendingFakeLookupResults[II]) SemaObj->IdResolver.RemoveDecl(ND); - PendingFakeLookupResults.erase(It); + // FIXME: this works around module+PCH performance issue. + // Rather than erase the result from the map, which is O(n), just clear + // the vector of NamedDecls. + It->second.clear(); } } -- 2.7.4